Magnus-Induced Dynamics of Driven Skyrmions on a Quasi-One-Dimensional Periodic Substrate

TL;DR

This study explores the complex dynamics of driven skyrmions on a quasi-one-dimensional substrate, revealing novel velocity behaviors, phase transitions, and the influence of the Magnus force in both single and collective regimes.

Contribution

It provides a detailed numerical analysis of skyrmion motion under various conditions, highlighting the effects of the Magnus force and substrate interactions on dynamic phases and velocities.

Findings

Magnus force causes skyrmions to move both transverse and longitudinal to the drive.

Speed up effect occurs when the Magnus force aligns with the drive.

Multiple dynamical phases identified, including smectic, liquid, hexatic, and crystal phases.

Abstract

We numerically examine driven skyrmions interacting with a periodic quasi-one dimensional substrate where the driving force is applied either parallel or perpendicular to the substrate periodicity direction. For perpendicular driving, the particles in a purely overdamped system simply slide along the substrate minima; however, for skyrmions where the Magnus force is relevant, we find that a rich variety of dynamics can arise. In the single skyrmion limit, the skyrmion motion is locked along the driving or longitudinal direction for low drives, while at higher drives a transition occurs to a state in which the skyrmion moves both transverse and longitudinal to the driving direction. Within the longitudinally locked phase we find a pronounced speed up effect that occurs when the Magnus force aligns with the external driving force, while at the transition to transverse and longitudinal motion, the skyrmion velocity drops, producing negative differential conductivity. For collectively interacting skyrmion assemblies, the speed up effect is still present and we observe a number of distinct dynamical phases, including a sliding smectic phase, a disordered or moving liquid phase, a moving hexatic phase, and a moving crystal phase. The transitions between the dynamic phases produce distinct features in the structure of the skyrmion lattice and in the velocity-force curves. We map these different phases as a function of the ratio of the Magnus term to the dissipative term, the substrate strength, the commensurability ratio, and the magnitude of the driving force.