Distribution of the Energy Gap inkSpace for Superconducting Nb

Abstract

Examination of available tunneling data from junctions oriented on single-crystal niobium shows that the observed superconducting energy gap values are grouped nonrandomly in $k$ space. These groupings are consistent with a relationship between ${\Delta }_{\mathrm{}\left(k\right)\mathrm{}}$ and Fermi-surface topology, but also suggest a significant role for phonon anisotropy.