ARTIFICIALLY GENERATED BI-EPITAXIAL YBCO GRAIN-BOUNDARY JUNCTIONS ON SRTIO3 AND SAPPHIRE SUBSTRATES

In this work we present the fabrication and characterization of artifi cially generated bi-epitaxial YBCO grain boundaries on SrTiO3 and buff ered R-plane sapphire. The grain boundary is obtained by partly interp osing a MgO seed layer between a bare or buffered substrate and a CeO2 layer. We find that the structural perfection of the YBCO films decre ase as the complexity of the stacking sequence increases. By comparing the structural properties of the YBCO firn on the different stacking sequences with the transport properties of the fabricated devices, we found a strong correlation between the normalized junction resistance rho(N) and the degree of structural perfection in the superconducting film. The electrical behavior of the obtained junctions can be explain ed considering the grain boundary as a Josephson structure where the b arrier transparency is related with the degree of structural and textu ral perfection of each superconducting electrode, justifying the corre lation between the normalized junction resistance and the disorder in the YBCO films.