PROPERTIES OF QUASI-2-DIMENSIONAL SUPERCONDUCTORS NEAR A SDW INSTABILITY - APPLICATION TO ET-SALTS

We describe some organic superconductors, such as the ET salts, by a model of quasi-2D Fermi liquid, in which the Fermi surface exhibits a quasi-1D electron pocket, with good nesting properties, and a quasi-2D hole pocket, possibly close to a Van Hove singularity. Such properties are responsible for large magnetic fluctuations, which influence the electron self energy and, therefore, all the properties of the normal phase. In particular, a pseudo-gap in the quasiparticle spectrum is opened. We propose to interpret in this way the anomaly recently observed in the NMR relaxation time of kappa-(BEDT-TTF)(2)CuN(CN)(2)Br. Given the vicinity of a magnetic instability, a moderate magnetic field perpendicular to the most conducting plane can induce a SDW phase,which might explain the peculiar phase diagram recently ob served in kappa-(BEDT-TTF)(2)CuN(CN)(2)Cl.