Influence of the Al thickness of Nb/Al-AlOx/Nb Josephson junction on the magnetic field dependence of the Josephson current

Abstract

We have fabricated Nb/Al-AlOx/Nb Josephson junctions and have measured their current-voltage characteristics and the two-dimensional magnetic field dependence of the Josephson current. When the external magnetic fields (Hx, Hy) parallel to the junction plane are applied to the Josephson junction from two directions, two Fraunhofer diffraction patterns are observed in the (Hx, Hy) plane. In this study, we have fabricated several Nb/Al-AlOx/Nb Josephson junctions with different thicknesses of Al layer and have investigated the effect of the Al layer thicknesses on the two-dimensional magnetic field dependence of the Josephson current. The thicknesses of the Al layers in the Josephson junctions we fabricated are 5 nm, 25 nm, 50 nm, 100 nm and 200 nm. When the Al layer thickness was 5 nm and 25 nm thick, a subpeak of the Fraunhofer diffraction pattern was clearly observed. However, the subpeak of the Fraunhofer diffraction pattern was not obviously observed as the Al layer got thicker. In particular, when the Al layer was 200 nm thick, the subpeak of the Fraunhofer diffraction pattern was not observed at all.