Properties of superconductivity on the density wave background

Orateur : Pavel GRIGORIEV (Landau Institute, Chernogolovka)

We investigate the properties and the microscopic structure of superconductivity (SC), coexisting and sharing the common conducting band with density wave (DW). Such coexistence may take place when the nesting of the Fermi surface (FS) is not perfect. Then in the DW state some quasiparticle states remain on the Fermi level and lead to the Cooper instability. The soliton (nonuniform) DW state also leads to the Copper instability. The dispersion of the quasiparticles on the Fermi level in the DW state strongly differs from that without DW if the nesting is almost perfect, and so do the properties of SC on the DW background. The upper critical field Hc2 in such a SC state increases as the system approaches the critical pressure, where the ungapped quasiparticle states and superconductivity just appear. This upper critical field may considerably exceed the usual Hc2 value without DW. The SDW background strongly suppresses the singlet SC pairing, while it does not affect so much the triplet SC transition temperature. However, if the DW couples the electronic states with opposite sign of the SC order parameter, this suppression does not happen, as in d-wave high-Tc superconductors. The results obtained agree well with the experimental observations in layered organic metals (TMTSF)2PF6 and a-(BEDT-TTF)2KHg(SCN)4, where SC appears in the DW states under pressure and shows many unusual properties. Publications : [1]. L.P. Gor’kov, P.D. Grigoriev, « Soliton phase near antiferromagnetic quantum critical point in Q1D conductors », Europhysics Letters 71, 425 (2005). [2]. L.P. Gor’kov, P.D. Grigoriev, " Nature of superconducting state in the new phase in (TMTSF)2PF6 under pressure.", Phys. Rev. B 75, 020507 (2007). [3]. P.D. Grigoriev, “Properties of superconductivity on the density wave background with small ungapped Fermi surface pockets”, Phys. Rev. B 77, 224508 (2008). [4]. P.D.Grigoriev, “Superconductivity on the density-wave background with soliton-wall structure”, PhysicaB *404*, 513 (2009).

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