超電導体における磁束ピンニングの実験研究に関する最近の問題点

Abstract

A review is given on recent topics on experimental studies of flux pinning in superconductors, while theoretical problems were discussed in the preceding review article. Here we compare experimental results with theories on the elementary pinning force and the summation problem.Quantitative comparison of the elementary pinning force is not possible at this moment because of ambiguity in the summation theory. The dependence of the specific pinning force of grain boundaries on the impurity parameter shows a similar tendency to the calculations by Zerweck, Yetter et al., and Welch based on the electron scattering mechanism. This observed tendency is different from the prediction from the microscopic theory of Thuneberg. The summation theories are compared with experiments within a regime of strong pinning where conventional calculation of the elementary pinning force holds safely. Observed pinning forces seem to obey the linear summation derived from the mean field approximation theory.The other topics such as the saturation phenomenon and the strain scaling are also discussed.