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

The magnetic flux distribution from a transport superconducting current flowing through an YBa2Cu3O7 (YBCO) thin film bridge is observed using 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 reduces the electrically measured critical current compared with the value that could be reached without macroscopic defects. The observed reversibility of the main part of the sample is explained on the basis of theoretical calculations of the current-induced flux penetration: Perceptible penetration and trapping of the flux might be observed only upon the application of a current higher than approximately half the maximum critical current that could be reached in such a thin film without macroscopic inhomogeneities.