Domain walls at the SDW endpoint of (TMTSF) 2 PF 6 under pressure

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


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


(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


-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


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


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


Double transition in a which disappears when P increases.

PHASE C : SC visible along c*, b’ and a!

SCSC SCSDWSDWSDW


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


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


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


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


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


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 ?

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Domain walls at the SDW endpoint of (TMTSF) 2 PF 6 under pressure

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