EXPERIMENTAL EVALUATION OF THE NONLINEAR SURFACE-RESISTANCE OF YBA2CU3O7-X STEP-EDGE GRAIN-BOUNDARY JOSEPHSON-JUNCTIONS

The temperature, microwave current, and de magnetic field dependencies of the effective surface resistance R(s) of YBa2Cu3O7-x grain boundar y Josephson junctions have been investigated at 6 GHz. The junctions w ere prepared on stepped LaAlO3 substrates and incorporated into tapere d linear half-wavelength microstrip resonators. The characteristic par ameters of the heterogeneous resonator were analyzed theoretically con sidering the junction as a lumped element of complex impedance. The mi crowave properties of the junction could then be extracted and related to their characteristic de transport properties. The critical current I-c of the junction was found to limit the linear power dissipation i n the superconducting strip. At microwave currents above I-c, highly n onlinear microwave losses occurred, which displayed a characteristic m agnetic field modulation. At even higher currents, R(s) saturated at a level corresponding to the normal resistance R(n) of the junction.