Meissner Effect and Vortex Penetration in Josephson Junctions

Investigation of the magnetic field dependence of the maximum zero-voltage current of wide, high-current Josephson junctions has revealed behavior drastically different from the usual Fraunhofer pattern for narrow junctions. The experiments are interpreted as evidence for a Meissner effect for the insulating layer and adjacent penetration layers of wide junctions in low external fields, and for an eventual transition to a mixed state as the external field is increased from zero.