Critical currents of cross-type superconducting-normal-superconducting junctions in perpendicular magnetic fields

Abstract

The maximum supercurrent that can be carried in an applied perpendicular magnetic field by a superconducting--normal-metal--superconducting (SNS) junction consisting of a square normal-metal layer sandwiched between two crossed perpendicular superconducting strips is investigated theoretically and experimentally. For weak applied fields the critical current is suppressed reversibly, as induced Meissner screening currents flow into the SNS sandwich and generate a spatially varying magnetic field largely parallel to the junction, thereby altering the local phase difference. For stronger applied fields the critical current is changed irreversibly as vortices enter and become pinned in the junction. When the pinned vortices in the two superconductors are misaligned, the local magnetic field, which flows mostly parallel to the junction in carrying magnetic flux ${\ensuremath{\varphi}}_{0}$=hc/2e from one vortex to the other, strongly alters the phase difference across the junction near the two vortices. The theory predicts complex patterns of the supercurrent density, which should be directly observable using laser or electron-beam scanning techniques.