Anomalous Behavior of Hc3/Hc2 near Tc for Sn-In and In-Bi Alloy Systems

Abstract

Previously reported measurements of the ratio Hc3Hc2 for tin-rich Sn-In alloys and indium-rich In-Bi alloys have been extended in further detail, and include variations in foil thickness (6 - 300 μ). The anomalous behavior in the ratio very near Tc is found to be dependent on foil thickness. Each alloy system is characterized by a certain thickness, above which Hc3Hc2 decreases markedly as Tc is approached, and below which the opposite behavior takes place. The results can be interpreted qualitatively in terms of a sandwich model in which the strength of the pairing interaction is depressed in a layer at the surface of the sample. For the thickest samples (most nearly "semi-infinite"), there is good quantitative agreement with the recent theory of this proximity effect given by Fink and Presson.