We measured the two-dimensional magnetic field dependence of a Josephson current by applying external magnetic fields H_x and H_y parallel to the plane of a Nb/Al-AlO_x/Nb Josephson junction from two directions. In addition, we measured the modulation characteristics of the Josephson current by applying a magnetic field H_z in the direction perpendicular to the plane of the junction. When the perpendicular magnetic field H_z was applied to the Josephson junction and removed, the main peak of the Fraunhofer pattern did not return to the origin of the (H_x, H_y) plane completely because the magnetic flux was trapped in the Nb superconducting film around the Josephson junction. In the present study, we investigated the influence of the thickness of the base Nb layer on magnetic flux trapping in a Josephson junction by fabricating Josephson junctions with base Nb layers of different thickness. We found that the magnetic flux became increasingly difficult to be trapped in the Nb superconducting thin film with increasing thickness of the Nb superconducting film.

我们通过从两个方向施加平行于 Nb/Al-AlO _x /Nb 约瑟夫森结平面的外部磁场H _x和H _y来测量约瑟夫森电流的二维磁场依赖性。此外，我们通过在垂直于结平面的方向上施加磁场H _z来测量约瑟夫森电流的调制特性。当垂直磁场H _z施加到约瑟夫森结并去除时，弗劳恩霍夫图的主峰没有回到 ( H _x , H _y) 平面完全是因为磁通量被困在约瑟夫森结周围的 Nb 超导膜中。在本研究中，我们通过制造具有不同厚度的基极 Nb 层的约瑟夫森结，研究了基极 Nb 层的厚度对约瑟夫森结中磁通量俘获的影响。我们发现，随着 Nb 超导薄膜厚度的增加，磁通量越来越难以被困在 Nb 超导薄膜中。