FLUX-CREEP THROUGH COLUMNAR DEFECTS

We discuss thermal depinning of flux lines from single-line defects in the presence of an external current J. Starting from Langevin dynamic s the prefactor in the Arrhenius law for the escape rate R is derived. From this, we show the existence of a sharp depinning temperature in the limit J --> 0. Moreover, the effective activation energy and time scale involved in magnetic relaxation for a sample with columnar defec ts are calculated. The results allow a quantitative discussion of expe riments in the strong-pinning limit.