Crossover from intravalley to intervalley vortex motion in type-II superconductors with a periodic pinning array

Abstract

We have determined the transition from intravalley vortex motion (Campbell regime) to intervalley motion (critical state regime) in Pb thin films with and without a square array of holes (antidots) by means of ac susceptibility χ(T,H) measurements. The Campbell regime is characterized by a maximum dissipation χmax″ dependent on the ac excitation h but nearly temperature independent. In contrast, in the critical state regime, the height of the dissipation peak remains constant, whereas its position shifts to lower temperatures with increasing h. We introduce an alternative way for determining the temperature dependence of the ac onset of the Bean critical state by analyzing the critical current density J(T) extracted from the χ′(T) data at several h. We demonstrate that the presence of a periodic pinning array strongly affects the extension of the crossover area in the h−T diagram between these regimes. We show that this effect can be ascribed to the lower dispersion of the pinning energy together with the higher topological order for the antidot sample.

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