Anisotropic Many-Body Effects in the Quasiparticle Velocity of Nb

Abstract

Fermi radii and velocities are determined by deconvoluting de Haas---van Alphen data. Comparison of these data with accurate augmented---plane-wave band-structure results establishes the reliability of the augmented---plane-wave calculations and allows a determination of the anisotropic many-body enhancement factor $\ensuremath{\lambda}(\stackrel{\ensuremath{\rightarrow}}{\mathrm{k}})$. The Fermi-surface average $〈\ensuremath{\lambda}〉$ of 1.33 suggests a large electron-electron contribution. Our anisotropic $\ensuremath{\lambda}(k)$ provide a detailed test and guide for model calculations of many-body enhancement.