Clogging, diode and collective effects of skyrmions in funnel geometries

Using a particle-based model, we examine the collective dynamics of skyrmions interacting with a funnel potential under dc driving as the skyrmion density and relative strength of the Magnus and damping terms are varied. For driving in the easy direction, we find that increasing the skyrmion density reduces the average skyrmion velocity due to jamming of skyrmions near the funnel opening, while the Magnus force causes skyrmions to accumulate on one side of the funnel array. For driving in the hard direction, there is a critical skyrmion density below which the skyrmions become trapped. Above this critical value, a clogging effect appears with multiple depinning and repinning states where the skyrmions can rearrange into different clogged configurations, while at higher drives, the velocity-force curves become continuous. When skyrmions pile up near the funnel opening, the effective size of the opening is reduced and the passage of other skyrmions is blocked by the repulsive skyrmion-skyrmion interactions. We observe a strong diode effect in which the critical depinning force is higher and the velocity response is smaller for hard direction driving. As the ratio of Magnus force to dissipative term is varied, the skyrmion velocity varies in a non-linear and non-monotonic way due to the pile up of skyrmions on one side of the funnels. At high Magnus forces, the clogging effect for hard direction driving is diminished.

Automated summary

Using a particle-based model, the collective dynamics of skyrmions interacting with a funnel potential under dc driving are examined. The study finds that increasing skyrmion density reduces average velocity and leads to accumulation on one side of the funnel array. In the hard direction, a critical skyrmion density is identified below which trapping occurs, and above which a clogging effect is observed with multiple depinning and repinning states. The size of the funnel opening is reduced by the pile up of skyrmions, resulting in a diode effect where the critical depinning force is higher and the velocity response is smaller for hard direction driving.