DISTRIBUTION OF THE CRITICAL-CURRENT DENSITY AND FLUX TRAPPING IN YBA2CU3O7-DELTA RAMP-EDGE JOSEPHSON-JUNCTIONS

We have studied the spatial distribution of the critical current densi ty in YBa2Cu3O7_delta ramp edge Josephson junctions using low-temperat ure scanning electron microscopy. Applying this technique allows the i maging of the critical current density distribution with a spatial res olution of about 1 mu m. Our measurements show that the geometry of th e ramp-edge junction eases the trapping of magnetic flux quanta in the YBa2Cu3O7_delta layer covering the ramp edge. These trapped flux quan ta result in a spatially inhomogeneous magnetic field parallel to the barrier layer, which in turn results in a spatially modulated supercur rent density and an unusual magnetic field dependence of the critical current.