Crossover from real space to intraband pairing in the copper oxide superconductors

Abstract

We have investigated BCS-like models of layered superconductors with N = 2 conducting layers per unit cell, both in the real space or discrete layer representation, and in the band representation with interband pairing projected out. The single quasiparticles are assumed to propagate as free particles within the conducting layers with effective masses m 1 and m 2, and tunnel between neighboring layers with matrix elements J 1 and J 2,respectively. Intralayer pairing with strengths δ 01, δ 02 and interlayer pairing with strengths δ 1, δ 2 are both considered. for all such processes, J 1 and J 2 are pairbreaking parameters for interband pairing. The transition temperatures for real space and intraband pairing are compared, and a crossover from real space to intraband pairing occurs as the interlayer hopping is increased. This crossover usually occurs when J max/ gw c ≈ 1, where J max is the maximum interlayer tunneling matrix element, and ω c is the BCS cutoff energy for the appropriate pairing process, but can sometimes occur for smaller J max values.