Two Fluid superconductors

Abstract

AbstractAn approach to the theory of high‐Tc superconductivity is discused in which the semiconductor‐like layers between the copper‐oxide planes are more active participants in the superconductivity. Two types of states appear in the theory, a lattice of negative‐U sites and single particle (positive‐U) dispersive states. The negative‐U sites originate in oxygen vacancies and the single particle states in the copper‐oxide planes. The coupling between these two types of states lead to a two‐fluid superconductivity where the negative‐U sites give rise to a charged Bosonic fluid and the single particle states are a Cooper‐paired superconductor. The coupled Fermion‐Boson model for superconductivity is related both to theories of superconductivity in semiconductor‐metal eutectic alloys, and recent suggestions of s‐channel superconductivity of R. Freidberg and T. D. Lee. Basic aspects of general phenomenology are described. The breakdown of Fermi liquid theory in the normal state results from mixing of Fermions and Bosons at the Fermi energy. When the two‐particle states are filled, anti‐ferromagnetism arises from the positive‐U of the single particle states with a contribution from virtual excitation of two‐particle states. Prediction is made of a large class of superconducting materials based on metal‐semiconductor layering.