Controllable reduction of J sub c in YBa sub 2 Cu sub 3 O sub (7-delta) films.

The critical current in high quality thin films of the high T sub c superconductor, YBa sub c Cu sub 3 O sub (7-delta) can be controllably reduced by orders of magnitude using ion irradiation. This reduction in J sub c occurs without substantial degradation of T sub c or increase in room temperature resistivity. Using this technique, we have fabricated weak links that exhibit the ac Josephson effect at 77K.