Collective modes and superconductivity in an extended Hubbard model for copper oxide superconductors

A three-band extended Hubbard model for CuO₂ planes is explored within a self-consistent-field approximation. The collective modes for both charge and spin fluctuations are calculated, including leading-order self-energy corrections for the quasiparticle propagators; this leads to an approximate form for the renormalized quasiparticle interactions, used to study superconductive pairing. We find that spin fluctuations promote pairing of B1g symmetry (dₓ²-y²), and charge fluctuations between Cu and O induce either A1g (extended s) or B2g (dxy) pairing.