Measurement of perpendicular magnetic field dependence of the Josephson current by a three-dimensional scan of the external magnetic field

Abstract

Previously, we have investigated a perpendicular magnetic field dependence of Josephson current through Nb/Al-AlOx/Nb junctions, and have found that the Josephson current was irreversibly-modulated when a strong magnetic field was applied in the direction perpendicular to the junction plane. In the present study, we have investigated this perpendicular magnetic field dependence of Josephson current in detail by applying parallel magnetic fields (Hx, Hy) and a perpendicular magnetic field Hz from three directions. A main peak of Fraunhofer diffraction pattern in Ic-(Hx, Hy) characteristics shifted from the origin of (Hx, Hy) plane when the perpendicular magnetic field Hz was applied in the Josephson junction. Furthermore, the main peak did not return to the origin of the (Hx, Hy) plane even though the magnetic field Hz was removed. This meant that the magnetic flux was trapped in a superconducting thin film by application of the magnetic field Hz.