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Electron-Hole Liquid Model for High Tc-Superconductors

We propose a theoretical model for high-T c superconductivity based on the existence of two types of mobile charge carriers: electrons and hole-bosons. The bosons are assumed to be mobile in CuO2 planes and the electrons in separate parts of the crystal in order to prevent annihilation. We simulate this situation with a uniform mixture of electrons and bosons by adding a short-range repulsion between them. The model predicts the existence of a linear electronic sound mode which is analogous to the first sound in He-mixtures. The electron component contributes a linear term and the sound mode a cubic term in the electronic specific heat. The transition at Tc is interpreted as a λ—transition whereas the pairs are formed at a higher temperature TBCS- For small hole concentrations the charge carriers form an excitonic bound state of heavy fermion type which is immobile and hence provides an explanation for metal-insulator transition. The model predicts also the doping behaviour in agreement with experiment including the pressure dependence of T c. The specific heat linear term is predicted to increase with pressure for hole doped and to decrease for electron doped superconductors. The predictions are valid for all types of high T c-compounds and also for the new electron superconductors. The value of normalized slope of specific heat discontinuity at T c can exceed the maximum values obtainable by the BCS-and Eliashberg theories.