Specific heat of superconducting films of indium and of indium alloyed with magnetic impurities

Abstract

We have measured the discontinuity in the specific heat $\Delta c$ and the transition temperature $T_c$ for superconducting quench-condensed films of indium, and of indium-manganese and indium-chromium alloys. These are the first measurements of $\Delta c$ for a simple metal superconductor with magnetic $3-d$ transition-element impurities. It is useful to express the results in terms of $\Delta c_0$ and $T_{c0\mathrm{}}$, the values for the pure superconductor. The Shiba theory indicates that $\frac{\Delta c}{\Delta c_0}$ is depressed more rapidly than $\frac{T_c}{T_{c0\mathrm{}}}$ as magnetic impurities are introduced into a superconductor. Our results confirm this prediction, but show an even greater depression than the Shiba theory predicts. Similar results have been obtained by previous workers for $3-d$ magnetic impurities in transition-metal superconductors. The present work also shows that $\Delta c$ for pure indium increases with increasing disorder, where the degree of disorder is indicated by the residual resistivity of the sample. This result is to be expected qualitatively from Bergmann's studies of the transition temperature and energy gap width for disordered samples of indium. The present results, however, indicate that $\Delta c$ increases roughly ten times more rapidly with the degree of disorder than would be estimated from his results.