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 b etween YBa2Cu3O7-delta (YBCO) electrodes in high-T-c superconductor-no rmal-superconductor edge junctions. Ca-doped YBCO is an overdoped vers ion of YBCO, and it has an excellent lattice and thermal expansion mat ch with YBCO. We show that these junctions exhibit clean interfaces wi th resistances smaller than 10(-10) Omega cm(2). We present the temper ature dependence of the critical current density J(c) and the junction resistance R(n) for junctions with 200, 400, and 600 Angstrom thick b arriers of Y0.7Ca0.3Ba2Cu3O7-delta. As the temperature decreases, the resistance of the junction decreases faster than the resistance calcul ated from the resistivity of a Y0.7Ca0.3Ba2Cu3O7-delta film. We analyz e our data by considering various possibilities for the microstructure in the barrier region. We discuss the ideal conventional proximity ef fect, diffusion between the barriers and the electrodes, and doping fl uctuations inside the barrier. We find that combinations of these idea s explain the observed behavior with reasonable parameter.