Dissipation in ultra-thin current-carrying superconducting bridges; evidence for quantum tunneling of Pearl vortices

We have made zero-field current-voltage (IV) measurements of artificially layered high-Tc thin-film bridges. SQUID microscopy of these films provides Pearl lengths Λ longer than the bridge widths, and shows current distributions that are uniform across the bridges. At high temperatures and high currents the voltages follow the power law V ∝ In, with n = Φ02/8π2ΛkT + 1, in good agreement with the predictions for thermally activated vortex motion. At low temperatures, the IV's are better fit by ln V linear in I − 2, as expected if the low-temperature dissipation is dominated by quantum tunneling of individual Pearl vortices.