CURRENT-PHASE RELATION OF HIGH-T-C BICRYSTAL AND STEP-EDGE JOSEPHSON-JUNCTIONS

The real and imaginary part of the rf impedance of a phase-biased weak link based on YBa2Cu3O7-x thin films mere investigated experimentally at 77K. The investigated weak links: were step-edge or bicrystal Jose phson junctions incorporated into a washer type superconducting ring w ith a small inductance L=80...300pH. The ring was inductively coupled to a tank circuit with a resonant frequency of about 23 MHz. The phase shift alpha between the rf voltage and rf current through the tank ci rcuit was found to be a convenient measure of the change of inductance of a weak link. From the dependence of alpha on the magnetic flux in the ring one can deduce the current-phase relation I(Phi)=I(c)f(phi) o f the weak link The influence of thermal noise on f(phi) was estimated numerically using a Gaussian distribution of the noise amplitude. The experimentally observed dependence alpha(phi) for the bicrystal weak link can be sufficiently good described with f(phi) = sin (phi) and wi th a reasonable value of the noise amplitude. The step-edge junction s hows remarkable deviation from the sinusoidal current-phase relation.