Quantum collective creep: Effects of anisotropy, layering, and finite temperature.

Abstract

We determine the creep rates for classical and quantum motion in uniaxially anisotropic and layered superconductors within the framework of weak collective-pinning theory. In particular, we concentrate on the low- and intermediate-magnetic-field regime where single-vortex collective pinning is relevant. For a field aligned with the crystal c axis, we find that both the classical and the quantum creep rates are enhanced as compared with the isotropic results due to the increased elasticity of the vortices. For anisotropic superconductors the creep rates do not depend on the angle \ensuremath{\vartheta} between the magnetic field and the crystal ab plane and are also independent of the direction of motion. Identical results are obtained for layered superconductors within the large-angle region \ensuremath{\vartheta}>\ensuremath{\epsilon}, where ${\mathrm{\ensuremath{\epsilon}}}^{2}$=m/M1 denotes the mass anisotropy ratio. A more complex behavior is obtained in the small-angle region \ensuremath{\Vert}\ensuremath{\vartheta}\ensuremath{\Vert}, where the structure of the vortex cannot be approximated by a simple rectilinear object. Here the creep rates depend both on the angle \ensuremath{\vartheta} and on the direction of motion. We discuss the finite-temperature corrections to the quantum motion and determine the crossover temperature to the classical thermally activated behavior.