Thermally Activated Depinning of a Driven Flux Line Lattice

Abstract

We have performed simultaneous measurements of the resonance frequency, damping and resistivity of vibrating Y123 thin films to study the behavior of the depinning of a driven flux line lattice (FLL). The measurements show: (i) the depinning temperature remains unaffected up to a current density of 106 A/m2; (ii) at higher currents the depinning temperature and the width of the dissipation peak as a function of temperature decrease whereas its height increases; (iii) at high enough currents the dissipation at the depinning saturates. The observed “motional narrowing” appears to be in agreement with recently published ideas on a driven FLL with disorder recovering a quasi-ordered or “Bragg-glass” state by sliding it at high enough velocities. The dissipation peak measured at high currents can be quantitatively understood with a diffusion model without free parameters.