Nucleation of Superconductivity in Tantalum in a Decreasing Magnetic Field

Abstract

Measurements of the surface nucleation field ${H}_{c3}$ and the bulk supercooling field ${H}_{\mathrm{sc}}$, made on pure tantalum, show that these fields are identical only when $\ensuremath{\kappa}<0.39$, and that measurable supercooling occurs at all temperatures between ${T}_{c}$ and 1.4\ifmmode^\circ\else\textdegree\fi{}K. The measurements verify qualitatively the recent theoretical work of Park. Nearly ideal supercooling of the bulk cylindrical samples is achieved by using small auxiliary-field coils to field coils to eliminate nucleation at the sample ends. A new value for the Ginzburg-Landau parameter of the pure metal ${\ensuremath{\kappa}}_{0}=0.340\ifmmode\pm\else\textpm\fi{}0.01$ is derived from the data.