Strong-Coupling Superconductors, the Mössbauer Effect, and Localized Impurity Modes

Abstract
McMillan has recently proposed that in the strong-coupling theory of superconductivity certain expectation values for the lattice eigenfrequencies play a dominant role. We point out here that the Mössbauer effect can measure the important parameter in McMillan's theory in a rather direct fashion. Local-impurity-model calculations assuming isotopic impurities are presented, suggesting that McMillan's parameter is locally enhanced by heavy impurities in light lattices.