FABRICATION AND SUPERCONDUCTING TRANSPORT-PROPERTIES OF BICRYSTAL GRAIN-BOUNDARY JOSEPHSON-JUNCTIONS ON DIFFERENT SUBSTRATES

We have reproducibly fabricated YBa2Cu3O7-delta (YBCO) grain boundary Josephson junctions (GBJs) on SrTiO3 and MgO bicrystals as well as by introducing buffer layers between the c-axis oriented YBa2Cu3O7-delta, film and the SrTiO3 bicrystal substrate. For the additional layers nonsuperconducting Nd1.85Ce0.15CuOx (NCCO) and NdGaO3 were used. The effect of the layer structure on the superconducting transport properties of the GBJs was analyzed by measuring the current-voltage characteristics (IVCs), their derivatives, the resistive transition R(T), and the magnetic field dependence of the critical current I-c(B). YBCO-GBJs fabricated on MgO and SrTiO3 bicrystal substrates were found to have very similar low frequency characteristics. Fiske resonances were investigated to obtain information on the high-frequency properties. The Swihart velocity was found to be considerably smaller for GBJs fabricated on SrTiO3 as compared to MgO due to the large relative dielectric constant of SrTiO3 and the related stray capacitance.