YBa2Cu3O7−δ Josephson junctions on directionally ion beam etched MgO substrates

Shallow, 1–40 nm deep steps were ion beam milled at 60° angle of incidence to the normal of the MgO substrate in order to form Josephson junctions. Microbridges were patterned across the step boundary in films of YBa2Cu3O7−δ. They displayed critical current densities and critical current-normal resistance products that, on the whole, decreased with increasing step height, leveling off at about 5 nm. Transmission electron microscopy showed the presence of 45° [001]-tilt regions in the films close to the steps. Interferometers (dc-SQUIDs) showed magnetic field response at temperatures above 77 K and a noise level of about 1.5×10−8 Φ02/Hz at 10 Hz and 4.2 K.