Multiple-Transition Effects in Superconducting Filamentary Crystals of Tin

Citation

Webb, Donald Harris (1965) Multiple-Transition Effects in Superconducting Filamentary Crystals of Tin. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/F2A2-M776. https://resolver.caltech.edu/CaltechETD:etd-01272004-085635

Abstract

This paper reports some interesting effects involving stepped transitions from the superconducting to the normal state, and vice versa in filamentary crystals (whiskers). The problem, as conceived when the experiments were undertaken, was to study the behavior of critical-field curves and the hysteresis effect, in a broader region of temperature and field than previously reported, and to compare results with calculations made according to the Ginzburg-Landau theory. The crystals were produced by extrusion under high pressure from plates of tin, and mounted on glass; the transitions were observed by measuring voltage across the samples, as they passed through the transition induced by varying the temperature in a constant external magnetic field.

Contrary to what had been expected, the resistance was observed to change from zero to normal, and vice versa, in discrete steps. In each particular stage of the transition, the resistance was apparently constant even though the temperature was continuously changing. The new effect was most prominently evinced when the sample axis was inclined slightly to the field. The effect was found only in the first-order transition region.

The conjectured interpretation proceeds along the lines of work of Little and Parks, who first found evidence of quantized Abrikosov vortex lines in the intermediate state of filamentary samples. In further corroboration of this hypothesis, the dependence of the new effect on angular orientation was investigated. The data regarding the upper limit of transition regions are consistent with predictions of Tinkham, calculated on a vortex-line model. The lower limit of transition regions was found to be irregular and not very sensitive to field orientation. If the proposed interpretation is correct, then we have a more clear-cut verification of quantized vorticity than what has been previously reported--first, because the observed jumps are sharp; secondly, because they are observed (generally) throughout the intermediate state, not merely in the limit where R/R_N is small.

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