Pairing interaction and superconducting transition temperature in the d-p model

Effective pairing interaction and superconducting transition temperature T-c are investigated on the basis of the simplest d-p model by using the auxiliary particle method together with the 1/N-expansion theory. The pairing interaction mediated by both charge and spin fluctuations is calculated by considering higher order terms in the 1/N-expansion within the random phase approximation(RPA) to find that it is attractive only for the d(x2-y2) channel. T-c is calculated by solving a linearized Eliashberg equation to confirm that it can be finite only for d(x2-y2) pairing. Doping dependence of T-c seems to be consistent with experiments with a reasonable choice of the parameter for the charge-transfer energy. The highest T-c is obtained at a hole-doping rate delta = 0.15 and estimated to be similar or equal to 100 K. It is also shown that the spin fluctuation plays a dominant role in the system to realize the high-T-c superconductivity rather than the charge fluctuation does.