Analysis of the effect of oxygen doping and pressure on superconducting transition temperature in metal oxides

Abstract

The two-orbital Hubbard model is used to obtain formulas for the fermion excitation spectrum in the energy bands hybridized by the Anderson interaction. An analysis of lower part of the energy spectrum leads to a formula for the superconducting transition temperature T _c associated with the pairing of quasiparticles in one of the correlated bands. The dependence of T _c on pressure is analyzed, and the individual influence of carrier density enhancement and interaction strength is obtained as a function of oxygen concentration. The experimental discrimination made by Honma et al. [Solid State Commun 98, 395 (1996)] in Y_0.9Ca_0.1Ba₂Cu₃O_7−δ by separating out the contributions due to carrier density and pairing strength can be reproduced quantitatively, and perhaps with further refinement, so can the carrier concentration. Although the prediction of the absolute value of the transition temperature using the present model is not accurate, it is clear that it furnishes a reasonably accurate description of the change in transition temperature with pressure. The component contributions due to the change in carrier concentration and due to the change in interaction strength as a function of oxygen concentration are also in reasonable agreement with the experimental results.