We explore the dynamic response of vortex lines in a Pb thin film with a periodic array of antidots by means of ac-susceptibility measurements. For low drive field amplitudes, within the Campbell regime, vortex motion is of intra-valley type and the penetration depth is related to the curvature of the pinning potential well, α. For dc-fields below the first matching field H1, α reaches its highest value associated with a Mott Insulator-like phase where vortex lines are strongly localized at the pinning sites. For H1<Hdc<H2, the response is mainly due to the interstitial vortices and α drops to smaller values as expected for this metallic-like regime. Strikingly, for H2<Hdc<H3, we observe that α reduces further down. However, for H3<Hdc<H4, a reentrance in the pinning strength is observed, due to a specific configuration of the flux line lattice which strongly restricts the mobility of vortices. We present a possible explanation for the measured α(Hdc) dependence based on the different flux line lattice configurations.
@article{arxiv.cond-mat/0301118,
title = {Field-dependent Vortex Pinning Strength in a Periodic Array of Antidots},
author = {A. V. Silhanek and S. Raedts and M. Lange and V. V. Moshchalkov},
journal= {arXiv preprint arXiv:cond-mat/0301118},
year = {2009}
}