Interaction among superconducting weak links in a bulk sample of YBaCuO at 77 K

The DC and AC Josephson effects have been directly observed for a piece of superconducting material about 5 mm*1 mm*0.2 mm which was cut from a bulk sample of Y/sub 1/Ba/sub 2/Cu/sub 3/. the I-V (current voltage) characteristics were similar to those of a microbridge. When the sample was irradiated by 35.6-GHz microwaves, about 30 Shapiro steps on the I-V curves were observed at 77 K. Microwave-induced steps at both n(hf/2e) and 2n(hf/2e) were coexistent in the sample. It was found that the step width is not always consistent with the Josephson I-V relation. This phenomenon might result from complex interaction among a variety of superconducting links in the bulk sample of Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub y/.<
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