Vortex Motion Modulated by a Self Field in a Large Josephson Junction

Motion of a vortex array (flux flow) in a large Josephson junction is studied both theoretically and experimentally. An expression for dc current-voltage (I-V) characteristics of a large junction in a flux-flow state, which is caused by the external dc magnetic field and current, is obtained by taking account of the self field due to the dc current through the junction as well as the large loss due to the surface resistance of junction electrodes. It is shown that the spacially uniform flux flow is crucially modulated by the self field in a high-velocity region of the flux flow. As a result, the magnitude of the current peak in I–V curves decreases significantly and saturates with respect to both the length and the quality factor of the junction, which is confirmed by experiments with large Pb-PbxOy-Pb junctions.