Model calculation for electronic pairing in copper oxides.

Abstract

The interaction kernels due to charge and spin fluctuations are calculated in a simple tight-binding band model for the electronic structure of copper oxide planes. For a superconducting order parameter with d-wave symmetry, we find self-consistent solutions in which the pairing spin fluctuations dominate over the depairing charge fluctuations and large values of the critical temperature ${\mathit{T}}_{\mathit{c}}$ are possible. By adding a small phonon contribution we get a small but finite isotope-effect coefficient (\ensuremath{\alpha}) for ${\mathit{T}}_{\mathit{c}}$ of about 100 K. We also find a large increase in \ensuremath{\alpha} with decreasing ${\mathit{T}}_{\mathit{c}}$ due to impurity scattering or band filling. For a suitable choice of parameters the \ensuremath{\alpha}(${\mathit{T}}_{\mathit{c}}$) curves are close to the experimental results.