Current-phase relationship of YBa2Cu3O7-x ramp-edge josephson junctions

The current-phase relation (CPR) of high-T-c ramp-edge Josephson junctions (YBa2Cu3O7-x/PrBa2Cu3O7/YBa2Cu3O7-x) was investigated experimentally in the temperature range 65 < T < 85 K. The investigated junctions were incorporated into a washer-shaped superconducting loop with inductance L approximate to 80 pH forming a single-junction interferometer. The CPR was obtained from the measurement of the impedance of the phase-biased junction. We show that, for junctions with sufficiently small critical current I-c, the CPR is sinusoidal. In the case of larger critical current, deviations of the apparent CPR from sinusoidal dependence were found. These deviations can be described by thermal fluctuations of the magnetic flux in the loop. So we conclude that, for all investigated junctions, the "true" CPR is sinusoidal. (C) 2000 American Institute of Physics. [S0003-6951(00)03501-4].