NOISE STUDY OF A HIGH-T-C JOSEPHSON-JUNCTION UNDER NEAR-MILLIMETER-WAVE IRRADIATION

Noise studies of both the de and ac Josephson effects have been perfor med on a high-T-c ramp-type Josephson junction irradiated at 176 GHz. Well-established analytical results for noise in overdamped RSJs are u sed to model the measured I-V characteristics, and their agreement is excellent. Noise-rounded I-V curves at the critical current and the fi rst and second Shapiro steps under coherent 176 GHz radiation have bee n studied in detail at several temperatures and rf power levels. The n oise temperatures inferred from these simulations are close to the phy sical temperatures. An increase of noise temperatures at high radiatio n power levels is a result of radiation heating, which could be due to a bolometric effect.