SUPERCONDUCTING TRANSPORT CHARACTERISTICS OF YBA2CU3O7-DELTA GRAIN-BOUNDARY JUNCTIONS

We report on the superconducting transport characteristics of YBa2Cu3O7-delta grain boundary junctions (GBJs) fabricated by laser ablation deposition on SrTiO3 bicrystals. For narrow GBJs with a width smaller than about 4 times their Josephson penetration depth, the current-voltage characteristics can be modeled closely by the resistively shunted junction (RSJ) model and the magnetic field dependence of the critical current is Fraunhofer pattern like. The temperature dependence of the critical current is proportional to (1 - T/T(c))2 close to T(c). The characteristic voltages V(c) = J(c)gb rho-N, where J(c)gb is the critical current density and rho-N the normal resistance times unit area of the GBJs, range between 0.2 and 8mV at 4.2K and scale proportional to (1/rho-N)1.5. The transport characteristics of the GBJs are in agreement with a SNINS-type junction model.