Dimensionality of collective pinning in2H−NbSe2single crystals

Abstract

ac susceptibility measurements have been used to determine the dimensionality of the collective pinning in $2H\ensuremath{-}{\mathrm{NbSe}}_{2}$ crystals. We have analyzed the thickness dependence of the critical current versus field $[{J}_{c}(H)]$ curves for thicknesses between 6 and 166 \ensuremath{\mu}m. Down to 15 \ensuremath{\mu}m ${J}_{c}(H)$ is independent of the thickness showing that the pinning is three dimensional. This is in agreement with estimates from collective pinning theory. Deviations occur for the 6 \ensuremath{\mu}m thick sample near the peak-effect regime, possibly indicating a crossover to two-dimensional behavior. In the thicker samples the peak effect clearly cannot be assigned to a dimensional crossover. The frequency dependence reflects a crossover from a Campbell regime to a nonlinear regime related to small flux creep effects.