QUANTUM DEPINNING OF VORTICES IN TYPE-II SUPERCONDUCTORS

We investigate the phenomenon of quantum depinning of vortices in high resistivity amorphous thin films and in high temperature superconduct ors for the situation of weak collective pinning. Fluctuations of the vortex system produce a smoothing of the pinning potential and thereby a strong renormalization of the critical current density j(c)(T)propo rtional to(1+[u(2)]/xi(2))(-kappa), With large exponents kappa(2D)=5/2 and kappa(3D)=11/2 for the regimes where the collective pinning invol ves two- and three-dimensional bundles of vortices. We determine the m ean squared displacement amplitude [u(2)] within a quantum statistical ensemble for the cases of a dissipative vortex dynamics (amorphous ma terial) and for a Hamiltonian dynamics dominated by the Hall force (ox ide superconductors) and present results for the renormalized critical current density j(c)(T).