Current densities in low-angle grain boundaries of YBCO

Magnetooptical imaging has been used to investigate low-angle grain boundar ies (LAGB's) in YBCO thin films at T = 5 K. This technique allows us to vis ualize the flux density distribution with a spatial resolution of a few mic rometers. By a numerical analysis of the experimental data the local curren t distribution in a LAGB has been determined. It is shown that the current density across the grain boundary depends strongly on the local Aux density which leads to a crossover in the pinning scenario at the LAGB.