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

A three-band extended Hubbard model for CuO sub 2 planes is explored within a weak-coupling approximation scheme. The collective modes for both charge and spin fluctuations are calculated, including leading-order self-energy corrections for the quasiparticle propogators; this leads to an approximate form for the renormalised quasiparticle interactions, used to study superconductive pairing. We find that spin fluctuations promote pairing of B sub (1g) symmetry (d sub x sup 2 sub (-y) sup 2), and charge fluctuations between Cu and O induce either A sub (1g) (extended s) or B sub (2g) (d sub (xy)) pairing.