Comparison of Flux Bundle Size between Three-Dimensional Y-123 and Two-Dimensional Bi-2212 Superconductors

Abstract

Flux bundle size is estimated for a three-dimensional bulk Y-123 superconductor prepared by a quench and melt growth process and the result is compared with previously estimated result for a two-dimensional single crystal Bi-2212 superconductor. The longitudinal elastic correlation length along the c-axis, l ₄₄, which was considered to correspond to the longitudinal flux bundle size, was directly measured using the Campbell method. It was shown that this length depends only on the flux pinning strength and is independent of the dimensionality of the superconductor. On the other hand, it was found that the transverse flux bundle size estimated from the observed relaxation rate and l ₄₄ depends on the dimensionality and is likely to take a larger value for a superconductor with higher dimensionality. That is, the typical number of flux lines in the flux bundle is 1 for Bi-2212 and 5 for Y-123. This difference causes a large difference in the pinning potential. This speculation is quite different from the image drawn in the pancake vortex model.