Properties of (Hg,Re)Ba2CaCu2Oy -tilt bicrystal grain boundary Josephson junctions on buffer layers
Abstract:(Hg0.9Re0.1)Ba2CaCu2Oy [(Hg, Re)-1212] grain boundary Josephson junctions have been fabricated on SrTiO3 (STO) -tilt bicrystal substrates with thin CeO2 and Y0.9La0.2Ba1.9Cu3Oy (YLBCO) buffer layers. These buffer layers effectively suppressed the formation of undesirable precipitates, which existed along the grain boundaries in (Hg, Re)-1212 films directly fabricated on STO bicrystal substrates without a buffer layer. The junctions on both the buffer layers exhibited resistively shunted junction (RSJ)-type current–voltage (I–V) characteristics and more homogeneous current distribution than those for the junctions on the STO bicrystal substrate. For the junctions on the YLBCO buffer layers, RSJ-type I–V curves were observed at temperatures up to 112–114 K, being very close to the film Tc of 115–117 K, while a substantially lower junction Tc was observed for those on the CeO2 buffer layers. The junctions on YLBCO exhibited more systematic variations of junction parameters with the misorientation angle than those for the junctions on STO. These results and the reduction of the critical current density with apparently smaller than that for the junctions on STO are probably attributed to no inclusion of precipitates and superior crystallinity near the grain boundaries. The junctions on the YLBCO buffer layers with = 36.8° were found to have a magnitude of Ic suitable for applications to superconducting quantum interference devices (SQUIDs) at temperatures higher than 77 K. The dc SQUIDs fabricated using such junctions exhibited voltage–flux modulation at temperatures up to 110 K.
Document Type: Research Article
Publication date: June 1, 2005