Magnetic field effects on the CDW and SC states in -(BEDT-TTF) 2 KHg(SCN) 4
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Transcript of 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)2KHg(SCN)4
Dieter Andres, Sebastian Jakob, Werner Biberacher,
Karl Neumaier and Mark KartsovnikWalther-Meißner-Institut, Bayerische Akademie der Wissenschaften, Garching, Germany
Ilya Sheikin
Laboratoire National des Champs Magnétiques Intenses, Grenoble, France
Harald Müller
European Synchrotron Radiation Facility, Grenoble, France
Natalia Kushch
Institute of Problems of Chemical Physics, Chernogolovka, Russia
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c
a
-(BEDT-TTF)2KHg(SCN)4: basic featuresS
CH
BEDT-TTF molecule:bis(ethylenedithio)-tetrathiafulvalene
a
b
||(300K) 10 20 m•cm /|| ~ 104 105 a/c 2
(300K) / (1.4K) ~ 102 t ||/t 670 ,coh/|| 2.210-6
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
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-(BEDT-TTF)2KHg(SCN)4: basic features
2D Fermi surface
CDW formation at 8 K
Nesting instability of the Fermi surface
Q
very low!!
small CDW kBTCDW high sensitivity to external conditions: pressure, magnetic field
[P. Foury-Leylekian et al., PRB 2010]
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Q+
Q-
CDW in a magnetic field
Pauli paramagnetic effect: suppresses CDW [W. Dieterich & P. Fulde,
1973]
2BB/vF
B
Q- < Q+
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, W. Biberacher, M.K., et al., JETP Lett. 2000
~ 23 T
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: A. Buzdin & V. Tugushev, JETP 1983 D. Zanchi et al., PRB 1996; P. Grigoriev & D. Lyubshin , PRB 2005
CDWx
CDW0
NM
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CDW in a magnetic field
Orbital effect (requires an imperfectly nested FS): stimulates CDW
);2cos(2)cos(2)( yyyyFxF katkatkkv k Ftt
4( vt + t ’ ) / F
ky
c
kx
~ t’/ v F
-c
)0'(DWDW tTT
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CDW in a magnetic field
Orbital effect (requires an imperfectly nested FS): stimulates CDW
);2cos(2)cos(2)( yyyyFxF katkatkkv k Ftt
4( vt + t ’ ) / F
ky
c
kx
~ t’/ v F
-c
I n a 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:
)0'(DWDW tTT
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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]
D. Andres, M.K., et al., PRB 2001
-(BEDT-TTF)2KHg(SCN)4
CDW in a magnetic field
Orbital effect (requires an imperfectly nested FS): stimulates CDW
Theory:
D. Zanchi et al., PRB 1996
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R
(deg)
CDW in a magnetic field
Orbital effect (requires an imperfectly nested FS): stimulates CDW
-90 -60 -30 0 30 60 90
R x 20
P = 2.8 kbarT = 0.7 K
6.5 T
9 T
4.3 T
1 T
R (
arb
. uni
ts )
(deg.)
Angle-dependent MagnetoResistance Oscillations (AMRO) in -(BEDT-TTF)2KHg(SCN)4
P > Pc ambient pressure
M.K. et al., SSC 1994
normal state
CDW state
normal state
field-induced
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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]
D. Andres, M.K., et al., PRB 2001
-(BEDT-TTF)2KHg(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. Gor’kov & A. Lebed, J. Phys. Lett. (Paris) 1984
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CDW in a magnetic field
Field-induced CDW (FICDW) transitions
The “slow oscillations”
appear at P Pc 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]
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CDW in a magnetic field
Field-induced CDW (FICDW) transitions
A. Kornilov et al., PRB 2002
FICDW
in -(BEDT-TTF)2KHg(SCN)4
FISDW
in (TMTSF)2PF6
A. Lebed, JETP Lett. 2003
FICDW is weaker than FISDW due to the paramagnetic effect! FICDW is weaker than FISDW due to the paramagnetic effect!
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Superconductivity vs. CDW
0.05 0.10 0.150.0
0.5
1.0
3.03.5 4.0
R(
T )
/R(
16
0m
K)
T (K)
P [kbar] =
0.05 0.10 0.150.0
0.5
1.0
2 kbar1.5 kbar
0 kbar
R(
T )
/R(
30
0m
K)
T (K)
0.05 0.10 0.15
60.0
63.3
66.7
R
(Ohm
)
T (K)
P = 0 kbar; sample #1
Sample #2:zero resistancebut no Meissner!
0.05 0.10 0.150
1
2
3
R
(Ohm
)T (K)
P = 0 kbar sample #2R
(
Oh
m)
0 1 2 3 4
0.01
0.1
1
10
SC
Normal metalCDW
T (
K )
P ( kbar )
R 0 R = 0
Resistance at zero field
See also: H. Ito et al., SSC 85 1005 (1993) – inhomogeneous superconductivity at P = 0
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Superconductivity vs. CDW
0.1 0.2 0.3 0.435
40
45
50
0.1 0.2 0.3 0.445
50
55
60
65
P = 2 kbar0.5 A
2 A
0.05 A
3.0 kbar
R
()
T (K)
3.5 kbar
R
()
T (K)
P =
0 2 445
50
55
60
0 2 435
40
45
50
P = 2 kbar
R
()
B (mT)
180 mK 160 mK 140 mK 120 mK 100 mK
110 mK 100 mK 95 mK
B (mT)
P = 3.5 kbar
R
()
Onset of superconductivity
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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
0 2 40.0
0.2
0.4
T (
K)
P (kbar)
CDWNormal metal
SC
CDW+SC
R = 0R 0
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Superconductivity in a magnetic field; P > Pc
Critical field layers
0 20 40 60 80 1000
1
2
3
4
5
6
B (
mT
)
T (mK)
3.0 kbar 3.5 kbar 4.0 kbar
at P = 3 kbar: (0) 250 nm
cf. mean free path 1m
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Superconductivity in a magnetic field; P > Pc
Critical field // layers
0 20 40 60 80 100 1200
100
200
300
400
Ma
gn
etic
fie
ld (
mT
)
Temperature (mK)
R(T)R(H)
GL: Hc2 (Tc-T )
Hp0: Chandrasekhar-Clogston paramagnetic limit
dHc2/dT 12 T/K
(0) = 1.0 nm d/2;
||(0)/ (0) 250!
1.6Hp0
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Superconductivity in a magnetic field; P > Pc
-80 -60 -40 -20 0 20 40 60 80 100
1
10
100
-2 -1 0 1 2
100
200
300
data thin film anisotropic GL
90°-
T = 90 mK
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Superconductivity in a magnetic field; P > Pc
-4 -2 0 2 4
10
100
102 mK 90 mK 40 mK
Hc2
(,T
)/H
c2(0
,T )
90o -
Direct manifestation of the paramagnetic pair-breakingDirect manifestation of the paramagnetic pair-breaking!
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Summary
0 2 40.0
0.2
0.4
T (
K)
P (kbar)
CDWNormal metal
SC
-4 -2 0 2 4
10
100
102 mK 90 mK 40 mK
Hc2
(,T
)/H
c2(0
,T )
90o -
CDW state:
•rich phase diagram due to the interplay of
competing Pauli paramagnetiPauli paramagnetic and orbital orbital
effects of magnetic field
SC state:
•at P < Pc: coexists with the CDW state; the
SC onset temperature is drastically increased
in the coexistence region;
•at P > Pc: bulk SC state with a highly
anisotropic Hc2 near Tc(0) and a clear
manifestation of paramagnetic pair-breaking paramagnetic pair-breaking
at H // layers.