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-T-c thin-film bridges. SQUID microscopy of these films provides Pearl lengths. 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 proportional to I-n, with n = phi(2)(0)/8 pi(2)Lambda kT + 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.