magnetic field induced charge-density-wave transitions: the role of orbital and pauli effects

M. Kartsovnik 22.04.23

Magnetic field induced charge-density-wave transitions:

the role of orbital and Pauli effects

Dieter Andres, Werner Biberacher and Karl Neumaier Walther- Meißner-Institut, Garching, Germany

Harald Müller European Synchrotron Radiation Facility, Grenoble, France

Natalia Kushch Institute of Problems of Chemical Physics, Chernogolovka, Russia

Mark Kartsovnik

Walther-Meißner-Institut, BADW, Garching, Germany


Outline

-(BEDT-TTF)2KHg(SCN)4: layered crystal structure, Fermi surface, etc.

Influence of magnetic field on the charge-density wave (CDW)

– Pauli paramagnetic effect;

– orbital effect

Field-induced CDW (FICDW) in -(BEDT-TTF)2KHg(SCN)4 under

pressure:

B layers;

tilted fields: Commensurate Splitting effect

Summary


-(BEDT-TTF)2KHg(SCN)4: basic features

CDW formation

at 8 K

very low

!!

2D Fermi surface

Nesting instability

of the Fermi surfaceQ

||(300 K) 30 – 100cm;

/|| ~ 104 105;

||(300 K)/ (1.4 K) 102

T. Mori et al., 1990


0.0 0.2 0.4 0.6 0.8 1.00.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

TCDW/TCDW(0)Theory: D. Zanchi et al., PRB 1996;

P. Grigoriev&D.Lyubshin , PRB 2005

0.0 0.2 0.4 0.6 0.8 1.0

0.0

0.5

1.0

1.5

2.0

TCDW/TCDW(0), exp

Phase diagram of -(BEDT-TTF)2KHg(SCN)4

P. Christ et al., JETP Lett. 2000

~ 23 T

suppresses CDW

Spin splitting deteriorates the nesting conditions for a CDW

Q+

Q-

Q- < Q+

B

Pauli effect (isotropic)


4( vt + t ’ ) / F

ky

c

kx

~ t’/ v F

-c

Orbital effect (B || z)

requires an imperfectly nesting FS:

)2cos(2)cos(2)( )( yyyyx katkatk k

)0'( tTT cc In magnetic field:

zFy Bv

e

dt

dk

;

zFyc Bvae

y ~ 1/Bz

electrons become

effectively more 1D

lB = 2vF/

c

y =

ay(4

t / c

)

Real space orbit:


D. Zanchi et al.,

PRB 1996

Orbital effect (B || z)

0 2 4 6 8 100

5

10

15

20

25

30

2.3 kbar

3.6 kbar

1.8 kbar

0 kbar

B [T

]

T [K]

-(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

4( vt + t ’ ) / F

ky

c

kx

~ t’/ v F

-c


The “slow oscillations”

• approximately periodic with 1/B

• appear at P Pc 2.5 kbar

FICDW: experiment; B || z

SdHo

• display a weak hysteresis

P = 3 kbar



• approximately periodic with 1/B

• appear at P Pc 2.5 kbar

• display weak hysteresis

• slightly shift with temperature

The “slow oscillations”

behaviour consistent with the FICDW scenario!!



A. Kornilov et al., PRB 2002

FICDW is weaker than FISDW due to the Pauli effect! A. Lebed, JETP Lett. 2003

FICDW

in -(BEDT-TTF)2KHg(SCN)4

FISDW

in (TMTSF)2PF6


FICDW: role of the Pauli effect

N = 5 4 3 2

1

0

4N = 33

2

1

2

1

0

0

no Pauli effect (FISDW) Pauli effect on (FICDW)

Qx = 2kF + NG Qx = 2kF QP + NG

G = 2eayBz/h

QP = 2BB/hvF


FICDW: role of the Pauli effect

4N = 33

2

1

2

1

0

0

no Pauli effect (FISDW) Pauli effect on (FICDW)

Qx = 2kF + NG

A. Lebed, JETP Lett. 2003

Qx = 2kF QP + NG

G = 2eayBz/h

QP = 2BB/hvF

SDWeff

CDWeff gg

BBt c /1)(/2


FICDW in a tilted field

2QP = MG

A. Lebed, JETP Lett. 2003

N = 3,4 2,3

1,2

0,1

0

Commensurate splitting (A. Bjelis et al., 1999; A. Lebed, 2003) “Spin-zero”

2QP = (M + 1/2)G

with M - integer


FICDW in a tilted field: experiment

cos1

222/1

B

FP

vea

Q

GM y

Spin-zero condition:

T = 0.4 K



cos1

222/1

B

FP

vea

Q

GM y


1st CS angle1st CS angle



cos1

222/1

B

FP

vea

Q

GM y


1st CS angle1st CS angle

vF 1.2105 m/s


Summary

The orbital effect causes FICDW transitions in -(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

magnetic field induced charge-density-wave transitions: the role of orbital and pauli effects

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