Perpendicular applied magnetic field dependence of Josephson current and measurement of trapped magnetic flux in Nb superconducting thin film by vibrating sample magnetometer

Abstract

We found hysteresis in Josephson current when sufficiently strong magnetic field Hz is applied in the direction perpendicular to the junction plane. This is because the magnetic flux is trapped in a superconducting thin film. So, we fabricated the simplified vibrating sample magnetometer, and we have measured the trapped magnetic flux in Nb superconducting thin film by vibrating the sample near the search coil. When a perpendicular magnetic field Hz was applied to the sample, many vortices were trapped in the perimeter of the sample. However, when a perpendicular applied magnetic field Hz was removed, many vortices were trapped in the central part of the sample. Furthermore, we confirmed that Josephson current was modulated by the parallel magnetic field generated by the vortices.

Two-dimensional magnetic field dependence of Josephson current and resonant current steps at finite voltage of square shape superconducting tunnel junctions

“…13 In the case adding the magnetic field H z perpendicular to the junction plane, the I c -H z dependences had hysteresis phenomena. 14,15 After adding the H z field and depressing the I c value, by the method of alternating the H z field, recovering the critical value of the Josephson current can be performed. 15 At finite voltage in the current-voltage characteristics, the resonant current steps were observed, [16][17][18] which was used to estimate the capacitance per unit area 1 and was also able to be used as Josephson analog amplifier.…”