Role of Internal Stresses and Kinetic Energy Reduction in Layered Superconductors

Abstract

74.20.Fg; 74.62.Fj We have considered an extended Hubbard model for the superconducting ceramics. The driving force for superconductivity in the single band model is the nearest-neighbour interaction augmented by the on-site and inter-site volume charge coupling. The transition to superconductivity is also supplemented by the decrease of kinetic energy obtained in the modified mean-field approximation, which is applied to the inter-site interactions. The BCS equation is solved numerically for the single band model with on-site and inter-site Coulomb interaction, and on-site and inter-site volume charge coupling. It is shown, that a physically reasonable set of electron-deformation coupling constants, together with kinetic energy decrease, will significantly lower the nearest-neighbour interaction required for the d-wave superconductivity.