Magnetic field effects on the cdw and sc states in bedt ttf 2 khg scn 4
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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-Mei ß ner-Institut , Bayerische Akademie der Wissenschaften , Garching , Germany Ilya Sheikin

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Magnetic field effects on the cdw and sc states in bedt ttf 2 khg scn 4

Magnetic field effects on the CDW and SC states in -(BEDT-TTF)2KHg(SCN)4

Dieter Andres, Sebastian Jakob, Werner Biberacher,

Karl Neumaier and Mark Kartsovnik

Walther-Meißner-Institut, BayerischeAkademiederWissenschaften, Garching, Germany

Ilya Sheikin

Laboratoire National des Champs MagnétiquesIntenses, Grenoble, France

HaraldMüller

European Synchrotron Radiation Facility, Grenoble, France

Natalia Kushch

Institute of Problems of Chemical Physics, Chernogolovka, Russia


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

BEDT-TTF molecule:

bis(ethylenedithio)-tetrathiafulvalene

b

c

a

a

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

r||(300K) 10 - 20 mW•cmr/r|| ~ 104- 105ra/rc 2

r (300K) / r (1.4K) ~ 102t ||/t  670  ,coh/||  2.210-6


Q

Nestinginstability

of the Fermi surface

  • CDW formation

    at8 K

verylow!!

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

2D Fermi surface

[P. Foury-Leylekian et al., PRB 2010]

smallDCDW kBTCDWhighsensitivitytoexternalconditions:

pressure, magneticfield


CDW in a magneticfield

  • Pauli paramagnetic effect: suppresses CDW [W. Dieterich & P. Fulde, 1973]

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

P. Christ, W. Biberacher, M.K., et al., JETP Lett. 2000

Q-

TCDW/TCDW(0), exp

2mBB/hvF

B

NM

CDWx

~ 23 T

CDW0

Q+

Q-< Q+

TCDW/TCDW(0)

Theory: A. Buzdin & V. Tugushev, JETP 1983

D. Zanchi et al., PRB 1996;

P. Grigoriev & D. Lyubshin, PRB 2005


CDW in a magneticfield

  • Orbital effect (requires an imperfectly nested FS): stimulates CDW


Real spaceorbit:

Dy ~ 1/Bz

electrons become

effectively more 1D

CDW in a magneticfield

  • Orbital effect (requires an imperfectly nested FS): stimulates CDW


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

D. Andres, M.K., et al., PRB 2001

CDW in a magneticfield

  • Orbital effect (requires an imperfectly nested FS): stimulates CDW

Theory:

D. Zanchiet al., PRB 1996


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

D. Andres, M.K., et al., PRB 2001

FICDW at t^’ > t^’ * ???

CDW in a magneticfield

  • Orbital effect (requires an imperfectly nested FS): stimulates CDW

Theory:

D. Zanchiet al., PRB 1996

L. Gor’kov& A. Lebed, J. Phys. Lett. (Paris) 1984


CDW in a magneticfield

  • Field-induced CDW (FICDW) transitions

The “slow oscillations”

SdHo

  • appear at P  Pc  2.5 kbar

  • approximately periodic

  • with 1/B

P = 3 kbar

  • display a weak hysteresis

Positions of the FICDW transitions can be fitted with

t^  0.5 meV

[A. Lebed, PRL 2010]


CDW in a magneticfield

  • Field-induced CDW (FICDW) transitions

FISDW

in (TMTSF)2PF6

FICDW

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

A. Kornilov et al., PRB 2002

FICDW is weaker than FISDW due to the paramagnetic effect!

A. Lebed, JETP Lett. 2003


Superconductivity vs. CDW

R  0

R = 0

Sample #2:

zero resistance

but no Meissner!

R^ (Ohm)

  • Resistance at zero field

See also: H. Ito et al., SSC 85 1005 (1993) – inhomogeneoussuperconductivityatP = 0


Superconductivity vs. CDW

  • Onset of superconductivity


Superconductivity vs. CDW

  • Onset of superconductivity

CDW+SC

R  0

R = 0

The SC onset temperature is 3 times higher

in the SC/CDW coexistence region!


Superconductivity in a magneticfield; P > Pc

  • Critical field ^ layers

at P = 3 kbar:x||(0)  250nm

cf. meanfreepath  1m


Superconductivity in a magneticfield; P > Pc

  • Critical field // layers

1.6Hp0

Hp0: Chandrasekhar-Clogston

paramagneticlimit

GL: Hc2 (Tc-T )

dHc2/dT 12 T/K

 x^(0) = 1.0 nmd/2;

x||(0)/ x^(0)  250!


Superconductivity in a magneticfield; P > Pc

Directmanifestationoftheparamagnetic pair-breaking!


Summary

  • CDW state:

  • richphasediagram due totheinterplayof

  • competingPauli paramagneticandorbital

  • effectsofmagneticfield

  • SC state:

  • at P < Pc: coexistswiththe CDW state; the

  • SC onsettemperatureisdrasticallyincreased

  • in thecoexistenceregion;

  • at P >Pc:bulk SC statewith a highly

  • anisotropic Hc2nearTc(0) and a clear

  • manifestationofparamagnetic pair-breaking

  • at H // layers.


Qx = 2kF + NG,

G = eayBz/

CDW in a magneticfield

  • Field-induced density wave transitions, t^’>t^’*:

-kF

kF

B


CDW in a magneticfield

  • Field-induced CDW (FICDW) transitions

Commensurate splitting

(A. Bjelis et al., 1999; A. Lebed, 2003)

N =

3,4

2,3

“Spin-zero”

1,2

0,1

0

2QP = MG

2QP = (M + 1/2)G

with M - integer


CDW in a magneticfield

  • Field-induced CDW (FICDW) transitions

4

4

3

3

2

N =

N =

5

3

2

2

1

1

1

0

0

0

Pauli effect on (FICDW)

no Pauli effect (FISDW)

Qx = 2kFQP + NG

Qx = 2kF + NG

G = 2eayBz/

QP = 2mBB/vF


CDW in a magneticfield

  • Field-induced CDW (FICDW) transitions

4

3

3

2

N =

2

A. Lebed, JETP Lett. 78, 138 (2003)

1

1

0

0

Pauli effect on (FICDW)

no Pauli effect (FISDW)

Qx = 2kFQP + NG

Qx = 2kF + NG

G = 2eayBz/

QP = 2mBB/vF


CDW in a magneticfield

  • Field-induced CDW (FICDW) transitions

Spin-zero condition:

 vF 1.2105 m/s


Superconductivity vs. CDW

  • Onset of superconductivity

Low Tc

 weakfluctuations!

CDW+SC

Ginzburg-Levanyuk

parameter:

Gi(2)~ 10-5

R  0

R = 0

The SC onset temperature is 3 times higher

in the SC/CDW coexistence region!


Superconductivity in a magneticfield; P > Pc

B (mT)

  • Critical field ^ layers


Superconductivity in a magneticfield; P > Pc

  • Critical field // layers


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