Author(s) : Shwetha G. Bhat and Dr. P.S. Anil Kumar 3O4s) : Shwetha G. Bhat and Dr. P.S. Anil Kumar Affiliation(s) : Department of Physics, Indian Institute of Science, Bangalore –

Author(s) : Shwetha G. Bhat and Dr. P.S. Anil Kumar

Affiliation(s) : Department of Physics, Indian Institute of Science, Bangalore

– 560012, INDIA

Email of Presenter : [email protected]

Title : Study on Fe3O4/MgO/GaAs systems for spin injection

experiments

Abstract:

It is seen that the insertion of insulator in between the ferromagnet and

semiconductor always increases the efficiency of spin injection of ferromagnet into

semiconductor eliminating the problem of resistance mismatch between the two.

Fe3O4 is believed to be a half metallic ferrimagnet, and hence it can be expected to

have a very high spin polarization. MgO being a very good insulator with the

selective Δ-like energy bands has a very good lattice match with Fe3O4 and GaAs.

The growth of oriented films is confirmed by x-ray diffraction measurement. The

magnetization measurement of Fe3O4 shows a clear Verwey transition around 120K

as well as a clear M-H loop at room temperature. Devices of Fe3O4/MgO/GaAs

(doped) were fabricated to carry out the electrical Hanle measurements with the 3-

terminal non-linear (NL) geometry. From the I-V measurements it is seen that the

junction behaves purely as a tunnel junction. The transport measurements clearly

indicate the spin injection from Fe3O4 to GaAs through MgO as a function of the

tunnel current. Depending the nature of current either injection or accumulation

current, the shape of the plot of NL voltage vs. magnetic field is accordingly modified.

If the insulator thickness is reduced, then the NL voltage showed no dependency of

magnetic field, with I-V characteristic being Schottky natured.

Author(s) : Deep Narayan Biswas, Partha Sarathi Mandal, Shyma R.

Varier, Nishaina Sahadev and Kalobaran Maiti

Affiliation(s) : TATA INSTITUTE OF FUNDAMENTAL RESEARCH


Title : Evidence of unusual spin polarization of the surface states of

W(110) surface.

Abstract:

We studied the surface electronic structure of W(110) surface employing spin and

angle resolved photoemission spectroscopy. Experimental results exhibit highly

dispersive linear bands corresponding to the surface states and signature of Dirac

cones. Spin resolved spectra exhibit unusual spin character of the energy.

Author(s) : Debmalya Chakraborty and Amit Ghosal

Affiliation(s) : Indian Institute of Science Education and Research, Kolkata


Title : Impurity Effects on Strongly Correlated d-wave

Supercondutors

Abstract:

The effect of impurities on strongly correlated High Tc Superconductors (HTSC) is

investigated in the framework of disordered Hubbard Model. The strong electronic

correlation, inherent to the undoped parent HTSC compounds (Mott insulator), is

treated using Gutzwiller approximation leading to removal of double occupancy. The

resulting t-J like model with all terms up to order t2/U, but with inhomogenously

renormalized parameters, is treated within Bogoliubov-de Gennes mean field theory

that captures the physics of spatial inhomogeneity in all the order parameters. Our

results for single particle density of states (DOS) as well as two particle correlation

functions, such as, Off-diagonal Long Range order (ODLRO), show that the strong

correlations make the superconductor robust to impurities than the equivalent

uncorrelated case. This robustness is primarily due to a complex interplay of spatial

organization of different orders in the background of a significantly smaller ‘effective’

disorder. Our finding is justified through detailed analysis of DOS, ODLRO and

spatial profiles of different order parameters. It will be demonstrated that the effect of

a single impurity plays a crucial role in explaining our qualitative findings.

mailto:[email protected]

Author(s) : Narjes Gorjizadeh, Su Ying Quek

Affiliation(s) : Institute of High Performance Computing (IHPC)


Title : Interface Effects on Tunneling Magnetoresistance in Organic

Spintronics: Can Amine-Au link groups with Au/Fe Leads give

Reproducible Magnetoresistance?

Abstract:

Organics are promising alternatives to conventional semiconductors for spintronics

applications. Besides low cost and mechanical flexibility, the weak spin-orbit

interaction in organic systems can give rise to longer spin-coherence time and

distances compared to inorganic semiconductors.1 Chemical functionalization can

also lead to magnetic centers within the molecules, with the potential for interesting

spintronic effects. However, organic spintronics still lacks a benchmark system with

reproducible magnetoresistance (TMR), TMR being highly sensitive to interface

effects. A key breakthrough in molecular electronics was the discovery of amine-Au

and other link groups that give reproducible conductance.2 Here, we use first

principles calculations to explore if the same amine-Au link groups can give

reproducible magnetoresistance with Au-covered Fe leads. We show that the TMR

can be larger and less sensitive to contact geometry than in previously studied thiol-

Ni junctions. However, the TMR is in general very sensitive to symmetry and to the

number of Au layers in the junction, due to complications from interface and quantum

well states. Our results pave the way for understanding how to achieve reproducible

TMR in organic spintronics, and sheds light on origins of TMR in experiments where

the organic is separated from magnetic electrodes by a non-magnetic spacer.

References

1. Rocha et al, Nature Materials 4, 335 (2005)

2. Venkataraman, et al, Nano Lett. 6, 458 (2006)

Author(s) : Priti Gupta*, A. A. Rahman, Nirupam Hatui, Mahesh Gokhale

Mandar M. Deshmukh and Arnab Bhattacharya

Affiliation(s) : Department of Condensed Matter Physics and Materials

Science, Tata Institute of Fundamental Research, Mumbai,

India


Title : Group III-Nitride quantum wells grown on CVD graphene

Abstract:

Graphene films are stable at high-temperature, flexible, optically transparent,

and have good electrical and thermal conductivities. Chemical vapour deposition

(CVD) can be used to synthesize large area films of graphene, which when used as

a substrate for III-N growth may make it possible to realize novel devices [1]. We

have recently reported the MOVPE growth of III-N films on graphene allowing a facile

method to make free-standing nitride layers [2]. In this work we report the synthesis

and optical characterization of semi-polar InGaN/GaN and GaN/AlGaN quantum well

structures grown on a graphene layer.

CVD-grown graphene layers on Cu were transferred onto SiO2-coated silicon

substrates. The III-N layers were deposited by a low pressure MOVPE using

standard precursors. We have grown various AlGaN alloys on AlN buffer layers, and

optimized the MOVPE deposition parameters such as temperature, V/III ratio and

pressure to obtain, under appropriate conditions, (10-11) oriented semi-polar layers.

Various multi-quantum well stacks of GaN(QW)/AlGaN(barrier) and InGaN

(QW)/GaN (barrier) were grown. These layers, though polycrystalline, are of high

quality and show strong room temperature photoluminescence (PL) (Fig. 1) and

should pave the way to develop optoelectronic nitride devices on graphene.

Fig. 1: Room/low temperature PL from a 20-period GaN/AlGaN multiquantum

well stack grown on graphene

3. References

[1] K. Chung, C-H. Lee and G-C. Yi, Science 330, (2010) 655;

[2] P. Gupta, A.A. Rahman, et al., “MOVPE growth of (Al, Ga)N on graphene”, Paper

Fr. A2-1, Proc. Intl. conference on MOVPE, ICMOVPE-16, May 20-25,2012, Busan

Korea

Author(s) : Tran Thi Thu Hanh, Yoshinari Takimoto, and Osamu Sugino

Affiliation(s) : The Institute for Solid State Physics, The University of Tokyo,

Kashiwa, Chiba 277-8581, Japan


Title : Ab initio Modeling of the Hydrogen Adsorption on Pt(111)

Surface

Abstract:

The hydrogen adsorption on the Pt(111) electrode surface has been intensively

investigated. To gain insight into detailed atomistic picture on the equilibrium

coverage and structure, we have constructed a lattice gas model by determining the

on-site energy and the interaction parameters using the first principles total-energy

calculation. Therein atop, fcc, hcp and bridge sites are covered by hydrogen atoms

under various coverage conditions (0ML < Θ ≤ 1ML) and the total-energy

calculations are done for the (1x1), (2x2) and (3x3) cells. The total-energies of (3x3)

cell, corrected by the zero-point energy (ZPE), are found well fitted to the lattice gas

model. With this model, the Monte Carlo (MC) simulation has been performed. The

first-principles calculation combined with MC simulation successfully explains the

interaction of H atoms on the Pt(111) surface. We are calculating to identify the

active site of the hydrogen adsorption on the Pt(111) surface, which has been

hitherto conceptually discussed but has not been shown by an atomistic simulation.

Author(s) : Manish Kumar, Jyoti Thakur, Mukhtiyar Singh, Hardev Singh

Affiliation(s) : Department of Physics, Kurukshetra University, Kurukshetra-

136119 INDIA


Title : ab-initio investigation of Half metallicity in ordered and

disordered CoFeMnSi quaternary Heusler alloy

Abstract:

An ab-initio investigations of electronic and magnetic properties of ordered

and disordered CoFeMnSi quaternary Heusler alloy (HA) has been made using full

potential linearized augmented plane wave (FPLAPW) method based on density

functional theory (DFT). The generalized gradient approximation (GGA) governs the

exchange-correlation (XC) potentials in the present calculations. We observe that the

increasing Mn concentration in Co1-xFeMn1+xSi (x = 0, 0.25, 0.50 and 0.75) lowers

the total magnetic moment due to antiparallel alignment of extra Mn-atom to original

Mn-atom. Further, ordered CoFeMnSi Heusler alloy is a true half-metallic

ferrromagnet with integer magnetic moment of 4.00 μB per formula unit and mainly

localized at Mn site. The magnetic moment decreases with increase of Mn-disorder

in CoFeMnSi. The variation of half metallicity with increasing Mn-disorder is also

analyzed. This type of quaternary Heusler alloys can be proved an ideal candidate

for spin valves and magnetic tunnel junction applications.

Author(s) : A.R. Kumarasinghe1 *, F. Bondino2, R.N. Wijesinghe1, S.

George1, K.M. Nalin de Silva1, P. R. Kidambi3, S. Hoffman3,

P. Hiralal3 and Gehan A J Amaratunga1,3

Affiliation(s) : 1Sri Lanka Institute of Nanotechnology (SLINTEC), Zone 1,

EPZ, Biyagama, Colombo, Sri Lanka, 2Beamline BACH, IOM

CNR, Laboratorio Nazionale TASC, Area Science Park,

Bassovizza Edificio MM - S.S. 14 Km. 163,5, I-34149,

Basovizza (TS), Trieste, Italy, 3Centre of Advanced Photonics

and Electronics, Department of Engineering, University of

Cambridge, 9 J.J. Thomson Avenue, Cambridge, CB 3 0 FA,

UK,

Email of Presenter : [email protected], [email protected],

[email protected]

Title : C-K-edge NEXAFS, core level photoemission and Raman

spectroscopy of multilayer graphene oxide membrane and

natural graphite from vein

Abstract:

Synchrotron radiation (SR) based core level photoemission spectroscopy, C and O

K-edge X-ray absorption spectroscopy (NEXAFS) and micro Raman spectroscopy

are used to investigate the structural and electronic properties of graphene oxide

(GO) multilayer membrane produced using natural graphite from vein. The multilayer

membrane was chosen because of its easy fabrication procedure and its foreseen

wide range of applicability. Electronic properties of GO membrane prepared using

infrequent form of precursor graphite are reported for the first time here. In the C 1s

region of the multilayer GO, distinctly separated peaks are observed at higher

binding energy (BE) region, which are attributed to the higher order hybridized

carbons presence in the membrane. The broad full-width half maximum (FWHM) of

the C 1s main peak at a BE of 284.7 eV indicates that other forms of carbons such

as vacancies and hydrogenated species (C-H) are also present. The C K-edge

NEXAFS spectrum of GO becomes featureless in the photon energy range

295-311eV where strong absorption and number of electronic transitions are

observed for the precursor vein graphite. The suppression of the features (i.e.,

featurelessness) at higher photon energies shows that the membrane behaves as a

material composed of strongly decoupled layers. Neither hydrogenated nor

oxygenated carbon species are observed with precursor graphite according to the C

1s core level spectra. The C K-edge NEXAFS for the precursor graphite reveals that

the distribution of the density of states in unoccupied orbitals of this new type of

precursor graphite is similar to that of man-made highly oriented pyrolytic graphite

(HOPG). This observation is further verified by micro Raman spectroscopy where a

very small D peak at a wavenumber of 1355 cm-1 and strong G peak at a

wavenumber of 1575 cm-1 are observed. The D/G ratio, which is ~ 0.0337, is more

comparable to HOPG than commercial flake graphite. A new peak is observed at

photon energy of 287 eV in the C K-edge NEXAFS spectrum of the precursor

graphite which may have resulted in from the molecular nature of sp2 bonded carbon

suggesting that there are isolated pentagonal defects in the graphene plane of the

precursor graphite which give a C60 like curvature and pseudo molecular signatures.

Key words: electronic properties, graphite oxide membrane, self-assembled layers,

synchrotron radiation, C K-edge NEXAFS, core level photoemission.

*Corresponding author. Email: [email protected],

[email protected], Tel: 0094-11-4650507, Fax: 0094-11-4741995.

Permanent Institute: Faculty of Science and Technology, UWU, 90000, Sri Lanka.

Author(s) : Suchun Li1,2,3, Chee Kwan Gan3, Young-Woo Son4, Yuan Ping

Feng1,2, and Su Ying Quek3

Affiliation(s) : 1NUS Graduate School for Integrative Sciences and

Engineering, National University of Singapore, Singapore

2Department of Physics, National University of Singapore,

Singapore

3Institute of High Performance Computing, A*STAR, Singapore

4Korea Institute for Advanced Study, Seoul 130-722, South

Korea


Title : Length-Independent Transmission Peaks in Nanostructured

AGNR-Junctions

Abstract:

The prospect of all-carbon nanoelectronics has motivated significant interest in the

transport of electrons through graphene nanoribbon (GNR) junctions. Bottom-up

synthesis approaches now offer atomic control over the widths of armchair edge

GNRs (AGNR) [1] while top-down lithographic methods offer possibilities of creating

nanostructured GNR junctions [2]. In this work, we explore, using a first principles

scattering state approach [3], electron transport through nanostructured AGNR

junctions, in which the central scattering region consists of an AGNR connected

seamlessly to wider AGNRs (which make up the two electrodes of the junction). At

the interface between the central AGNR segment and the wider AGNR electrodes,

the armchair edges of the narrower and wider AGNRs are joined by either zigzag

edges or armchair edges (the two most stable edge configurations). We predict that

when both interfaces have zigzag edges, transmission near the Fermi level is

dominated by resonant transmission peaks whose energies are, contrary to

expectation, independent of the length of the central AGNR region. We show that

these peaks arise from interactions between the zigzag edges at the two interfaces,

and discuss why the energies of these peaks are length-independent. We also

predict that these peaks are useful in producing negative difference resistance.

[1] S. Linden et al., Phys Rev Lett 108, 216801 (2012)

[2] L. Tapaszto et al., Nature Nanotechnology, 3, 397 (2008); X. Wang et al., Nature

Chemistry 2, 661 (2010)

[3] H. J. Choi et al., Phys Rev B, 76, 155420 (2007)

Author(s) : Watchara Liewrian

Affiliation(s) : Department of Physics, Faculty of Science,

King Mongkut's University of Technology Thonburi (KMUTT)

126 Pracha U-thit Rd.,Bangmod Tung-Kru,Bangkok 10140,

Thailand


Title : Interplay between the exchange interaction and the orbital

effect of perpendicular magnetic field in graphene junction:

Spin-polarized transport

Abstract:

We theoretically investigate the effect of magnetic vector potential and exchange

interactions on the spin-polarized transport properties of 6massless Dirac particles in

graphene junction. By combining the orbital effect and the Zeeman interaction of

magnetic fields in graphene junction, it is found that the junction mimics behavior of

half-metallic tunneling junction, in which it acts as a metal to particles of one spin

orientation but as an insulator or a semiconductor to those of the opposite

orientation. The idea of the half-metallic tunneling junction can provide a source of

∼100% spin-polarized current. Adjustment of the position of the Fermi level in

ferromagnetic layer by placing a gate voltage on top of the ferromagnetic layer shows

that reverse of the orientation of the completely spin-polarized current passing

through the junction is controlled by adjusting the gate voltage. These interesting

characteristics should lead to a practical gate voltage controlled spin filtering and

spin-polarized switching devices.

Author(s) : Shiuan-Fan Liou

Affiliation(s) :


Title : Edge Excitations of Bose-Einstein Condensate on Honeycomb

Lattice

Abstract:

Edge excitations of bosonic condensates on honeycomb lattice are investigated.

By considering weakly interacting bosons in the tight-binding limit with on-site and

nearest-neighboring interactions respectively, it is found that edge phonons generally

emerge as excitations of condensates either inside the gap between bulk acoustic

spectrum and optical spectrum or attached as an edge acoustic mode to the bulk

acoustic spectrum. Origins of edge phonons are analyzed. In particular, it is found

that even though excitations are governed by a non-Hermitian Hamiltonian, edge

phonons inside the bulk phonon spectrum gap have the same topological origin as

that of the BDI class in the classification of topological insulators. Possible

extensions to other lattices are briefly discussed.

Author(s) : Ya-Lin Lo

Affiliation(s) : Department of Physics National Taiwan University


Title : Length- and temperature-dependent crossover of charge

transport across molecular junctions

Abstract:

We study the electronic transport in a molecular junction, in which each unit is

coupled to a local phonon bath, using the non-equilibrium Green's function method.

We observe the conductance oscillates with the molecular chain length and the

oscillation period in odd-numbered chains depends strongly on the applied bias. This

oscillatory behavior is smeared out at the bias voltage near the phonon energy. For

the phonon-free case, we find a crossover from tunneling to thermally activated

transport as the length of the molecule increases. In the presence of electron-phonon

interaction, the transport is thermally driven and a crossover from the thermally

suppressed to assisted conduction is observed.

[1] Ya-lin Lo, Shih-Jye Sun, Ying-Jer Kao, PRB 84 075106(2011)

Author(s) : Xin Luo and Su Ying Quek

Affiliation(s) : Institute of High Performance Computing, Singapore


Title : Theoretical Study of High-frequency Raman Modes in Bulk and

Few Trilayer MoS2

Abstract:

MoS2, a prototypical transition metal dichalcogenide semiconductor, has attracted

great interest due to its unique physical properties and potential industry applications,

especially in low dimensions. MoS2 consists of weakly interacting trilayers (TLs;

three atomic planes in 1 TL). Raman spectroscopy has been proposed as a means

to count the number of TLs in thin films, because Raman frequencies are sensitive to

thickness. However, controversial experimental results have been reported for the

evolution trend of E12g mode with thickness [1,2]. Here, we combine the first-

principles density functional perturbation theory calculations and a force constants

model to elucidate the effect of decreasing thickness on Raman frequencies in MoS2,

and compare our results with experiment. Based on our force constants model, we

find that if the force constants are kept the same from bulk to 2D, the predicted

frequencies of both A1g and E12g modes decrease with decreasing thickness.

However, when the effect of larger force constants at the surface is taken into

account, this surface effect tends to harden the frequencies, causing an anomalous

blue shift in the E12g mode, in agreement with density functional calculations and the

experiment by Lee et al. [1]. In contrast, the frequency of the A1g mode still

decreases with decreasing thickness, in excellent agreement with experiment. We

further predict that accumulated strain can explain the red shift in the E12g mode that

was observed in the experiment by Matte et al. [2], where a bent TL is shown in their

TEM image.

[1] Lee, C. et al.ACS Nano 4, 2695 (2010)

[2] Matte, H.S.S.R. et al. Angew. Chem. 122, 4153 (2010)

Author(s) : Harsan Haijiao Ma(马海蛟)

Affiliation(s) : 1NUSNNI-NanoCore, National University of Singapore,

Singapore 117411, Singapore


Singapore 117542, Singapore


Title : LaAlO3/SrTiO3 superlattices on SrTiO3(110)

Abstract:

Two dimensional electron gas(2DEG) emerging at the interface of

LaAlO3/SrTiO3(001) was attributed to electronic reconstruction at the interface

because of polar catastrophe. Further more, unexpected 2EDEG at the interface of

LaAlO3/SrTiO3(110) and LaAlO3/SrTiO3(111) even amorphous LaAlO3 on

SrTiO3(001) showing very interesting behavior such as conducting anistropy has

being explored which is difficult to understand by polar catastrophe model. Here we

report transport results in LaAlO3/SrTiO3 superlattices on SrTiO3(110) substrate.

Resistance vs temperature(RT) measurement in different configurations and along

different directions show very different features and Angular Dependence

Magnetoresistance(ADMR) measurement and magnetioresistance measurement

also show very interesting behavior. Signatures of SrTiO3(001) structure phase

transitions were observed in the RT behavior of 2DEG. 2θ and 4θ components

apeared in ADMR of 2DEG in LaAlO3/SrTiO3 superlattices on SrTiO3(110) and show

different properties for different directions.

Author(s) : Carina B. Maliakkal, Azizur A. Rahman, John P. Mathew,

Nirupam Hatui, Priti Gupta, Ritam Sinha, T. S. Abhilash,

Mandar M. Deshmukh and Arnab Bhattacharya

Affiliation(s) : Department of Condensed Matter Physics and Materials

Science, Tata Institute of Fundamental Research, Homi

Bhabha Road, Mumbai 400005.


Title : Synthesis and Characterization of GaN Nanowires

Abstract:

Semiconductor nanowires are being intensely researched as building blocks for

nanoscale electronic and photonic device applications. GaN based materials are

ideal candidates for optoelectronic devices in the near UV and visible spectral region.

In this work we have fabricated GaN nanowires using metalorganic chemical vapor

deposition via different routes. Non catalytic and selective area growth techniques

resulted only in short stubby hexagonal islands or pyramidal features. Gold catalyst

mediated growths demonstrated thin nanowires under certain growth conditions.

Under similar conditions longer wires were obtained on r, c and m plane sapphire

substrates by using a nickel catalyst formed in-situ from the decomposition of nickel

nitrate (Fig. 1). Scanning electron microscopy, energy dispersive X-ray spectroscopy,

transmission electron microscopy, photoluminescence and cathodo-luminescense

were used to characterise the samples. Electrical contacts to the GaN nanowires

were made using electron beam lithography. Electrical properties of the as grown

wires were studied using field effect transistor geometry.

Figure 1: GaN nanowires grown using Ni

catalyst

Author(s) : S. Mathew,1,2, K. Gopinadhan,1,2 T. K. Chan,3,6 X. J. Yu,1,4 D.

Zhan,5 L. Cao,6 A. Rusydi,1,4,6 M. B. H. Breese,3,4,6

S. Dhar,1,2 Z. X. Shen,5

T. Venkatesan,1,2 and John TL Thong,1

Affiliation(s) :

1,2NUSNNI-NanoCore, National University of Singapore 117576

2Department of Electrical and Computer Engineering,

National University of Singapore, Singapore, 117576

3Center for Ion Beam Applications (CIBA), Department of Physics,

National University of Singapore, Singapore 117542

4Singapore Synchrotron Light Source (SSLS),

National University of Singapore, Singapore 117603

5Division of Physics and Applied Physics, School of Physical and

Mathematical Sciences,

Nanyang Technological University, Singapore 637371


Singapore 117542


Title : Magnetism in MoS2 induced by proton irradiation

Abstract:

Molybdenum disulphide, a diamagnetic layered dichalcogenide solid, is found to

show magnetic ordering at room temperature when exposed to a 2 MeV proton

beam. The temperature dependence of magnetization displays ferrimagnetic

behavior with a Curie temperature of 895 K. A disorder mode corresponding to a

zone-edge phonon and a Mo valence higher than +4, have been detected in the

irradiated samples using Raman and X-ray photoelectron spectroscopy,

respectively. The possible origins of long-range magnetic ordering in irradiated MoS2

samples will be discussed.

Author(s) : Vineeth Mohanan Parakkat, P.S.Anil Kumar

Affiliation(s) : Department of Physics, Indian Institute of Science Bangalore


Title : Investigation of Electron Magnon Interaction in Ferromagnetic

nanostructures

Abstract:

Magnon contribution to the resistance of film and nanowires of Permalloy is

investigated by magnetotransport measurements. The temperature dependence of

high field MR (upto 5T) of Permalloy films indicate the magnon contribution to

resistivity. By patterning films into nanowires we are able to observe and distinguish

Anisotropic-Magnetoresistance (AMR) and Magnon Magnetoresistance (MMR)

contributions by varying their width thereby tuning their shape anisotropy. Nanowires

of thickness 20nm and varying widths down to 160nm were prepared by e-beam

lithography and Pulsed Laser Deposition. A linear non-saturating longitudinal MR

observed in high field regime for NiFe nanowires could never be explained using

AMR but only MMR can account for it. MMR follows as MMR s)B, where M is

magnetization along the easy axis, Ms saturation magnetization, B magnetic field

sat

saturation. A cross over in magnetoresistance at low field from AMR-dominant to

MMR-dominant one was observed as wire width reduces since the AMR value is

getting reduced from 1.2% for 650nm wide wire to 0.26% for 160nm, however the

contributions from the electron-magnon interactions still persist. The MMR proves to

be an excellent way of determining M/Ms, understanding the magnetization reversal

mechanisms in nanostructures, domain wall dynamics and also fundamental

problems like electron magnon interactions.

Author(s):

Thanh Thi Kim Nguyen

Affiliation(s):

Department of Physics, University of Cincinnati, Cincinnati,

Ohio 45221, USA.

Institute of Physics and Electronics, Vietnam Academy of

Science and Technology, Hanoi 10000, Vietnam.

Email of Presenter: [email protected]

Title: Dynamic response of a single-electron transistor in the ac

Kondo regime

Abstract:

A single-electron transistor (SET) in a magnetic field irradiated with microwaves is

studied theoretically in non-equilibrium Kondo regime. The two fold effect of

frequency- -microwaves is considered as follows: the voltage oscillates with

number). We describe the system by the Kondo model at a specific point in the

Toulouse limit. A non-perturbative technique is proposed, namely, the non-equilibrium

the microwave irradiation is considered affecting only the voltage, one sees the Kondo

satellites as stated in the previous studies. Moreover, the features of the differential

conductance and magnetic susceptibility of a SET become richer when the Kondo

couplings are considered oscillating on time. We obtain the satellite peak splitting. It

explains the possibilities one can find in experimental results that the distance

between peaks, which appear in the differential conductance - magnetic amplitude

characteristics G(H) or in the differential conductance - dc voltage characteristics

G(Vdc), can be smaller than

Author(s) : Satyapal S. Rathore and Satish Vitta

Affiliation(s) : Department of Metallurgical Engineering and Materials

Science, IIT Bombay, Mumbai – 400 076; India


Title : ‘Glassy’ behavior in multiferroic Ba3NbFe3Si2O14

Abstract:

‘Geometrically frustrated’ systems in which arrangement of magnetic spins and

interaction between them lead to unconventional ground states has attracted intense

research activity as many novel magneto-electric multiferroics belong to this class. A

recent addition to this family is Fe – Langasite, Ba3NbFe3Si2O14 (BNFSO) with

frustrated triangular (a-b plane) and helical (c-axis) arrangement of Fe3+ spins. In the

present work a detailed investigation of the magnetic and dielectric response of

BNFSO is performed in order to understand the correlation between its magnetic and

electric phase transitions.

The structural characterization performed by X-ray powder diffraction at room

temperature and the subsequent Rietveld refinement reveals that polycrystalline

BNFSO crystallize in a hexagonal P321 structure. The BNFSO orders

antiferromagnetically with a Nèel transition temperature, TN ~ 26 K, in good

agreement with single crystal studies. The temperature dependence of ac magnetic

susceptibility in the frequency range 10 Hz to 1 KHz shows two clear peaks. A

frequency independent peak at TN~26 K signaling a transition to first order

antiferromagnetic ordered state. And a high temperature frequency dependent spin-

glass like behavior with activation energy of ~ 68 meV. The dielectric response (10

Hz to 1 MHz) is in agreement with magnetic studies and also shows relaxor-like

frequency dispersion above TN with activation energy 71 meV. However, unlike

magnetic transition the dielectric transition near TN was observed to be of dispersive

in nature with activation energy of 30 meV. The high and low temperature ‘glassy’

magnetic and dielectric behaviors above TN were observed for first time in BNFSO

and are attributed to the onset and completion of magnetic ordering respectively.

These studies clearly show that nature of magnetic and dielectric transitions at TN are

different for single crystal and polycrystalline Ba3NbFe3Si2O14.

mailto:[email protected]

Author(s) : Nishaina Sahadev, Deep Narayan Biswas, Sangeeta Thakur,

Khadiza Ali, Geetha Balakrisnan, kalobaran Maiti

Affiliation(s) : TATA INSTITUTE OF FUNDAMENTAL RESEARCH


Title : Evidence of Bulk nature of Kondo effect and different surface

potentials in CeB6

Abstract:

We have studied the electronic structure of CeB6 using photoemission spectroscopy.

We made surface and bulk sensitive measurements. Experimental results show that

the Kondo effect is a bulk phenomenon. Also the Medelung potential at the surface is

different from the bulk.

Author(s) : Nihit Saigal and Sandip Ghosh

Affiliation(s) : Tata Institute of Fundamental Research, Mumbai, India-

400005


Title : Reflectance Contrast Spectroscopy for Distinguishing Between

Monolayer and Bilayer Graphene

Abstract:

The authors report a reflectance contrast spectroscopy study to distinguish between

monolayer and bilayer graphene on silicon dioxide covered silicon substrate. They

describe a setup built for reflectance measurements with high spatial resolution,

which uses a combination of a pin-hole and a microscope with a high magnification

objective lens. The measured reflectance contrast spectra are subsequently

compared with simulations in order to identify mono/bilayer graphene.

Author(s) : Anjan Soumyanarayanan1,2, Michael M. Yee1, Yang He1,

Jasper van Wezel3,4, D.J. Rahn5, Kai Rossnagel5, Eric W.

Hudson6, Michael R. Norman3, and Jennifer E. Hoffman1

Affiliation(s) : 1 Harvard University, 2 Massachusetts Institute of Technology, 3

Argonne National Laboratory, 4 University of Bristol, 5 Kiel

University, 6 Pennsylvania State University


Title : Quantum Phase Transition from Triangular to Stripe Charge

Order in NbSe2

Abstract:

The competition between proximate electronic phases produces a complex

phenomenology in strongly correlated systems. In particular, fluctuations with charge

and spin density waves, and their effects on superconductivity, have been difficult to

study in the presence of chemical disorder. Here we image a previously unknown

unidirectional (stripe) charge density wave (CDW) smoothly interfacing with the

familiar triangular CDW on the surface of the stoichiometric superconductor NbSe2,

with wavelengths differing by 15%. Our low temperature measurements rule out

thermal fluctuations, and point to local strain as the tuning parameter for this

quantum phase transition. We use this discovery to resolve two longstanding

debates about the anomalous spectroscopic gap and the role of Fermi surface

nesting in the CDW phase of NbSe2. Our results highlight the importance of local

strain in governing phase transitions and competing phenomena, and suggest a new

direction of inquiry for resolving similarly longstanding debates in cuprate

superconductors and other strongly correlated materials.

Author(s) : Phitsini Suvarnaphaet

Affiliation(s) : Department of Physics, Faculty of Science, Mahidol University,

272 Rama 6 Rd., Ratchathewi, Bangkok 10400 Thailand

Email of Presenter : [email protected], [email protected]

Title : A Chemical Vapor Sensor from Graphene/Nanographite

Assembly

Abstract:

Graphene and nanographite, a low dimensional assembly of sp2 hybridized carbon

atoms in a honeycomb packing, have attracted tremendous attention in various fields

due to their superior properties. We have investigated a chemical vapor sensor that

is easily integrated, low-cost, disposable and highly sensitive by using a mixture of

graphene and nanographite as a sensitive area. The assembly of

graphene/nanographite film was deposited on the gold-coated interdigitated

microelectrodes (IDEs). The homogeneity and the presence of ohmic behavior of

sensitive area from graphene/nanographite assembly were confirmed by van der

Pauw technique. The sensor sensitivity was carried out using four-point probe

method at room temperature for detecting common chemicals in laboratory, including

ammonia, ethanol and acetone. The results showed that the electrical resistance was

changed significantly as a function of time exposure to chemical vapor. The

resistance change may be due to either the adsorption of chemical molecules on the

sensitive area or the charge transfer phenomenon between chemical molecules and

the sensitive area. The information from this demonstration could be very useful for

future development of low-cost and disposable chemical sensor based on graphene

and nanographite.

Author(s) : Nguyen Thi Thuy and Tran Minh Tien

Affiliation(s) : Institute of Physics, Vietnam Academy of Science and

Technology, Ha Noi, Vietnam


Title : Topological insulating phase in the Haldane - Falicov - Kimball

model

Abstract:

Effects of electron correlations on a topological insulating phase are

studied within a combination of the Haldane and the Falicov - Kimball

model. The Haldane model provides the existence of topological

insulating phase, while electron correlations are the essence of the

Falicov - Kimball model. A mean field approximation is adopted to

investigate the combined model. There is a competition between the trivial

topological charge-ordered phase and topological one. A phase diagram

is also presented.

Author(s) : Keola Wierschem and Pinaki Sengupta

Affiliation(s) : Nanyang Technological University


Title : Spin supersolid phase of the extended Shastry-Sutherland

model

Abstract: The Shastry-Sutherland model is a quantum lattice model of

antiferromagnetic Heisenberg spins arranged in a frustrated geometry composed of a

basic square lattice with additional orthogonal connections on every other square

plaquette. We refer to the corresponding bonds as J1 and J2, respectively. In the

limit of J1 << J2, the orthogonal J2 bonds dominate, leading to an exact ground state

of spin singlet dimers on each J2 bond. Here we show that for a generalized Shastry-

Sutherland model with anisotropic exchange and ferromagnetic transverse

interactions, the addition of crosswise connections on the remaining square

plaquettes can lead to the formation of a magnetic field induced spin supersolid

phase. Using quantum Monte Carlo techniques, we demonstrate the coexistence of

diagonal and off-diagonal order in this phase, and study the nearby magnetic phase

diagram. We also discuss the possible implications for several rare-earth tetraboride

compounds whose low temperature magnetic properties are captured by the

extended Shastry-Sutherland model considered here.

Author(s) : Jhih-Shih You1,2, Hao Lee1,2, Shiang Fang1,2, Miguel A.

Cazalilla3,4,5, and Daw-Wei Wang1,2

Affiliation(s) : 1.Physics Department and Frontier Research Center on

Fundamental and Applied Sciences of Matter, National Tsing-Hua

University, Hsinchu, Taiwan

2.Physics Division, National Center for Theoretical Sciences,

Hsinchu, Taiwan

3.Centro de Fsica de Materiales CSIC-UPV/EHU, Paseo Manuel de

Lardizabal 5, E-20018 San Sebastian, Spain

4.DIPC, Paseo Manuel de Lardizabal 4, E-20018 San Sebastian,

Spain

5.Graphene Research Centre National University of Singapore, 6

Science Drive 2, Singapore 117546


Title : Tuning the Kosterlitz-Thouless transition to zero temperature in

anisotropic boson systems

Abstract:

We study the two-dimensional Bose-Hubbard model with anisotropic hopping.

Focusing on the effects of anisotropy on superfluid properties such as the helicity

modulus and the normal-to-superfluid [Berezinskii-Kosterlitz-Thouless (BKT)]

transition temperature, two different approaches are compared: large-scale quantum

Monte Carlo simulations and the self-consistent harmonic approximation (SCHA).

For the latter, two different formulations are considered, one applying near the

isotropic limit and the other applying in the extremely anisotropic limit. Thus we find

that the SCHA provides a reasonable description of superfluid properties of this

system provided the appropriate type of formulation is employed. The accuracy of

the SCHA in the extremely anisotropic limit, where the BKT transition temperature is

tuned to zero (i.e., at a quantum critical point) and therefore quantum fluctuations

play a dominant role, is particularly striking.

Documents

Author(s) : Shwetha G. Bhat and Dr. P.S. Anil Kumar 3O4s) : Shwetha G. Bhat and Dr. P.S. Anil Kumar Affiliation(s) : Department of Physics, Indian Institute of Science, Bangalore –