Dynamics of Magnus Dominated Particle Clusters, Collisions, Pinning and Ratchets

Abstract

Motivated by the recent work in skyrmions and active chiral matter systems, we examine pairs and small clusters of repulsively interacting point particles in the limit where the dynamics is dominated by the Magnus force. We find that particles with the same Magnus force can form stable pairs, triples and higher ordered clusters or exhibit chaotic motion. For mixtures of particles with opposite Magnus force, particle pairs can combine to form translating dipoles. Under an applied drive, particles with the same Magnus force translate; however, particles with different or opposite Magnus force exhibit a drive-dependent decoupling transition. When the particles interact with a repulsive obstacle, they can form localized orbits with depinning or unwinding transitions under an applied drive. We examine the interaction of these particles with clusters or lines of obstacles, and find that the particles can become trapped in orbits that encircle multiple obstacles. Under an ac drive, we observe a series of ratchet effects, including ratchet reversals, for particles interacting with a line of obstacles due to the formation of commensurate orbits. Finally, in assemblies of particles with mixed Magnus forces of the same sign, we find that the particles with the largest Magnus force become localized in the center of the cluster, while for mixtures with opposite Magnus forces, the motion is dominated by transient local pairs or clusters, where the translating pairs can be regarded as a form of active matter.

Ultrafast Ratchet Dynamics of Skyrmions by Defect Engineering in Materials with Poor Conductivity Under Gigahertz Magnetic Fields

“…As shown by our results, magnetic fields of about 50 mT can trigger efficient ratchet motion along defect tracks or edges in a speed of about 100 m/s. Note, the presence of defects or edges in the skyrmion system lowers the spatial symmetry of the system, and ratchet motion of skyrmion along a defect track or edge can actually be induced by time-varying sources without time asymmetry 43,44 . The reported mechanism therefore provides a general and feasible strategy to efficiently drive skyrmion in both metallic and insulating systems based on racetrack structures.…”