New possibilities for niobium-based Josephson tunneling

Preparation of high quality Nb/ZrOx/Pb and Nb/TiOx/Pb Josephson tunnel junctions based on single-crystal niobium thin films is reported. Vm values up to 70 mV, as measured at 4.2 K, were obtained as a result of thermal oxidation of the freshly coated surfaces. The specific capacitance of these junctions varies from 0.010–0.022 pF/μm2, as determined from Fiske modes and the Josephson diffraction patterns. The use of added thermally oxidized metallic coatings on single-crystal Nb surfaces is shown to modify the tunneling parameters systematically and to offer new possibilities for fabricating all refractory metal Josephson devices.