Fluctuation-Induced Diamagnetism above Tc in Al and Al—Ag Alloys
We report here observations of the enhanced diamagnetism in bulk, cylindrical single crystals of pure aluminum and its alloys, for which the impurity in all cases is silver. The diamagnetism occurs above the thermodynamic transition temperature and is attributed to the formation of an appreciable number of Cooper pairs by means of fluctuations in the superconducting order parameter. It is clear from these measurements that these materials exhibit, or nearly exhibit, the universal magnetic field-dependent behavior previously reported by Gollub et al. 1 and successfully explained by the theories of Lee and Payne2 and Kurkijärvi et al. 3 for pure superconductors. Theoretical calculations by these same authors, extended to establish the form of the universal scaling law for both clean and dirty materials, will be shown, however, to be in disagreement with experiment.
KeywordsSuperconducting Order Parameter Fluctuation Magnetization Flux Transformer Empirical Scaling Factor Dirty Material
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