Restoration of the Josephson Current by Applying a Vertical Magnetic Field

We studied the modulation characteristics of the Josephson current through the Nb/Al-AlOx /Nb tunnel junction by applying an external magnetic field parallel to the junction plane two-dimensionally. We can obtain much information about uniformity in a tunnel barrier through a two-dimensional scan of the external magnetic fields. Furthermore, we also studied the modulation characteristics of the Josephson current when the magnetic field is applied in the direction perpendicular to the junction plane. The Josephson current is reduced when the strong perpendicular magnetic field is applied to the Josephson junction because the magnetic flux is trapped in Nb superconducting thin film. In this paper, we attempt to restore the reduced Josephson current due to the trapped magnetic flux by applying the alternating magnetic field perpendicular to the junction plane. When the perpendicular magnetic field of 150 A/m was applied to the Josephson junction and then the perpendicular magnetic field of 150 A/m was removed, the Josephson current was reduced from 0.6 to 0.45 mA. We restored the Josephson current to 0.5 mA by applying the alternating magnetic field of 100 A/m in the direction perpendicular to the junction plane.