ENHANCEMENT OF CRITICAL-CURRENT AND MAGNETIC-FIELD IN A DEFECTED JOSEPHSON TUNNELING JUNCTION

Abstract

A Josephson junction with a length of 10 times the Josephson penetration depth (lambda(J)) and a defect size of 0.5 lambda(J) to 2 lambda(J) in different positions has been studied by a mechanical simulation. It was found that the defect modulated the current distribution tremendously when it was near the edge of the junction. A surprising enhancement of the critical current under the field was observed when the defect was located at 0.5 lambda(J) and had a size from 0.5 lambda(J) to 2 lambda(J), which was much larger than the conventional pinning size: the coherent length xi. This effect could be attributed to a self-field, which was either generated by the current itself or by the applied magnetic field, penetrating into the defect smoothly and being pinned at the defect. A repulsive interaction between the self-field and the external field kept any further flux from abruptly penetrating into the junction. The increment in the critical current under the applied field was up to 125% of the original defect-free one. By fitting two defects of the same size of 2 lambda(J) and positioning them at 0.5 lambda(J) to both edges of the junction, the zero field critical current and the critical magnetic field were enhanced up to 150% of a defect-free junction.