Dependence of superconducting critical temperature on oxygen content in YBa2 Cu3 O7-y compounds: a model of a two-component boson gas

Abstract

Many properties of high-temperature superconductors clearly indicate that a mechanism different than the BCS one is responsible for their superconductivity. It seems that bipolaronic models can give sufficient explanation of essential problems in terms of Bose-Einstein condensation of hole pairs in real space. The only difficulty of a too large effective mass of the conventional bipolaron may be avoided by considering Chakraverty's peroxitons (O−-Cu+ -O−) which are true bosons with relatively low mass. According to the structure of YBa2 Cu3 O7-y we propose to treat it as a two-component boson system which consists of a quasi-one-dimensional boson gas for the Cu1-O1 chains and a quasi-two-dimensional boson gas for the Cu2-O2-O3 layers. As a first approximation we treat both subsystems as ideal boson gases. The oxygen content influences strongly the number of peroxitons in chains and layers as well as their effective masses and, therefore, critical temperature of the system. Within the proposed approach we expect different superconducting phases and critical temperatures depending on oxygen content.