title: Origin of reversed vortex ratchet motion.
abstract: We experimentally demonstrate that the origin of multiply reversed rectified vortex motion in an asymmetric pinning landscape not only is a consequence of the vortex-vortex interactions but also essentially depends on the ratio between the characteristic interaction distance and the period of the asymmetric pinning potential. We study four samples with different periods d of the asymmetric potential. For large d the dc voltage V(dc) recorded under a ac excitation indicates that the average vortex drift is from bigger to smaller dots for all explored positive fields. As d is reduced, a series of sign reversals in the dc response are observed as a function of field. We show that the number of sign reversals increases as d decreases. These findings are in agreement with recent computer simulations and illustrate the relevance of the different characteristic lengths for the vortex rectification effects.
authors.affiliation: INPAC-Institute for Nanoscale Physics and Chemistry, K.U. Leuven, Celestijnenlaan 200D, B-3001 Leuven, Belgium.
authors.forename: W
authors.initials: W
authors.lastname: Gillijns
authors.forename: A V
authors.initials: AV
authors.lastname: Silhanek
authors.forename: V V
authors.initials: VV
authors.lastname: Moshchalkov
authors.forename: C J Olson
authors.initials: CJ
authors.lastname: Reichhardt
authors.forename: C
authors.initials: C
authors.lastname: Reichhardt