Magnetic flux dynamics in inhomogeneous high-T c superconductors in weak fields

Abstract

Features of magnetic flux dynamics in samples of the high temperature superconductor YBa 2Cu 3O x have been experimentally investigated in weak magnetic fields (10 −3−1 Oe) and at 77K. The experiments were carried out in a sample arrangement including a field coil, a flat sample perpendicular to the field, and an RF-SQUID along a common axis. Samples of both high and low quality thin films, as well as polycrystalline ceramics were investigated. Attention is focused on the inhomogeneous thin film, which show unusual “flux jumps” for small field changes. We find strong evidence for abrupt penetration of flux to the center of the samples. Such behavior, which would be expected within ‘spin-glass” like models, is also found in other inhomogeneous type-II superconductors.