Pairing by dynamic charge fluctuations in the extended Hubbard model

We consider superconductivity mediated by a charge-transfer resonance (CTR) in the weak-coupling approach to the three-band extended Hubbard model for the copper oxide superconductors. Our effective pairing interaction contains the dynamics of the CTR, and local-field effects. Unlike previous work, we solve the linearized Eliashberg equations on the lattice while retaining the full momentum dependence of the interaction and wave functions. We find that the highest ${\mathit{T}}_{\mathit{c}}$ occurs for an admixture of the extended and uniform s-wave states and we obtain the frequency dependence of the gap function.