Coexistence of s- and d-wave gaps due to pair-hopping and exchange interactions

Abstract

I investigate the superconductivity of the three-band t–J–U model derived from the three-band Hubbard model using the Schrieffer–Wolff transformation. My model is designed considering the hole-doped high-T c superconducting cuprate. The model does not exclude the double occupancy of Cu sites by d electrons, and there is a pair-hopping interaction between the d and p bands together with the exchange interaction. I analyse the superconducting transition temperature, electronic state, and superconducting gap function based on strong coupling theory and find that the superconductivity emerges due to the pair-hopping and exchange interactions via the Suhl-Kondo mechanism. In the superconducting state, the extended s- and -wave superconducting gaps coexist, where both charge fluctuations and d–p band hybridization are key ingredients.