High-temperature superconductivity of perovskites in a two-band model

Abstract

An interband model of high-T _c superconductivity according to which the pairing of holes appears due to repulsive interband interaction has been developed. The actual region of the momentum space is enlarged as compared with the BCS mechanism and an electronic energy scale occurs for T _c. Transition temperature depends essentially on the Fermi level position. Maximal values of T _c are reached in case E _F located in the region of the bands overlap. Theoretical curves of the T _c dependence on the concentration of holes agree with the experiment. The dependence of superconducting gaps on temperature and carrier concentration have been found. From the free energy near T _c containing two gap order parameters the expressions for the entropy, specific heat and H _c have been derived. The pairing, induced by the interband interaction, is investigated also for fullerene compounds A _x C ₆₀, where the actual bands are separated by a semiconducting gap.

Key Words:

• high-temperature superconductivity
• perovskites
• superconducting gaps
• specific heat
• fullerene