Multiband superconductor model with exchange-like interband interaction

Abstract

We investigate a multiple-band superconductor model taking into account the interband BCS-like matrix elements originating in the exchange-like integral K at each atomic site as well as the usual intraband BCS interaction and the on-site Coulomb energy U. A mean field treatment discloses that K diminishes the effect of U, elevating T c substantially if K≲U. When the Fermi surfaces of two bands mutually nest, an interband ladder diagram divergently enhances the effect of K. These effects are asserted to realize the high T c in cuprate superconductors. The values of2Δ o/k BT c are shown to range in 2 ∽ 8. The isotope effect is also discussed.