Abstract
We study the delocalization by bulk randomness of a single flux line (FL) from an extended defect, such as a columnar pin or twin plane. In three dimensions, the FL is always bound to a planar defect, while there is an unpinning transition from a columnar pin. Transfer matrix simulations confirm this picture, and indicate that the divergence of the localization length from the columnar defect is governed by a liberation exponent ν = 1.3 ± 0.6, for which a "mean-field" estimate gives ν ≈ 0.78. The results, and their extensions, are compared to other theories. The effects may be observable in thin samples close to Hc1.
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