Ginzburg-Landau Parameter of Film Specimens

Abstract

Results of magnetization measurements on thin superconducting films in magnetic fields transverse to the plane of the film are reported. The temperature dependence of the field, $H_{\perp }$, which causes a transition into the normal phase was determined for specimens of pure indium and tin as well as for alloy films containing these metals as solvents. The data are used to define a Ginzburg-Landau parameter $K_1\mathrm{}\left(T\right)\mathrm{}$, and are compared with various functional forms for the temperature dependence of this parameter that have been proposed. By extrapolating $K_1\mathrm{}\left(T\right)\mathrm{}$ to the transition temperature, the usual Ginzburg-Landau parameter $K$ is obtained. Values of the electron mean free path are also deduced from measurements of the residual resistance ratio in the normal phase. For the indium-based specimens the dependence of $K$ on electron mean free path is in good agreement with the theoretical expression of Gor'kov. It is concluded that no single functional form for the dependence of $K_1$ on temperature can describe the data. Rather, the form varies continuously as the electron mean free path changes. In particular, in the pure limit the transition field varies appreciably more rapidly than theoretical predictions based on the microscopic theory of superconductivity.