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

Abstract

Measurements were made of the dicontinuity δc in the specific heat at the superconducting transition for quench-condensed films of indium--manganese, and indium--chromium. Manganese and chromium are 3-d transition elements, and retain their magnetism when dissolved in indium. This is the first investigation of this sort where 3-d magnetic impurities have been studied in a simple metal superconductor. Magnetic impurities depress the superconducting transition temperature Tc, and predictions based on the Shiba theory for classical spins in superconductors indicate that δc is also depressed by the presence of magnetic impurities. It is useful to express the results in terms of δc0 and Tc0, the values for the pure superconductor. The Shiba theory indicates that δc/δc0 is depressed more rapidly than TcTc0 as magnetic impurities are introduced into a superconductor. The results of the present work confirm this prediction, but show an even greater depression of δc/δc0 relative to TcTc0 than the Shiba theory predicts. Similar results have been obtained by previous workers who dissolved 3-d magnetic impurities in transition metal superconductors. This work also shows that δc 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 the results of Bergmann.