Electronic States in High-T_c Copper-Oxide Superconductors. II

Abstract

The electronic states in the CuO₂-layer have been studied by using the p-d model with the help of the auxiliary boson method for treating the local electronic correlation properly. What have been found are: at sufficiently low temperature the electronic states form coherent bands, whose width and intensity are strongly depending upon number of doped carriers (more significantly for holes than electrons) and the p-d charge transfer energy. In particular, when the number of doped-holes n_h is small, a new band form around the Fermi level inside the energy gap and its width and intensity are proportional to n_h. Even then the Fermi surface is still determined by the total number of unpaired electrons which are mainly of the localized d-electrons.