CHARGE-FLUCTUATION-INDUCED AND SPIN-FLUCTUATION-INDUCED PAIRING INTERACTION IN AN EXTENDED HUBBARD-MODEL FOR COPPER-OXIDE SUPERCONDUCTORS

A self-consistent and conserving approximation scheme is used to derive the general equations for the quasiparticle self-energies and the dynamic charge and spin susceptibilities in the extended three-band Hubbard model for the CuO2 planes. For inter- and on-site Coulomb repulsions V and U satisfying the condition V greater than or similar to 3/2+1/8 U we obtain a charge transfer resonance at q=0 which gives rise to a large attractive pairing interaction. The pairing interaction with momentum transfers q=0 and q=(pi, 0) is estimated to be strongly attractive over a large range of energies, while it becomes strongly repulsive for q=(pi, pi).