Nonequilibrium Phases and Segregation for Skyrmions on Periodic Pinning Arrays

TL;DR

This study uses particle-based simulations to explore how skyrmions behave on periodic pinning arrays, revealing various dynamical phases influenced by the Magnus force and pinning strength, including segregation phenomena.

Contribution

It introduces a detailed analysis of skyrmion dynamics on periodic pinning arrays, highlighting the role of the Magnus force in phase transitions and segregation.

Findings

Identification of multiple dynamical phases including interstitial flow, moving disordered, and clustered states.

Segregation arises from drive-dependent skyrmion Hall angles in strong pinning regimes.

Phase evolution depends on system density, Magnus-to-dissipative ratio, and skyrmion-to-pinning site ratio.

Abstract

Using particle-based simulations, we examine the collective dynamics of skyrmions interacting with periodic pinning arrays, focusing on the impact of the Magnus force on the sliding phases. As a function of increasing pinning strength, we find a series of distinct dynamical phases, including an interstitial flow phase, a moving disordered state, a moving crystal, and a segregated cluster state. The transitions between these states produce signatures in the skyrmion lattice structure, the skyrmion Hall angle, the velocity fluctuation distributions, and the velocity-force curves. The moving clustered state is similar to the segregated state recently observed in continuum-based simulations with strong quenched disorder. The segregation arises from the drive dependence of the skyrmion Hall angle, and appears in the strong pinning limit when the skyrmions have nonuniform velocities, causing different portions of the sample to have different effective skyrmion Hall angles. We map the evolution of the dynamic phases as a function of the system density, the ratio of the Magnus force to the dissipative term, and the ratio of the number of skyrmions to the number of pinning sites.