IMPURITY AND FLUCTUATION EFFECTS IN SUPERCONDUCTORS

Abstract

The theoretical explanation of the phenomenon of superconductivity,based fundamentally on Cooper's idea of the formation of bound singlet pairs of electrons near the Fermi surface under the action of phonon inter-action, demands the existence of a spatial correlation between electrons at a distance of order-4 cms, the coherence length) and of a superconducting order parameter governing the phase transition at the critical temperature. In an alloy, the electrons get scattered by impurities and since this scattering takes place at arbitrary angles, the correlation between electrons is very sensitive to the scattering process. Thus impurities must affect the properties of a metal in superconducting state. Different types of impurities, even when present in small concentration, have different effects on super-conducting properties....