Dimensionality of collective pinning in2H−NbSe2single crystals

ac susceptibility measurements have been used to determine the dimensionality of the collective pinning in 2H-NbSe2 crystals. We have analyzed the thickness dependence of the critical current versus field [Jc(H)] curves for thicknesses between 6 and 166 μm. Down to 15 μm Jc(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 μm 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