SDW
M(SC)
SDW
SDW
M(SC)
M(SC)
Domain walls at the SDW endpoint of
(TMTSF)2PF6 under pressure
C.Pasquier,
N. Kang, B.Salameh, P. Auban-Senzier, D.Jérome
Laboratoire de Physique des Solides, Orsay
S. Brazovskii
LPTMS, Orsay
Acknowledgments: P. Grigoriev
Outline
SDW
SC
SDW
SC
SDW
• Superconductivity at the border of density wave
states
• The case of (TMTSF)2ReO4
• Phase separation in (TMTSF)2PF6
SC
SC/CDW proximity
SDW
SC
SDW
SC
SDW
SC
TTF [Ni(dmit)2]2
1TTaS2
CDW
SC
L.Brossard et al , PRB (1990)
Per2 [Au(mnt)2]
Superconductivity at the
end point of a charge
density wave state
in organic and inorganic
systems
Tc,max 6-8K
D. Graf et al, EPL, 85 27009 (2009)
TiSe2
A. F. Kusmartseva et al., PRL 103, 236401 (2009)
SC/(SDW or AF) proximity
SDW
SC
SDW
SC
SDW
SC
(TMTTF)2X & (TMTSF)2X
-(BEDT-TTF)2X
Superconductivity at the
end point of a spin density
wave (or AF) state
in organic and inorganic
systems
S. Nandi et al., PRL 104, 057006
(2010).
SC/DW proximity
SDW
SC
SDW
SC
SDW
Superconductivity at the end point of density wave is therefore a common feature
in unconventional superconductivity.
How does SC emerge from a density wave state ?
We will focus on a 1D organic systems, essentially (TMTSF)2PF6
It appears that there is a phase coexistence with the formation of domains and not
‘stripes’.
We have to be careful and check that such phase coexistence is not due to
structural transition like in (TMTSF)2ReO4: what happens in this case ?
SC
SDW
Phase coexistence in (TMTSF)2ReO4
SC
SDW
SC
SDW
SC
b
c
Insulator
Metal
Moret R., Pouget J.-P., Comes R. and Bechgaard K., Phys.Rev.Lett., 49 (1982) 1008
Parkin S.S.P. Jérome D. and Bechgaard K., Mol.Cryst.Liq.Cryst., 79 (1981) 213
SC at low Temperature above 8kbar
a
SC
SDW
SC
SDW
ANISOTROPIE (c/a)
200
0
0.3000
0.6000
0.9000
1.200
1.500
1.800
2.100
2.400
2.700
3.000
3.300
3.600
3.900
4.200
4.500
4.800
5.100
5.400
5.700
6.000
180
160
Température (K)
140
120
100
80
60
40
20
(log scale)
200
0
0.3000
0.6000
0.9000
1.200
1.500
1.800
2.100
2.400
2.700
3.000
3.300
3.600
3.900
4.200
4.500
4.800
5.100
5.400
5.700
6.000
180
160
140
120
100
80
60
40
20
6
7
8
9
10
6
11
7
8
9
10
Pression (kbar)
Pression (kbar)
ANISOTROPIE (c/b)
(log scale)
200
Self- organisation along a
0
0.3000
0.6000
0.9000
1.200
1.500
1.800
2.100
2.400
2.700
3.000
3.300
3.600
3.900
4.200
4.500
4.800
5.100
5.400
5.700
6.000
180
160
Température (K)
SC
ANISOTROPIE (b/a)
(log scale)
Température (K)
SDW
Phase coexistence in (TMTSF)2ReO4
140
120
100
80
60
40
20
6
7
8
9
Pression (kbar)
10
C.Colin et al., EPL, 75, 301 (2006)
SDW
Phase coexistence in (TMTSF)2ReO4
SC
SDW
SC
SDW
SC
a
2 possible orientations for each anion
(2a,2c)
Simple model : anisotropic Ising model
Onsager (1941)
Pseudospin :
(a,2c)
|+> if lattice parameter = 2a
|-> if lattice parameter = a
anisotropic interactions between spins 
anisotropic interactions between chains
Pouget, Ravy,…
Metal
Semiconductor
Filaments or anisotropic bubbles
oriented along a
SDW
Phase coexistence in (TMTSF)2PF6
SC
SDW
SC
SDW
SC
b-axis
a-axis
c-axis
SDW
Phase coexistence in (TMTSF)2PF6
SC
SDW
SC
SDW
PHASE A : SC visible along c* only!
SC
along c
P: 7.1kbar
321mK
dV/dI (k)
3
2
87mK
-4
-2
0
2
(A)
4
SC
SDW
Phase coexistence in (TMTSF)2PF6
SC
SDW
SC
SDW
SC
PHASE B : SC visible along c* and b’!
4
2
c
0
5
dV/dI(a.u.)
20
b
a
6
0
c =0 at low T
Double transition in b which
disappears when P increases.
Clear non-linearities as a function of current
Some features are field independent
P: 8.0 kbar
10
0
0
1
2
3
Temperature (K)
(b)
50
amcm
(a)
b (mcm
ccm)
8
T: 360mK
H (G)
0
38
50
76
105
134
161
171
4
3
2
1
-0.6 -0.4 -0.2
0.0 0.2
(mA)
0.4
0.6
SDW
Phase coexistence in (TMTSF)2PF6
SC
SDW
SC
SDW
PHASE A: 7.5kbar
PHASE B: 8kbar
H
Non linearities at zero bias persist
up to high fields.
They appear with SC at low pressure
and disappear for PPc0
SC
SDW
Phase coexistence in (TMTSF)2PF6
SC
SDW
SC
SDW
SC
PHASE C : SC visible along c*, b’ and a!
Double transition in a which
disappears when P increases.
SDW
c
Phase coexistence in (TMTSF)2PF6
SC
SDW
SC
SDW
b
a
SDW
SDW
SD
W
SD
W
SDW
SDW
SDW
Tunnel junctions Josephson junctions
From bubbles to slabs by adjusting hydrostatic pressure
SC
SDW
Phase coexistence in (TMTSF)2PF6
SC
SDW
SC
SDW
How to understand this texture evolution ?
Why SC does appear first along c (the worst conducting direction!!!!) ?
Many theories have been developed for cuprates…
…..but only one theory seems to fit our data
S. Brazovskii, L.P. Gorkov and A.G. Lebed, JETP 56 (1982) 683
Soliton model : L.P.Gorkov, P.D.Grigoriev, EPL 71,425 (2005); PRB, 75, R20507 (2007)
Existence of soliton domain walls (metallic) perpendicular to a- axis
and expected peak of the anisotropy sb,c / sa at the DW / Metal transition
c
b
a
SDW
SDW
SD
W
SD
W
SDW
SDW
SDW
See also experiments by Lee et al (PRL 2002,PRL 2005)
SC
SDW
Phase coexistence in (TMTSF)2PF6
SC
SDW
SC
SDW
SC
An image with the hands of the soliton model : how do metal (SC) emerge from a DW
Ecreation of a soliton < SDW gap
DSDW
DSDW
Low pressure:
Homogeneous SDW
DSDW
N. Kang et al. PRB (2010)
DSC
Phases B and C:
Bands in the SDW gap
‘soliton phase’
Phase A:
Midgap state in SDW gap
DSC
High pressure :
SC homogeneous phase
Journées labo, 7 Octobre 201
SDW
Phase coexistence in (TMTSF)2PF6
SC
SDW
SC
SDW
SC
We believe that the deep in dV/dI characteristics is related to this particular band
structure (as we are doing tunneling experiments!)
PHASE B: 8kbar
DSDW
DSDW
Low pressure:
Homogeneous SDW
DSDW
DSC
Phases B and C:
Bands in the SDW gap
‘soliton phase’
Phase A:
Midgap state in SDW gap
DSC
High pressure :
SC homogeneous phase
SDW
c
Phase coexistence in (TMTSF)2PF6
SC
SDW
SC
SDW
b
a
SDW
SDW
SD
W
SD
W
SDW
SDW
? Why c first ???
E (k )  2ta cos ka  2tb0 cos kb
Q s tan dard  (1 / 2,1 / 2, qc )
Experiments :
Q nesting  (1 / 2,  1 / 4, qc )
J.P.Pouget, S.Ravy, Synth. Metals 85,1523 (1997)
T.Takahashi et al, JPSJ 55,1364 (1986)
SDW
SC
SDW
c
Phase coexistence in (TMTSF)2PF6
SC
SDW
SC
SDW
b
a
SDW
SDW
SD
W
SD
W
SDW
SDW
SDW
Why c first ???
E ' (k )  2t 'b cos 2kb  2tc cos kc
Eanti (k )  E ' (k  Q nesting )  E ' (k )
= deviation from nesting
governs the evolution from SDW to metal
As qb ¼, the term in kb is small, the term in kc is dominant.
So ‘’’’’everything’’’’’ is fixed along ka and kb but not kc.
SC
Conclusion
SDW
SC
SDW
SC
SDW
We have followed experimentally the evolution of the Metal (SC) concentration
in the SDW matrix in (TMTSF)2PF6:
bubbles - filaments - slabs evolution
This evolution is understandable within a ‘soliton model’
Future : Is this evolution observable in other 1D systems or other materials
with SDW/SC competition at the mesoscopic scale?
Is it related to the particular Fermi surface of (TMTSF)2PF6 where
electrons for SC and SDW come from the same band.
Same features for CDW/SC competition ?
SC
SDW
SC
SDW
SC
SDW
SC
SDW
SC
SDW
SC
SDW
Cargese
SC
August 18, 2011
The ‘green flash’
spot ?