Theory of energy bands and related properties of 4d-transition metals. II. The electron-phonon matrix element, superconductivity and ion core enhancement

Abstract

For pt.I see ibid., vol.7, p.613 (1977). The variation of the electronic contribution eta to the electron-phonon mass enhancement is studied across the 4d transition metal series within the Gaspari-Gyorffy rigid muffin tin (RMT) approximation. The pd and df matrix elements are expressed in terms of band parameters. It is shown that hybridization enhances the p density of states for Nb, but reduces it for transition metals to the right of the series, whose superconductivity is, therefore, determined by df scattering which still remains dominant even after a 50% reduction by screening of the RMT results. The importance of the ion core in enhancing the scattering through orthogonality constraints and reduction in effective screening, is illustrated by studying the large volume dependence of eta shown by the early transition metals and rare earths.