Mean-field analysis in the p-d model of oxide superconductors

A highly correlated p-d model of cuprate oxide superconductors is analyzed by use of composite operators on CuO2 clusters. A minimal set of composite operators to describe the electronic state is identified from the criterion that the order of the approximation is determined by coupling constants multiplied by the weight of their respective operators. It is shown that the intensity transfer among bands with hole doping is well described within the mean-field approximation. Effects of the nearest-neighbor spin correlation are investigated and it is shown that the band dispersions are strongly affected. By the local antiferromagnetic correlation, the band dispersion of the upper Hubbard band is flattened in the whole Brillouin zone, while that of the p dominant band near the Fermi level is flattened only around a certain region centered at the zone boundary. In the moderately doped region, the Fermi surface is consistent with a large Fermi surface.