Identifying the pairing mechanism in high-Tc superconductors

It is argued that the origin of the high transition temperatures observed in Ba1-xKxBiO3 and the copper-oxide superconductors with perovskite-related structures is due to two factors: overlap of a partially filed σ* band of primarily cation character and a π or π* band of mostly O-2pπ parentage permits charge transfer between cation and anion subarrays with oxygen-atom displacement perpendicular to a M-O-M bond axis and bondlength mismatch places the M-O-M bondlength under a compressive or tensile stress. Relief of a compressive stress by the bending of a M-OP-M bond from 180 degrees introduces a strong electron-lattice interaction with holes; a 180 degrees Cu-O-Cu bond allows strong electron-lattice coupling with electrons of a Cu2+/+ redox couple, but not with holes in a Cu3+/2+ redox couple