Distribution of the critical current density and flux trapping in YBa ₂Cu₃O_7-δ ramp-edge Josephson junctions

We have studied the spatial distribution of the critical current density in YBa₂Cu₃O_7-δ ramp edge Josephson junctions using low-temperature scanning electron microscopy. Applying this technique allows the imaging of the critical current density distribution with a spatial resolution of about 1 μm. Our measurements show that the geometry of the ramp-edge junction eases the trapping of magnetic flux quanta in the YBa₂Cu₃O_7-δ layer covering the ramp edge. These trapped flux quanta result in a spatially inhomogeneous magnetic field parallel to the barrier layer, which in turn results in a spatially modulated supercurrent density and an unusual magnetic field dependence of the critical current.