Abstract
We investigate the mass enhancement factor and the superconducting transition temperature in the d–p model for the high-Tc cuprates. We solve the Éliashberg equation using the third-order perturbation theory with respect to the on-site Coulomb repulsion U. We find that when the energy difference between the d-level and p-level is large, the mass enhancement factor becomes large and Tc tends to be suppressed owing to the difference of the density of state for d-electron at the Fermi level. From another viewpoint, when the energy difference is large, the d-hole number approaches unity and the electron correlation becomes strong and enhances the effective mass. This behavior for the electron number is the same as that for the f-electron number in the heavy fermion systems. The mass enhancement factor plays an essential role in understanding the difference in Tc between the LSCO and YBCO systems.
