ac Susceptibility Transition in Type-II Superconductors and Surface Critical Currents

Abstract

The ac susceptibility transition below ${H}_{c3}$ has been investigated as a function of ac field amplitude, in cylindrical samples of Pb-Bi alloys ($l<~\ensuremath{\kappa}<~5$). Converting the ac fields to critical surface currents ${J}_{c}$ permits comparison with the values calculated by Abrikosov and Park. The present results agree with those of Swartz and Hart, and of Rollins and Silcox. Although above ${H}_{c2}$ the qualitative behavior is similar to the theoretical calculations, the magnitudes are found to be lower. At ${H}_{c2}$ a sharp break is found in ${J}_{c}$, as reported previously. $\frac{{J}_{c}\ensuremath{\kappa}}{{H}_{c}}$ is found to be independent of $\ensuremath{\kappa}$ within experimental error. Surface roughness and slight sample misalignment could have lowered the observed ${J}_{c}$.