Charge fluctuations, charge-transfer instabilities, and superconductivity in a three-band model of CuO2 planes

We apply a recently developed quasiparticle theory for strongly correlated systems to a three-band model of Cu-O planes. We allow for Cu-O hybridization, Cu-O intersite repulsion, and a large on-site repulsion at the Cu sites (which will be treated as infinite). We use the large spin degeneracy (1/N) expansion to study (i) the interplay between charge-transfer instabilities and phase separation in the mean-field (N=∞ limit) phase diagram of this model and (ii) the pairing interactions induced by the charge fluctuations (calculated to leading order in 1/N) in the proximity of these instabilities