Aspects of Optical Properties in Conventional and Oxide Superconductors

Abstract

We review the effect of elastic and inelastic scattering on the normal state infrared conductivity, and describe modifications to the real and imaginary parts which result from a transition to an s-wave superconducting state. The zero frequency limit of the imaginary part is related to the temperature-dependent penetration depth and, at finite frequency, provides information about the superconducting gap. In the high T_c cuprates the gap appears to have d-wave symmetry. This profoundly modifies both the real and the imaginary parts of the optical conductivity. After describing these modifications we introduce the conductivity-derived scattering rate, which directly probes the inelastic scattering processes, and is much larger in the oxides than in conventional superconductors. This quantity is also significantly modified by the d-wave symmetry of the gap.