OBSERVATION OF MICROSCOPIC CURRENTS IN SUPERCONDUCTING CERAMICS

The microscopic screening currents circulating in the grains of the ce ramic high-T-c superconductor YBa2Cu3O7-delta in a magnetic field are visualized by computing the current density with high spatial resoluti on of more than 10(6) pixels from magneto-optic images taken at the sp ecimen surface with the same high resolution. Having solved several te chnical and mathematical problems, we can visualize the supercurrent d ensity distribution inside and between the grains of a macroscopic pol ycrystalline specimen and make quantitative statements. Our method may thus be used to optimize the current-carrying capability of supercond ucting ceramics. [S0163-1829(98)09817-8].