Magnetic field effects on the CDW and SC states in -(BEDT-TTF)
2 KHg(SCN) 4 Dieter Andres, Sebastian Jakob, Werner Biberacher,
Karl Neumaier and Mark Kartsovnik Walther-Meiner-Institut,
Bayerische Akademie der Wissenschaften, Garching, Germany Ilya
Sheikin Laboratoire National des Champs Magntiques Intenses,
Grenoble, France Harald Mller European Synchrotron Radiation
Facility, Grenoble, France Natalia Kushch Institute of Problems of
Chemical Physics, Chernogolovka, Russia
Slide 2
c a -(BEDT-TTF) 2 KHg(SCN) 4 : basic features BEDT-TTF
molecule: bis(ethylenedithio)-tetrathiafulvalene a b || (300K) 10
20 m cm / || ~ 10 4 10 5 a / c 2 (300K) / (1.4K) ~ 10 2 t || /t 670
,coh / || 2.2 10 -6 T. Mori et al., Bull. Chem. Soc. Jpn. 1990; R.
Rousseau et al., J. Phys. I (France) 1996; P. Foury-Leylekian et
al., PRB 2010
Slide 3
-(BEDT-TTF) 2 KHg(SCN) 4 : basic features 2D Fermi surface CDW
formation at 8 K Nesting instability of the Fermi surface Q very
low!! small CDW k B T CDW high sensitivity to external conditions:
pressure, magnetic field [P. Foury-Leylekian et al., PRB 2010]
Slide 4
Q+Q+ Q-Q- CDW in a magnetic field Pauli paramagnetic effect:
suppresses CDW [W. Dieterich & P. Fulde, 1973] 2BB/vF2BB/vF B Q
- < Q + T CDW /T CDW (0), exp Phase diagram of -(BEDT-TTF) 2
KHg(SCN) 4 P. Christ, W. Biberacher, M.K., et al., JETP Lett. 2000
~ 23 T T CDW /T CDW (0) Theory: A. Buzdin & V. Tugushev, JETP
1983 D. Zanchi et al., PRB 1996; P. Grigoriev & D. Lyubshin,
PRB 2005 CDW x CDW 0 NM
Slide 5
CDW in a magnetic field Orbital effect (requires an imperfectly
nested FS): stimulates CDW
Slide 6
CDW in a magnetic field Orbital effect (requires an imperfectly
nested FS): stimulates CDW y ~ 1/B z electrons become effectively
more 1D Real space orbit:
Slide 7
D. Andres, M.K., et al., PRB 2001 -(BEDT-TTF) 2 KHg(SCN) 4 CDW
in a magnetic field Orbital effect (requires an imperfectly nested
FS): stimulates CDW Theory: D. Zanchi et al., PRB 1996
Slide 8
R (deg) CDW in a magnetic field Orbital effect (requires an
imperfectly nested FS): stimulates CDW Angle-dependent
MagnetoResistance Oscillations (AMRO) in -(BEDT-TTF) 2 KHg(SCN) 4 P
> P c ambient pressure M.K. et al., SSC 1994 normal state CDW
state normal state field-induced
Slide 9
D. Andres, M.K., et al., PRB 2001 -(BEDT-TTF) 2 KHg(SCN) 4 CDW
in a magnetic field Orbital effect (requires an imperfectly nested
FS): stimulates CDW Theory: D. Zanchi et al., PRB 1996 FICDW at t
> t * ??? L. Gorkov & A. Lebed, J. Phys. Lett. (Paris)
1984
Slide 10
CDW in a magnetic field Field-induced CDW (FICDW) transitions
The slow oscillations appear at P P c 2.5 kbar approximately
periodic with 1/B SdHo display a weak hysteresis P = 3 kbar
Positions of the FICDW transitions can be fitted with t 0.5 meV [A.
Lebed, PRL 2010]
Slide 11
CDW in a magnetic field Field-induced CDW (FICDW) transitions
A. Kornilov et al., PRB 2002 FICDW in -(BEDT-TTF) 2 KHg(SCN) 4
FISDW in (TMTSF) 2 PF 6 A. Lebed, JETP Lett. 2003 FICDW is weaker
than FISDW due to the paramagnetic effect!
Slide 12
Superconductivity vs. CDW Sample #2: zero resistance but no
Meissner! R (Ohm) R 0 R = 0 Resistance at zero field See also: H.
Ito et al., SSC 85 1005 (1993) inhomogeneous superconductivity at P
= 0
Slide 13
Superconductivity vs. CDW A. Kusmartseva et al., PRL 2009 Cu x
TiSe 2 NbSe 3 S. Yasuzuka et al., J. Phys. Soc. Jpn. 2005 R. Yomo
et al., PRB 2005 ZrTe 3 (TMTSF) 2 PF 6 I. J. Lee et al., PRL
2002
Slide 14
Superconductivity vs. CDW Onset of superconductivity
Slide 15
The SC onset temperature is 3 times higher in the SC/CDW
coexistence region! The SC onset temperature is 3 times higher in
the SC/CDW coexistence region! Superconductivity vs. CDW Onset of
superconductivity CDW+SC R = 0 R 0
Slide 16
Superconductivity in a magnetic field; P > P c Critical
field layers at P = 3 kbar: (0) 250 nm cf. mean free path 1 m
Slide 17
Superconductivity in a magnetic field; P > P c Critical
field // layers GL: H c2 (T c -T ) H p0 : Chandrasekhar-Clogston
paramagnetic limit dH c2 /dT 12 T/K (0) = 1.0 nm d/2; || (0)/ (0)
250! 1.6H p0
Slide 18
Superconductivity in a magnetic field; P > P c T = 90
mK
Slide 19
Superconductivity in a magnetic field; P > P c Direct
manifestation of the paramagnetic pair-breaking Direct
manifestation of the paramagnetic pair-breaking!
Slide 20
Summary CDW state: rich phase diagram due to the interplay of
Pauli paramagnetiorbital competing Pauli paramagnetic and orbital
effects of magnetic field SC state: at P < P c : coexists with
the CDW state; the SC onset temperature is drastically increased in
the coexistence region; at P > P c : bulk SC state with a highly
anisotropic H c2 near T c (0) and a clear paramagnetic
pair-breaking manifestation of paramagnetic pair-breaking at H //
layers.
Slide 21
CDW in a magnetic field Field-induced density wave transitions,
t >t *: B kFkF -k F Q x = 2k F + NG, G = ea y B z /
Slide 22
CDW in a magnetic field Field-induced CDW (FICDW) transitions
2Q P = MG N =3,43,42,32,3 1,21,2 0,10,1 0 Commensurate splitting
(A. Bjelis et al., 1999; A. Lebed, 2003) Spin-zero 2Q P = (M +
1/2)G with M - integer
Slide 23
CDW in a magnetic field Field-induced CDW (FICDW) transitions N
=5 4 3 2 1 0 4 33 2 1 2 1 0 0 no Pauli effect (FISDW) Pauli effect
on (FICDW) Q x = 2k F + NG Q x = 2k F Q P + NG G = 2ea y B z / Q P
= 2 B B/ v F
Slide 24
CDW in a magnetic field Field-induced CDW (FICDW) transitions 4
N = 33 2 1 2 1 0 0 no Pauli effect (FISDW) Pauli effect on (FICDW)
Q x = 2k F + NG Q x = 2k F Q P + NG A. Lebed, JETP Lett. 78, 138
(2003) G = 2ea y B z / Q P = 2 B B/ v F
Slide 25
CDW in a magnetic field Field-induced CDW (FICDW) transitions
Spin-zero condition: v F 1.2 10 5 m/s
Slide 26
The SC onset temperature is 3 times higher in the SC/CDW
coexistence region! The SC onset temperature is 3 times higher in
the SC/CDW coexistence region! Superconductivity vs. CDW Onset of
superconductivity CDW+SC R = 0 R 0 Ginzburg-Levanyuk parameter: Gi
(2) ~ 10 -5 Low Tc weak fluctuations!
Slide 27
Superconductivity in a magnetic field; P > P c B (mT)
Critical field layers
Slide 28
Superconductivity in a magnetic field; P > P c Critical
field // layers