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 YBa{sub 2}Cu{sub 3}O{sub 7} films. The bridges have a length scale down to {ital L}{congruent}500 A. Supercurrents were observed to flow across the bridge structures with critical current densities up to {ital J}{sub {ital c}}{congruent}1.3{times}10{sup 9} A/cm{sup 2}, 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 {xi}{much lt}{ital L}{le}{Lambda}, with {xi} the coherence length and {Lambda} the London penetration depth. The highest {ital J}{sub {ital c}} is in good agreement with the critical depairing mechanism.