Domain walls at the SDW endpoint of (TMTSF)2PF6 under pressure
C.Pasquier,
Laboratoire de Physique des Solides, OrsayS. Brazovskii
LPTMS, OrsayAcknowledgments: P. Grigoriev
SDW
SDW
SDW M(SC)
M(SC)
N. Kang, B.Salameh, P. Auban-Senzier, D.Jérome
M(SC)
SCSC SCSDWSDWSDW
Outline
• Superconductivity at the border of density wave states
• The case of (TMTSF)2ReO4
• Phase separation in (TMTSF)2PF6
SCSC SCSDWSDWSDW
SC/CDW proximity
Superconductivity at the end point of a charge density wave state
in organic and inorganic systems
SC
CDW
L.Brossard et al , PRB (1990)
A. F. Kusmartseva et al., PRL 103, 236401 (2009)
TiSe2
Per2 [Au(mnt)2]
D. Graf et al, EPL, 85 27009 (2009)
1T-TaS2
Tc,max 6-8K
TTF [Ni(dmit)2]2
SCSC SCSDWSDWSDW
SC/(SDW or AF) proximity
S. Nandi et al., PRL 104, 057006 (2010).
Superconductivity at the end point of a spin density
wave (or AF) state in organic and inorganic
systems
-(BEDT-TTF)2X
(TMTTF)2X & (TMTSF)2X
SCSC SCSDWSDWSDW
SC/DW proximity
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 ?
SCSC SCSDWSDWSDW
Phase coexistence in (TMTSF)2ReO4
Moret R., Pouget J.-P., Comes R. and Bechgaard K., Phys.Rev.Lett., 49 (1982) 1008Parkin S.S.P. Jérome D. and Bechgaard K., Mol.Cryst.Liq.Cryst., 79 (1981) 213
SC at low Temperature above 8kbar
a
b
cInsulator
Metal
SCSC SCSDWSDWSDW
Phase coexistence in (TMTSF)2ReO4
Self- organisation along a
6 7 8 9 1020
40
60
80
100
120
140
160
180
200
ANISOTROPIE (b/a)
Pression (kbar)
Te
mp
éra
ture
(K
)
00.30000.60000.90001.2001.5001.8002.1002.4002.7003.0003.3003.6003.9004.2004.5004.8005.1005.4005.7006.000
6 7 8 9 10 1120
40
60
80
100
120
140
160
180
200
Pression (kbar)
Te
mp
éra
ture
(K
)
00.30000.60000.90001.2001.5001.8002.1002.4002.7003.0003.3003.6003.9004.2004.5004.8005.1005.4005.7006.000
ANISOTROPIE (c/a)
6 7 8 9 1020
40
60
80
100
120
140
160
180
200
Pression (kbar)
Tem
péra
ture
(K
)
00.30000.60000.90001.2001.5001.8002.1002.4002.7003.0003.3003.6003.9004.2004.5004.8005.1005.4005.7006.000
ANISOTROPIE (c/b)
C.Colin et al., EPL, 75, 301 (2006)
(log scale) (log scale)
(log scale)
SCSC SCSDWSDWSDW
Phase coexistence in (TMTSF)2ReO4
(2a,2c)
(a,2c)
Metal Semiconductor
2 possible orientations for each anion
Simple model : anisotropic Ising model
Pseudospin :
|+> if lattice parameter = 2a
|-> if lattice parameter = a
anisotropic interactions between spins anisotropic interactions between chains
Filaments or anisotropic bubbles oriented along a
Onsager (1941)
Pouget, Ravy,…
a
SCSC SCSDWSDWSDW
Phase coexistence in (TMTSF)2PF6
c-axis
a-axis
b-axis
SCSC SCSDWSDWSDW
Phase coexistence in (TMTSF)2PF6
-4 -2 0 2 4
2
3321mK
dV/d
I (k
)
(A)
P: 7.1kbar
87mK
SC along c
PHASE A : SC visible along c* only!
SCSC SCSDWSDWSDW
Phase coexistence in (TMTSF)2PF6
c =0 at low TDouble transition in b which disappears when P increases.
Clear non-linearities as a function of currentSome features are field independent
PHASE B : SC visible along c* and b’!
0 1 2 3
0
2
4
6
8
0
10
20
0
50
-0.6 -0.4 -0.2 0.0 0.2 0.4 0.61
2
3
4
5
c
cm)
Temperature (K)
(b)
b
a
P: 8.0 kbar
b (m
cm
c
(a)
am
cm
H (G)
171161134105765038
dV/d
I(a.
u.)
(mA)
T: 360mK
0
SCSC SCSDWSDWSDW
Phase coexistence in (TMTSF)2PF6
Non linearities at zero bias persist up to high fields.
They appear with SC at low pressure and disappear for PPc0
PHASE A: 7.5kbar
PHASE B: 8kbar
H
SCSC SCSDWSDWSDW
Phase coexistence in (TMTSF)2PF6
Double transition in a which disappears when P increases.
PHASE C : SC visible along c*, b’ and a!
SCSC SCSDWSDWSDW
Phase coexistence in (TMTSF)2PF6
From bubbles to slabs by adjusting hydrostatic pressure
Josephson junctionsTunnel junctions
a
c b
SDW
SC
SDW
SDW SDWSDW
SCSC SC
SDW
SC
SDW
SC
SC
SC
SCSC SCSDWSDWSDW
Phase coexistence in (TMTSF)2PF6
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
Soliton model :Existence of soliton domain walls (metallic) perpendicular to a- axisand expected peak of the anisotropy b,c / a at the DW / Metal transition
S. Brazovskii, L.P. Gorkov and A.G. Lebed, JETP 56 (1982) 683L.P.Gorkov, P.D.Grigoriev, EPL 71,425 (2005); PRB, 75, R20507 (2007)
a
c b
SDW
SC
SDW
SDW SDWSDW
SCSC SC
SDW
SC
SDW
SC
SC
See also experiments by Lee et al (PRL 2002,PRL 2005)
SCSC SCSDWSDWSDW
Phase coexistence in (TMTSF)2PF6
An image with the hands of the soliton model : how do metal (SC) emerge from a DW
Ecreation of a soliton < SDW gap
N. Kang et al. PRB (2010)
Journées labo, 7 Octobre 2010
SDW
Low pressure:Homogeneous SDW
SDW
Phases B and C: Bands in the SDW gap
‘soliton phase’
SC
SDW
Phase A: Midgap state in SDW gap
High pressure : SC homogeneous phase
SC
SCSC SCSDWSDWSDW
Phase coexistence in (TMTSF)2PF6
We believe that the deep in dV/dI characteristics is related to this particular band structure (as we are doing tunneling experiments!)
SDW
Low pressure:Homogeneous SDW
SDW
Phases B and C: Bands in the SDW gap
‘soliton phase’
SC
SDW
Phase A: Midgap state in SDW gap
High pressure : SC homogeneous phase
SC
PHASE B: 8kbar
SCSC SCSDWSDWSDW
Phase coexistence in (TMTSF)2PF6
a
c b
SDW
SC
SDW
SDW SDWSDW
SCSC SC
SDW
SC
SDW
SC
SC
? Why c first ???
bbaa ktktE cos2cos2)( 0k
),4/1,2/1( cnesting qQ
),2/1,2/1(tan cdards qQ
J.P.Pouget, S.Ravy, Synth. Metals 85,1523 (1997)T.Takahashi et al, JPSJ 55,1364 (1986)
Experiments :
SCSC SCSDWSDWSDW
Phase coexistence in (TMTSF)2PF6
a
c b
SDW
SC
SDW
SDW SDWSDW
SCSC SC
SDW
SC
SDW
SC
SC
Why c first ???
ccbb ktktE cos22cos'2)(' k
governs the evolution from SDW to metal)(')(')( kQkk EEE nestinganti
= deviation from nesting
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.
SCSC SCSDWSDWSDW
Conclusion
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 whereelectrons for SC and SDW come from the same band.
Same features for CDW/SC competition ?
SCSC SCSDWSDWSDW
SCSC SCSDWSDWSDWCargese August 18, 2011
The ‘green flash’ spot ?