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 superconductors 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 (Formula presented)(T)∝(1%2b〈(Formula presented)〉/(Formula presented)(Formula presented), with large exponents (Formula presented)=5/2 and (Formula presented)=11/2 for the regimes where the collective pinning involves two- and three-dimensional bundles of vortices. We determine the mean squared displacement amplitude 〈(Formula presented)〉 within a quantum statistical ensemble for the cases of a dissipative vortex dynamics (amorphous material) and for a Hamiltonian dynamics dominated by the Hall force (oxide superconductors) and present results for the renormalized critical current density (Formula presented)(T). © 1996 The American Physical Society.

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