Modulation characteristics of a Josephson current are usually measured by applying the external magnetic field parallel to the junction plane from one direction, and uniformity in tunnel barrier is discussed. So far, we have measured two-dimensional magnetic field dependence of a square Josephson junction by independently scanning the magnetic field (Hx,Hy) parallel to the junction plane from two directions. We can get a lot of information about spatial critical current distribution in a Josephson junction by observing the magnetic field dependence of a Josephson junction in two dimensions. This time, we have fabricated the different-shaped Josephson junctions and investigated the shape dependency of two-dimensional magnetic field dependence of a Josephson junction. We observed the Ic-(Hx,Hy) characteristics of triangular, hexagonal, and circular Josephson junctions quite different from the Ic-(Hx,Hy), characteristics of a square Josephson junction. Furthermore, we simulated two-dimensional magnetic field dependence of a Josephson junction by calculating the superconducting current density distribution in each magnetic field. The simulation results agreed well with experimental results.

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.

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