CRITICAL-CURRENT IN YBCO THIN-FILM BRIDGE STUDIED USING MAGNETOOPTIC TECHNIQUE

The magnetic flux distribution from a transport superconducting curren t flowing through an YBa2Cu3O7 (YBCO) thin film bridge is observed usi ng a ferrimagnetic garnet indicator with in-plane magnetic anisotropy. After switching off the current from the maximum value that provides the electrically detected critical regime, the expected remanent flux was not observed. The only place where the irreversible magnetization takes place is a linear defect that crosses the bridge and thus reduce s the electrically measured critical current compared with the value t hat could be reached without macroscopic defects. The observed reversi bility of the main part of the sample is explained on the basis of the oretical calculations of the current-induced flux penetration: Percept ible penetration and trapping of the flux might be observed only upon the application of a current higher than approximately half the maximu m critical current that could be reached in such a thin film without m acroscopic inhomogeneities.