YBa2Cu3O7 thin‐film step junctions on MgO substrates

Josephson junctions have been made by the evaporation of epitaxial YBa2Cu3O7 over steps etched in (001) MgO. Such junctions differ from those grown on perovskite substrates in that the c‐axis of the film grows approximately normal to the local substrate surface, so the junction comprises two tilt grain boundaries. Results are reported for junctions formed by this process which showed Josephson currents at temperatures up to 89 K and resistively shunted junctionlike current‐voltage curves. A weak magnetic field applied normal to the substrate gave Fraunhofer patterns indicative of good current uniformity across the junction. The dc SQUIDs show deep modulation, and promising noise performance.