Dissipation in ultra-thin current-carrying superconducting bridges;   evidence for quantum tunneling of Pearl vortices
  We have made current-voltage (IV) measurements of artificially layered high-$T_c$ thin-film bridges. Scanning SQUID microscopy of these films provides values for the Pearl lengths $\Lambda$ that exceed the bridge width, and shows that the current distributions are uniform across the bridges. At high temperatures and high currents the voltages follow the power law $V \propto I^n$, with $n=\Phi_0^2/8\pi^2\Lambda k_B T+1$, and at high temperatures and low-currents the resistance is exponential in temperature, 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 $I^{-2}$. This is expected if the low temperature dissipation is dominated by quantum tunneling of Pearl vortices. 
F. Tafuri, J.R. Kirtley, D. Born, D. Stornaiuolo, P.G. Medaglia, P.   Orgiani, G. Balestrino, and V.G. Kogan