Flux Creep in Two-Dimensional Vortex Glasses Near H c1

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Abstract
We consider an impure thin superconducting film in its mixed phase with the magnetic field parallel to the film plane. We show that i) the description of the system of flux lines can be mapped onto a random-field XY-model without vortices; ii) when the mean flux line distance is large compared to the thin-film penetration depth, the steric repulsion between flux lines prevents the depinning from the disorder at all temperatures, i.e. the system is always in its vortex glass phase; iii) we apply our findings to obtain the current-voltage characteristics U(j) and the relaxation of the magnetization M(t) which show unusual power law dependences, U(j) ∝ jδ(T) and M(t) ∝ t−1/δ(T), for small currents j and large times t, respectively.