Shapiro Spikes and Negative Mobility for Skyrmion Motion on Quasi-One-Dimensional Periodic Substrates

TL;DR

This paper investigates the complex dynamics of skyrmions on quasi-one-dimensional substrates under combined drives, revealing novel phenomena like Shapiro spikes, negative mobility, and absolute transverse mobility due to the Magnus effect.

Contribution

It introduces a numerical model demonstrating how the Magnus term induces unique phase locking behaviors and mobility phenomena in skyrmion motion on periodic substrates.

Findings

Observation of velocity spikes instead of Shapiro steps.

Identification of negative mobility where skyrmions move opposite to the drive.

Discovery of conditions for absolute transverse mobility.

Abstract

Using a simple numerical model of skyrmions in a two-dimensional system interacting with a quasi-one dimensional periodic substrate under combined dc and ac drives where the dc drive is applied perpendicular to the substrate periodicity, we show that a rich variety of novel phase locking dynamics can occur due to the influence of the Magnus term on the skyrmion dynamics. Instead of Shapiro steps, the velocity response in the direction of the dc drive exhibits a series of spikes, including extended dc drive intervals over which the skyrmions move in the direction opposite to the dc drive, producing negative mobility. There are also specific dc drive values at which the skyrmions move exactly perpendicular to the dc drive direction, giving a condition of absolute transverse mobility.