Magneto-optical studies of flux pinning in high-temperature superconductors

Abstract

Quantitative magneto-optical imaging of magnetic flux distributions has developed in a powerful tool for the analysis of the local transport properties of superconductors. It allows a model-independent determination of the current density distribution of thin films and, thus, the local current density through individual defects. Also, local metastable properties are detectable, such as the local electric field distribution E with a high sensitivity down to 10 ˇ12 V/m caused by thermally activated flux creep. Based on these tools, in this paper we present a systematic comparison of vortex pinning, vortex movement and current transfer of two kinds of planar defects which are typically present in high-temperature superconducting thin films: low-angle grain boundaries and antiphase boundaries. Special attention is drawn to the local magnetic field dependence of the critical current density and to the spatial distribution of E, giving insight into the collective behavior of vortices at planar defects.