Modulation Characteristics of DC Josephson Current Through Nb Tunnel Junction by Applying External Magnetic Field in Perpendicular Direction
Perpendicular magnetic field dependences of the Josephson current through tunnel junction were first measured. Niobium/aluminum-oxide/niobium (200/5/150 nm in thickness) superconducting tunnel junctions were fabricated by DC-magnetron apparatus with a load-lock chamber. Josephson current Ic through the superconducting junction is usually changed by the external magnetic field in one direction to check the barrier uniformity. To obtain more information of the barrier uniformity, we have changed the external magnetic field in two directions (Hx and Hy : parallel field to the junction plane) parallel to the junction plane. The shape of Ic -Hx curve and Ic -Hy curve were the Fraunhofer pattern in the Ic -Hx -Hy dependence of the junction with uniform barrier. This Ic -Hx -Hy dependence has no hysteresis. In this study, we have first applied the external magnetic field Hz perpendicular to the junction plane and have obtained Ic -Hz characteristics using three pairs of Helmholtz coils. In the case that the perpendicular field Hz < 2400 A/m, the Ic -Hz characteristics have a little hysteresis. The shape of Ic -Hz characteristics was similar to the Fraunhofer pattern. In the case that the perpendicular field Hz > 2400 A/m, the Ic -Hz characteristics have strong hysteresis. The Josephson current Ic always disappeared in the case that Hz > 7000 A/m. Two recovering methods of this current Ic were (a) alternating Hz field and (b) heating the sample to the room temperature and again cooling to the liquid He temperature.
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Document Type: Research Article
Publication date: 2012-06-01
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