YBCO JOSEPHSON-JUNCTIONS BASED ON ARTIFICIALLY GENERATED BIEPITAXIAL GRAIN-BOUNDARY

In this paper we report the in-plane fabrication and the characterizat ion of artificially engineered biepitaxial grain boundaries (GB) obtai ned by partly interposing a MgO seed layer between a bare or even-buff ered substrate and a Ce(O)2 thin layer. The main peculiarity of this t echnique can be summarized by the capability to locate and engineer a single 45 degrees-tilted GB at any stage of the device preparation. Th e junctions, realized by patterning the grain boundary occurring in th e overhanging YBCO film, show Josephson current modulation in a large temperature range with an I(c)R(n) value of about 200 mu V at 4.2 K, t he R(n) value being constant over the whole superconducting region. Un der microwave irradiation, the I-V characteristics display several Sha piro steps while, according to the Resistively Shunted Junction (RSJ) behaviour, the step heights have the typical current biased junction d ependence.