Specific Heat of Superconducting Films of Indium and of Indium Alloyed with Magnetic Impurities

摘要

Measurements were made of the dicontinuity delta c 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 T/sub c/, and predictions based on the Shiba theory for classical spins in superconductors indicate that delta c is also depressed by the presence of magnetic impurities. It is useful to express the results in terms of delta c sub 0 and T/sub c0/, the values for the pure superconductor. The Shiba theory indicates that delta c/ delta c sub 0 is depressed more rapidly than T/sub c//T/sub c0/ as magnetic impurities are introduced into a superconductor. The results of the present work confirm this prediction, but show an even greater depression of delta c/ delta c sub 0 relative to T/sub c//T/sub c0/ 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 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 the results of Bergmann. (ERA citation 04:014005)