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"MAMA-HYBRIDS –
Multifunctional Hybrids and Organics” Ischia, October 22
nd-24
th, 2012
II
III
The MAMA-Hybrids workshop is organized in the framework of the FP7 Coordination and Support
Action European Project "MAMA: unlocking research potential for multifunctional advanced
materials and nanoscale phenomena" under Grant Agreement No. 264098.
MAMA- Hybrids is the third of a series of meetings that are organised within the MAMA project
and are fully funded by the European Commission.
The aim of the workshop is to join together leading scientists involved in the field of fabrication,
characterization, and modeling of multifunctional hybrids and organics, in order to address their
fundamental aspects and novel functionalities also emerging from the coupling of different
materials and phenomena. Indeed this research is moved forward by the continuous developments
in the fabrication techniques, which make possible the reliable realization of complex
heterostructures consisting of layers only a few nanometers thick coupled through high quality
contacts.
One among the many fundamental and challenging issues in the context of hybrids materials is to
design and explore the coupling between materials with vastly different properties such as
ferromagnets, antiferromagnets, superconductors, ferroelectrics, multiferroics, geometrically
frustrated spin systems, heavy fermions, organics and others. Considering the enormous number of
combinations and the inherent complexity behind the various collective phenomena possibly
involved, the outcome is highly non trivial with a huge potential for generating novels state of
matter and multifunctionalities as well as new devices with a great technological impact.
The ultimate goal of the event is to promoting knowledge exchange in the field of multifunctional
material science and eventually encourage new collaborations and information exchanges among
different groups involved in the investigation of novel hybrids functional materials.
The MAMA-Hybrids Chairs
Mario Barra and Carla Cirillo
IV
Conference Chairmen
M. Barra (CNR SPIN, Italy)
C. Cirillo (CNR SPIN, Italy)
Scientific Committee
C. Attanasio (Università di Salerno, Italy)
A. Barthelemy (Unité Mixte de Physique CNRS/Thales, Palaiseau Cedex, France)
A. Cassinese (Università di Napoli “Federico II”, Italy)
S. Iannotta (CNR IMEM, Italy)
Y. Iwasa (Unversity of Tokio, Japan)
D. Larbalestier (Florida State University, Tallahassee, USA)
S. Picozzi (CNR SPIN, Italy)
G. Rijnders (University of Twente, The Netherlands)
A. Romano (Università di Salerno, Italy)
P. Rudolf (Rijksuniversiteit Groningen, The Netherlands)
A. Ustinov (Karlsruhe Institute of Technology, Germany)
J. Van Den Brink (IFW Dresden, Germany)
V
Organizing Committee
A. Ambrosio (CNR SPIN, Italy)
F. Chiarella (CNR SPIN, Italy)
F. V. Di Girolamo (CNR SPIN, Italy)
A. Guarino (Università di Salerno, Italy)
G. Santoro (CNR SPIN, Italy)
MAMA Workshop Coordinator
C. Cirillo (CNR SPIN, Italy)
Workshop Organizing Agency
WEB Site
Maurizio Cembalo (CNR SPIN, Italy)
VI
Attending Companies
VII
Table of Contents
Workshop Program ....................................................................................................................................... IX
Poster Session ............................................................................................................................................... XII
Session 1: Monday, October 22nd
2012 ......................................................................................................... 1
1.1 Superconductivity and electronics of new carbon materials ............................................................. 2
1.2 Optimizing Picene molecular assembling by Supersonic Molecular Beam Deposition .................. 3
1.3 NMR Study of the A15 and fcc Cs3C60 superconducting phases ..................................................... 4
1.4 Mutiferroicity and Magnetoelectricity in a Metal-Organic Framework .......................................... 5
1.5 Crystal symmetry and properties at interfaces of epitaxial perovskites .......................................... 6
1.6 Experimental Evidence of Hybrid Improper Ferroelectricity .......................................................... 7
1.7 Tailoring oxide ferroelectric films for organic and microwave sensor technology ......................... 8
1.8 The role of the interfaces in novel superconducting CaCuO2/SrTiO3 superlattices ........................ 9
1.9 Interference Phenomena and Long–Range Proximity Effect in SFS Systems ............................... 10
1.10 All-oxide superconductor/ferroic hybrids ....................................................................................... 11
1.11 Spin-orbital coupling at triplet superconductor-ferromagnet interfaces ..................................... 12
1.12 Transport and structural properties of Nb/PdNi/Nb superconducting heterostructures ........... 13
1.13 Magnetoresistance and spin-transfer torque in hybrid superconductor/ferromagnet
structures .................................................................................................................................................... 14
1.14 Magnetic Josephson Junctions ......................................................................................................... 15
1.15 Josephson current through spin-filtering barriers ......................................................................... 16
1.16 The robust odd frequency paring in ferromagnet/superconductor hybrids ................................ 17
1.17 Electronic Transport Properties of Nanostructured Superconductor/Ferromagnet Point
Contacts ...................................................................................................................................................... 18
Session 2: Tuesday, October 23rd
2012 ....................................................................................................... 19
2.1 Intermolecular electron transport of model molecules investigated by break junctions on the
level of individual molecules ..................................................................................................................... 20
2.2 Charge transport and charge traps in PDIF-CN2 : an n-type semiconductor in three
modifications compared to p-type organic semiconductors .................................................................. 21
2.3 Organic position sensitive photodetectors based on wedge dono-acceptor bilayers with
complementary thickness .......................................................................................................................... 22
2.4 Scanning Kelvin Force Microscopy on Hybrid Solar Cells ............................................................. 23
2.5 Charge transfer processes in organic nano- and hetero-structures. .............................................. 24
2.6 Theoretical study of crystalline PDI-FCN2 ........................................................................................ 25
2.7 Bias Stress effects in n-type Perylene Diimide transistors ............................................................... 26
2.8 Transport Properties of Ni decorated Carbon Nanotube Fibres .................................................... 27
2.9 Non-conducting and non-magnetic interfaces of LaAlO3/SrTiO3 made by sputter deposition .... 28
2.10 Exploring low dimensional transport in SrTiO3–based heterostructures .................................... 29
2.11 Transport properties of LaAlO3/SrTiO3 mesoscopic devices ........................................................ 30
2.12 On the origin of the two dimensional electron gas at the polar/non polar oxide interfaces........ 31
2.13 Manipulating interface magnetism at complex oxide interfaces: Novel functionalities in
magnetic tunnel junctions ......................................................................................................................... 32
2.14 Monocrystalline porous ZnO nanostructures from hybrid organic-inorganic precursors:
formation processes and patterning ......................................................................................................... 33
2.15 Circular dichroism of chemisorbed DPED chiral molecule films ................................................. 34
VIII
Session 3: Wednesday, October 24th
2012 .................................................................................................. 35
3.1 Optical patterning of polymers embedding photo-active molecules ............................................... 36
3.2 Helical-wavefront-sensitive material displacement on the surface of an azo- polymer film under
optical vortex illumination ........................................................................................................................ 37
3.3 Back-action effects on the electronic current in a Carbon Nanotube nanomechanical resonator 38
3.4 Edge-dependent transport in graphene ............................................................................................. 39
3.5 Heat interferometry with Josephson junctions ................................................................................. 40
3.6 A Single Electron Transistor to probe the excitation spectrum of a YBCO nanoisland .............. 41
3.7 Novel superconducting materials and hybrids for advanced superconducting detectors ............ 42
3.8 The generic requisites of the absolute superconducting magnetoresistance effect in FM-SC-FM
trilayers ....................................................................................................................................................... 43
Poster Session: Tuesday, October 23rd
17:00 -19:00 .................................................................................. 44
P.1 Charge transfer at the interface between Sexithiophene (T6) and N,N’-bis (n-octyl)-
dicyanoperylenediimide (PDI-8CN2) Heterostructures investigated by UPS measurements ............. 45
P.2 Effect of Inhomogeneous Magnetization on the Superconducting Properties of Nb/Py/Nb
Trilayers: Evidence of Spin-Triplet Superconductivity ......................................................................... 46
P.3 Transport properties of organic devices: from intrinsic carrier motion to disorder dominated
hopping ....................................................................................................................................................... 47
P.4 Visualizing Vortex dynamics in Superconducting/Ferromagnetic thin film heterostructures by
low temperature Magnetic Force Microscopy ........................................................................................ 48
P.5 Single-Crystal Organic Charge-Transfer Interfaces probed using Schottky-Gated
Heterostructures ........................................................................................................................................ 49
P.6 Scanning Tunneling Microscopy and Spectroscopy study on the Metal-quinoline/La0.7Sr0.3MnO3
interface ...................................................................................................................................................... 50
P.7 Odd-Frequency Triplet Pairing in Mixed-Parity Superconductors .............................................. 51
P.8 Investigation of resistive switching behavior and nanoscale electronic transport of Au/Nb-
doped SrTiO3 junctions ............................................................................................................................. 52
P.9 Superconducting FeSe0.5Te0.5 thin films: a morphological and structural investigation with
scanning tunnelling microscopy and X-ray diffraction .......................................................................... 53
P.10 Electronic redistribution and charge localization at organic-organic and organic-dielectric
interfaces probed by optical second harmonic generation .................................................................... 54
P.11 Zeolite Nanoparticles formation using a Dendrimer Template .................................................. 55
P.12 Nonlocal thermoelectric symmetry relations in ferromagnet-superconductor proximity
structures .................................................................................................................................................... 56
P.13 Photophysics at organic/inorganic semiconductor interfaces ..................................................... 57
P.14 Using muons as microscopic spin probes for organic devices ..................................................... 58
P.15 Charge transport in single-crystal organic semiconductors ....................................................... 59
P.16 Quantum pumping theory of organic-inorganic hybrid nanodevices ........................................ 60
P.17 Laser as a flexible Heat Source for Deposition and Analysis of functional Materials .............. 61
P.18 Quantum capacitance of few-layer graphene ............................................................................... 62
Index of presenting contributors .................................................................................................................. 63
IX
Workshop Program
Monday, October 22nd Time Topic Speaker
8.45-9.00 Welcome
Chairman: Bertram Batlogg
9.00 - 9.30
Invited
Superconductivity and electronics of new carbon materials
Y. Kubozono
9.30 - 9.50
Oral
Optimizing Picene molecular assembling by Supersonic Molecular Beam Deposition
S. Gottardi 9.50 - 10.10
Oral
NMR Study of the A15 and fcc Cs3C60 superconducting phases
D. Pontiroli 10.10 - 10.30
Oral
Multiferroicity and Magnetoelectricity in a Metal-Organic Framework
A. Stroppa
10.30 - 10.50 Coffee break
Chairman: Jacobo Santamaria
10.50 - 11.20
Invited
Crystal symmetry and properties at interfaces of epitaxial perovskites
G. Koster 11.20 - 11.50
Invited
Experimental Evidence of Hybrid Improper Ferroelectricity
C. Adamo
11.50 – 12.10
Oral
Tailoring oxide ferroelectric films for organic and microwave sensor technology
R. Wördenweber 12.10 - 12.30
Oral
The role of the interfaces in novel superconducting CaCuO2/SrTiO3 superlattices
C. Aruta
12.30 - 14.30 Lunch
Chair Chairman: Jan Aarts 14.30 - 15.00
Invited
Interference Phenomena and Long–Range Proximity Effect in SFS Systems
A.I. Buzdin 15.00 - 15.30
Invited
All-Oxide Superconductor/Ferroic Hybrids
J. E. Villegas 15.30 - 15.50
Oral
Spin-orbital coupling at triplet superconductor-ferromagnet interfaces
P. Gentile 15.50 - 16.10
Oral
Transport and structural properties of Nb/PdNi/Nb superconducting heterostructures
E. Silva
16.10 - 16.30
Oral
Magnetoresistance and spin-transfer torque in hybrid superconductor/ferromagnet structures
R. Citro
16.30 - 16.50 Coffee break
Chair Chairman: Carmine Attanasio
16.50 - 17.20
Invited
Magnetic Josephson Junctions
M. Blamire
17.20 - 17.50
Invited
Josephson current through spin-filtering barriers
F. S. Bergeret
17.50 - 18.10
Oral
The robust odd frequency paring in ferromagnet/superconductor hybrids
S. Kawabata
18.10 - 18.30
Oral
Electronic Transport Properties of Nanostructured Superconductor/Ferromagnet
Point Contacts
G. Goll
X
Tuesday, October 23rd
Time Topic Speaker
Chair Chairman: Alberto Morgante
9.00 - 9.30
Invited
Intermolecular electron transport of model molecules investigated by break junctions on
the level of individual molecules
D. Mayer
9.30 - 9.50
Oral
Charge transport and charge traps in PDIF-CN2 : an n-type semiconductor in three modifications
compared to p-type organic semiconductors
B. Batlogg 9.50 - 10.10
Oral
Organic position sensitive photodetectors based on wedge donor-acceptor bilayers with
complementary thickness
J. Cabanillas- Gonzalez
10.10 - 10.30
Oral
Scanning Kelvin Force Microscopy on Hybrid Solar Cells
M. Biasucci
10.30 - 10.50 Coffee break
Chair Chairman: Yoshihiro Kubozono
10.50 - 11.20
Invited
Charge transfer processes in organic nano- and hetero-structures
A.Morgante
11.20 - 11.40
Oral
Theoretical study of crystalline PDI-FCN2
R. Colle
11.40 - 12.00
Oral
Bias Stress effects in n-type Perylene Diimide transistors
A. Cassinese
12.00 - 12.20
Oral
Transport Properties of Ni decorated Carbon Nanotube Fibres
M. Salvato
12.20 - 13.50 Lunch
Chair Chairman: Javier Villegas
13.50 - 14.20
Invited
Non-conducting and non-magnetic interfaces of LaAlO3/SrTiO3 made by sputter deposition
J. Aarts
14.20 - 14.50
Invited
Exploring low dimensional transport in SrTiO3–based heterostructures
C. Bell
14.50 - 15.10
Oral
Transport properties of LaAlO3/SrTiO3
mesoscopic devices
D. Stornaiuolo
15.10 - 15.30
Oral
On the origin of the two dimensional electron gas at the polar/non polar oxide interfaces
U. Scotti di Uccio
15.30-15.50 Coffee break
Chair
Chairman: Fabio Miletto
15.50 - 16.20
Invited
Manipulating interface magnetism at complex oxide interfaces: Novel functionalities in
magnetic tunnel junctions
J. Santamaria 16.20 - 16.40
Oral
Monocrystalline porous ZnO nanostructures from hybrid organic-inorganic precursors:
formation processes and patterning
R. Mosca 16.40 - 17.00
Oral
Circular dichroism of chemisorbed DPED chiral molecule films
M. A. Ortì Nino 17.00 - 19.00
Poster Session
20.30
Social Dinner
XI
Wednesday, October 24th
Time Topic Speaker
Chair Chairman: Stefano Lettieri
9.00 - 9.30
Invited
Optical patterning of polymers embedding photo-active molecules
A.Camposeo
9.30 - 9.50
Oral
Helical-wavefront-sensitive material displacement on the surface of an azo-polymer
film under optical vortex illumination
A.Ambrosio 9.50 - 10.10
Oral
Back-action effects on the electronic current in a Carbon Nanotube nanomechanical resonator
A. Nocera 10.10 - 10.30
Oral
Edge-dependent transport in graphene
H. Goto 10.30 - 10.50 Coffee break
Chairman: Ruggero Vaglio
10.50 - 11.20
Invited
Heat interferometry with Josephson junctions
F. Giazotto 11.20 - 11.50
Invited
A Single Electron Transistor to probe the excitation spectrum of a YBCO
nanoisland
F. Lombardi 11.50 - 12.10
Oral
Novel superconducting materials and hybrids for advanced superconducting detectors
G. Pepe 12.10 - 12.30
Oral
The generic requisites of the absolute superconducting magnetoresistance effect in
FM-SC-FM trilayers
D. Stamopoulos
12.30 - 12.45
Closing words
XII
Poster Session P.1 Charge transfer at the interface between Sexithiophene (T6) and N,N’-bis
(n-octyl)- dicyanoperylenediimide (PDI-8CN2) Heterostructures investigated by
UPS measurements. M.Barra, F. Ciccullo, A. Cassinese, F. V. Di Girolamo, L. Aversa, R.
Verucchi, S. Iannotta
P.2 Effect of Inhomogeneous Magnetization on the Superconducting Properties
of Nb/Py/Nb Trilayers: Evidence of Spin-Triplet Superconductivity - C. Cirillo, E.
A. Ilyina, A. Garcia-Santiago, J. M. Hernandez, J. Tejada, and C. Attanasio
P.3 Transport properties of organic devices: from intrinsic carrier motion to
disorder dominated hopping - S. Ciuchi, S. Fratini, Didier Mayou
P.4 Visualizing Vortex dynamics in Superconducting/Ferromagnetic thin film
heterostructures by low temperature Magnetic Force Microscopy - C. Di Giorgio,
A. Scarfato, M. Iavarone, M. Longobardi, F. Bobba; G. Karapetrov, V. Novosad and A.M.
Cucolo1,2
P.5 Single-Crystal Organic Charge-Transfer Interfaces probed using Schottky-
Gated Heterostructures – I. Gutiérrez Lezama, M. Nakano, N. A. Minder, Z. Chen, F. V. Di
Girolamo, A. Facchetti and A. F. Morpurgo
P.6 Scanning Tunneling Microscopy and Spectroscopy study on the Metal-
quinoline/La0.7Sr0.3MnO3 interface - A. Gambardella, R. Cecchini, P. Graziosi, I. Bergenti,
F. Biscarini and V. Dediu
P.7 Odd-Frequency Triplet Pairing in Mixed-Parity Superconductors - P. Gentile,
C. Noce, A. Romano, G. Annunziata, J. Linder and M. Cuoco
P.8 Investigation of resistive switching behavior and nanoscale electronic
transport of Au/Nb-doped SrTiO3 junctions - A. Gerbi, R. Buzio, A. Gadaleta, L.
Anghinolfi, F. Bisio, E. Bellingeri, A.S. Siri, D. Marré
P.9 Superconducting FeSe0.5Te0.5 thin films: a morphological and strutural
investigation with scanning tunnelling microscopy and X-ray diffraction - Andrea
Gerbi, Renato Buzio, Emilio Bellingeri, Shrikant Kawale, DanieleMarrè, Antonio Sergio Siri,
Andrea Palenzona, and Carlo Ferdeghini
P.10 Electronic redistribution and charge localization at organic-organic and
organic-dielectric interfaces probed by optical second harmonic generation - S.
Lettieri, F. Ciccullo, A. Cassinese, P. Maddalena
P.11 Zeolite Nanoparticles formation using a Dendrimer Template - L. Bonaccorsi,
P. Calandra, E. Proverbio and D. Lombardo
XIII
P.12 Nonlocal thermoelectric symmetry relations in ferromagnet-
superconductor proximity structures - P. Machon, M. Eschrig, W. Belzig
P.13 Photophysics at organic/inorganic semiconductor interfaces - M. M. Mróz, D.
Granados , D. Fuster, Y. Gonzalez, L. Gonzalez and J. Cabanillas-Gonzalez
P.14 Using muons as microscopic spin probes for organic devices - L. Nuccio, L.
Schulz, M. Willis, T. Kreouzis, W. P. Gillin, A. Suter, T. Prokscha, E. Morenzoni, C. Bernhard, A.
J. Drew
P.15 Charge transport in single-crystal organic semiconductors - C. A. Perroni, A.
Nocera, V. Marigliano, V. Cataudella
P.16 Quantum pumping theory of organic-inorganic hybrid nanodevices - F.
Romeo , R. Citro
P.17 Laser as a flexible Heat Source for Deposition and Analysis of functional
Materials – W. Stein
P.18 Quantum capacitance of few-layer graphene - E. Uesugi, H. Goto, R. Eguchi, Y.
Kubozono
XIV
1
Session 1:
Monday, October 22nd
2012
2
1.1 Superconductivity and electronics of new carbon materials
Yoshihiro Kubozono1, Xuexia He
1, Kazuya Ternishi
1, Eri Uesug
1, Ritsuko Eguchi
1, Hidenori Goto
1,
Takashi Kambe2
1Research Laboratory for Surface Science, Okayama University, Okayama 700-8530, Japan
2Department of Physics, Okayama University, Okayama 700-8530, Japan
Corresponding author: Yoshihiro Kubozono, Okayama University, Okayama 700-8530, Japan. E-mail:
Aromatic hydrocarbons (CnHm) consist of several fused benzene rings and -electron is
delocalized on the benzene frameworks. We recently discovered new superconductors of
aromatic hydrocarbon, picene (PI), [1], and the superconducting transition temperature, Tc, was 7
or 18 K for K3PI. Furthermore, the metal intercalated solids of phenenthrene (PHE) and
dibenzopentacene (DBP) showed the superconducting transition with Tc as high as ~5 and 33 K,
respectively [2,3]. In all aromatic hydrocarbons, three-electron donation from metal atoms to an
aromatic hydrocarbon molecule is a key for superconductivity. The three-electron donation is
experimentally confirmed by use of Raman spectroscopy [2,4]. The metal atoms are not
intercalated into the space between herringbone molecular layers (interlayer) but the space in the
herringbone molecular layer (intralayer), which was confirmed by change of lattice constants (a,
b and c) in intercalating metal atoms. The density of states at the Fermi level, D( F), were
determined to be 0.5 and 1.2 states eV-1
spin-1
(picene)-1
from ESR of 7 K and 18 K phases of
AxPI (A: alkaki metal atom) superconductors, showing that larger D( F) led to higher Tc. These
results can be explained by BCS theorem [2]. Very recently, Iwasa et al. measured the specific
heat for Ba1.5PHE and reported to be o/kBTc = 1.95, consistent with BCS theorem ( o/kBTc =
1.73) [5]. Thus the physical properties of aromatic hydrocarbon superconductors have been
gradually clarified. In this talk, I will show the synthesis methods for obtaining high-quality
aromatic superconductor samples, their physical properties and mechanism of superconductivity.
Further, I will talk on transport properties of graphene transistors, because they show the quite
interesting phenomena reflecting massless Dirac Fermion system. We investigated flat band
characteristic of graphene with zigzag edge. Furthermore, we investigated the difference in
transport and capacitance between ABA and ABC stacked trilayer graphenes, whose difference
was theoretically predicted. We often observed a peak at around neutral point in σ– Vg curve,
which exactly reflects flat band in zigzag edge, because the peak was enhanced in graphene with
large fraction of zigzag edges in channel region. The large difference in capacitance between
ABA and ABC stacked trilayer graphenes was also observed. The final purpose of our study on
graphene may be a realization of superconductivity in graphene. The preliminary investigation
on electrostatic electron doping suggested the difficulty in high-density electron accumulation
into graphene because of insufficient capacitance, implying the difficulty in electrostatic induced
superconductivity. Chemical and electrochemical doping of electrons may be indispensable for
high density electron accumulation, or induction of superconductivity in graphene.
[1] R. Mitsuhashi et al., Nature 464, 76 (2010).
[2] X. F. Wang et al., Nature Commun. 2, 507 (2011).
[3] M. Xue et al., Nature Scientific Report, 2:389 DOI: 10.1038/srep00389 (2012).
[4] Y. Kubozono et al., Phys. Chem. Chem. Phys. 13, 16476 (2011)
[5] Y. Kasahara et al. submitted.
3
1.2 Optimizing Picene molecular assembling by Supersonic Molecular Beam
Deposition
S. Gottardi1, T. Toccoli
1, S. Iannotta
1, P. Bettotti
2, A. Cassinese
3, M. Barra
3, L. Ricciotti
4, Y.
Kubozono5
1IMEM-CNR Divisione di Trento, Via alla Cascata 56/C, I-38123 Povo Trento (Italy)
2Laboratorio Nanoscienze, Department of Physics, University of Trento, Via Sommarive 14, I-
38050 Povo Trento (Italy) 3CNR-SPIN and Department of Physics Science, University of Naples “Federico II”, P.le Tecchio
80, 80125, Naples, (Italy) 4Department of Chemistry, University of Naples ”Federico II”, Via Cinthia, I-80126 Naples, (Italy)
5Research Laboratory for Surface Science, Okayama University Okayma 700-8530, (Japan)
Corresponding author: Stefano Gottardi. E-mail: [email protected]
Picene revealed recently to be a very interesting molecule for organic electronics, since it
was successfully applied to realize the active channels of FET able to work even in
ambient conditions or in oxygen atmosphere. Moreover, when intercalated with alkali
metals, picene was demonstrated to exhibit superconductivity at 18K, becoming the first
superconducting hydrocarbon. This discovery renewed the interest in the field of organic
superconductors and the superconductivity was also found in other alkali metals-
intercalated molecular-solids. The possibility to widely tune the electronic properties of
these systems is motivating an intense research activity on these compounds both from
theoretical and experimental point of view. So far, however, very little is known about the
self-assembling properties of picene molecules and no report is yet available to clarify the
deposition conditions able to assure the growth of high quality films. This is a fundamental
step to improve the electronic and optoelectronic properties of these materials making them
ready for future device application. Our work goes in this direction. Here we report an
investigation of the growth of picene by supersonic molecular beam deposition on thermal
SiOxSi and on a self-assembled monolayer of hexamethyldisiloxane (HMDS). The films
morphology show a structure with well separated islands which dimensions and heights
depend on the deposition conditions. At the same time the surface plays a relevant role in
the film growth. In particular on the hydrophobic HMDS the islands are characterized by
large regular crystallites of several microns with an average height of about 50nm, while
on bare silicon oxide the dimension is of about one microns and the average height is of
about 74nm; in both cases we observe very high and sharp island edges. We describe this
particular growth as a balancing mechanism involving the weak interaction between the
molecules and the surface and the strong picene-picene interaction that lead to a different
Schwoebel-Ehrlich barrier in the first layer respect the successive. We study also the
charge transport properties of these films by the fabrication of FETs devices in top and
bottom contact configuration. A maximum mobility value of 1.2cm2 volt
-1 sec
-1 is
measured in air in case of top contact devices. We compare the results achieved by
supersonic molecular beam deposition with the literature for evaporated picene thin films.
4
1.3 NMR Study of the A15 and fcc Cs3C60 superconducting phases
D. Pontiroli1, M. Aramini
1, M. Mazzani
1, M. Riccò
1, Y. Ihara
2, P. Wzietek
2 and H. Alloul
2
1Dipartimento di Fisica, Università di Parma, Via G. Usberti 7/a, 43124 Parma
2Laboratoire de Physique des Solides, Université Paris-Sud 11, CNRS UMR 8502 – 91405 Orsay,
France
Corresponding author: Dr. Daniele Pontiroli, Dipartimento di Fisica, Università di Parma, Via G. Usberti 7/a, 43124
Parma, Tel. +39 0521 905231. E-mail: [email protected]
Superconductivity (SC) in alkali intercalated fullerides has been studied since twenty years
ago, when it was discovered in K3C60 [1], featuring a relative high critical temperature (Tc)
of 19 K. In these compounds, the pair coupling is mediated by “on-ball” C60 phonons and
the scaling of Tc with the inter-ball C60 distance can be quite well described in the
framework of simple BCS theory. However, further experimental and theoretical works
indicated that the presence of electronic correlations must be taken into account if one
needs to describe in detail the electronic properties of these compounds [2].
Recently, the hyper-expanded fulleride A15-Cs3C60 attracted a strong interest, since it
shows an AF insulating ground state, which could be switched to a superconducting one
(Tc=38 K) simply by applying a moderate hydrostatic pressure, while preserving the initial
cubic symmetry [3]. The presence of a clear Mott-insulator transition and the observation
of a “bell-shaped” dependence of Tc on the applied pressure indicated that A15-Cs3C60
could represent a “model-system” for studying the SC mechanism in high-Tc
superconductors. Here we present a detailed study of the electronic properties of Cs3C60
superconducting phases, by means of solid state NMR spectroscopy measurements
performed under pressure. Cs3C60 is invariably found as a mixture of three polymorphs,
either simple cubic (A15), face centered cubic (fcc) and body centered orthorhombic (bco),
whose relative amount was easily determined by quantitative analysis of synchrotron
powder diffraction data. We found for the first time that in this system both A15 and fcc
exhibit a Mott transition to a superconducting phase, with different critical pressures (pc)
and Tc [4]. However, if one rescales Tc as a function of the unit volume per C60, the
diagrams of the two phases superimpose, thus establishing that the inter-ball distance is the
driving parameter for the electronic properties in Cs3C60. Below pc, the magnetic ground
state is quite different in the two phases, according to their different crystal structure. Clear
evidences of the presence of electronic correlations near the Mott transition emerged by
spin lattice relaxation T1 measurements across pc, which cannot be explained in a simple
BCS scenario [5].
[1] A. Hebard et al., Nature 350, 600 (1991) - [2] O. Gunnarsson, Rev. Mod. Phys. 69, 575 (1997)
[3] A.Y. Ganin et al., Nat. Mater. 7, 367 (2008) - [4] Y. Ihara et al., Phys. Rev. Lett. 104, 256402
(2010) - [5] Y. Ihara et al. Europhys. Lett. 94, 37007 (2011)
5
Metal-organic frameworks (MOFs) show increasing promise as materials for applications
in catalysis, gas storage and molecular recognition, and are also interesting from
fundamental condensed-matter physics point of view. Of particular interest are MOFs with
the perovskite architecture, which show hydrogen bonding-related multiferroic
phenomena, exhibiting both magnetic and ferroelectric ordering. Here, we focus on
[C(NH2)3]Cu(HCOO)3 , a compound that crystallizes in polar space group. We have
performed ab-initio calculations[1] and show theoretically, for the first time in a MOF, that
the ferroelectricity related to this polar structure induces a weak ferromagnetic coupling. In
inorganic perovskite-like compounds with the ABX3 composition, octahedral tilting and
Jahn-Teller effects are usually non-polar distortions. However, in this MOF cooperative
interactions between the formate framework and the central guanidinium cation via
hydrogen bonding breaks the inversion symmetry and induces a ferroelectric polarization.
Moreover, we show that the switching of polarization direction implies the reversal of the
weak ferromagnetic component, therefore allowing long sought-after electrical control of
the magnetization. These results therefore offer an important starting point for tailoring
multiferroic properties in this emerging class of materials for various technological
applications.
A. Stroppa et al, Angew. Chemie Int. Ed. 50, 5847 (2010)
1.4 Mutiferroicity and Magnetoelectricity in a Metal-Organic Framework
A. Stroppa1, P. Jain
2, P. Barone
1, M. Marsman
3, J.M. Perez-Mato
4, A. K. Cheetham
5, H. W. Kroto
2,
S. Picozzi1
1CNR-SPIN. L'Aquila, Italy
2Department of Chemistry and Biochemistry, Florida State University Tallahassee, FL 32306
(USA) 3University of Vienna, Faculty of Physics and Center for Computational Materials Science
(Austria) 4Departamento de Fisica de la Materia Condensada Facultad de Ciencia y Tecnologia, UPV/EHU,
Bilbao (Spain) 5Department of Materials Science and Metallurgy University of Cambridge (UK)
Corresponding author: Alessandro Stroppa, CNR-SPIN, L'AQUILA. E-mail: [email protected]
6
1.5 Crystal symmetry and properties at interfaces of epitaxial perovskites
Gertjan Koster
Faculty of Science and Technology and MESA+ Institute for Nanotechnology, University of Twente,
P.O. Box 217, 7500 AE Enschede, The Netherlands
Corresponding author: Gertjan Koster. E-maì: [email protected]
In complex oxide materials the occurrence of ferroelectric, ferromagnetic or other
properties are for the most part determined by the detailed oxygen coordination of metal
cations. More specifically, in the case of perovskite-type materials ABO3, where A and B
are metal cations, by the BO6 octahedral orientations and rotations. At interfaces in
epitaxial oxide hetero structures, for example magnetic junctions or capacitive structures,
this oxygen sub-lattice is found to be different from its bulk counterpart.
Here we will present recent experiments revealing a relationship between precise oxygen
ordering, electronic structure and transport properties using a system where photoemission
as well as transport measurements can be performed under identical controlled conditions.
Such a system is now available at the MESA+ laboratory in Twente also in collaboration
with the university of Amsterdam.
Photoemission spectra, both core-level as well as valence-band spectra of in particular the
3d and 4d elements are very sensitive to their anionic surroundings, for example the Ru 3d
peaks in SrRuO3 or Mn 2p peaks in LaSrMnO3, both important ferromagnetic metals. A
technique related to photoemission is x-ray photoelectron diffraction is subsequently used
to reveal the crystal structure near the model-interfaces.
Examples of oxygen sub-lattice engineering achieved by the insertion of oxide buffer
layers that disrupt the perovskite-type BO6 sub-lattice are found in materials that exhibit a
deviating oxygen sub-lattice from the six-fold oxygen coordination. The effects of such
buffer layers are subsequently studied by previously mentioned characterization techniques
and modeling. Often-encountered problems due to dead-layer effects, which normally
hamper many ferromagnetic or ferroelectric functional devices, could be tackled this way.
Besides improving the functionality of heterostructure devices one might expect to find
surprising properties not found in the bulk, for example a new ferromagnetic insulating
state, which has potential applications in spintronics.
7
1.6 Experimental Evidence of Hybrid Improper Ferroelectricity
C. Adamo1*
R. Misra2, E. Vlahos
3, J. A. Mundy
4, S. A. Denev
3, A. SenGupta
3, J. H. Lee
1,3, N. A.
Benedek4, T. Heeg
1, C. J. Fennie
4, V. Gopalan
4, D. A. Muller
4,5, P. Schiffer
2, and D. G. Schlom
1,5
1Department of Materials Science and Engineering, Cornell University, Ithaca, NY 14853-1501,
USA 2Department of Physics and Materials Research Institute, The Pennsylvania State University,
University Park, Pennsylvania 16802, USA 3Department of Materials Science and Engineering, The Pennsylvania State University, University
Park, Pennsylvania 16802, USA 4School of Applied and Engineering Physics, Cornell University, Ithaca, New York 14853-1501,
USA 5Kavli Institute at Cornell for Nanoscale Science, Cornell University, Ithaca, New York 14853-
1501, USA
Corresponding author: Department of Materials Science and Engineering, Cornell University, Ithaca, NY 14853-1501,
USA. E-mail: [email protected]
Functional oxides that exhibit exciting and potentially useful properties including
superconductivity, ferroelectricity, piezoelectricity, and magnetism are being intensively
studied. These properties, together with the possibility of tuning them through strain,
chemical doping or the application of external fields, make such functional oxides suitable
for use in microelectromechanical systems (MEMS), transistors, and field effect devices.
Moreover interfaces and superlattices of correlated oxides present new opportunities for
controlling and optimizing the magnetic and electric properties. Significant progress in the
growth of atomic-scale multilayers opens exciting opportunities in the design of materials
with novel properties. Recent examples include the new two-dimensional metallic state at
the interface between a band insulator as SrTiO3 and a Mott insulator like LaTiO3 (1-3)
and the emergence of improper ferroelectricity in PbTiO3/SrTiO3 superlattices (4).
In this talk I will present how to engineering thin films and superlattices with abrupt and
coherent interfaces by a reactive molecular-beam epitaxy. In particular, the effect of
dimensional confinement on manganites has been also investigated in thin films by
synthesizing a superlattice of two formula-unit-thick layers of CaMnO3 separated by CaO
double layers, i.e., the n=2 Ruddlesden-Popper phase Ca3Mn2O7. First-principles
calculations predicted that hybrid improper ferroelectricity, magnetoelectricity, andweak-
ferromagnetism are induced simultaneously by octahedron rotation modes in these layered
perovskites (5). Preliminary results related to superlattices for photocatalytic applications
will be also presented.
1. A. Ohtomo, D. A. Muller, J. L. Grazul, and H. Y. Hwang, Nature 419, 378 (2002)
2. S. Okamoto and A. J. Millis, Nature 428, 630 (2004)
3. S. S. A. Seo, W. S. Choi, H. N. Lee, L. Yu, K. W. Kim, C. Bernhard, and T.W.Noh, Phys. Rev.
Lett. 99, 266801 (2007)
4. E. Bousquet, M. Dawber, N. Stucki, C. Lichtensteiger, P. Hermet, S. Gariglio, J.-M.
Triscone, and P. Ghosez, Nature 452, 732 (2008)
5. N. Benedek and C. Fennie, Phys. Rev. Lett. 106, 107204 (2011)
8
1.7 Tailoring oxide ferroelectric films for organic and microwave sensor
technology
R. Wördenweber, T. Ehlig, J. Schubert, R. Kutzner, and E. Hollmann
Peter Grünberg Institute (PGI) and JARA – Fundamentals of Future Information Technologies,
Forschungszentrum Jülich, D-52425 Jülich, Germany
Corresponding author: Roger Wördenweber, Peter Grünberg Institute (PGI-8), Forschungszentrum Jülich, 52425
Jülich. E-mail: [email protected]
Depending on the growth conditions enormous strain can be induced into thin epitaxial
films that allows to modify structural, morphological and electronic properties of the film.
Especially for ferroelectric films the electronic modifications can be huge. Owing to the
strong connection between strain and ferroelectricity, large shifts of the Curie temperature
and polarization are observed in strained ferroelectric material.
We demonstrate that the lattice-mismatch of epitaxial SrTiO3 films on various crystalline
substrates induces (i) tetragonal, orthogonal or even shear distortions of the Perowskite
structure, (ii) generation of different types of defects, including nanogaps (size 10-25nm)
in controllable crystallographic directions, (iii) a dramatic shift of the Curie temperature,
(iv) an anisotropic polarization, and (v) an enhancement of the permittivity. The extent of
all effects depends on the lattice mismatch, i.e. choice of substrate, and can be affected by
the deposition parameters. Shifts of the Curie temperature by more than 200K and
enhancements of the room temperature permittivity from typically 300 to >7000 are
demonstrated. Frequency dependent measurements reveal a relaxor-type ferroelectric
behavior in the temperature regime of induced ferroelectricity. Finally, under well defined
conditions microcracks can be generated in the oxide films along well defined
crystallographic directions. These cracks can serve as natural nanocapacitors for sensor
devices. The model system demonstrates that lattice-misfit induced strain can be a
powerful tool to engineer the properties of heteroepitaxial films and, in particular, the
ferroelectric properties of STO, suitable for various applications in semiconductor
technology ranging from tunable high-frequency devices to microwave sensor concepts.
9
1.8 The role of the interfaces in novel superconducting CaCuO2/SrTiO3
superlattices
C. Aruta1*
, D. Di Castro2, N. Brookes
3, G. Ghiringhelli
4, D. Innocenti
2, T. L. Lee
5, M. Minola
3,4, M.
Moretti Sala3, C. Schlueter
3, A. Tebano
2, J. Zegenhagen
3 and G. Balestrino
2
1CNR-SPIN and Dipartimento di Scienze Fisiche, 80126 Napoli, Italy 2CNR-SPIN and Dipartimento di Ingegneria Informatica Sistemi e Produzione, Università di Roma
Tor Vergata, 00133 Roma, Italy 3ESRF, 38043 Grenoble, CEDEX 9, France
4CNR-SPIN and Dipartimento di Fisica, Politecnico di Milano, 20133 Milano, Italy
5Diamond Light Source Ltd, Didcot, OX11 0DE, UK
Corresponding author: Carmela Aruta, CNR-SPIN and Dipartimento di Scienze Fisiche, Via Cintia, Monte Sant’Angelo
- I-80126 – Napoli – Italy. E-mail: [email protected]
High transition temperature superconductivity in several heterostructures based on
insulating and metallic (non-superconducting) cuprates has been reported [1-4], as a result
of the electronic properties at the interface between the constituent blocks. Very recently,
novel superconducting superlattices (SLs) based on two insulating oxides, CaCuO2 and
SrTiO3, have been grown in the laboratory of Tor Vergata University in Rome [5].
Significant experimental evidence points towards the confinement of superconductivity to
within few unit cells at the CaCuO2/SrTiO3 interface and to the important role of additional
oxygen atoms placed at the interfaces during growth in oxygen rich environment. To
disentangle the role of each layer block and disclose the mechanism, giving rise to
superconductivity at the interface, we used soft x-ray absorption spectroscopy (XAS) at Cu
and Ti L-edges, and bulk sensitive core-level and valence-band hard x-ray photoelectron
spectroscopy (HAXPES).
Clear evidence of an increase in the concentration of holes delocalized on the Cu3d-O2p
band was obtained by XAS at Cu L-edge. On the contrary, no relevant changes in the XAS
spectra at Ti L-edge were observed between superconducting and non superconducting SL,
indicating that, not only the valence, but even the crystal-field in the Ti environment, are
affected by the oxidizing atmosphere used to obtain superconductivity. Additionally, O K-
edge spectra show doped holes with O2pz character, associated to apical oxygen.
HAXPES measurements revealed a rigid shift of all of the SrTiO3 core and valence band
levels, which can be explained in terms of interfacial polarity. The electrostatic built-in
potential is possibly suppressed by ionic mechanism, as confirmed by the width of the Ti2p
and Sr3d core levels. Furthermore, evidence for the extra-oxygen at the interface is
provided by the presence of side components at several core levels, due to ion sites with
different oxygen coordination. The important role of the interfaces in doping the CuO2
planes is also established by comparison of the Cu2p core level in superconducting and
non superconducting SLs.
The whole picture of the experimental results points toward an interfacial reconstruction by
oxygen redistribution, that in case of excess oxygen generates holes in the CuO2 planes.
Therefore the interface behaves as a charge reservoir for the CuO2 planes allowing
superconductivity in the CCO layers of the SLs.
[1] G.Balestrino et al. Phys. Rev.B 58, R8925 (1998) - [2] A. Gozar et al., Nature 455, 782-785 (2008) - [3]
S. Smadici et al., Phys. Rev. Lett. 102, 107004 (2009) - [4] C. Aruta et al., Phys. Rev. B 78, 205120 (2008),
[5] D. Di Castro et al., cond-mat arXiv:1107.2239
10
1.9 Interference Phenomena and Long–Range Proximity Effect in SFS Systems
A.I. Buzdin1, A. Mel'nikov
2, A. Samokhvalov
2
1Institut Universitaire de France and Universite Bordeaux I, FRANCE
2Institute for Physics of Microstructures, Russian Academy of Sciences, RUSSIA
Corresponding author: Alexander I. Buzdin. E-mail: [email protected]
We study different mechanisms of long range proximity effect in superconductor –
ferromagnetic structures both in clean and diffusive limits. Our consideration of these
limits is based on the quasiclassical Eilenberger equations and Usadel theory,
correspondingly. In the dirty limit a noticeable increase in the critical current appears only
for a system with noncollinear magnetic moments. Even a small modulation of the
exchange field along the quasiclassical trajectories is shown to provide a long range
contribution to the supercurrent due to the interference effects. This modulation of the
exchange field along trajectories experiencing multiple normal reflections at the system
boundaries can appear either due to the domain structure or due to the momentum
dependence of the exchange field caused by the spin – orbital effects.
11
1.10 All-oxide superconductor/ferroic hybrids
C. Visani
1, A. Crassous
1, Z. Sefrioui
2, R. Bernard
1, S Fusil
1, K. Bouzehouane
1, J. Tornos
2, C.
León2, J. Briatico
1, M. Bibes
1, A. Barthélémy
1, J. Santamaría
2, and Javier E. Villegas
1
1Unité Mixte de Physique CNRS/Thales and Université Paris Sud, France
2 GFMC, Universidad Complutense de Madrid, Spain
Corresponding author: Javier E. Villegas, Unité Mixte de Physique CNRS/Thales, 1 avenue A. Fresnel, 91767
Palaiseau, France, Phone : +33 169 41 58 56. Email : [email protected] .
Oxide perovskites offer many possibilities for the realization of hybrid structures. A large
variety of isostructural materials with different ground states (high-Tc superconductors,
insulators, ferromagnets, ferroelectrics) are available which, crucially, can be combined in
high-structural-quality heterostructures. The interactions at the interfaces between the
hybrid’s constituents often promote novel physical properties, which ultimately allows
engineering artificial materials with new functionalities.
One example of these is the nanoscale manipulation the superconducting condensate via
field-effects in superconductor/ferroelectric bilayers [1]. We show that, in this system, an
unusually large modulation of the superconducting critical temperature can be induced
upon reversal of the ferroelectric polarization. This, combined the ability to reversibly
design the ferroelectric domain structure, allows one to produce a nanoscale modulation of
the superconducting condensate. This opens new possibilities for superconducting nano-
electronic devices, which may exploit flux quantization and Josephson coupling.
Another example is given by the “hybridization” of the long-range phase-coherent charge
transport characteristic of superconductivity with the spin-polarized charge transport
characteristic of ferromagnetism, which we demonstrate in experiments with
heterostructures that combine cuprate superconductors and manganite half-metallic
ferromagnets [2]. The possibility to create this form of “spin-polarized supercurrents”
opens the door to a new class of spintronic devices.
[1] A. Crassous, R. Bernard, S. Fusil, K. Bouzehouane, D. Le Bourdais, S. Enouz-Vedrenne, J.
Briatico, M. Bibes, A. Barthélémy, and Javier E. Villegas, Phys. Rev. Lett. 107, 247002 (2011)
[2] C. Visani, Z. Sefrioui, J. Tornos, C. León, J. Briatico, M. Bibes, A. Barthélémy, J. Santamaría
and Javier E. Villegas, Nature Physics (2012), doi:10.1038/nphys2318.
[3] M. Eschrig, Phys. Today 64, 43 (2011).
Work supported by French ANR « SUPERHYBRIDS-II », RTRA « Triangle de la Physique » and
Marie-Curie IEF « PIXIE »
12
1.11 Spin-orbital coupling at triplet superconductor-ferromagnet interfaces
M. Cuoco1, P. Gentile
1, A. Romano
1, C. Noce
1, D. Manske
2, and P. M. R. Brydon
3
1 Dipartimento di Fisica ``E. R. Caianiello”,Università di Salerno and CNR-SPIN, I-84084
Fisciano (Salerno), Italy 2Max-Planck-Institut für Festkörperforschung, Heisenbergstr. 1, D-70569 Stuttgart, Germany
3Institut für Theoretische Physik, Technische Universität Dresden, D-01062 Dresden, Germany
Corresponding author: Dr. Paola Gentile, CNR-SPIN Salerno and Dipartimento di Fisica "E. R. Caianiello", Università
degli Studi di Salerno, Via Ponte don Melillo, I-84084 Fisciano (SA), Italy. E-mail: [email protected]
We determine the proximity effect and the stable magnetic configuration of a triplet
superconductor-ferromagnet (TSC-FM) junction in the clean regime due to the interplay
between spin-triplet superconductivity with px+ipy, px, or py symmetries and itinerant
ferromagnetism. We show that the direction of the magnetization can be controlled by
selecting the orbital symmetry of the TSC order parameter and the strength of the
ferromagnetic exchange for a junction with an interface parallel to the y-direction, i.e.
[010], in the xy plane. Using a self-consistent Bogoliubov- de Gennes approach, we
demonstrate that the various effects occurring in a TSC-FM hybrid, i.e. the suppression of
the TSC order parameter, the proximity behaviour, the change of the interface energy
spectrum, cooperate to stabilize a magnetization direction in the ferromagnet with a
configuration that is parallel or perpendicular to the d-vector or, equivalently, to the
Cooper pairs spin direction depending on the orbital symmetry. Here the d-vector is
assumed to be aligned along the z-direction. In particular, we show that for chiral spin
triplet order parameter the magnetic direction changes from being perpendicular to parallel
to the d-vector at a critical exchange field through a first-order phase transition. Otherwise
for the px (py) spin-triplet order parameter the Gibbs energy is minimized by a
magnetization that is parallel (perpendicular) to the d-vector for any amplitude of the
ferromagnetic exchange. [2] The results are coherent with previous non-selfconsistent
studies of the spin Josephson effect [3], therefore establishing the robustness of the effect
and the relation with the others that play a role in the physics of the TSC-FM junction.
[1] M. Cuoco, A. Romano, C. Noce, and P. Gentile, Phys. Rev. B 78, 054503 (2008)
[2] P. Gentile, M. Cuoco, A. Romano, C. Noce, D. Manske, P. M. R. Brydon, preprint (2012).
[3] P. M. R. Brydon, Phys. Rev. B 80, 224520 (2009). P. M. R. Brydon, Y. Asano, and C. Timm,
Phys. Rev. B 83, 180504 (2011).
13
1.12 Transport and structural properties of Nb/PdNi/Nb superconducting
heterostructures
E. Silva, C. Meneghini, S. Mobilio, T. Neisius, N. Pompeo, K. Torokhtii
Dipartimento di Fisica “E. Amaldi”, Università Roma Tre, 00146 Roma, Italy * CP2M, Paul
Cezanne University, Marseille, France
Corresponding author: Enrico Silva. E-mail: [email protected]
We study the effect of a ferromagnetic (F) layer on the transport properties of S/F/S
(Superconductor/Ferromagnet/Superconductor) heterostructures by means of microwave
(1-20 GHz) complex resistivity. Morphology and local atomic structure features have been
probed by high resolution-TEM and x-ray absorption fine structure (XAFS) spectroscopy.
S/F/S heterostructures and Nb (S) films (for comparison) have been grown by UHV dc
magnetron sputtering [1]: thin (1 nm <dF< 9 nm) PdNi layers, a weak-ferromagnet (F), are
sandwiched between Nb layers of nominal thickness dS=15 nm. TEM analysis shows
excellent crystallinity of the S layers (Nb) while PdNi (F) appear amorphous. Some
interface roughness and interdiffusion effects are detected. The XAFS data collected at the
Nb K edge provide details about the local structure with atomic resolution and provide
chemical order details. The Nb structure is only weakly affected by the F layer.
By combining wideband (1-20 GHz) Corbino disk [2] and dielectric resonator (8 GHz) [3]
techniques, the temperature dependence (3.3 K-Tc) of the London penetration depth and
the temperature and field dependence of the vortex-state parameters (flux-flow resistivity,
depinning frequency) were studied. Magnetic fields up to Hc2 were applied.
Both the London penetration depth and flux-flow resistivity exhibit conventional behavior
in the reference Nb films, albeit with significant differences in the vortex state with respect
to elementary models, and nonconventional behavior in S/F/S trilayers. A weakening of the
temperature dependence of the superconducting stiffness is inferred from the temperature
dependence of the penetration depth, and confirmed by the weaker pinning in S/F/S
structures. The flux flow resistivity suggests different quasiparticle excitations in S/F/S
with respect to pure Nb. We argue that even a very thin F layer does not act simply as a
pair-breaker but changes qualitatively the superconducting state. The structural and
morphological data suggest that disorder in Nb is not a key factor for the observed features.
[1] C. Cirillo et al., Supercond. Sci. Technol. 24, 024017 (2011)
[2] E. Silva, N. Pompeo, S. Sarti, Supercond. Sci. Technol. 24, 024018 (2011)
[3] K. Torokhtii, et al., Physica C, doi:10.1016/j.physc.2011.12.011
This work has been made in collaboration with Università di Salerno and Università “La
Sapienza”.
14
1.13 Magnetoresistance and spin-transfer torque in hybrid
superconductor/ferromagnet structures
R. Citro1,2
, F. Romeo1,2
1Dipartimento di Fisica “E. R. Caianiello”, Università di Salerno
2CNR-SPIN, Uo Salerno, Via Ponte don Melillo, I-84084 Fisciano (Sa), Italy
Corresponding author: F. Romeo, Dipartimento di Fisica “E. R. Caianiello”, Università di Salerno, Via Ponte don
Melillo, I-84084 Fisciano (Sa), Italy. E-mail: [email protected]
We study the magnetoresistance and the spin-transfer torque of a ferromagnet-
superconductor-ferromagnet (FSF) spin-valve structure, allowing for an arbitrary
magnetization misorientation and treating superconductivity of both s-wave and p-wave
type through a generalized scattering field theory [1, 2].
Taking fully into account Andreev reflection processes and spin-triplet correlations, we
analyze to what extent the magnetic torsion and the magnetoresistance are modified when
topological zero-energy states are present at the interfaces.
In this framework, we find that magnetoresistance curves display a strong oscillatory and
non-monotonous behavior as a function of the interlayer width d of the superconducting
region, being this a finite size effect associated to the microscopic properties of the
scattering region (e.g. coherence length, spin polarized transport through the
superconducting spacer, spin-flip at the interface, etc).
We show that a careful analysis of this behavior, considering different symmetries of the
order parameter, can characterize triplet and singlet superconductivity from the viewpoint
of the spin polarized transport through the device.
Our analysis also shows that a spin valve with a superconducting interstitial region makes
possible to compare by the same device the FSF (T<Tc) and FNF (T>Tc) spin-valve
physics by simply tuning the working temperature [3].
[1] F. Romeo and R. Citro, Phys. Rev. B 84, 024531 (2011)
[2] A. Sorgente, F. Romeo and R. Citro, Phys. Rev. B 82, 064413 (2010)
[3] S. Takahashi, H. Imamura, and S. Maekawa, Phys. Rev. Lett. 82, 3911 (1999); H. Yang, S.-H.
Yang, S. Takahashi, S. Maekawa, S. S. P. Parkin, Nature Materials 9, 586 (2010)
15
1.14 Magnetic Josephson Junctions
M. G. Blamire
Department of Materials Science and Metallurgy, University of Cambridge, Pembroke Street,
Cambridge CB2 3QZ, United Kingdom
Corresponding author: Mark G. Blamire. E-mail: [email protected]
Currents flowing in circuits containing ferromagnets transport spin as well as charge; this is the fundamental origin of effects such as giant magnetoresistance (GMR)and spintronics [1,2]. In contrast, the superconducting state is created by the pairing of electrons with antiparallel spins; this means that a supercurrent transports charge but not spin. Until very recently this would have made the idea of superconducting spin electronics completely paradoxical. Over the past decade, the coupling of superconductors and ferromagnets has become an extraordinarily dynamic field of research; stimulating an extensive theoretical interest [3] and applications of p-junctions have appeared in quantum logic devices.[4] The possibility that the alternative triplet pairing state could be induced in ferromagnets had been theoretically predicted and convincing evidence for long-range supercurrents in ferromagnets has now been independently obtained by several groups.[5-7] The central idea is that various forms of triplet pairing, as well as conventional singlet pairing, are possible at the interface between a superconductor and an inhomogeneous ferromagnet spin mixer (M).[8,9] Of these pairing symmetries, only the spin-aligned triplet state can be long-ranged in a homogeneous ferromagnet, and so the flow of a supercurrent through a thick ferromagnetic barrier inserted between two such interfaces is considered to be proof of triplet coupling. In order for spintronics to be realised, it is necessary for the triplet spin current to flow between magnetic layers as illustrated in Fig. 1 and that the magnitude of the critical current depends on the relative orientation of the magnetic layers. This paper will present preliminary evidence of this behaviour.
[1]M. N. Baibich, et al., Phys. Rev. Lett. 61, 2472 (1988).
[2]G. Binasch, P. Grunberg, F. Saurenbach, and W. Zinn, Phys. Rev. B 39, 4828 (1989).
[3]A. I. Buzdin, Rev. Mod. Phys. 77, 935 (2005).
[4]A. K. Feofanov, et al., Nature Photonics 6, 593 (2010).
[5]T. S. Khaire, M. A. Khasawneh, W. P. Pratt, and N. O. Birge, Phys. Rev. Lett. 104, 137002
(2010).
[6]M. S. Anwar, F. Czeschka, M. Hesselberth, M. Porcu, and J. Aarts, Phys. Rev. B 82, 100501
(2010).
[7]J. W. A. Robinson, J. D. S. Witt, and M. G. Blamire, Science 329, 59 (2010).
[8]F. S. Bergeret, A. F. Volkov, and K. B. Efetov, Phys. Rev. Lett. 86, 4096 (2001).
[9]M. Eschrig and T. Löfwander, Nature Physics (2008).
16
1.15 Josephson current through spin-filtering barriers
F. S. Bergeret, A. Verso, A. F. Volkov
Centro de Fisica de Materiales, CSIC-UPV, San Sebastian Spain, Donostia International Physics
Center, San Sebastian, Spain Ruhr-Universitaet Bochum, Germany
Corresponding author: F. S. Bergeret, Centro de Fisica de Materiales CSIC-UPV, Pº Manuel de Lardizabal 5, 20018
Donostia-San Sebastian, Spain. E-mail: [email protected]
We present theoretical results on the Josephson effect and quasiparticle current through a S-Isf-
S junction, where Isf is a spin-filter tunneling barrier and S denotes either superconducting
electrodes or superconductor-ferromagnet multilayer structures.
We describe how the spin-filter effect affects the differential conductance of the junction and the
singlet and triplet supercurrents. We compare our results with existing experiments and propose
a way to control triplet supercurrents.
17
1.16 The robust odd frequency paring in ferromagnet/superconductor hybrids
Shiro Kawabata1, Yasuhiro Asano
2, Yukio Tanaka
3, Alexander A. Golubov
4
1National Institute of Advanced Industrial Science and Technology (AIST), Japan
2Department of Applied Physics, Hokkaido University, Japan
3 Department of Applied Physics, Nagoya University, Japan
4Facultye of Science and Technology, University of Twente, The Netherlands
Corresponding author: National Institute of Advanced Industrial Science and Technology (AIST), Umezono 1-1-1,
Tsukuba, Ibaraki 305-0031, Japan. E-mail: [email protected]
Theoretical and experimental progress in superconductor/ferromagnet (SF) hybrid systems have
been impressive over the past decade [1]. It was predicted that, in contrast to even frequency
spin-singlet pairs, odd frequency spin-triplet pairs can penetrate very long distance in F in the
presence of certain kinds of magnetic inhomogeneity involving non-collinear magnetization [2].
Recently, experimental indirect evidences of such long-range odd frequency pairing have been
reported for spin-triplet long-range supercurrent in SFS junctions [3-5]. On the other hands,
Yokoyama and co-workers has been theoretically investigated the local density of states (LDOS)
in S/homogeneous-F hybrids and shown that the zero energy peak (ZEP) is formed when the
Exchange energy Eex is comparable to the Thouless energy Eth of F [6]. More importantly in such
a resonant condition, the short-range odd frequency pairs are dominated over even frequency
pairs at low energy. In this talk, we will present a systematic study on the odd-frequency paring
in S/inhomogeneous-F (SF1F2) hybrids. By solving the nonlinear Usadel equation numerically,
we have calculated LDOS in F1 and F2 layer. Then, we found that, in contrast to homogeneous
cases [6], the ZEP is formed in wide parameter regions of e.g., Eex, the barrier resistance, the F
layer thickness, the ralative magnetization angle between F1 and F2 layer, and so on. This
peculiar result strongly indicates that the ROBUST appearance of the odd frequency paring
in inhomogeneous-F based hybrids. More importantly, we found the purely long-range odd
frequency paring in the case of large Eex and long F2 limit in which even frequency and short-
range odd frequency pairs are almost completely suppressed. Thus the observation of ZEP in
LDOS in SF systems would be a direct evidence of the odd-frequency paring.We also discuss the
possible experimental realization of the robust odd frequency paring in an Nb/n-InAs/p-InMnAs
[7] and Nb/Cu/Ni/Cu junction [8].
[1] A. I. Buzdin, Rev. Mod. Phys. 77, 935 (2005). [2] F. S. Bergeret et al.,
Phys. Rev. Lett. 86, 4096 , (2001). [3] R. S. Keizer et al., Nature 439, 825
(2006). [4] T. S. Khaire et al., Phys. Rev. Lett. 104, 137002 (2010). [5] J. W.
A. Robinson et al., Science 329, 59 (2010). [6] T. Yokoyama et al., Phys.
Rev. B 75, 134510 (2007). [7] T. Akazaki et al., Phys. Rev. B 83, 155212
(2011). [8] K. M. Boden et al., Phys. Rev. B 84, 020510 (R) (2011).
18
1.17 Electronic Transport Properties of Nanostructured
Superconductor/Ferromagnet Point Contacts
G. Goll
1,2, J. Gramich
1, H. v. Löhneysen
1,2, M. Stokmaier
1, and C. Sürgers
2
1DFG-Centrum für Funktionelle Nanostrukturen, Karlsruher Institut für Technologie (KIT), 76131
Karlsruhe, Germany 2Physikalisches Institut, Karlsruher Institut für Technologie (KIT), 76131 Karlsruhe, Germany
Corresponding author: Prof. Dr. Gernot Goll, DFG- Centrum für Funktionelle Nanostrukturen, Karlsruher Institut für
Technologie, Wolfgang-Gaede-Str. 1a, 76131 Karlsruhe, Germany, Tel.: +49 721 608 48500. Email:
The spin-dependent electronic transport in hybrid material is an emerging field because of
potential applications in spintronics. Many fundamental and challenging issues are studied at
superconductor (S)/ferromagnet (F) interfaces by means of the proximity effect. The microscopic
process of the proximity effect, i.e. the finite pair amplitude outside S – of course also present
between S and a normal metal N – is Andreev reflection (AR) described as a coherent process of
an electron from N (or F) incident on S and being reflected as a hole, thus generating a Cooper
pair in S. Because of the spin structure of the Cooper pair – singlet for conventional
superconductors - AR can be used as a tool to investigate the spin-dependent transport through
an S/F interface. The spin polarization P can be determined from an analysis of the current
through the constriction using a theoretical model which takes into account two spin-dependent
transmission coefficients for the majority and minority charge carriers in the ferromagnet [1]. We experimentally investigate the spin-polarized transport through nanostructured S/F point
contacts at low temperatures with S = Al, Pb, as a ferromagnetic counter electrode we used Fe.
All samples are prepared by e-beam lithography and in-situ evaporation of the metals on either
side of a Si3N4 membrane with a nanostructured hole of typical diameter d = 10 - 40 nm,
resulting in clean metal interfaces. A thorough analysis of the contact properties of Pb/Fe
contacts including a direct measurement of the nanocontact size by scanning electron
microscopy allows for the first time a comparison with theoretical models for contact-size
estimates of heterocontacts. The ballistic transport regime for contacts with high Knudsen ratio is
corroborated by features in the Pb/Fe spectra such as phonon peaks and the critical pair-breaking
current of Pb [2]. The spin polarization P of the current through the S/F contact is determined by
an analysis of the Andreev spectra, i.e. the differential conductance dI/dV as a function of
applied bias V. A systematic dependence of P on the contact radius a and superconducting
transition temperature Tc is observed which sheds light on possible mechanisms for the normal
current-supercurrent conversion at the interface [3].
[1] F. Perez-Willard et al., Phys. Rev. B 69, 140502R (2004). - [2] J. Gramich et al., to be submitted.
[3] M. Stokmaier et al., Phys. Rev. Lett. 101, 147005 (2008).
19
Session 2:
Tuesday, October 23rd
2012
20
2.1 Intermolecular electron transport of model molecules investigated by break
junctions on the level of individual molecules
D. Mayer, X. Dong, A. Cassinese, A. Offenhäusser
Peter Grünberg Institut, PGI-8, Bioelectronics, Forschungszentrum Jülich GmbH, Germany, JARA
FIT: Jülich-Aachen Research Alliance
CNR-SPIN and Dipartimento di Fisica, Università di Napoli, Naples, Italy
Corresponding author: Dr, Dirk Mayer, PGI-8, Forschungszentrum Jülich GmbH, D-52425 Juelich, Germany, phone:
+49 2461 61 4023. E-mail: [email protected] http://www.fz-juelich.de/pgi/pgi-8/EN/Home/_node.html
Theoretical and experimental investigations of charge transport through (bio) molecules have
attracted considerable attention driven by the interest in fundamental aspects of charge transport
and the vision of future applications in molecular electronics and biosensorics. We are
addressing mechanistical questions of the relation between intra and intermolecular electron
transport in model molecules. Therefore, we established a mechanically controllable break
junction setup (MCBJ) where the molecules of interest are anchored between two
nanoelectrodes. First we investigated alkanedithiols with weak van der Waals type
intermolecular interactions. Based on I/V characteristics and transition voltage spectroscopy we
could demonstrate that alkanes can be considered as individual transport channels and
intermolecular electron transport is of minor importance.1
This changes if functional units are introduced into the molecules that can bridge two molecular
units together via metal ions. We have used aminooligocarboxylic acids, a general sequestering
agent, for build molecular junctions bridged by different metal ions. A statistical analysis of the
recorded conductance traces revealed that the complex conductance depends strongly on the type
of coupling ion.2 The conductance was found to be reciprocal dependent on the respective
complex stability.
Since metal complexes are mainly hold together by electrostatic interactions we also compared
the conductivity of electrostatically and covalently bridged metal – molecule – metal systems.
The obtained single molecule conductance of the electrostatically linked junctions was one order
of magnitude smaller than the conductance of covalently linked systems, which indicates that the
intermolecular electron transport through electrostatic interfaces has lower efficiency compared
to intramolecular electron transport.3 In addition, preliminary single molecule investigations of
the dicyanoperylene PDI8-CN2 have been conducted by means of an environmental break
junction setup to determine the single molecule conductance of this molecule.
In summary, we investigated the relation between inter- and intramolecular electron transport,
considered the role of metal ions in metal-organic complexes, and showed that electrostatically
bridged molecules have a lower conductance than the same molecules bridged by covalent
bonds. The observed relation between type of metal ion and conductivity of molecular junctions
may pave the way for novel design strategies of molecule based devices.
[1] D. Xiang, et.al. Chem. Commun. 47 (2011) 4760
[2] D. Xiang, et.al. Chem. Eur. J. 17 (2011) 13166
[3] Z. Yi, et.al. Chem. Commun. 46 (2010) 8014
21
2.2 Charge transport and charge traps in PDIF-CN2 : an n-type semiconductor
in three modifications compared to p-type organic semiconductors
B. Batlogg, R. Häusermann, K. Willa, T. Zimmerling, T. Mathis, A. Facchetti*
Laboratory for Solid State Physics, ETH Zurich, Switzerland,* Polyera Corporation, Skokie, Illinois
60077, USA
Corresponding author: Bertram Batlogg. E-mail: [email protected]
In this systematic and quantitative study of charge transport and charge trapping in the n-
type organic semiconductor PDIF-CN2 we have analyzed field-effect transistors (OFETs)
that involve the semiconductor in various modifications: high purity single crystal,
evaporated thin films and spin-coated thin films. In addition, we have incorporated various
gate dielectrics in order to modify the interface trap density (Cytop, SiO2 bare or with
HDMS treatment). The spectral trap density-of-states (DOS) has been found to vary by
orders of magnitude, with the lowest values in the single-crystal OFETs in the range of
1016
traps states /(eV cm3) and it is distinctly higher in the thin film OFETs. Interestingly,
these values compare very well with the trap DOS in typical p-type organic
semiconductors (e.g. rubrene and pentacene). Other systematics on the charge mobility will
be presented.
22
2.3 Organic position sensitive photodetectors based on wedge dono-acceptor
bilayers with complementary thickness
J. Cabanillas – Gonzalez1, O. Peña – Rodríguez
2,3, M. Schmidt
4, M. I. Alonso
4, A. R. Goñi
4, and M.
Campoy – Quiles4
1 Instituto Madrileño de Estudios Avanzados en Nanociencia (IMDEA-Nanociencia), Cantoblanco,
28049 – Madrid, Spain 2Centro de Microanálisis de Materiales, Universidad Autónoma de Madrid (CMAM-UAM),
Cantoblanco, E-28049 Madrid, Spain 3Instituto de Óptica, Consejo Superior de Investigaciones Científicas (IO-CSIC), C/ Serrano 121,
E-28006 Madrid, Spain
4Institució Catalana de Recerca i Estudis Avançats, (ICREA), Passeig Lluis Companys 23, 08010
Barcelona, Spain
Corresponding author: Juan Cabanillas-Gonzales. E-mail: [email protected]
The rich variety of organic compounds with absorption spectra spanning from UV to near-
IR offer unique possibilities for light harvesting in photodetectors. Appropriate
combination of two or more compounds with donor/acceptor character aims at improving
charge generation, simultaneously extending spectral sensitivity across a broad spectral
range. A dramatic dependence of spectral response upon single component size and
distribution is a phenomenon often reported in multi-component organic photodiodes,
either arranged on a single layer blend or a multi-layer configuration. Concerning
photodiodes based on donor / acceptor bilayers, the spectral response depends strongly
upon the relative thickness of the active layers. This is mainly due to two facts. First of all,
the incoming and reflected beams at the layer interfaces create a thickness dependent
interference pattern of the optical electric field within the device which determines the
light intensity distribution across the active area. In addition, changes in layer thickness
will shift the light harvesting zone in depth with a subsequent effect on charge collection
efficiency, (the so-called inner filter effect). A gradual change in layer thickness along the
device active layer implemented in a controlled manner enables spectral response
tunability, a concept with interesting implications in the field of light detection. In this
work we rely on the strong dependence of the optical electric field with layer thickness to
achieve spatially dependent spectral responses, which constitutes a proof-of-concept to
achieve position sensitive photodetection. We develop organic position sensitive
photodetectors by incorporating a lateral thickness gradient in the active layers of a
bilayer-like structure. As the thicknesses of the CuPc and C60 layers are varied, the optical
electric field distribution is modified. This results in a position dependent spectral
photoresponse in the advanced geometry. The spatial dependence of the photocurrent
response is modelled taking into account variations into the exciton population due to the
different in-plane optical field distribution. Additional characterization on the relative
concentration and distribution of material is provided by variable angle ellipsometry,
Raman microscopy and AFM. The results point to the presence of a diffuse interfacial
layer between CuPc and C60 in the CuPc rich positions.
23
2.4 Scanning Kelvin Force Microscopy on Hybrid Solar Cells
Mariano Biasiucci, Aurora Rizzo, Anna Lo Iudice, Giuseppe Gigli
NNL-CNR Nanoscience Institute c/o Dip. Fisica Ed. G. Marconi, La Sapienza University, Roma,
Italy and Electronical Engineering Department, Tor Vergata University, Via del Politecnico, 00133
Rome, Italy
- , Via
Arnesano, 73100 Lecce, Italy
Center for Biomolecular Nanotechnologies IIT@UniLe . Arnesano 73100 Lecce
Corresponding author: Mariano Biasiucci. E-mail: [email protected]
Using Scanning Kelvin Force Microscopy (SKFM), the surface potential changes across
double layered and bulk heterojunctions solar cells was investigated in the dark and under
illumination with white light. The photovoltage generated across donor-acceptor interface
of heterojunctions is correlated with the difference between the HOMO and LUMO levels
of the donor and acceptor respectively and also approximates the measured open-circuit
voltage (Voc) in completed solar cells. SKFM allowed us to map the Fermi level positions
within the donor and acceptor layers under illumination. We have investigated the
correlation between the nanoscale surface potential with Voc and power conversion
efficiency (PCE) of the hybrid solar cells. By monitoring the changes in the surface
potential of donor-acceptor heterojuntions we have obtained a useful guide to fabricate
high performance solar cells.
24
2.5 Charge transfer processes in organic nano- and hetero-structures.
Alberto Morgante
Istituto IOM-CNR, Dipartimento di Fisica, Univarsità di Trieste
Corresponding author: Alberto Morgante. E-mail: [email protected]
The performances and efficiency of organic material based devices are strongly affected by
charge transfer processes at interfaces (organic-organic and organic-inorganic). To
improve the device performances, these processes and their correlation with the electronic
structure of the interfaces must be understood. Spectroscopic studies based on synchrotron
radiation experimental techniques of these hetero-structures will be presented, in particular
the application of the Resonant PhotoEmission Spectroscopy (RPES) to various organic
molecule based systems. The chemical specificity and the possibility to conduct
experiments that provide a time scale for charge dynamics make the RPES a powerful tool
to study organic heterojunctions and in particular to probe the charge transfer processes at
organic interfaces. Some specific cases of interest for organic photovoltaics and molecular
electronics that will be presented are the study of the role of inter-molecular interaction on
through-space charge transfer characteristics in π-stacked molecular systems, the electronic
coupling, morphology and charge transfer rates at the donor-acceptor (D/A) interfaces
between C60 and either flat- or contorted hexabenzocorones (HBC) and the relation with
improved internal (IQE) and external (EQE) quantum efficiency of devices based on these
shape-matched molecular systems. The case of ammine terminated organic overlayers will
be discussed in connection with recent results of break junction experiments. In this case,
the comparison of RESPES and break junction results could elucidate the link between the
quantum and the meso-scopic properties of such systems. The models used in RPES data
analysis to extract the time scale of the excited charge delocalisation and the spatial
correlation of core, valence occupied and unoccupied molecular states will be also
discussed.
25
2.6 Theoretical study of crystalline PDI-FCN2
Renato Colle1,2
, Giuseppe Grosso2,3
, Layla Martin-Samos4, Laura Ricciotti
5, Antonio Cassinese
6
1DICAM University of Bologna, via Terracini,28 40136 Bologna, Italy
2DF University of Pisa, Largo Pontecorvo,3 56127 Pisa, Italy
3NEST-Istituto di Nanoscienze-CNR, Pz. San Silvestro,12 56127 Pisa, Italy
4 CNR-IOM Democritos, via Bonomea,265 34136 Trieste, Italy
5 Department of Chemistry, University of Naples ”Federico II”, Via Cinthia, I-80126 Naples, Italy
6 CNR-SPIN and Department of Physics Science, University of Naples “Federico II”, P.le tecchio
80 ,80125, Naples, Italy
Corresponding author: Renato Colle. E-mail: [email protected]
We investigate structural, electronic and optical properties of PDI-FCN2 which has been
demonstrated recently as high-mobility, ambient stable, n-type organic single crystal
material for organic field effect transistors (OFET). Our study is based on DFT with
inclusion of van der Waals interactions for what concerns ground state properties of the
system, and on the first-principles many-body GW-BSE (Bethe Salpeter) theory for the
treatment of its excitation properties.
From the optimized geometrical structure obtained for the PDIF-CN2 single crystal, we
evaluate the X-spectrum which favorably agrees with existing measured spectra on films.
The electronic structure evaluated for the optimized geometry highlights strong anisotropy
in the electronic bands curvature which roots at the molecular packing in the crystal, and is
responsible of the charge mobility anisotropy. The evaluated band structure provides a
sound basis for the interpretation of the optical measured spectra in terms of allowed
interband transitions. We demonstrate that crystalline PDIF-CN2 is a direct-gap
semiconductor with onset of the optical transitions at the Brillouin zone border. Many-
body effects are also included.
26
2.7 Bias Stress effects in n-type Perylene Diimide transistors
M. Barra1, F. V. Di Girolamo
1, F. Ciccullo
1, N. A. Minder
2, I. Gutierrez-Lezama
2, A. Morpurgo
2, A.
Cassinese1
1CNR-SPIN and Dep. of Physics Science, University of Naples, Piazzale Tecchio 80, Naples Italy
2DPMC and GAP, University of Geneva, 24 Quai Ernest-Ansermet, CH-1211 Geneva, Switzerland
Corresponding author: Antonio Cassinese - CNR-SPIN and Dep. of Physics Science, University of Naples, Piazzale
Tecchio 80, Naples Italy . E-mail: [email protected]
The bias stress (BS) phenomenon is the main source of operational instability in the
organic field-effect transistors (OFET) and represents the most serious obstacle to their
commercial introduction [1]. This effect, which basically consists in a continuous time
decay of the drain-source (IDS) current when the transistors are driven in the accumulation
regime for a prolonged time, has been widely investigated for p-channel OFET.
Conversely, in n-channel transistors, it has so far received little attention and few
experimental data are currently available.
In this contribution, we report on the BS effects occurring in both thin-film and single-
crystal transistors based on Perylene Diimide molecules, being today among the most
interesting n-type semiconducting compounds thanks to their highly robust charge
transport properties also in air [2]. Firstly, we discuss the BS phenomenon in thin-film
devices fabricated by evaporating PDI8-CN2 molecules on both bare and
hexamethyldisyloxane (HMDS)-treated SiO2 gate dielectrics. Our results indicate that, in
these devices, the chemical properties of the interface between dielectric barrier and
semiconductor play a major role in the BS effect, suggesting also the possibility that its
physical origin is related to the occurrence of electrochemical reactions involving water
and oxygen. When the BS effect was analyzed in PDIF-CN2 single-crystal transistors with
Cytop gate dielectric, we found that the amount of stress is very small as compared to all
(p-channel) organic transistors studied in the past [3]. The IDS(t) decrease in these OFET is
of only 10% in air even when they are driven in the accumulation regime for an entire
week (Fig.1). By fitting the experimental IDS(t) curves with the stretched exponential
model, the characteristic time constant is found to be higher than 109 sec, being two
orders of magnitude larger than the best values reported previously for p-channel OFET.
Moreover, we observe that the BS effect tends to saturate for stressing periods larger than
1-2 days. Although, n-type OFET have been traditionally considered to be more sensitive
on charge trapping process, our results highlight that a right combination of materials
allows almost completely cancelling the BS effect in these devices.
[1] H. Sirringhaus, Reliability of Organic Field-Effect Transistors, Adv. Mater. 21, (2009) 3859
[2] B. A. Jones, A. Facchetti, M. R. Wasielewski, T. J. Marks, J. Am. Chem. Soc. 129, (2007)
15259 - [3] M. Barra, F. V. Di Girolamo, N. A. Minder, I. Gutierrez-Lezama, Z. Chen, A.
Facchetti, A. F. Morpurgo, A. Cassinese, Applied Physics Letters 100, 133301 (2012).
27
2.8 Transport Properties of Ni decorated Carbon Nanotube Fibres
M. Salvato1, M. Cirillo
1, M. Lucci
2, I. Ottaviani
2, M.L. Terranova
3, E. Tamburri
4, S. Orlanducci
5,
N. Behabtu4, C. Young
4, M. Pasquali
4
1Dipartimento di Fisica, CNR-SPIN and MINAS Laboratory Università di Roma “Tor Vergata”I-
00133 Roma-Italy 2Dipartimento di Fisica and MINAS Laboratory Università di Roma “Tor Vergata”I-00133 Roma-
Italy 3Dipartimento di Scienze e Tecnologie Chimiche and MINAS Laboratory Università di Roma “Tor
Vergata”I-00133 Roma-Italy 4Chemical and Biomolecular Engineering, MS-362, Rice University, Houston, Texas 77251-1892,
USA
Corresponding author: Matteo Salvato Dipartimento di Fisica, Università di Roma “Tor Vergata” Via della Ricerca
Scientifica 1, 00133 Roma, Italy. E-mail: [email protected]
Granular systems based on magnetic metallic materials present some aspects in their transport
properties which suggest their use in nanotechnology industry for information storage devices,
read heads, magnetic sensors and actuators, bit writing at high frequency etc. These systems are
usually available in form of films, nanowires or nanotubes and are designed for nanoelectronic
applications. On the other hand, tens of meters of Carbon Nanotube Fibres can be actually
produced with uniform electrical and mechanical properties which are peculiar for substrate use.
Following the hybridization tendency between nanosystems of different nature and the already
established tendency to favour a bottom up technology in contrast to the outdated top down
methods for electronic nanodevices fabrication, we deposited Ni nanoparticles on CNT fibres by
electrodeposition method and study their electrical properties as a function of the deposition
time. The experimental data show a semiconducting-metallic transition with increasing the
electrodeposition time due to the increasing dimensions of the Ni nanoparticles deposited on the
fibres surface. In the semiconducting regime, the conduction mechanism is governed by hopping
between the different Ni nanoparticles whereas electron-phonon interactions are responsible for
the resistivity in the metallic regime. An intermediate regime governed by tunnel enhanced by
thermal fluctuation is also evidenced. The physical properties of the best metallic samples are
comparable to that observed in metallic nanowires obtained with traditional fabrication
techniques.
28
2.9 Non-conducting and non-magnetic interfaces of LaAlO3/SrTiO3 made by
sputter deposition
J. Aarts1, M. Dildar
1, Q. Xu
2, S. Harkema
3, H. W. Zandbergen
2
1Kamerlingh Onnes Laboratorium, Leiden University, the Netherlands.
2National Centre for High Resolution Microscopy, Kavli Institute for Nanoscience, Delft Technical
University, the Netherlands 3Faculty of Science and Technology and MESA+ Institute for Nanotechnology,
University of Twente, the Netherlands
Corresponding author: Jan Aarts. E-mail: [email protected]
We have investigated the interface properties of LaAlO3 grown on TiO2-terminated SrTiO3
(001) fabricated by RF sputtering in a high-pressure oxygen atmosphere at temperatures
around 900 °C. The LaAlO3 films are smooth with flat surfaces and have the correct
tetragonal phase. Transmission electron microscopy shows atomically sharp, coherent and
continuous interfaces while EELS measurements show some slight intermixing. However,
we find these interfaces to be non-conducting. Moroever, careful studies by SQUID
magnetometry do not show signs of magnetism. No conductance was found either when
amorphous LaAlO3 films were deposited. For films grown by molecular beam epitaxy, it
was found that the elemental ratio of La to Al has to be below 0.97 in order to have a
conducting interface [1]. In our case this ratio, determined by TEM / EDX, is found to be
1.07 (taking a LAO crystal as a reference). This suggests that intrinsic electronic
reconstruction is not the main phenomenon even in conducting interfaces fabricated by
pulsed laser deposition. The reason for the higher ratio found in our films probably has to
do with the high oxygen pressure during deposition, and a connection between oxygen
stoichiometry and La /Al ratio.
[1] M.P. Warusawithana, A.A. Pawlicki, T. Heeg, D.G. Schlom, C.Richter, S. Paetel, J. Mannhart,
M. Zheng, B. Mulcahy, J. N. Eckstein, W. Zander, and J. Schubert, Bulletin of the APS 55,nr. 2
(2010), abstract ID BAPS.2010.MAR.B37.1.
29
2.10 Exploring low dimensional transport in SrTiO3–based heterostructures
Christopher Bell
SLAC National Accelerator Laboratory
Corresponding author: Christopher Bell, SLAC National Accelerator Laboratory, Menlo Park, 94025 CA, USA.
Email: [email protected]
At low temperatures bulk SrTiO3 is on the border of ferroelectricity, and can be doped to
create a low density superconductor with high electron mobility. These fascinating
properties have motivated the recent interest in low dimensional SrTiO3 heterostructures.
The conductivity at the asymmetrically confined LaAlO3/SrTiO3 interface [1], and in
particular its control with a field effect gate [2, 3], is one example where we can explore
novel low dimensional physics. At the same time, studies of symmetrically confined 2D
superconductivity and 2D quantum oscillations in Nb:SrTiO3 [4, 5] offer additional control
and insights into this fascinating quantum material. I will compare and contrast these two
different ways of constraining the electrons.
I will also present data from our collaborative efforts using real space imaging of the
magnetism and superfluid density by scanning SQUID microscopy, which have provided
an extremely powerful complementary tool to transport studies, in these fascinating
systems [6, 7, 8].
[1] A. Ohtomo and H. Y. Hwang, Nature 427, 423 (2004).
[2] A. D. Caviglia et al., Nature 456, 624 (2008).
[3] C. Bell et al., Phys. Rev. Lett. 103, 226802 (2009).
[4] Y. Kozuka et al., Nature 462, 487 (2009).
[5] M. Kim et al., Phys. Rev. Lett. 107, 106801 (2011).
[6] J. Bert et al., Nature Phys. 7, 767 (2011).
[7] B. Kalisky et al., Nature Commun. (accepted), condmat/1201.1063
[8] J. Bert et al., (submitted), condmat/1205.4064
30
2.11 Transport properties of LaAlO3/SrTiO3 mesoscopic devices
Daniela Stornaiuolo, Stefano Gariglio, Nuno J. G. Couto, Alexandre Fête, Andrea D. Caviglia,
Gabriel Seyfarth, Didier Jaccard, Alberto F. Morpurgo, and Jean-Marc Triscone
DPMC, University of Geneva, Switzerland
Corresponding author: Daniela Stornaiuolo, DPMC - Université de Genève, 24 Quai Ernest Ansermet, CH - 1211
Genève 4. E-mail: [email protected]
The two dimensional electron gas (2DEG) present at the interface between LaAlO3 and
SrTiO3 (LAO/STO) [1] possesses a unique range of properties, making it one of the most
interesting system in oxide electronics. The characteristic parameters derived from the
electronic band structure and from transport analyses are radically different from 2DEGs
based on classical semiconducting heterostructures [2]. Moreover, the LAO/STO transport
properties can be tuned from insulating to superconducting using electric field effect [3].
This heterostructure is therefore particularly interesting for the investigation of quantum
transport in tunable nano-devices.
Using electron beam lithography, we realized LAO/STO bridges with lateral dimensions
down to 500 nm. In order to prove the lateral confinement of the 2DEG, we measured
universal conductance fluctuations in the magnetoconductance of the devices, and
followed their evolution as function of the temperature and of the gate voltage. The devices
also exhibit superconducting behavior, with a critical current scaling with their dimensions
and tunable using field effect.
These results prove the possibility to realize mesoscopic devices based on the 2DEG at the
LAO/STO interface and open an interesting prospective for the realization of tunable
devices, operating both in the normal and in the superconducting regime.
[1] A. Ohtomo and H.Y. Hwang, Nature (London) 427, 423 (2004);
[2] S. Gariglio, M. Gabay, and J.-M. Triscone, Nature Nano. 5, 13 (2010), J. Mannhart and D. G.
Schlom, Science 327, 1607 (2010
[3] N. Reyren, et al., Science 317, 1196 (2007); A. Caviglia et. al, Nature 456, 624 (2008).
31
2.12 On the origin of the two dimensional electron gas at the polar/non polar
oxide interfaces
U. Scotti di Uccio1, C. Aruta,
1 E. Di Gennaro,
1 D. Maccariello,
1 F. Miletto Granozio,
1 P. Perna,
1
Mohamed Riaz,1 A. Gadaleta,
2 Ilaria Pallecchi,
2 Daniele Marrè
2, C. Cantoni,
3 M. Varela,
3 S. J.
Pennycook.3
1CNR-SPIN and Dipartimento di Scienze Fisiche, Univ. Di Napoli Federico II, Via Cintia 80126
Napoli 2CNR-SPIN and Dipartimento di Fisica, Univ. di Genova, via Dodecaneso 33, 16146 Genova, Italy
3Materials Science and Technology Division, Oak Ridge National Laboratory, 1 Bethel Valley
Road, Oak Ridge, Tennessee 37831-6116, USA
Corresponding author: Umberto Scotti di Uccio. E-mail: [email protected]
The origin of the 2DEG at the polar/ non polar LaAlO3/SrTiO3 interfaces is still debated. In
this talk, issues regarding the fabrication procedure and the interface perfection will be
addressed, in order to evaluate the possible role of defects. To this aim, ablation plasma
diagnostics, RHEED analyses, HRTEM data will be shown. The results allow to clarify
both the extent of intermixing due to subplantation of heavy atoms during the growth and
the extent of oxygen vacancies formation. The similarities with the recently discovered
LaGaO3/SrTiO3 and NdGaO3/SrTiO3 interfaces will be presented, by mentioning growth
and physical properties of the samples, such as electrical transport.
32
2.13 Manipulating interface magnetism at complex oxide interfaces: Novel
functionalities in magnetic tunnel junctions
F. A. Cuellar1, J. Garcia-Barriocanal
1, D. Arias
1, Z. Sefrioui
1, C. Leon
1 , N. Nemes
1, M. Bibes
2, and
A. Barthélémy2, M. Garcia Hernandez
3, Y. H. Liu
4, S. G. E. te Velthuis
4, M. R. Fitzsimmons
5, M.
Varela6, S. J. Pennycook
6 and J. Santamaria
1
1GFMC, Depto. Física Aplicada III, U. Complutense de Madrid, 28040 Madrid, Spain
2 Unité Mixte de Physique CNRS/Thales, Campus de Polytechnique, 1, Avenue A. Fresnel, 91767
Palaiseau (France) and Université Paris-Sud, 91045 Orsay (France) 3Instituto de Ciencia de Materiales de Madrid (ICMM-CSIC). 28049 Cantoblanco. Madrid.
4Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, USA
5 Los Alamos National Laboratory, Los Alamos NM 87545 USA
6Condensed Matter Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee
37831-6031, USA
Corresponding author: Jacobo Santamaria, GFMC, Depto. Física Aplicada III, U. Complutense de Madrid, 28040
Madrid, Spain. Email: [email protected]
The discovery of unexpected properties at the interfaces between complex oxides have
triggered the launch of a novel field of research which has produced a number of exciting
results in recent years. The main thrust of this emerging field comes from its promise of
independently manipulating important quantities controlling electron correlations.
Controlling the state of strain has a direct influence on important parameters such as band
width or hopping integral and eventually also on orbital occupancy and ordering. Modified
bonding at the interface may be at the bottom of the appearance of interesting novel
behaviours not appearing in the bulk constituents. The possibility of tailoring the electronic
structure of interfaces has driven an important effort towards the design of interfaces with
specific functionalities. In this talk I will examine several interface problems in oxide
heterostructures with special focus on the possibility of creating novel interfacial magnetic
states. They originate at the modification of the orbital occupancy resulting from the
modified bonding at the interface. I will discuss the effect of these low dimensional
magnetic states in determining the macroscopic magnetic response of heterostructures and
the possibility of manipulating them to design novel functionalities in magnetic tunnel
junctions.
33
2.14 Monocrystalline porous ZnO nanostructures from hybrid organic-
inorganic precursors: formation processes and patterning
Lucia Nasi, Davide Calestani, Patrizia Ferro, Tullo Besagni, Filippo Fabbri, Paolo Fedeli, Francesca
Licci, Roberto Mosca
CNR-IMEM, Parco Area delle Scienze 37a, I-43124 Parma, Italy
Corresponding author: Roberto Mosca, CNR-IMEM, Parco Area delle Scienze 37/a, 43124 Parma, Italy, Tel. +39
0521269214, FAX +39 0521269206. E-mail: [email protected]
Zinc oxide (ZnO) is considered a very interesting material owing to its direct wide band
gap [3.37 eV at room temperature (RT)] and high exciton binding energy (60 meV). Its use
in several applications, such as electronic, optoelectronic, electrochemical and
electromechanical devices, has been already demonstrated, and interest is increasing due to
the possibility to synthesize ZnO in a large number of different nanostructures that allow
novel devices to be achieved. Recently attention has been devoted to the fabrication of
porous ZnO nanostructures since large surface areas and a high surface-to-volume ratio
make porous materials interesting for a variety of applications such as catalysts, nanosieve
filters, solar cells and gas sensors.
In this communication we report about the processes that allow monocrystalline porous
ZnO nanosheets and nanobelts to be obtained from the ZnS(en)0.5 (en=ethylenediamine)
hybrid organic-inorganic precursor synthesized by a solvothermal route. In particular it is
shown that porous ZnO nanostructures are obtained through the topotactic transformation
ZnS(en)0.5 ZnS ZnO induced by proper thermal treatments. The properties of obtained
porous ZnO nanostructures are thoroughly investigated by SEM, TEM,
cathodoluminescence and electrical measurements and related to functional properties such
as photocatalysis efficiency. Finally it is shown that porous ZnO nanostructures can be
obtained as supported on proper substrates and that their distribution can be patterned by
patterning the hybrid precursor growth. Possible applications are envisaged for these
nanostructures due to the possibility to combine porosity, mono-crystallinity and patterned
growth.
34
2.15 Circular dichroism of chemisorbed DPED chiral molecule films
M.A. Niño1*, F.J. Luque
2, I.A. Kowalik
3, D. Arvanitis
4, R. Miranda
1,2, J. J. de Miguel
2
1IMDEA-Nanociencia, Campus UAM, 28049-Madrid, Spain
2Dpto. Física de la Materia Condensada, Universidad Autónoma de Madrid, 28049-Madrid, Spain
3Institute of Physics, Polish Academy of Sciences, Al Lotnikow 32/46, PL-02-668 Warsaw, Poland
4Dpt. of Physics and Astronomy, Uppsala University, Box 516, SE-7120 Uppsala, Sweden
Corresponding author: Miguel Angel Niño Orti. E-mail: [email protected]
Chiral molecules have been intensively investigated in Chemistry and life sciences since
their discovery by Pasteur: the fundamental asymmetry in living beings, which only use
one type of enantiomer, is yet unexplained [1]. From the point of view of magnetism, the
presence of a magnetic field naturally defines a chiral orientation in space: effects such as
magnetochiral dichroism [2] have been demonstrated, consisting in the asymmetry in the
absorption of photons by chiral molecules depending on the direction of light propagation
being parallel or antiparallel to an external magnetic field. Also, chiral layer have been
shown to scatter electrons differently depending on their spin, opening up the possibility to
use these materials as spin filters [3].
We have grown ultrathin films of different enantiomers of DPED (1,2-Diphenyl-1,2-
ethanodiol), deposited by Molecular Beam Epitaxy (MBE) in UHV, on clean and on Co
covered Cu(100) single crystal. Dichroism and magnetism have been studied using
absorption of circularly polarized x rays (XAS) at the carbon K edge at I1011 beamline at
MaxLab. Growing films of the two enantiomers and using different helicities for the x rays
we observe clear dichroic effects at photon energies coincident with C-C and C-H p
orbitals. This dichroism show opposite sign for the two different enantiomers studied, that
allow us to probe the molecular chirality and to identify electronic states associated to
specific chiral centres.
The effect of the chiral molecule film on the magnetism of an ultrathin cobalt film on
Cu and its magnetic response has also been characterized by x ray magnetic circular
dichroism (XMCD) measurements at both the Co L-edges as well as the adsorbate atoms C
K-edge: we observe a strong change in the XMCD asymmetry of the Co atoms after the
adsorption of DPED on top of the film, indicating a possible charge transfer.
[1] R.A. Rosenberg, Top. Curr. Chem 298, 279 (2011)
[2] G.L.J.A. Rikken, E. Raupach, Nature 390, 493 (1997)
[3] K. Ray, S.P. Ananthavel, D.H. Waldeck, R. Naaman, Science 283, 814 (1999)
35
Session 3:
Wednesday, October 24th
2012
36
3.1 Optical patterning of polymers embedding photo-active molecules
Andrea Camposeo1, Antonio Ambrosio
2, Fabio Borbone
3, Antonio Roviello
3,
Pasqualino Maddalena2, Dario Pisignano
1,4
1NNL, Istituto Nanoscienze-CNR, Università del Salento, via Arnesano, I-73100, Lecce, Italy
2CNR-SPIN U.O.S. Napoli and Dipartimento di Scienze Fisiche, Università degli Studi di Napoli
Federico II, Complesso Universitario di Monte Sant’Angelo, Via Cintia, I-80126, Napoli, Italy 3Dipartimento di Chimica, Università degli Studi di Napoli Federico II, Complesso Universitario di
Monte Sant’Angelo, Via Cintia, I-80126, Napoli, Italy
4Dipartimento di Matematica e Fisica “Ennio De Giorgi”, Università del Salento, via Arnesano, I-
73100 Lecce, Italy
Corresponding author: Andrea Camposeo. E-mail: [email protected]
The development of nanopatterning methods for organic materials attracts strong attention,
mainly because the inclusion of a wavelength-scale periodic or quasi-periodic structure in
optoelectronic devices constitutes a strategic approach in order to increase the efficiency of
light extraction in organic-based-light emitting systems and to enhance light trapping in
light-sensitive devices. Among other approaches, mixing photoactive molecules, such as
azobenzene molecules or polymers, with the active compounds of a photonic system, can
represent a strategic way for obtaining systems that combine patterning capability (through
the azobenzene photo-isomerization) with light emission/detection. In fact, the mass
migration phenomenon occurring on the free surface of azobenzene-containing polymers
illuminated by light of appropriate wavelength can be employed to pattern polymeric films
constituted by an azo-polymer containing a photoluminescent chromophore.
In this work, we will review our recent results on the nanostructuring of polymers
containing azobenzene chrmophores, by one- and two-photon laser scanning techniques.
By two-photon patterning, that employs the diffraction limited spot of the 800 nm
wavelength pulsed laser, we have realized structures with features down to 250 nm, far
below the half-wavelength diffraction limit of the focused laser beam. Moreover, we have
demonstrated the possibility to pattern a luminescent polymer blend containing azobenzene
chromophores, by means of a laser scanning technique, thus realizing photoluminescent
features whose shapes and spatial distribution can be arranged by exploiting the light-
polarization dependence of the mass migration process.
37
3.2 Helical-wavefront-sensitive material displacement on the surface of an azo-
polymer film under optical vortex illumination
Antonio Ambrosio1, Lorenzo Marrucci
1, Fabio Borbone
2, Antonio Roviello
2, Pasqualino
Maddalena1
1CNR-SPIN U.O.S. Napoli and Dipartimento di Scienze Fisiche, Università degli Studi di Napoli
Federico II, Complesso Universitario di Monte Sant’Angelo, Via Cintia, I-80126, Napoli, Italy 2Dipartimento di Scienze Chimiche, Università degli Studi di Napoli Federico II, Complesso
Universitario di Monte Sant’Angelo, Via Cintia, I-80126, Napoli, Italy
Corresponding author: Antonio Ambrosio, CNR-SPIN U.O.S. Napoli, Dipartimento di Scienze Fisiche, Complesso
Universitario di Monte Sant’Angelo, Via Cintia, 80126 – Napoli (Italy). E-mail: [email protected]
The illumination of a film of a polymer containing azobenzene moieties by means of
linearly polarized light, in the UV/Visible wavelengths region, leads to the orientation of
the azobenzene units perpendicularly to the light polarization direction. This results, after
many trans-cis-trans isomerization cycles of the azo-unit, from the reduction of the
transition probability when the rod-like trans-isomer is perpendicular to the electric field
vector. This mechanism has been proposed for holographic data storage on this polymeric
support. However, in 1995 a new phenomenon has been observed, the material-
displacement (mass-migration) on the free surface of azobenzene-containing polymers.
Here we report about a new feature in patterning azo-polymers deriving by light- matter
interaction where the film is sensitive to the phase information carried out by optical
vortexes of different topological charges.
In fact, we have found the unexpected experimental observation of spiral-shaped relief
patterns on the surface of an azopolymer that has been illuminated with a vortex laser
beam, that is a beam having a helical wavefront. The spiral handedness of the polymer
pattern is determined by the vortex one. This result is quite surprising because the common
understanding hitherto was that these surface patterns respond to the light intensity
distribution and its gradients. The intensity pattern of a vortex beam is shaped as a
“doughnut” and carries no information whatsoever about the vortex handedness. We found
an explanation for our observations that links them to a peculiar interference effect
occurring between longitudinal and transverse field components of the vortex beam.
Furthermore, we have found out that the main features of the observed phenomenon can be
predicted by a phenomenological theory that does not rely on a specific microscopic model
and therefore, in this sense, is a model-independent interpretation.
Our finding [1] will benefit the development of new lithography schemes as well as the
interpretation of the phenomenon driving the material-displacement and the imaging of
phase-related information.
The research leading to these results has received funding from the FP7/ 2007-2013 under
grant agreements N. 264098 – MAMA.
[1] A. Ambrosio, L. Marrucci, F. Borbone, A. Roviello, P. Maddalena, Light-induced spiral mass
transport in azo-polymer films under vortex-beam illumination, Nature Communications, 3:989
(2012)
38
3.3 Back-action effects on the electronic current in a Carbon Nanotube
nanomechanical resonator
A. Nocera*, C. A. Perroni
**, V. Marigliano Ramaglia
***, V. Cataudella
**
** CNISM, Dipartimento di Fisica E. Amaldi, Universita' di Roma Tre, Via della Vasca Navale 84,
I-00146 Roma, Italy * CNR-SPIN, Universita' degli Studi di Napoli Federico II, Complesso Universitario Monte
Sant'Angelo, Via Cintia, I-80126 Napoli, Italy ***
CNISM, Universita' degli Studi di Napoli Federico II, Complesso Universitario Monte
Sant'Angelo, Via Cintia, I-80126 Napoli, Italy
Corresponding author: Alberto Nocera Address: Dipartimento di Fisica E. Amaldi, Universita' di Roma Tre, Via della
Vasca Navale 84, I-00146 Roma, Italy. Tel: 08176433. E-mail: [email protected],
We study a general model describing a self-detecting single electron transistor realized by a
suspended carbon nanotube actuated by a nearby antenna. The main features of the device,
recently observed in a number of experiments, are accurately reproduced. When the device is
in a low current-carrying state, a peak in the current signals a mechanical resonance. On the
contrary, a dip in the current is found in high current-carrying states. In the nonlinear vibration
regime of the resonator, we are able to reproduce quantitatively the characteristic asymmetric
shape of the current-frequency curves. We show that the nonlinear effects coming out at high
values of the antenna amplitude are related to the effective nonlinear force induced by the
electronic flow. The interplay between electronic and mechanical degrees of freedom is
understood in terms of an unifying model including in an intrinsic way the nonlinear effects
driven by the external probe.
39
3.4 Edge-dependent transport in graphene
H. Goto1, E. Uesugi
1, R. Eguchi
1, A. Fujiwara
2, and Y. Kubozono
1, 3
1Research Laboratory for Surface Science, Okayama University, Okayama 700-8530, Japan
2Radiation Research Institute, SPring-8, Hyogo 679-5198, Japan
3Reserach Center of New Functional Materials for Energy Production, Storage and Transport,
Okayama University, Okayama 700-8530, Japan
Corresponding author: Hidenori Goto, Okayama University, Okayama 700-8530, Japan. E-mail:
Graphene has two kinds of edges depending on their orientations; armchair and zigzag edges.
Graphene nanoribbon (GNR) with armchair edges has no carriers at the charge neutrality point,
while GNR with zigzag edges has singular density of states originating from flat band localized
at the zigzag edges[1]. Distinct electronic properties and geometries characterizing each edge
have been studied by scanning tunneling spectroscopy (STS)[2], transmission electron
microscopy (TEM)[3], and micro-Raman spectroscopy[4]. But the edge-dependent transport of
GNR has not yet been observed because of the experimental difficulty to prepare atomically
ideal edges[5]. Furthermore, the zigzag edge has high chemical reactivity and can lead to
interesting phenomena such as spin polarization and superconductivity. Thus, to clarify the edge
transport in graphene is of crucial importance in view of fundamental research and practical
application.
In this report, we study the edge-dependent transport properties by applying the side gate voltage
Vsg to graphene field-effect transistors (FETs) with ionic liquid. First, we prepared two-terminal
graphene FETs with micromechanical cleavage of graphene and conventional photolithographic
technique. Next, the devices were coated with photoresist except one side of the edge, on which
the ionic liquid (BMIM[PF6]) was dropped. The ionic liquid serves as a self-assembled gate
electrode closely spaced from the edge. Since the voltage drop across the ionic liquid/graphene
interface occurs within electric double layer (EDL) as thin as 1 nm, we can selectively control
the electronic state at the nanometer-sized region from the edge.
Some devices showed the conductance peak at the neutrality point, which suggested the peak of
density of states. Raman spectroscopic mapping was carried out to relate the transport property
with the edge geometry. The presence(absence) of D peak at 1350 cm-1
corresponds to the
armchair(zigzag) edge[4]. Raman mapping with the spatial resolution of 1 µm correlated the
conductance peak to zigzag edge. Thus, the conductance peak originates from the flat band
localized at zigzag edges. This is the first experimental proof of the edge-dependent transport in
graphene. Our side gate technique opens the promising possibilities to study the one dimensional
transport along the edge and to develop the edge-functional graphene devices.
[1] M. Fujita et al., J. Phys. Soc. Jpn. 65, 1920 (1996)
[2] Y. Kobayashi et al., Phys. Rev. B 71,193406 (2005)
[3] Ç. Ö. Girit et al., Science 323, 1705 (2009)
[4] C. Casiraghi et al., Nano Lett. 9, 1433 (2009)
[5] M. Y. Han et al., Phys. Rev. Lett. 98, 206805 (2007)
40
3.5 Heat interferometry with Josephson junctions
F. Giazotto and M. J. Martínez-Pérez
NEST, Istituto Nanoscienze-CNR and Scuola Normale Superiore
Corresponding author: F. Giazotto, NEST, Istituto Nanoscienze-CNR and Scuola Normale Superiore, Piazza S.
Silvestro 12, I-56127 Pisa, Italy. E-mail: [email protected]
The investigation of thermal transport in solid-state nanodevices, usually referred to as
caloritronics, is a research field which is nowadays garnering an increasing attention since
the impressive advances in nanoscience. The latter are suggesting that caloritronics is a
central issue at the nanoscale, where heat plays a key role in determining the physical
properties of the system. In this context, manipulation and control of heat currents is of
great relevance for a number of applications, and conceiving devices allowing to tune the
amount of heat transferred through nanocircuits would represent an important
breakthrough. Toward this direction the prototype of a thermal modulator in the form of a
heat transistor has been recently reported [1] with the demonstration of electrostatic control
of heat currents flowing through a superconducting circuit.
On the other hand, in analogy to electric interference which is at the basis of the most
widespread interferometer, i.e., the superconducting quantum interference device
(SQUID), Maki and Griffin predicted in 1965 [2] that thermal current flowing through a
temperature-biased Josephson tunnel junction is a stationary periodic function of the
quantum phase difference between the superconductors. The interplay between
quasiparticles and Cooper pairs condensate is at the origin of such phase-dependent heat
current, and is unique to Josephson junctions. In this scenario, a temperature-biased
SQUID would allow heat currents to interfere thus implementing the thermal version of the
electric Josephson interferometer. The dissipative character of heat flux makes this
coherent phenomenon not less extraordinary than its electric (non-dissipative) counterpart.
Albeit weird, this striking effect has never been demonstrated so far.
In this presentation we shall report the first experimental realization of a heat
interferometer. We investigate heat exchange between two normal metal electrodes kept at
different temperatures and tunnel-coupled to each other through a thermal `modulator' in
the form of a DC-SQUID. Heat transport in the system is found to be phase dependent, in
agreement with the original prediction [2]. With our design the Josephson heat
interferometer yields magnetic-flux-dependent temperature oscillations of amplitude up to
~ 21 mK, and provides a flux-to-temperature transfer coefficient exceeding ~ 60 mK/Φ0 at
235 mK (Φ0 ≈ 2×10-15
Wb is the flux quantum). Besides offering remarkable insight into
thermal transport in Josephson junctions, our results represent a significant step toward
phase-coherent mastering of heat in solid-state nanocircuits, and pave the way to the design
of novel-concept coherent caloritronic devices.
[1] O.-P. Saira, M. Meschke, F. Giazotto, A. M. Savin, M. Möttönen, and J. P. Pekola, Phys. Rev.
Lett. 99, 027203 (2007)
[2] K. Maki and A. Griffin, Phys. Rev. Lett. 15, 921 (1965).
41
3.6 A Single Electron Transistor to probe the excitation spectrum of a YBCO
nanoisland
D. Gustafsson, T. Bauch, D. Golubev and F. Lombardi
Department of Microtechnology and Nanoscience, Chalmers University of Technology, SE-412 96
Göteborg, Sweden.
Institute of Nanotechnology, Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-
Platz 1, 76344 Eggenstein-Leopoldshafen, Germany
Corresponding author: Floriana. Lombardi. E-mail: [email protected]
A prerequisite to understand the microscopic origin of the high critical temperature
superconductivity in cuprates is to establish the nature of the ground state and of the low
energy excitations. In such systems a predominant order parameter with a dx2
-y2
–wave
symmetry is well consolidated. However deviations from this state, such as an admixed dx2
-
y2 +is (or idxy ) leading to a full superconducting gap and time reversal symmetry breaking,
have been theoretically predicted and actively searched for in numerous experimental
studies. Up to now, the existence of such a complex order parameter remains highly
controversial. In this talk I will describe an unambiguous experiment that uses a Single
Electron Transistor as a spectroscopic nanotool ,with an unprecedented energy resolution,
to demonstrate a gapped Fermi surface in a nanometer sized YBa2Cu3O7−δ island, where
charging effects are pronounced. We find that the energy required for adding an extra
electron to the island depends on the parity (odd/even) of excess electrons and increases
with magnetic field. This demonstrates the occurrence of a subdominant imaginary order
parameter removing the nodal quasiparticle states.
42
3.7 Novel superconducting materials and hybrids for advanced superconducting
detectors
G. P. Pepe
University of Napoli Federico II & CNR SPIN, c/o Dept. Physical Sciences, P.le Tecchio 80, 80125
Napoli (Italy)
Corresponding author: Giampiero Pepe. E-mail: [email protected]
Superconductors are highly suitable materials for radiation detection. Several detector
types have been proposed, with properties of fast detection or high wavelength resolution
over a wide range of frequencies. Their performances depend mainly on the relaxation
processes involving phonons, quasi-particles and Cooper pairs occurring during the energy
cascade following the absorption of the radiation in the superconductor. The non-
equilibrium relaxation times together with some superconducting properties represent the
key parameter in choosing the most suitable superconducting material in view of its use as
an active element inside a cryogenic detector. We focus our attention on best choices of
materials and hybrids according to the role they have in hot electron photo-detectors and
superconducting tunnel junction devices, looking also to potentials in this field of novel
superconductors offered by cuprates and pnictides.
43
3.8 The generic requisites of the absolute superconducting magnetoresistance
effect in FM-SC-FM trilayers
D Stamopoulos, E Aristomenopoulou, E Manios, D Niarchos
Institute of Materials Science, NCSR ”Demokritos”, 153-10, Aghia Paraskevi, Athens, Greece
Corresponding author: Dimosthenis Stamopoulos, Tel. +302106503330. E-mail: [email protected]
In recent years the transport properties of hybrid ferromagnet-superconductor-ferromagnet
(FM-SC-FM) trilayers (TLs) have attracted much interest both theoretically and
experimentally due to the exotic features that uncover and the possible utilization in future
applications. Generally, the transport properties of the TL are controlled by both the in-
plane (surface parallel) and the out-of-plane (surface normal) magnetization configuration
of the outer FM layers. In most cases theory has focused on the in-plane configuration by
proposing that antiparallel (parallel) alignment of the FM magnetizations enhances
(suppresses) SC. This expectation was confirmed by experiments that clearly resolved the
so-called superconducting spin-valve effect [SSVE], observed as a dip in the measured
magnetoresistance. The influence of the out-of-plane magnetization components of the
outer FM layers on the transport properties of the SC interlayer have not been adequately
addressed up to now. Recent experiments of ours provided evidence that the more simple
superconducting magnetoresistance effect [SMRE], realized as a peak in the measured
magnetoresistance, can be pronounced in FM-SC-FM TLs when the FM and SC
ingredients are carefully chosen. Specifically, experiments conducted on NiFe-Nb-NiFe
TLs showed that the SMRE peaks correlate with the peaks observed in the out-of-plane
magnetization components of the outer FM layers at coercivity, giving evidence that the
transverse magnetic coupling of the outer FM layers through stray fields that pierce the SC
interlayer is probably the underlying cause of the SMRE. Our efforts are currently focused
on Co-Nb-Co TLs since Co can serve as a model FM ingredient that selectively exhibits
in-plane and out-of-plane magnetic anisotropy of shape origin. Here we show that
relatively thick Co outer layers greatly impact the SMRE observed in Co-Nb-Co TLs since
we uncover an absolute SMRE of magnitude 100% when the thickness of the Nb interlayer
is carefully adjusted to dNb=15-19 nm. On the contrary, for relatively thin Co outer layers
the SMRE is strongly suppressed.
Magnetization and magnetoresistance data will be presented on an extended range of Co
outer layers and Nb interlayer thicknesses, assisted by micromagnetic simulations and
magnetic force microscopy experiments. Those combined data on the NiFe-based and Co-
based TLs uncover the requisites for the observation of an absolute SMRE and provide
strong evidence that across the superconducting transition the SMRE is influenced by out-
of-plane stray-fields, attaining pronounced values when the respective coercive fields
coincide, thus enabling the transverse magnetic coupling of the outer FM layers through
the SC interlayer. In the light of these results possible applications are discussed.
44
Poster Session:
Tuesday, October 23rd
17:00 -19:00
45
We report on the observation of an interfacial charge transfer effect in high quality
Sexithiophene (T6)/ N,N’-bis (n octyl)-dicyanoperylenediimide (PDI-8CN2) heterostructures,
composing the active channels of field-effect transistors (HeOFETs). Bilayered heterostructures
with different T6 and PDI-8CN2 thicknesses have been fabricated and characterized by means
of electrical measurements, Atomic Force Microscopy and ex-situ Ultraviolet Photoemission
spectroscopy (UPS, with He I and He II photons). Bulk films of T6 showed HOMO and
(calculated) LUMO energy positions basically aligned to literature results, while PDI-8CN2
energy levels differ from the expected configuration, with the HOMO being 2.8eV below the
Fermi edge, in principle making possible the matching between the T6-HOMO and PDI-8CN2-
LUMO levels. Indications of charge transfer at organic/organic interface have been obtained by
means of both electrical measurements and UPS analysis. In comparison with single layer
(unipolar) devices, the electrical response (output and transfer-curves) of HeOFETs shows the
presence of ambipolar transport, a considerable enhancement of the active channel
conductivity, the shift of the threshold voltages and a negative trans-conductance behaviour.
The energy level scheme constructed from UPS data will be presented for various bilayered
heterostructures, suggesting the possible occurrence of different phenomena at the hetero-
interfaces, such as interface dipoles or band bending.
P.1 Charge transfer at the interface between Sexithiophene (T6) and N,N’-bis
(n-octyl)- dicyanoperylenediimide (PDI-8CN2) Heterostructures investigated by
UPS measurements
M.Barra1, F. Ciccullo
1, A. Cassinese
1, F. V. Di Girolamo
1, L. Aversa
2, R. Verucchi
2, S. Iannotta
2
1CNR-SPIN and Dipartimento di Fisica Università di Napoli Federico II, Napoli,Italy.
2 Istituto dei
Materiali per l’Elettronica ed il Magnetismo, IMEM–CNR, Via alla Cascata 56/C – Povo, 38123
Trento, Italy
Corresponding author: Mario Barra - CNR-SPIN and Dep. of Physics Science, University of Naples “Federico II” , P.le
Tecchio 80, 80125 Naples (Italy). E-mail: [email protected]
46
We report measurements of the temperature dependence of the parallel upper critical field,
Hc2||(T), in proximity coupled Nb/Py/Nb trilayers in which the thickness of the Py layer, dPy,
changes from 20 nm up to 432 nm. When dPy is in the range 150-250 nm a coupling between
the two superconducting outer layers is observed with Hc2||(T) showing a linear behavior from
Tc down to temperatures relatively far from the critical transition temperature. We believe that
this is due to a long-range proximity effect generated by the inhomogeneous magnetization
related to the presence of stripe domains of proper size in thick Py layers.
[1] C. Cirillo, E. A. Ilyina, J. M. Hernandez, A. Garcia-Santiago, J. Tejada, C. Attanasio, submitted.
P.2 Effect of Inhomogeneous Magnetization on the Superconducting Properties
of Nb/Py/Nb Trilayers: Evidence of Spin-Triplet Superconductivity
C. Cirilloa, E. A. Ilyina
a, A. Garcia-Santiago
b, J. M. Hernandez
b, J. Tejada
b, and C. Attanasio
a
a CNR-SPIN Salerno and Dipartimento di Fisica “E.R. Caianiello”, Università degli Studi di
Salerno, Fisciano (Sa), Italy b Grup de Magnetisme, Departament de Fisica Fonamental, Facultat de Fisica, and Institut de
Nanociencia i Nanotecnologia IN2UB, Universitat de Barcelona, Barcelona, Spain
Corresponding author: CNR-SPIN Salerno and Dipartimento di Fisica “E.R. Caianiello”, Università degli Studi di
Salerno, I-84084 Fisciano, Salerno, Italy. E-mail: [email protected]
47
Organic semiconductors are the fundamental blocks for plastic organic electronics which
includes among all OLEDs plastic screens. One of the most interesting class of materials are the
so-called "acenes" molecules made up of linearly fused benzene rings such as pentacene or a
similar molecule the rubrene.
The plasticity of such a kind of materials is ultimately due to the weak van der Waals inter-
molecular bonds which stabilize the crystal phase. However at room temperature the inherently
large thermal molecular motions act as strong electron scatterers, leading to apparent electron
mean-free-paths comparable or even smaller than the intermolecular distances. Therefore the
very nature of semiclassical transport based on Boltzmann equation is insufficient to
appropriately describe the charge transport mechanism in these materials.
Starting from the Kubo formula for the conductivity, we explore two possible [1,2]
generalizations beyond Boltzmann transport theory that can both account for the interplay
between highly conducting band states and strongly localized tail states, a key issue in the
transport properties of organic semiconductors and devices.
The two methods follow naturally from two alternative formulations of the Kubo response
theory, and qualitatively differ in the inclusion or not of quantum localization effects, whose
relevance is controlled by the typical timescale of disorder fluctuations. When applied to a
model that describes the crossover regime between intrinsic “band-like” motion and disorder-
dominated hopping relevant to current experimental systems, the two methods give
qualitatively similar results. This reflects a common underlying idea of the coexistence of
carriers of a different nature at different energy scales.
[1] S. Ciuchi S. Fratini "Band dispersion and electronic lifetimes in crystalline organic semiconductors"
Phys. Rev. Lett. 106, 166403 (2011).
[2] S. Fratini and S. Ciuchi "Band-like motion and mobility saturation in organic molecular
semiconductors" Phys. Rev. Lett. 103, 266601 (2009).
P.3 Transport properties of organic devices: from intrinsic carrier motion to
disorder dominated hopping
S. Ciuchi, S. Fratini*, Didier Mayou*
Istituto dei Sistemi Complessi CNR, CNISM and Dipartimento di Fisica, Università dell’Aquila, via
Vetoio, I-67100 Coppito-L’Aquila, Italy - *Institut Néel-CNRS and Université Joseph Fourier, Bôıte
Postale 166, F-38042 Grenoble Cedex 9, France
Corresponding author: S. Ciuchi, Dipartimento di Fisica, Università dell’Aquila, via Vetoio, I-67100 Coppito-
L’Aquila, Italy. E. mail [email protected]
48
P.4 Visualizing Vortex dynamics in Superconducting/Ferromagnetic thin film
heterostructures by low temperature Magnetic Force Microscopy
C. Di Giorgio1, A. Scarfato
1, 2, M. Iavarone
2,3, 4, M. Longobardi
1, 2, F. Bobba
1, 2; G. Karapetrov
3, V.
Novosad3 , and A.M. Cucolo
1,2
1.
"E.R. Caianiello" Physics Department and NANOMATES, Research Centre for nanomaterials
and nanotechnology, University of Salerno, Fisciano (SA), Italy. 2
CNR-SPIN Salerno, Fisciano (SA), Italy. 3
Materials Science Division, Argonne National Laboratory, Argonne, IL, United States. 4
Physics Department, Temple University, Philadelphia, PA, United States.
Corresponding author: Cinzia Di Giorgio. E-mail: [email protected]
Physics of the interplay between ferromagnetic (F) order and superconducting (S) order
has recently received a renewed interest due to the observation of cohexistence of F and S
in new classes of materials as pnictides and ruthenates. The F/S system offers a knob to
experimentally investigate new physical phenomena associated with the competition
between the superconducting vortex lattice and spatial confinement due to magnetic
pinning. Low temperature Magnetic Force Microscopy (LT-MFM) experiments on
magnetically coupled Permalloy (Py)/Nb bilayers show the effect of the magnetic pinning
on the formation of vortices (V) and antivortives (AV) and the corresponding dynamics.
In our work, thin film bilayers of Nb/Py with Nb thickness in the range 100 360 nm and
Py thicknesses in the range 1 4 mm were deposited on Si substrates. The study of domain
structure and the superconducting vortices were carried out by using an Omicron cryogenic
Scanning Force Microscope in LT-MFM mode. We used commercial micro-fabricated Si
cantilevers with magnetic coating (Veeco MESP LM), fo of about 75 kHz, magnetic
moment of 0.3×10-16
Am2 and coercivity <3·10
4 A/m. In our experiments, the tips were
magnetized upward prior to imaging.
The focus of the present study is the analysis of vortex dynamics in Py(1 μm)/SiO2(10
nm)/Nb(360 nm) thin film heterostructures as resulted from LT-MFM frequency shift
maps. Above the Nb Tc, the stripe-like Py stray field is visualized with half-periodo wPy =
520 nm. Below the Nb Tc, in zero applied field, the supercurrents established in the Nb
layer completely screen the out-of-plane component of the Py stray field. When the
samples are cooled in a uniform external magnetic field, V are formed in chain-like
configurations along the stripes with the same polarity. By decreasing and reversing the
applied field, for low intensity, we have found a rigidity of the vortex configuration. At
higher valus of external magnetic field (100-130 Oe) the pressure exerted by AV
overcomes the effective pinning causing AV “avalanches” that enter abruptly in the F/S
system.
References
A. Buzdin, Rev. Mod. Phys. 77, 935 (2005)
A. Yu Aladyshkin et al. Supercond. Sci. Technol. 22, 053001 (2009)
This research was partially supported through a “Rientro dei cervelli” grant by the Italian Ministry
for Education, University and Research (MIUR).
49
Heterojunctions represent the building block in a wide class of innovative devices; in
electronics, for instance, they have paved the way for the realization of multipurpose field effect
transistors (e.g. ambipolar and light emitting). In this regard, a noticeable enhancement of the
electrical conductivity, even leading to metallic behaviour [1] has been demonstrated, resulting
of particular interest for applications; charge transfer has been invoked as the mechanism at the
origin of this behaviour. The problem has been widely investigated, mostly in the case of thin
film devices [2], but issues related to the morphology and to the individuation of the place
where the carriers are accumulated complicates the clarification of the transport mechanism. In
our work we have overcome these issues by carefully choosing the semiconductors and the
device configuration. We have focused our attention on organic single crystals, which represent
a case study due to the high reproducibility of their properties [3]. In the device configuration
the heterostructure is formed by PDIF-CN2 and rubrene single crystals; rubrene is laminated on
a chromium stripe, with which it forms a Schottky barrier. The barrier and the low
concentration of dopants in the rubrene guarantee that charge carriers are solely accumulated in
the PDIF-CN2. Transfer curves indicates that the conduction is due to electrons; at lowering
temperature, band-like behavior is observed down to less than 150 K, with the electron mobility
remaining as high as 1 cm2/Vs at 50 K in the best devices. Furthermore, the charge carrier
density at VG = 0 exhibits a linear temperature dependence, which cannot be atributed to a
thermal activated behaviour. The results can be explained using a simple model accounting for
the alignment of the rubrene HOMO band with the bottom of the LUMO band of PDIF-CN2.
Schottky gated heterostructures have been consequently demonstrated to be a powerful tool for
probing the electrical properties of semiconductors and allowed tuning the charge carrier
density at the interface between two organic semiconductors. Moreover, the band alignment at
the heterointerface modified, actually improving, the electrical properties of PDIF- CN2.
[1] H. Alves, A. S. Molinari, H. Xie & A. F. Morpurgo, Nature Materials 7, 574 (2008).
[2] Haibo Wang and Donghang Yan, NPG Asia Mater. 2, 69 (2010).
[3] Electronic properties of single-crystal organic charge transfer interfaces probed using Schottky-gated
hetrostructures, I.G. Lezama, M. Nakano , N. Minder , Z. Chen , F. Di Girolamo , A. Facchetti, A. F.
Morpurgo, in press in Nature Materials
P.5 Single-Crystal Organic Charge-Transfer Interfaces probed using Schottky-
Gated Heterostructures
Ignacio Gutiérrez Lezama1, Masaki Nakano
2, Nikolas A. Minder
1, Zhihua Chen
3, 4, Flavia V. Di
Girolamo 1, 5
, Antonio Facchetti 3, 4
and Alberto F. Morpurgo1
1 DPMC and GAP. University of Geneva, 24 quai Ernest Ansermet, CH1211 Geneva, Switzerland -
2CERG, RIKEN Advanced Science Institute, Wako, Saitama 351-0198, Japan -
3Polyera
Corporation, 8045 Lamon Avenue, Skokie, IL 60077, USA - 4CHEM, Northwestern University,
2145 Sheridan Road, Evanston, IL 60208, USA - 5CNR-SPIN and University of Naples, p.le Tecchio
80, 80125 Naples, Italy –
Corresponding author: Flavia Viola Di Girolamo CNR-SPIN p.le Tecchio 80, 80125 Naples (Italy). E-mail:
50
P.6 Scanning Tunneling Microscopy and Spectroscopy study on the Metal-
quinoline/La0.7Sr0.3MnO3 interface
A. Gambardella, R. Cecchini, P. Graziosi, I. Bergenti, F. Biscarini and V,. Dediu
Consiglio Nazionale delle Ricerche – Istituto per lo studio dei Materiali Nanostrtturati (CNR-
INSM) via P. Gobetti 101, 40129 Bologna Italy.
Corresponding author: Alessandro Gambardella, CNR_ISMN via P. Gobetti 101, 40129 Bologna, Italy. E-mail:
The interfacial electronic properties between organic semiconductors and a ferromagnetic
half-metals represent an important topic in the field of organic spintronics.
Scanning Tunnelling Microscopy and Spectroscopy (STM-STS) had proven to be a
powerful tool to investigate these issues locally with resolution on the nanometer scale. We
report on Tris(8-hydroxyquinolinato) aluminium (Alq3) and Tris-(8-hydroxyquinoline)
metal complex (Inq3) thin films, deposited by vacuum evaporation on La0.7Sr0.3MnO3
(LSMO) substrates, and thicknesses ranging from 1 to 10 nm. STM images at molecular
resolution shows the tendency to form chain-like aggregates for very low substrate
coverage that we can tentatively ascribe to substrate-mediated interactions.
When coverage increases, the large scale morphology shows the tendency to an amorphous
growth, as confirmed by the roughness analysis. Spectroscopy curves indicate the
saturation of differential conductance towards an insulating behaviour by increasing the
organic layer thickness.
51
The topic of unconventional proximity effect and quantum states in hybrid
ferromagnet/superconductor systems [1] is at the center of a wide investigation especially for
the possibility of generating spin triplet odd-in-time (STOT) superconducting pairs which
propagate within strong diffusive ferromagnets over very long distances, comparable with the
penetration length scale of spin singlet pairs in a normal metal. This long-range proximity effect
may offer the possibility to exploit completely polarized supercurrents in the rapidly developing
field of spintronics. The recent experimental efforts addressing the generation and detection of
STOT pair correlations have been based on the theoretical prediction that magnetic
inhomogeneity is a key aspect to generate odd-in-time pairing, at least for singlet
superconductors. However, in all devices so far realized the fine tuning of the magnetic profile
is a complicate task, and this in turn probably hampers the controlled manipulation of spin
triplet super-currents. To avoid this problem, we propose an alternative perspective for the
generation of STOT pair correlations, looking at the almost unexplored context of
unconventional superconductors (US), and also considering hybrid ferromagnet/superconductor
systems. We show that the generation of STOT pair correlations is intimately connected to the
symmetry breaking in US. We found, in particular, that the main source of STOT correlations is
provided by the presence of mixed parity states [2]. Such feature is of fundamental importance
in the context of the symmetry determination of US and it turns out to be relevant also for
hybrids, since it can lead to STOT correlations without invoking magnetic inhomogeneities or
non-collinearity. The great variety of US available at the present time, from high-temperature
cuprates, to felectrons superconductors, cobaltates, ruthenates, iron based, organics and many
others, allows a realistic experimental implementation of our predictions, that can thus help to
make a significant advance in a reliable production of a new generation of experiments and
devices.
[1] M. Cuoco et al., Phys. Rev. B 78, 054503 (2008); A. Romano et al., Phys. Rev. B 81, 064513
(2010). [2] P. Gentile et al., e-print arXiv:1109.4885v1 (2011).
P.7 Odd-Frequency Triplet Pairing in Mixed-Parity Superconductors
P. Gentilea, C. Noce
a, A. Romano
a, G. Annunziata
a, J. Linder
b and M. Cuoco
a
a Dipartimento di Fisica “E. R. Caianiello”, Università degli Studi di Salerno and CNRSPIN, I-
84084 Fisciano (Salerno), Italy - b Department of Physics, Norwegian University of Science and
Technology, N-7491 Trondheim, Norway
Corresponding author: Dr. Paola Gentile CNR-SPIN Salerno and Dipartimento di Fisica "E. R. Caianiello", Università
degli Studi di Salerno, Via Ponte don Melillo, I-84084 Fisciano (SA), Italy - Phone: +39 089 969149 Fax: +39 089
969658. E-mail : [email protected]
52
P.8 Investigation of resistive switching behavior and nanoscale electronic
transport of Au/Nb-doped SrTiO3 junctions
A. Gerbia, R. Buzio
a, A. Gadaleta
b, L. Anghinolfi
b, F. Bisio
a, E. Bellingeri
a, A.S. Siri
a,b, D. Marré
a,b
a CNR-SPIN Institute for Superconductivity, Innovative Materials and Devices, C.so Perrone 24,
16152 Genova, Italy b
Physics Department, University of Genova, Via Dodecaneso 33, 16146 Genova, Italy
Corresponding author: Andrea Gerbi CNR-SPIN Corso Perrone 24, 16152 Genova. E-mail: [email protected]
Whenever a Schottky barrier is formed at the junction between large work function metals
and electron-doped SrTiO3 (STO) samples, the macroscopic rectifying transport is
accompanied by a resistance switching (RS) behavior. This is likely due to local, field-
induced accumulation or depletion of oxygen vacancies at the vicinity of the metal/STO
interface, that in turn might lead to redox processes responsible for the appearance of
resistance switching [1]. Metal/Nb-doped STO junctions represent a model system for the
elucidation of the physical mechanisms driving RS. Several investigations recently
addressed the RS dependence on few intrinsic and extrinsic physical parameters. There is
no doubt that a deeper insight was gained when the macroscale studies were complemented
by the use of local probes, addressing junctions response at the nanoscale [2].
Here we describe the fabrication and electrical characterization of Au/Nb:STO single-
crystal junctions with nanometer thick metal electrodes. We observe an unexpected
phenomenon, namely the coexistence within the same device of highly rectifying
properties - under laboratory air - and bipolar RS - under reducing vacuum conditions. We
explore this phenomenology by systematically studying the junction response under
different oxygen and inert gas atmospheres [3].
Since nanometer-scale alterations of the Schottky barrier represent one of the microscopic
mechanisms proposed to explain RS, we report on novel Scanning Tunnelling Microscopy
- Ballistic Electron Emission Microscopy (STM-BEEM) experiments aimed to directly
visualize and quantify the local inhomogeneities of the effective Schottky barrier height.
This approach represents an original strategy to attempt a correlation with the macroscopic
response of the studied system [4].
[1] R. Waser et al. Adv. Mater. 21, 2632 (2009). [2] K. Szot et al. Nat. Materials 5, 312 (2006).
[3] R. Buzio, A. Gerbi, A. Gadaleta et al. “Oxygen dependence of carrier transport and resistive-
switching in Au/Nb:SrTiO3 Schottky junctions” in preparation
[4] A. Gerbi, R. Buzio, A. Gadaleta et al. “Hot electron transport in Au/Nb:SrTiO3 structure
studied by ballistic electron emission spectroscopy” in preparation
53
P.9 Superconducting FeSe0.5Te0.5 thin films: a morphological and structural
investigation with scanning tunnelling microscopy and X-ray diffraction
Andrea Gerbia, Renato Buzio
a, Emilio Bellingeri
a, Shrikant Kawale
a, Daniele Marrè
a,b, Antonio
Sergio Siria,b
, Andrea Palenzonac, and Carlo Ferdeghini
a
a CNR-SPIN, Corso Perrone 24, 16152 Genova, Italy -
b Dipartimento di Fisica, Università degli
Studi di Genova, Via Dodecaneso 33 Italy - c Dipartimento di Chimica, Università degli Studi di
Genova, Via Dodecaneso 31 Italy
Corresponding author: Andrea Gerbi CNR-SPIN Corso Perrone 24, 16152 Genova. E-mail: [email protected]
It is so far established that high quality, epitaxial FeSexTe1-x thin films can be grown by
pulsed laser deposition (PLD) and that tensile and compressive stresses build up during
thickening of the film and affect the critical temperature (Tc) in a remarkable way [1-3].
Accordingly, a complex phenomenology has been reported and Tc values up to 21 K have
been observed. It is therefore interesting to address the mechanisms of stress formation and
release during the deposition of such materials. Similar studies have been challenged for
metal and semiconductor thin films, where a detailed investigation of the growth and
surface structure allowed an exploration of the relationship between morphology, stress
and transport properties [4]. In this context it has been shown that the deposition rate
effectively controls the amount of strain accumulated during the growth process [5]. Here
we report a low-temperature (4.8K) scanning tunnelling microscopy (STM) and x-ray
diffraction (XRD) investigation of 150 nm thick FeSe0.5Te0.5 superconducting films
epitaxially grown by PLD. We describe surface morphology and discuss its relationship
with film structure and Tc for two deposition rates. Samples with critical temperature Tc
above the bulk value (>16 K) show large atomic terraces, and a square lattice of periodicity
3.8 A associated with the Se/Te surface termination. Differences in the height coordinate
of the chalcogenide atoms are clearly visible at the atomic level. On the contrary, samples
with lower Tc (11 K) show hillocks generated by a spiral surface growth driven by
threading dislocations of screw character. A comparative x-ray diffraction analysis reveals
differences of compressive strain for the two classes of specimens. Variations in the
deposition rate are found to affect film growth and inner strain, which ultimately tune Tc
[6].
[1] Bellingeri E. et al., Appl. Phys. Lett. 96 102512 (2010) - [2] Wang M. J. et al Phys. Rev. Lett.
103 117002 (2009) - [3] Huang S. X. et al Phys. Rev. Lett. 104 217002 (2010) - [4] Springholtz G.
and Wiesauer K. 2002 Phys. Rev. Lett. 88 015507 (2002) - [5] Tello J. S. et al Phys. Rev. Lett. 98
216104 (2007) -[6] Gerbi et al. Supercond. Sci. Technol. 25 012001 (2012)
54
Electronic redistribution and charge localization at interfaces between ultra-thin films of
different materials play a key role in a number of applications and devices. Specific studies on
charge layers at organic/organic and organic/oxide interfaces are often based on electrical
characterization analysis, while less-explored approaches based on laser spectroscopy allow
contact-free probing of buried interfaces. In particular, Electric-field controlled optical second
harmonic generation (SHG) gained wide recognition for its ability to determine the electronic
structure of interfaces, offering peculiar advantages over other techniques (e.g. absence of
material damage, no charging effects, large optical penetration depth, time and energy
resolution allowing spectroscopy of electronic states as well as study of their dynamics, etc).
Furthermore, SHG allows to probe all interfacial charge and not the mobile charge only, as
well allowing to probe built-in electric fields associated to charge accumulation/depletion at
interfaces, thus even in absence of charge transport (as in ultra-thin incomplete layers).
Here we discuss recent results on optical probing of electronic redistribution and charge
accumulation at organic/organic as well as organic/dielectric (SiO2) interfaces where organic
FET channels are formed. Organic thin films and heterostructures based on electron- and hole-
transporting oligomers (PDI8-CN2 and 6T, respectively) have been deposited and investigated
by polarization-resolved SHG. An ad-hoc developed model based on superposition of 2D and
3D charge and effective polarization P2
(originating from organic surface and organic/SiO2
interface, respectively) was used to describe electronic redistribution in PDI8-CN2/SiO2 and
6T/PDI8-CN2 interfaces. Correlation between effective interface polarization and film
thicknesses reveals a way to probe both charge accumulation layer and local built-in field at
both kinds of interfaces without recurring to in-situ electrical characterization.
The results suggest the presence of intrinsic accumulation layer extending up to 4-6 molecular
layers in PDI8-CN2, strengthening the picture in which such materials acts as a “proper” n-type
semiconductor. Finally, we will show why such SHG analysis, as sensitive to net total charge,
is expected to be less influenced by spatial correlation than charge transport analysis: this
underlines novel possibilities offered by combination of SHG and in electrical analysis.
P.10 Electronic redistribution and charge localization at organic-organic and
organic-dielectric interfaces probed by optical second harmonic generation
S. Lettieri*, F. Ciccullo, A. Cassinese, P. Maddalena
SPIN-CNR and Dipartimento di Scienze Fisiche, Napoli, Italy
Corresponding author: Stefano Lettieri, SPIN-CNR UoS Napoli, Via Cintia 80126 Napoli, Italy. E-mail:
55
P.11 Zeolite Nanoparticles formation using a Dendrimer Template
L. Bonaccorsi1, P. Calandra
2, E. Proverbio
1 and D. Lombardo
2*
1 Dipartimento di Chimica Industriale e Ingegneria dei Materiali, Università di Messina, Salita
Sperone, 31 – 98166 S. Agata (Messina), Italy
2 CNR - Istituto per i Processi Chimico-Fisici, Viale Ferdinando Stagno d’Alcontres, 37, I-98158
Messina, (ITALY)
Corresponding author: Domenico Lombardo (CNR- IPCF) Consiglio Nazionale delle Ricerche - Istituto per i Processi
Chimico-Fisici, Viale Ferdinando Stagno d’Alcontres, 37, I-98158 Messina, (ITALY). Phone:+39 090 39762222 . E-
mail: [email protected]
A Small Angle X-ray Scattering (SAXS) investigation has been performed to study the
self-assembly process generated by the addition of a polyamidoamine dendrimer during the
zeolite LTA formation process. The presence of a condensed cationic Na+ charge all
around the dendrimers, which is responsible for the intense electrostatic interparticle
interaction potential, stimulate the condensed growth of the zeolitic phase onto the
dendrimer substrate. The experimental inter-dendrimer structure factor S(q), analysed in
the framework of liquid integral equation theory, allows the estimation of the dendrimer
effective surface charge through the modeling of the interparticle interaction. The presence
of the charge in the surface of the dendrimer, influences the crystallites aggregation as well
as the long-range assembly conditions for the zeolite growth [1]. The current investigation
emphasizes the potentials of using hybrid organic–inorganic networks in the synthetic
construction of functional materials with high-order structures for application in material
science and biotechnology [2-3].
References
[1] Lombardo D., Bonaccorsi L., Longo A., Proverbio E., Calandra P. Journal of Non-Crystalline
Solids 357, 771 (2011).
[2] Lombardo D. Langmuir 25, 3271(2009).
[3] Bonaccorsi L., Lombardo D., Longo A., Proverbio E., Triolo A. Macromolecules 42, 1239
(2009).
56
P.12 Nonlocal thermoelectric symmetry relations in ferromagnet-
superconductor proximity structures
P. Machon1, M. Eschrig
2, W. Belzig
1
1 Department of Physics, University of Konstanz, D-78457 Konstanz, Germany
2 Department of Physics, Royal Holloway, University of London, Egham Hill, EGHAM, TW20 OEX,
UK
Corresponding author: Peter Machon. E-mail: [email protected]
The symmetries of thermal and electric transport coefficients in quantum coherent
structures are related to fundamental thermodynamic principles by the Onsager reciprocity.
We generalize Onsager’s symmetry relation to nonlocal thermoelectric currents in a three
terminal ferromagnet-superconductor heterostructur including spin-dependent crossed
Andreev reflection and direct electron transfer processes. We proof this general symmetry
by applying spin-dependent boundary conditions for quasiclassical Green’s functions in
both the clean and the dirty limit. We predict an anomalously large local thermopower and
a nonlocal Seebeck effect, which can be explained by the spin-dependent spectral
properties.
57
The use of hybrid organic/inorganic semiconductor interfaces as charge photogeneration centres
in solar cells offers important advantages respect to fully organic photovoltaics devices (OPV).
Organic/inorganic networks with donor–acceptor distances below the typical exciton diffusion
length in organic semiconductors can be devised in controlled geometries to provide
photogeneration quantum yields close to 100%. Moreover, the possibility of creating direct
electron paths to the collecting electrode by appropriate patterning of the inorganic
semiconductor in defined geometries implies a reduction in non-geminate recombination, one
of the main drawbacks of fully organic bulk heterojunction (BHJ) solar cells. Losses in solar
cells efficiency in OPVs are often related to charge trapping and recombination at molecular
defects, chemical impurities or crystalline boundaries. Those can be minimized by designing
morphologies where free percolation paths are provided for electrons and holes towards the
collecting electrodes.
In order to reach these objectives a further understanding on the photophysical processes
occurring at hybrid interfaces is needed. We perform time resolved photoluminescence at
different temperatures on a GaAs/In0.4Ga0.6As quantum well (3 nm) buried in a GaAs matrix
at 10nm from the surface. The surface is coated with a poly(3-hexylthiophene) (P3HT)
conjugated polymer, a prototypical donor conjugated polymer (CP) in BHJ solar cells. This
combination could have interesting implications for solar cells applications since it exploits
broad absorption and moderate hole transport of P3HT, with excellent electron transport
properties of the inorganic semiconductor. The energy offset between the GaAs conduction
band and LUMO level of P3HT is about 0.7eV suggesting that charge transfer from inorganic
to organic is feasible.
Optical spectroscopy experiments confirm that efficient PL quenching from CP occurs, thus
indicating an efficient exciton dissociation process taking place at the P3HT/GaAs interface.
We discuss these results in terms of the electronic configuration of both semiconductors at the
interface.
P.13 Photophysics at organic/inorganic semiconductor interfaces
M. M. Mróz1*
, D. Granados1 , D. Fuster
2, Y. Gonzalez
2, L. Gonzalez
2 and J. Cabanillas-Gonzalez
1
1 Instituto Madrileño de Estudios Avanzados (IMDEA-Nanociencia), Cantoblanco, 28049 Madrid,
Spain
2 IMM-Instituto de Microelectronica de Madrid (CNM, CSIC), Isaac Newton 8, E-28760 Tres
Cantos Madrid, Spain
Corresponding author: Marta Magdalena Mroz. E-mail: [email protected]
58
Spintronics has shown a remarkable and rapid development, for example from the initial
discovery of giant magnetoresistance in spin valves to their ubiquity in hard-disk read heads.
One future avenue that may expand the spintronic technology is to take advantage of the long
spin coherence time as well as of the flexibility intrinsic to organic semiconductors (OSCs),
where it is possible to engineer and control their electronic properties and tailor them to obtain
new device concepts [1]. However, advancements in understanding the behaviour of hybrid
organic/inorganic spintronic devices have been slowed down by the lack of experimental
techniques able to directly measure the polarization of injected carriers from a buried interface
in operational devices. Here we show how it is possible to use the technique of low energy
muon spin rotation (LEM) to obtain a direct and depth-resolved measurement of the spin
polarization of the injected charge-carriers in a fully functional organic spin valve. In a LEM
experiment a 100% polarized beam of positive muons with tunable energy is implanted in the
sample, the implantation depth depending on the initial muon energy.
Muons decay to a positron, a muon antineutrino and an electron neutrino, with the emission
direction of the positron being correlated with the muon's spin at the time of decay. Thus, by
measuring the direction and the timing of decay positrons, it is possible to follow directly the
evolution of the spin of the muons as a function of time. The local magnetic field experienced
by the muon can be determined through the measurement of the Larmor precession of the muon
spin. In this way, muons act as passive local magnetic microprobes, by directly measuring the
magnetic field distribution at the implanted site with very high sensitivity. By measuring the
local magnetic field with current on and current off it is possible to extract the contribution of
the spin-polarized current. Using different implantation energies finally allows to obtain the
depth-resolution [2]. We will also show that, using LEM, we were able to prove that we can
control the spin polarization of extracted charge-carriers from an OSC by the inclusion of a thin
interfacial layer of polar material. The electric dipole moment brought about by this layer shifts
the OSC highest occupied molecular orbital with respect to the Fermi energy of the
ferromagnetic contact. This approach allows us full control of the spin band appropriate for
charge-carrier extraction, opening up new spintronic device concepts for future exploitation.
References:
[1] I. Bergenti et al., Org. Electron. 5, 309 (2004) - [2] A.J. Drew et al., Nature Mater. 8, 109 (2009)
[3] L. Schulz et al., Nature Mater. 10, 39 (2010).
P.14 Using muons as microscopic spin probes for organic devices
L. Nuccio1,2
, L. Schulz1, M. Willis
2, T. Kreouzis
2, W. P. Gillin
2, A. Suter
3, T. Prokscha
3, E.
Morenzoni3, C. Bernhard
1, A. J. Drew
2
1 Physics Department, University of Fribourg, Fribourg, Switzerland -
2 School of Physics and
Astronomy, Queen Mary University of London, London, United Kingdom - 3
Laboratory for Muon-
Spin Spectroscopy, Paul Scherrer Institute, Villigen, Switzerland
Corresponding author: Laura Nuccio. Address: Physics Department, University of Fribourg, Ch. du Musée 3, 1700
Fribourg, Switzerland. Telephone: +41 (0)263009078. E-mail: [email protected]
59
P.15 Charge transport in single-crystal organic semiconductors
C. A. Perroni1*, A. Nocera
2, V. Marigliano
1, V. Cataudella
1
1CNR-SPIN and Dipartimento di Scienze Fisiche, Università “Federico II” -
2Università Roma Tre
and CNISM
Corresponding author: Dr. Carmine Antonio Perroni, tel. +39-081-6-76855. E-mail: [email protected], Web:
http://people.na.infn.it/perroni
Spectral, optical, and transport properties of organic semiconductors are analyzed in
single-crystal-based field-effect transistors. Different approaches have been used for
models with electron coupling to low frequency inter-molecular modes [1,2]: the self-
consistent Born approximation valid for weak electron-phonon coupling, the coherent
potential approximation exact for infinite dimensions, and numerical diagonalization for
finite lattices. With increasing temperature, the width of the spectral functions gets larger
and larger, making the approximation of a quasiparticle less accurate. On the contrary,
their peak positions are never strongly renormalized in comparison with the bare ones. As
expected, the density of states is characterized by an exponential tail corresponding to
localized states at low temperature. For weak electron-lattice coupling, the optical
conductivity follows a Drude behavior, while for intermediate electron-lattice coupling, a
temperature-dependent peak is present at low frequency. For high temperatures and low
particle densities, the mobility always exhibits a power-law behavior as a function of
temperature. With decreasing particle density, at low temperature, the mobility shows a
transition from metallic to insulating behavior. Results are discussed in connection with
available experimental data in oligoacenes.
In particular, the effects of dimensionality [3] and the interplay between low frequency
inter-molecular and high-frequency intra-molecular modes [4] have been investigated.
Finally, the interplay between electron-phonon coupling and disorder strength have been
analyzed in organic semiconductors grown on polarizable gates [5,6].
[1] V. Cataudella, G. De Filippis and C.A. Perroni, Phys. Rev. B 83, 165203 (2011). - [2] C.A.
Perroni, A. Nocera, V. Marigliano Ramaglia, and V. Cataudella, Phys. Rev. B 83, 245107 (2011).
[3] F. Gargiulo, C.A. Perroni, V. Marigliano Ramaglia, and V. Cataudella, Phys. Rev. B 84,
245204 (2011). - [4] C.A. Perroni, V. Marigliano Ramaglia, and V. Cataudella, Phys. Rev. B 84,
014303 (2011). - [5] C.A. Perroni and V. Cataudella, Phys. Rev. B 85, 155205 (2012). - [6] C.A.
Perroni and V. Cataudella, EPL in press.
60
P.16 Quantum pumping theory of organic-inorganic hybrid nanodevices
F. Romeo1,2
, R. Citro1,2
1Dipartimento di Fisica “E. R. Caianiello”, Università di Salerno, &
2CNR-SPIN Via Ponte don
Melillo, I-84084 Fisciano (Sa), Italy
Corresponding author: F. Romeo, Dipartimento di Fisica “E. R. Caianiello”, Università di Salerno, Via Ponte don
Melillo, I-84084 Fisciano (Sa), Italy. E-mail: [email protected]
We study the coherent particles transport in hetero-elastic nanodevices characterized by
inhomogeneous elastic response along the transport direction. In these systems the charge
density mechanically interacts with internal degrees of freedom that control the spatial
configuration of the device leading to interesting emerging functionalities. The simplest
system belonging to this class of nanodevices is an organic molecule (elastically soft part)
connected to two external inorganic leads (elastically hard part). A minimal description for
the above system is given in terms of the center of mass dynamics of the soft part
(considered classical) and its coupling to the charge state activated during the transport.
Adopting this paradigmatic model, which is called deformable quantum dot[1,2], we study
the signatures of the inhomogeneous elastic response of the system in the context of
quantum pumping[3]. We find that the dependence of the current from the elastic response
of the organic part induces interesting dynamical phase effects [1] modifying the usual
current-phase relation of the hard (i.e. non-deformable) case[4]. The effects of non-
linearity are discussed in the framework of memory effect devices [2], while a comparison
with the case of a strongly interacting (non-deformable) dot is also made [5].
[1] F. Romeo, R. Citro, "Quantum pumping in deformable quantum dots", Phys. Rev. B 80, 235328
(2009)
[2] F. Romeo, R. Citro, "Memory effects in adiabatic quantum pumping with parasitic nonlinear
dynamics", Phys. Rev. B 82, 085317 (2010)
[3] D. J. Thouless, Phys. Rev. B 27, 6083 (1983)
[4] P. W. Brouwer, Phys. Rev. B 58, (R)10135 (1998)
[5] F. Romeo, R. Citro, "Parasitic pumping currents in an interacting quantum dot", Phys. Rev. B
82, 165321 (2010)
61
P.17 Laser as a flexible Heat Source for Deposition and Analysis of functional
Materials
Wolfgang Stein
SURFACE systems + technology GmbH + Co KG Hückelhoven, Germany
Corresponding author: Wolfgang Stein. E-mail: [email protected]
Thin film deposition processes for functional materials require precise control of the
substrate temperature, sometimes at very high temperatures. Heating stages to provide the
necessary thermal energy are influencing the local conditions around the substrate and part
of the process parameters. During the characterization of such materials, especially if
structured to form a sensor or other devices it is often necessary to focus heat to small spots
of sub mm dimensions. For all these different applications laser is a possible solution.
During the last 20 years applications of laser heating were published [1-6]. High intensive
laser light, precise applied to the substrate offer a wide range of advantages. The freedom of
chemical or physical side effects guarantees best vacuum conditions and minimal energy
transfer into a deposition system for a given substrate temperature. Theoretically no limits
in temperature and heating rates exist. But all of these features are only possible, if the
system is well designed, which means:
- optical properties of the substrate are recognized and define finally the type of laser
- beam profile guarantees a homogeneous temperature profile
- substrate fixing does not disturb the temperature profile
- a contact free temperature measurement is possible
- the temperature measurement is not disturbed from the process
Different solutions exist to meet all of the above points [7]. Diode laser with it’s near IR
wavelength are the most flexible tool but with clear limits for most oxide electronic
substrates like STO or others. CO2 laser are the solution for such materials, both solutions
are presented. In the analytical field the light fibre using diode laser offer the most
flexibility. Spot sizes of 200µm to 2mm are useful in this field. Non existing electrical or
magnetically fields around the substrate and limited heat transfer to the analytical elements
guarantees the lowest disturbance to the analytical process and take care of the highest
resolution.
[1] P.E. Dyer, A. Issa, P.H. Key, P. Monk, Supercond. Sci. Technol. 3, 472 (1990) - [2] K.H. Wu,
C.L. Lee, J.Y. Juang, T.M. Uen, Y.S. Gou, Appl. Phys. Lett. 58, 1089 (1991) - [3] S.J. Barrington,
R.W. Eason, Rev. Sci. Instrum. 71, 4223 (2000) - [4] S. Ohashi, M. Lippmaa, N. Nakagawa, H.
Nagasawa, H. Koinuma, M. Kawasaki, Rev. Sci. Instrum. 70, 178 (1999) [5] H. Lippmaa, T.
Furumochi, S. Ohashi, M. Kawasaki, H. Koinuma, T. Satoh, T. Ishida, H.Nagasawa, Rev. Sci.
Instrum. 72, 1755 (2001) - [6] W. Stein, MRS spring meeting 2006, GG13.6 (Laser Heating, a
challenging new Technology for small Substrates in Oxide Deposition Processes)
[7] W. Stein, T. Heeg, Superconductivity and Functional Oxides Como 2012, ( Laser heating of
HTSC substrates: challenges,problem,solutions)
62
P.18 Quantum capacitance of few-layer graphene
E. Uesugi, H. Goto, R. Eguchi, Y. Kubozono
Research Laboratory for Surface Science, Okayama University, Okayama 700-8530, Japan
Corresponding author: Eri Uesugi, Okayama University, Okayama 700-8530, Japan.
E-mail: [email protected]
Electronic properties in graphene have been studied so far around the charge neutrality
point, but highly doped graphene has recently attracted much interest because of the
following reason. By doping 0.25 carriers per carbon atom, graphene indicates exotic
phenomena such as chiral superconductivity [1], CDW [2], and SDW [3]. In the structure
of graphene field effect transistors (FETs), the carrier density is determined by the product
of the applied gate voltage Vg and the capacitance Ctotal between the gate electrode and the
graphene. We expect that ionic liquid gate enables the accumuration of high-density carrier
owing to the formation of electric double layer in thickness below 1 nm. However, the
previous studies demonstrated that the carrier doping into single layer graphene (SLG) is
not efficient [4, 5]. This is because Ctotal consists of a series connection of geometrical
capacitance Cg and quantum capacitance Cq, that is 1/ Ctotal = 1/ Cg +1/ Cq, where Cq is
proportional to the density of state D(ɛ) and defined as Cq = e2D(ɛ) [6]. Even if the ionic
liquid has large Cg, the extremely small D(ɛ) in SLG reduces Ctotal.
In this presentation, we report the capacitance of few-layer graphene (FLG) with
changing the layer number n systematically. Since D(ɛ) significantly depends on n, we
might find optimal n for the carrier doping. We prepared two-terminal graphene FET with
n = 1 to 10. The capacitance Ctotal is related to the conductivity σ; |dσ/dVg| = μCtotal, where
the carrier mobility μ is estimated from the back gate voltage dependence of the
conductivity. Ctotal is found to be maximum at n = 4, indicating that the carrier injection is
most effective. Here, the carrier density is estimated to be 4.7×1013
cm-2
(0.003 /carbon
atom) at |Vg| = 2 V. To increase Ctotal more, we may require the chemical doping or the
assistance of the additional doping by the solid gate with high dielectric constant.
To give physical meaning of n dependence of Ctotal, we calculated Cg and Cq which
minimize the energy and theoretically formulated obtained Ctotal as a function of n. The
calculated result is in good agreement with the measured values. For n < 4, Ctotal is
dominated by Cq and increases with n. For n > 4, the gate electric field is perfectly
screened and then Ctotal saturates. In order to fully understand the conductive and inductive
properties of graphene, we are now trying to measure the capacitance directly by AC
measurement. Furthermore, measurement of stacking (ABA/ABC) dependent capacitance
of trilayer graphene is in progress.
[1] R. Nandkishore et al., Nature Phys. 8, 2208 (2012). - [2] G. Li et al., Naurue Phys. 6, 109
(2010). - [3] D. Makogon et al., Phys. Rev. B 84, 125404 (2011). - [4] J. Ye et al., PNAS 108,
13002 (2011). - [5] J. Xia et al., Nature Nano. 4, 505 (2009). - [6] S. Luryi, Appl. Phys. Lett. 52,
501 (1988).
63
Index of presenting contributors
A
Aarts J. · 28
Adamo C. · 7
Ambrosio A. · 37
Aruta C. · 9
B
Barra M. · 45
Batlogg B. · 21
Bell C. · 29
Bergeret F. S. · 16
Biasiucci M. · 23
Blamire M. G. · 15
Buzdin A.I. · 10
C
Cabanillas-Gonzalez J. · 22
Camposeo A. · 36
Cassinese A. · 26
Cirillo C. · 46
Citro R. · 14
Ciuchi S. · 47
Colle R. · 25
D
Di Giorgio C. · 48
Di Girolamo F. V. · 49
G
Gambarderlla A. · 50
Gentile P. · 12, 51
Gerbi A · 53
Gerbi A. · 52
Giazotto F. · 40
Goll G. · 18
Goto H. · 39
Gottardi S. · 3
K
Kawabata S. · 17
Koster G. · 6
Kubozono Y. · 2
L
Lettieri S. · 54
Lombardi F. · 41
Lombardo D. · 55
M
Machon P. · 56
Mayer D. · 20
Morgante A. · 24
Mosca R. · 33
Mróz M. M. · 57
2
N
Niño M.A. · 34
Nocera A. · 38
Nuccio L. · 58
P
Pepe G. P. · 42
Perroni C. A. · 59
Pontiroli D. · 4
R
Romeo F. · 60
S
Salvato M. · 27
Santamaria J. · 32
Scotti di Uccio U. · 31
Silva E. · 13
Stamopoulos D. · 43
Stein W. · 61
Stornaiuolo D. · 30
Stroppa A. · 5
U
Uesugi · 62
V
Villegas J.E. · 11
W
Wördenweber R. · 8
