Strong-Coupling Theory of Superconductive Electron-Electron Interaction for High-T_c Oxide Superconductors

Abstract

We discuss the role of the spin exchange interaction for high- T c Y–Ba type copper oxide superconductors. We then formulate a strong-coupling theory for our recently proposed mechanism for high- T c oxide superconductors by a two-band model of lighter and heavier electrons while taking into account an infrared divergent effect due to the Fermi surface of the lighter electrons. We show how to theoretically derive a very high experimental ratio, twice the energy gap at T =0, over the transition temperature, 2Δ(0)/ k T c , to be in the range from 4.5 to 7.5.