Effect of impurity scattering on microwave conductivity of adx2−y2superconductor

Abstract

We study the effect of impurity scattering in the Born and unitary limit on the microwave conductivity peak observed in ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{6.95}.$ This peak has been widely interpreted as due to the collapse of the inelastic scattering rate on entering the superconducting state. We assume ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ symmetry and model the reduction in scattering rate through the application of a cutoff at low energies on the spectral density of the fluctuation spectrum causing the superconductivity. We find that, while the data for Zn doping can be understood with unitary scattering, the Ni data require intermediate strength coupling and are not consistent with Born scattering.