Superconducting and normal state properties of dilute indium-tin alloys: Bulk and thin film

Abstract

Measurements are reported of normal-state and superconducting-state properties of bulk and thin-film indium-tin alloys. For the bulk samples, whose compositions were in the range 0-5.8 at.% tin, the residual resistivities, critical magnetic fields, and critical temperatures were measured. It is shown that both similarity conditions are well obeyed for the critical fields of samples containing 0-1.8 at.% Sn, for which detailed data were taken. High-purity films were produced containing up to 5 at.% tin. From resistance measurements, the critical temperatures, critical fields, thicknesses, and residual resistivities of the films were obtained. The formula for boundary scattering due to Fuchs has been recast into a more convenient form from which one may calculate the intrinsic mean free path and intrinsic resistivity directly from the measured resistivity and thickness. From the resistivity measurements, one may infer a value for the product of intrinsic resistivity and mean free path, l, of 1.6×10-11 cm2. The critical-temperature measurements indicate that bulk and film specimens having the same composition do not have the same critical temperature. On the basis of a model which attributes the shift in critical temperature to stress effects, formulas are derived from which one may calculate the stress in a film as well as the equivalent (i.e., stress-shifted) bulk critical field for any film. However, the stress-shifted bulk critical-field curves obtained in this way for the indium alloy films are nearly the same as one would have obtained under the assumption of similarity. Analysis of the critical-temperature results indicates that while stresses in the most dilute films are probably relieved by ordinary dislocation flow, some other mechanism, perhaps twinning, dominates in the more concentrated alloys. The largest uniaxial stress calculated for the films studied was 2.6×109 dyn/cm2, which was obtained for a film of indium containing 2.6 at.% tin. © 1965 The American Physical Society.