Resistance Transitions in Superconducting Tantalum

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Abstract
A study has been made of the superconducting to normal transition in outgassed tantalum wires induced by the application of an external longitudinal magnetic field. It was found that in most cases the transition, as determined from resistance measurements, consisted of an almost discontinuous appearance of resistance; followed by a rather gradual rise in resistance until the full residual resistance was restored. Flux measurements showed that the sharp portion of the transition corresponded to the magnetic, or "bulk" transition. The behavior of the broad portion of the transition was of the type commonly associated with superconducting "filaments." Although the "filamentary" properties were found to be extremely sensitive to localized contamination and the thermal history of a specimen, they did not appear to depend exclusively on such inhomogeneities, and a systematic variation with residual resistance could be discerned. Plastic deformation altered the characteristics only in proportion to the corresponding increase in residual resistance. A small amount of supercooling which was independent of the "filamentary" phenomena was sometimes observed in the "bulk" transition.

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