Contraction of atomic orbitals in the oxygen anion network and superconductivity in metal oxide compounds

Özet

Anion network in the $CuO-2$ plane of metal-oxide compound is considered as an intrinsic-hole metal with holes rather than electrons comprising a Fermi liquid immersed in the background of negative $O^{2-}$ ions. Due to the contraction of p-orbital of oxygen as a result of occupation by a hole, hole hopping between nearest neighbor sites (i,j) is dependent upon hole occupation as $t_{ij,\sigma}$ = $t_o + V_{n_i,-\sigma} n_{j,-\sigma}$ + $W_{(n_i,-\sigma + n_j,\sigma)}$. Coupling parameters W and V (additive and multiplicative "contraction interaction" terms) result in the binding of holes into singlet, on-site configuration, or into triplet, nearest-neighbor-site configuration, due to W and V respectively. In the weak coupling limit, W results in the BCS type of superconductive pairing (singlet, s-wave), whereas multiplicative contraction V provides for either singlet, d-wave, or triplet, p-wave-like pairing states. It is concluded that the latter state may result in a plausible mechanism for high-Tc superconductivity in metal oxide compounds. The superconducting p-phase is shown to be in accord with recently published symmetry tests of the order parameter in oxides.