Evaluation of supercurrent distribution in high-T-c superconductor by scanning SQUID microscopy

Scanning SQUID microscope (SSM) is a powerful tool for observing small magn etic flux. It measures the z-component signal of flux density, but it is al so available for observation of current distribution by inverting the Biot- Savart's law. We report the two-dimensional vector mapping of current distr ibutions in high-T-c superconducting YBa2Cu3O7-gamma (YBCO) thin films obta ined by converting magnetic-field data measured by SSM. The current distrib ution contains those from both transport supercurrent and vortex current. T he transport supercurrent is found to flow mainly along the edge of a strip line. The results are in good qualitative agreement with the calculated res ults based on simple London model, The YBCO films with an artificial grain boundary, i.e. Josephson boundary are also observed. The transport current seems to flows with avoiding the vortices, and an irregular vortex is obser ved at a point of grain boundary. (C) 2001 Elsevier Science B.V. All rights reserved.