CHARGE-TRANSFER INSTABILITY AND SUPERCONDUCTIVITY

Superconductivity in the system near charge transfer instability is investigated for CuO2 layer structure. By treating the transfer between Cu and O perturbatively, the effective interaction of O holes is derived and the possible symmetries of superconductivity is studied. The critical temperatures of superconductivity are estimated as a function of the doping rate, delta, based on weak-coupling approximation and are found to have characteristic delta-dependences depending on symmetry. We also examined the possible ground states with n = 1, 2, 3 or 4 holes for a wide range of the Coulomb repulsions on Cu sites and O sites.