VORTEX QUANTUM NUCLEATION AND TUNNELING IN SUPERCONDUCTING THIN-FILMS- ROLE OF DISSIPATION AND PERIODIC PINNING

We investigate the phenomenon of decay of a supercurrent in a supercon ducting thin film in the absence of an applied magnetic field. The res ulting zero-temperature resistance derives from two equally possible m echanisms: 1) quantum tunneling of vortices from the edges of the samp le; and 2) homogeneous quantum nucleation of vortex-antivortex pairs i n the bulk of the sample, arising from the instability of the Magnus f ield <<vacuum>>. We study both situations in the case where quantum di ssipation dominates over the inertia of the vortices. We find that the vortex tunneling and nucleation rates have a very rapid dependence on the current density driven through the sample. Accordingly, whilst no rmally the superconductor is essentially resistance-free, for the high current densities that can be reached in high-T-c films a measurable resistance might develop. We show that edge-tunneling appears favoured , but the presence of pinning centres and of thermal fluctuations lead s to an enhancement of the nucleation rates. In the case where a per i odic pinning potential is artificially introduced in the sample, we sh ow that current-oscillations will develop indicating an effect specifi c to the nucleation mechanism where the vortex pair-production rate, t hus the resistance, becomes sensitive to the corrugation of the pinnin g substrate. In all situations, we give estimates for the observabilit y of the studied phenomena.