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

The two-orbital Hubbard model is used to obtain formulas for the fermion ex citation spectrum in the energy bands hybridized by the Anderson interactio n. 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 enhan cement and interaction strength is obtained as a function of oxygen concent ration. The experimental discrimination made by Honma et al. [Solid State C ommun 98, 395 (1996)] in Y0.9Ca0.1Ba2Cu3O7-delta d by separating out the co ntributions due to carrier density and pairing strength can be reproduced q uantitatively, and perhaps with further refinement, so can the carrier conc entration. Although the prediction of the absolute value of the transition temperature using the present model is not accurate, it is clear that it fu rnishes a reasonably accurate description of the change in transition tempe rature with pressure. The component contributions due to the change in carr ier concentration and due to the change in interaction strength as a functi on of oxygen concentration are also in reasonable agreement with the experi mental results. (C) 1999 American Institute of Physics. [S1063-7761(99)0080 1-X].