2-COMPONENT SUPERCONDUCTIVITY .2. COPPER-OXIDE HIGH-TC SUPERCONDUCTORS

A systematic relationship between the Cu-O-based high-T(c) materials and a two-component theory is developed. The two components are mobile-single-particle states associated with Cu-O planes and localized paired (negative-U) states associated with oxygen vacancies. The focus is on identification of the relevant electronic states in theoretical calculations and experimental observations. The family of Cu-O-based materials is discussed and an understanding is developed of the implications of layering and dimensionality, oxygenation, and doping. The relationship to superconducting properties is developed through the pair-density dependence and single-particle-density dependence of superconductivity. Comparisons with existing experimental data are made, distinctive experimental results are predicted. New directions for finding high-T materials are suggested both within the Cu-O-based family and in the more general class of materials which share with the Cu-O-based family the structure of metal-semiconductor layering and can be formed with off-stoichiometric compositions.