We show that ac driven skyrmions interacting with an asymmetric substrateprovide a realization of a new class of ratchet system which we call a vectorratchet that arises due to the effect of the Magnus term on the skyrmiondynamics. In a vector ratchet, the dc motion induced by the ac drive can bedescribed as a vector that can be rotated clockwise or counterclockwiserelative to the substrate asymmetry direction. Up to a full $360^{\circ}$rotation is possible for varied ac amplitudes or skyrmion densities. Incontrast to overdamped systems, in which ratchet motion is always parallel tothe substrate asymmetry direction, vector ratchets allow the ratchet motion tobe in any direction relative to the substrate asymmetry. It is also possible toobtain a reversal in the direction of rotation of the vector ratchet,permitting the creation of a reversible vector ratchet. We examine vectorratchets for ac drives applied parallel or perpendicular to the substrateasymmetry direction, and show that reverse ratchet motion can be produced bycollective effects. No reversals occur for an isolated skyrmion on anasymmetric substrate. Since a vector ratchet can produce motion in anydirection, it could represent a new method for controlling skyrmion motion forspintronic applications.
展开▼
