FABRICATION AND CHARACTERIZATION OF YBCO JOSEPHSON-JUNCTIONS BASED ONARTIFICIALLY GENERATED BI-EPITAXIAL GRAIN-BOUNDARY

In this paper we report the thin-film in-plane fabrication and the str uctural characterization of artificially engineered grain boundaries o btained by partly interposing an MgO seed layer between the SrTiO3 (ST O) substrate and the CeO2 buffer layer. X-ray pole figures show that f ilms grown onto the seed layer are slightly disordered with respect to the remaining part of the sample. The junctions, realized by patterni ng the grain boundary occurring in the overhanging YBCO film show Jose phson current modulation in a large temperature range with an I(c)R(n) value of about 230 mu V at 9 K, the R(n) value being constant over th e whole superconducting region. Under microwave irradiation, the I-V c haracteristics display several Shapiro steps while in accordance with the resistively shunted junction (RSJ) behavior, the step heights have the typical current-biased junction dependence.