SUBMILLIMETER WAVE RESPONSE OF A HIGH T(C) SUPERCONDUCTING MICROBRIDGE

We observed the ac Josephson effect, the "Shapiro step," at the high frequency of 584 GHz in an YBa2Cu3O7-delta grain boundary Josephson junction at 4.2 K for the first time. This Shapiro step grew to about 8% of the critical current without irradiation. We also noted that the critical current was gradually suppressed with increasing power. The critical current with irradiation was suppressed to about 97% of the critical current without irradiation. Detailed investigation revealed the consistency between the above two phenomena.