PROPERTIES OF HIGH-T-C JOSEPHSON-JUNCTIONS WITH Y0.7CA0.3BA2CU3O7-DELTA BARRIER LAYERS

We report the use of Y0.7Ca0.3Ba2CU3O7-delta as an epitaxial barrier between YBa2Cu3O7-delta (YBCO) electrodes in high-T-c superconductor-normal-superconductor edge junctions. Ca-doped YBCO is an overdoped version of YBCO, and it has an excellent lattice and thermal expansion match with YBCO. We show that these junctions exhibit clean interfaces with resistances smaller than 10(-10) Omega cm(2). We present the temperature dependence of the critical current density J(c) and the junction resistance R(n) for junctions with 200, 400, and 600 Angstrom thick barriers of Y0.7Ca0.3Ba2Cu3O7-delta. As the temperature decreases, the resistance of the junction decreases faster than the resistance calculated from the resistivity of a Y0.7Ca0.3Ba2Cu3O7-delta film. We analyze our data by considering various possibilities for the microstructure in the barrier region. We discuss the ideal conventional proximity effect, diffusion between the barriers and the electrodes, and doping fluctuations inside the barrier. We find that combinations of these ideas explain the observed behavior with reasonable parameter.