Tunneling Characteristics of YBaCuO/MgO/Pb Planar Tunnel Junctions and Observation of Josephson Effect

Abstract
The measurements on reproducible YBa2Cu3O y (YBCO)/MgO/Pb planar tunnel junctions by an in situ fabrication technique are reported. A thin MgO (1.8–6.0 nm) is used as an insulating barrier. The observed tunnel characteristics exhibit a gap opening structure around 20 mV and the zero bias anomaly, similar to those of YBCO/MgO/Au tunnel junctions as previously reported. For junctions with low tunnel resistance, Josephson current is observed. Josephson critical current against external magnetic field exhibits a Fraunhofer-like pattern. Shapiro steps are also observed under microwave irradiation.

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