1. Magnetic field induced charge-density-wave transitions: the role of orbital and Pauli effects
Mark Kartsovnik
Walther-Meißner-Institut, BADW, Garching, Germany

2. Outline

3. a-(BEDT-TTF)2KHg(SCN)4: basic features
r||(300 K)  30 – 100 Wcm;
r^/r|| ~ ;
r||(300 K)/ r||(1.4 K)  102
T. Mori et al., 1990
2D Fermi surface
Nesting instability
of the Fermi surface
CDW formation
at  8 K
very low!! Q

4. Pauli effect (isotropic)
Spin splitting deteriorates the nesting conditions for a CDW
TCDW/TCDW(0), exp
Phase diagram of a-(BEDT-TTF)2KHg(SCN)4
P. Christ et al., JETP Lett. 2000
~ 23 T Q+ Q-
TCDW/TCDW(0)
Theory: D. Zanchi et al., PRB 1996;
P. Grigoriev&D.Lyubshin , PRB 2005 B
suppresses CDW
Q- < Q+

5. Orbital effect (B || z) Dy ~ 1/Bz Real space orbit: electrons become
effectively more 1D
Real space orbit:

6. Orbital effect (B || z) FICDW at t^’ > t^’ * Theory
a-(BEDT-TTF)2KHg(SCN)4
D. Andres et al.,
PRB 2001
Theory
FICDW at t^’ > t^’ *
due to Landau quantization of the unnested FS pocket
D. Zanchi et al.,
PRB 1996

7. FICDW: experiment; B || z
SdHo
The “slow oscillations”
approximately periodic
with 1/B
appear at P  Pc  2.5 kbar
display a weak hysteresis
P = 3 kbar

8. FICDW: experiment; B || z
The “slow oscillations”
approximately periodic
with 1/B
appear at P  Pc  2.5 kbar
display weak hysteresis
slightly shift with temperature
 behaviour consistent with the FICDW scenario!!

9. FICDW: experiment; B || z

10. FICDW: experiment; B || z
in a-(BEDT-TTF)2KHg(SCN)4
FISDW
in (TMTSF)2PF6
A. Kornilov et al., PRB 2002
FICDW is weaker than FISDW due to the Pauli effect!
A. Lebed, JETP Lett. 2003

11. FICDW: role of the Pauli effect
N = 5 4 3 2 1 4
N = 3 2 1
no Pauli effect (FISDW)
Pauli effect on (FICDW)
Qx = 2kF + NG
Qx = 2kF  QP + NG
G = 2eayBz/h
QP = 2mBB/hvF

12. FICDW: role of the Pauli effect4
N = 3 2 1
A. Lebed, JETP Lett. 2003
no Pauli effect (FISDW)
Pauli effect on (FICDW)
Qx = 2kF + NG
Qx = 2kF  QP + NG
G = 2eayBz/h
QP = 2mBB/hvF

13. FICDW in a tilted field Commensurate splitting “Spin-zero” 2QP = MG
(A. Bjelis et al., 1999; A. Lebed, 2003)
“Spin-zero”
N =
3,4
2,3
1,2
0,1
2QP = MG
2QP = (M + 1/2)G
with M - integer
A. Lebed, JETP Lett. 2003

14. FICDW in a tilted field: experiment
T = 0.4 K
Spin-zero condition:

15. FICDW in a tilted field: experiment
1st CS angle
Spin-zero condition:

16. FICDW in a tilted field: experiment
1st CS angle
Spin-zero condition:
 vF  1.2105 m/s

17. Summary
The orbital effect causes FICDW transitions in a-(BEDT-TTF)2KHg(SCN)4
at pressures above Pc = 2.5 kbar
The Pauli effect, in general, weakens the FICDW instability
The interplay between the orbital and Pauli effects can be controlled by
changing the field orientation:
- the FICDW is enhanced at commensurate splitting angles
- the FICDW is suppressed at „spin-zero“ angles