Flux Penetration and Overcritical Currents in Flat Superconductors with Irradiation-Enhanced Edge Pinning: Theory and Experiment

Abstract

Penetration of perpendicular magnetic flux into a ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}\mathrm{Ca}{\mathrm{Cu}}_{2}{\mathrm{O}}_{8+}\ensuremath{\delta}$ single crystal platelet with irradiation-enhanced pinning in its edge zone is observed by magneto-optics. When the flux front reaches the inner boundary of the irradiated zone, magnetic flux leaks to the center and then gradually fills the unirradiated zone from the middle. 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 calculations assuming a nonlinear resistivity with different critical current densities in the central and edge zones of a disk or strip.