APEX OXYGEN AND EFFECTIVE PAIRING INTERACTION AMONG PLANAR OXYGEN QUASI-PARTICLES IN COPPER-OXIDE SUPERCONDUCTORS

In this article we address the problem of the possible role of the apex oxygen for the superconducting properties of copper oxides. We consider the relevant microscopic model and with the help of a canonical transformation derive the effective interaction among planar oxygen quasiparticles. This interaction is definitely attractive for realistic values of the model parameters. The correlation between the position of the apex-oxygen energy level, the strength of the attraction and the magnitude of the superconducting transition temperature are derived. This offers microscopic support for findings originating from the compilation of many results for a wide class of high-T-c superconductors.