OBSERVATION OF ULTRAHIGH CRITICAL CURRENT DENSITIES IN HIGH-TC SUPERCONDUCTING BRIDGE CONSTRICTIONS

Narrow bridge structures were precisely fabricated (using novel ion-beam-milling techniques) on pulsed-laser-deposited YBa2Cu3O7 films. The bridges have a length scale down to L congruent-to 500 angstrom. Supercurrents were observed to flow across the bridge structures with critical current densities up to J(c) congruent-to 1.3 x 10(9) A/cm2, the highest critical current densities yet reported. The current-density magnitudes are consistent with the Onsager-Feynman vortex-ring-creation mechanism (for producing voltages across narrow constrictions) in the length scale region of zeta << L less-than-or-equal-to LAMBDA, with zeta the coherence length and LAMBDA the London penetration depth. The highest J(c) is in good agreement with the critical depairing mechanism.