Nonglassy relaxation by double kinks inYBa2Cu3O7−δwith columnar defects

Abstract

We present long-term relaxation measurements of the irreversible magnetization in ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ single crystals with columnar defects. Within the single vortex pinning regime we find a nonglassy response at intermediate currents, in between the half loops and superkinks glassy regimes. We demonstrate that such behavior is due to double kink excitations whose critical nucleus has a size independent of current, and occur even in the presence of pinning energy dispersion.