Abstract
We investigate effects of the repulsive interaction Upd between holes on the nearest-neighbor Cu- and O-sites in the d-p model with infinite repulsion on the Cu site using the auxiliary boson technique and the 1⁄N expansion method. It is found that the condition for a metal-insulator (M-I) transition to occur at the half-filled case is modified. We then investigate the charge susceptibility; it is found that the thermodynamic charge susceptibility is enhanced by Upd except for the region around the critical point of the M-I transition. It is found to diverge at a certain value of Upd, which implies an instability toward a phase separation. On the basis of these calculations, we obtain phase diagrams, which consist of the metallic, unstable (phase-separating) and insulating phases. Furthermore, we calculate the quasiparticle interaction and find that the charge fluctuation induces attractive interaction comparable in magnitude to the repulsive interaction originating from the on-site repulsion Ud in both of the s- and d-wave channel; in the immediate vicinity of the instability, the attraction can overcome the repulsion.
