Flux distributions of an artificially granular YBa 2Cu 3O 7− δ thin film observed using magneto-optic imaging

Abstract

Flux distributions in a YBa 2Cu 3O 7− δ thin film with artificial granularity are observed by means of magneto-optic imaging. At low magnification, flux patterns generated exclusively by the intergranular currents flowing in the intergranular area (“effective medium”) are directly observed. The properties of this effective medium are studied by taking flux density profiles that reveal the intergranular current density. As the observations at high magnifications show the flux penetration and pinning within the individual disks, we can identify and study the different contributions of the intergranular and intragranular current densities to the flux patterns. We show that our model sample reproduces several features observed, e.g., in Ag-sheathed (Pb,Bi) 2Sr 2Ca 2Cu 3O 10+ δ tapes.