ON THE BCS THEORY OF SUPERCONDUCTIVITY IN SYSTEMS WITH OVERLAPPING BANDS .2. OVERLAP, HYBRIDIZATION, ANTIFERROMAGNETISM, CHARGE-TRANSFER, AND SYMMETRY SHIFTS IN HIGH-T-C CUPRATES

A mean-field (MF) theory is proposed in the Green's function method of paper I which, in the same scheme, accounts for antiferromagnetism (AF), charge transfer (CT), and superconductivity (SC) in d-p cuprates. The AF, dominant in the narrow-bandwidth regime, is determined by level separation. This gives way to a broad-bandwidth CT state which spills over and cooperates with SC, resulting in high T-c. Our spinor representation of the pairing t-model (PtM) allows for easy understanding of the gradual evolution of states, on the basis of simple energy symmetry. PtM energy profiles are exhibited and reproduce results from other MF models as limiting cases. The SC is foreshadowed by level equalisation, strong vibronic admiring, and anti-adiabatics that manifest, in the quasiparticle spectrum, the Jahn-Teller effect. The latter is observed as an orthorhombic <-> tetragonal transition in the cuprates. Modelling high-T-c SC on CT-renormalised phonon (ion plasma) modes, reproduces the experimental T-c for most known cuprates. We believe that the present theory embodies novel solutions to the basic problems of normal and SC cuprates, in the simple Bardeen-Cooper-Schrieffer (BCS)-type model.