Superconductivity, localization and crystallographic phase transition in La(2-x)SrXCuO(4-y)

We report a resistive investigation of superconductivity in the system La2 xSrxCuO4 y on samples which have been analysed by thermogravimetric techniques for oxygen deficiency determination. A maximum superconductive transition temperature is observed in La2 xSrxCuO4 y near the tetragonal-orthorhombic phase transition, together with a resurgence of high temperature superconductivity in non-substituted La2CuO4 y. Drastic localization effects are observed in the vicinity of x = 0.04 with no sign of superconductivity at low temperature. These observations are coherent with a simple BCS scheme with a band filling dominated by Sr-doping and localization effects dominated by an interplay between 0 vacancies and Sr-doping. This situation leads to half-filling of the band near x = 0.04 with enhanced electron localization via Umklapp scattering through a near nested Fermi surface. Moreover, our data suggest some contribution of antiferromagnetic fluctuations to the superconducting pairing mechanism. J. Physique 48 (1987) 1181-1186 JUILLET 1987,