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

SDW. M(SC). SDW. M(SC). SDW. M(SC). Domain walls at the SDW endpoint of (TMTSF) 2 PF 6 under pressure. C.Pasquier , Laboratoire de Physique des Solides, Orsay S. Brazovskii LPTMS, Orsay Acknowledgments: P. Grigoriev. N. Kang, B.Salameh , P. Auban-Senzier, D.Jérome. Outline.

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

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  1. SDW M(SC) SDW M(SC) SDW M(SC) Domain walls at the SDW endpoint of (TMTSF)2PF6 under pressure C.Pasquier, Laboratoire de Physique des Solides, Orsay S. Brazovskii LPTMS, Orsay Acknowledgments: P. Grigoriev N. Kang, B.Salameh, P. Auban-Senzier, D.Jérome

  2. Outline • Superconductivity at the border of density wave states • The case of (TMTSF)2ReO4 • Phase separation in (TMTSF)2PF6

  3. SC/CDW proximity TTF [Ni(dmit)2]2 1T-TaS2 CDW SC Superconductivity at the end point of a charge density wave state in organic and inorganic systems L.Brossard et al , PRB (1990) Per2 [Au(mnt)2] TiSe2 Tc,max6-8K A. F. Kusmartseva et al., PRL 103, 236401 (2009) D. Graf et al, EPL, 85 27009 (2009)

  4. SC/(SDW or AF) proximity (TMTTF)2X & (TMTSF)2X Superconductivity at the end point of a spin density wave (or AF) state in organic and inorganic systems -(BEDT-TTF)2X S. Nandi et al., PRL 104, 057006 (2010).

  5. 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 ?

  6. Phase coexistence in (TMTSF)2ReO4 b Insulator Metal c a 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

  7. Phase coexistence in (TMTSF)2ReO4 (log scale) (log scale) Self- organisation along a (log scale) C.Colin et al., EPL, 75, 301 (2006)

  8. Phase coexistence in (TMTSF)2ReO4 (2a,2c) (a,2c) Metal Semiconductor a 2 possible orientations for each anion Simple model : anisotropic Ising model Onsager (1941) Pseudospin : |+> if lattice parameter = 2a |-> if lattice parameter = a anisotropic interactions between spins  anisotropicinteractions between chains Pouget, Ravy,… Filaments or anisotropic bubbles oriented along a

  9. Phase coexistence in (TMTSF)2PF6 b-axis a-axis c-axis

  10. Phase coexistence in (TMTSF)2PF6 PHASE A : SC visible along c* only! SC along c

  11. Phase coexistence in (TMTSF)2PF6 PHASE B : SC visible along c* and b’! 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

  12. Phase coexistence in (TMTSF)2PF6 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

  13. Phase coexistence in (TMTSF)2PF6 PHASE C : SC visible along c*, b’ and a! Double transition in a which disappears when P increases.

  14. Phase coexistence in (TMTSF)2PF6 b c a SC SC SC SC SC SC SC SC SDW SDW SDW SDW SDW SDW SDW Josephson junctions Tunnel junctions From bubbles to slabs by adjusting hydrostatic pressure

  15. Phase coexistence in (TMTSF)2PF6 b c a 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- axis and expected peak of the anisotropy sb,c /sa at the DW / Metal transition S. Brazovskii, L.P. Gorkov and A.G. Lebed, JETP 56 (1982) 683 L.P.Gorkov, P.D.Grigoriev, EPL 71,425 (2005); PRB, 75, R20507 (2007) SC SC SC SC SC SC SC SDW SDW SDW SDW SDW SDW SDW See also experiments by Lee et al (PRL 2002,PRL 2005)

  16. Phase coexistence in (TMTSF)2PF6 An image with the hands of the soliton model : how do metal (SC) emerge from a DW DSDW DSC DSDW Ecreation of a soliton < SDW gap DSDW DSC Phase A: Midgap state in SDW gap Phases B and C: Bands in the SDW gap ‘soliton phase’ Low pressure: Homogeneous SDW High pressure : SC homogeneous phase N. Kang et al. PRB (2010) Journées labo, 7 Octobre 2010

  17. 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!) DSDW DSC DSDW DSDW DSC PHASE B: 8kbar Phase A: Midgap state in SDW gap Phases B and C: Bands in the SDW gap ‘soliton phase’ Low pressure: Homogeneous SDW High pressure : SC homogeneous phase

  18. Phase coexistence in (TMTSF)2PF6 b c a ? Why c first ??? SC SC SC SC SC SC SC SDW SDW SDW SDW SDW SDW SDW Experiments : J.P.Pouget, S.Ravy, Synth. Metals 85,1523 (1997) T.Takahashi et al, JPSJ 55,1364 (1986)

  19. Phase coexistence in (TMTSF)2PF6 b c a Why c first ??? = deviation from nesting SC governs the evolution from SDW to metal SC SC SC SC SC SC 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. SDW SDW SDW SDW SDW SDW SDW

  20. 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 where electrons for SC and SDW come from the same band. Same features for CDW/SC competition ?

  21. Thankyou for your attention

  22. Cargese August 18, 2011 The ‘green flash’ spot ?

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