TEMPERATURE-DEPENDENCE OF THE CURRENT-PHASE RELATION FOR YBA2CU3O7-X STEP-EDGE JOSEPHSON-JUNCTIONS

The current-phase relation (CPR) of YBa2Cu3O7-x step-edge Josephson ju nctions was investigated experimentally at various temperatures. The i nvestigated junctions were incorporated into a washer-shaped supercond ucting ring with inductance L similar to 300 pH. The ring was inductiv ely coupled to a tank circuit with a resonance frequency between 9 MHz and 40 MHz. The CPR was obtained from the measurement of the impedanc e of the phase-biased junction. At high temperatures and low critical current the experimentally observed CPR is sinusoidal. The same result s were obtained at low temperatures when the rms flux noise in the rin g is negligible. In the case of larger critical current and finite noi se, deviations of the apparent CPR from sinusoidal dependence were fou nd. The deviations can be described by thermal fluctuations of the mag netic flux in the ring. (C) 1998 American Institute of Physics.