Raman scattering of hght off a superconducting alloy containing paramagnetic impurities

Abstract

Raman scattering of light off a superconductor doped with a small concentration of paramagnetic impurities is discussed without recourse to the quasiparticle approximation. The scattering efficiency defined in terms of Kubo's nonlinear response theory in a form suitable for systematic diagrammatic expansion is used as the starting point. This is examined in the four-component Eliashberg-Gorkov space for the case of constant transition-matrix elements, in the limit of small momentum transfer (London limit), and in the Eliashberg approximation of neglecting the momentum dependence of the electronic self-energy. For the specific case of Fe impurities in quenched In films numerical calculations have been made for the ratio of the scattering efficiency in the superconducting and normal states as a function of the reduced frequency and temperature for different impurity concentrations.