High-magnetic-field critical currents in thin films of YBa₂Cu₃O₇

Abstract

Critical current densities measured in bulk high-T_c superconductors are low, and fall dramatically in applied magnetic fields¹. This has raised doubts about the future use of high-T_c materials in superconducting machines and magnets. Thin films are known to perform much better in the absence of fields, but the effect of large magnetic fields on their critical currents has not been reported. Here we present measurements on high-quality polycrystal-line thin films, which demonstrate that technologically useful current densities can be sustained at 77 K in high fields. The critical current density is strongly dependent on the direction of the applied field, reflecting the crystallographic anisotropy. Our results show that the material required to make high-field magnets will need to be crystallographically orientated, but not necessarily mono-crystalline.