FLUX-PENETRATION AND OVERCRITICAL CURRENTS IN FLAT SUPERCONDUCTORS WITH IRRADIATION-ENHANCED EDGE PINNING - THEORY AND EXPERIMENT

Penetration of perpendicular magnetic flux into a Bi(2)Sr(2)CaCu(2)O(8 +)delta single crystal platelet with irradiation-enhanced pinning in i ts edge zone is observed by magneto-optics. When the flux front reache s the inner boundary of the irradiated zone, magnetic flux leaks to th e center and then gradually fills the unirradiated zone from the middl e. We observe vortex motion against the flux-density gradient (driven by the vortex curvature) and large ''overcritical'' Meissner currents in the flux-free zone. The measured flux profiles agree with planar ca lculations assuming a nonlinear resistivity with different critical cu rrent densities in the central and edge zones of a disk or strip.