Superconducting Transitions of Amorphous Bismuth Alloys

Abstract

Measurements have been made of the critical temperatures $T_c$ of binary-alloy films composed of amorphous bismuth with lead, thallium, or antimony in concentrations up to 13 at.%. The curves showing $T_c$ a function of impurity concentration are nearly linear, as expected for a superconductor with no crystalline anisotropy. The slopes of the curves are not simply related to the valence or free-atom size of the impurity atoms. It is suggested that this may be explainable by extending Faber and Ziman's theory of the breakdown of Linde's rule for liquid alloys. The transitions of the films into the superconducting state are extremely sharp (∼5 mdeg wide). This indicates strongly that the electromagnetic coherence length does not limit the sharpness of the transition.