Multivalence Resonance-Condensation Model for Electron Pairing and Superconductivity in High Tc Superconductors: A Possible Novel and Universal Origin of Superconductivity

The multivalence resonance-condensation model (MVRC model) is suggested as a possible novel and universal origin of high T_c superconductivity and successfully applied to various high T_c oxide superconductors with perovskite-related structure, such as strongly anisotropic layered cuprates and almost isotropic bismuthates. The MVRC state is Bose condensation of the resonance hybrids between two kinds of multivalence states of the cations Cu^1+,2+,3+(Bi^3+,4+,5+, Pb^2+,3+,4+, etc.) responsible for the superconductivity and is shown from its simple geometrical configuration on the actual crystal lattice planes to provide a unified picture of the superconducting state of all these systems in a consistent manner. Most importantly, the model reveals the inherent deep connection of superconductivity with the fundamental and universal nature of matter, i.e., the chemical bond. Thus, the model is expected to be a guiding chemical and structural principle in both the search for new superconductors and the construction of a new quantitative theoretical model.