Photonic orbital angular momentum transfer and magnetic skyrmion rotation

Abstract

Magnetic skyrmions are chiral quasiparticles that show promise for future spintronic applications such as skyrmion racetrack memories and logic devices because of their topological stability, small size (typically ∼ 3 - 500 nm), and ultralow threshold force to drive their motion. On the other hand, the ability of light to carry and deliver orbital angular momentum (OAM) in the form of optical vortices has attracted a lot of interest. In this work, we predict a photonic OAM transfer effect, by studying the dynamics of magnetic skyrmions subject to Laguerre-Gaussian optical vortices, which manifests a rotational motion of the skyrmionic quasiparticle around the beam axis. The topological charge of the optical vortex determines both the magnitude and the handedness of the rotation velocity of skyrmions. In our proposal, the twisted light beam acts as an optical tweezer to enable us displacing skyrmions over large-scale defects in magnetic films to avoid being captured.

Edge states in a two-dimensional honeycomb lattice of massive magnetic skyrmions

“…By mapping the massless Thiele's equation into the Haldane model [41], they predicted the chiral edge modes near the gyration frequency of the single soliton. However, it is well known that magnetic bubbles and skyrmions in particular manifest an inertia in their gyration motion [42,43]. The mass effect thus should be taken into account for developing a full theory on the coupled skyrmion oscillations.…”

Optically enriched and guided dynamics of active skyrmions

“…The experimental sample fabrication techniques used throughout this study are highly reminiscent of those used in the multi-billion-dollar LC display industry, which can potentially stimulate the translation of our findings to the consumer markets. Previous studies have shown the ability to use specialty experimental systems involving micropatterned substrates [50], thickness gradients, and structured beams of light to control skyrmionic structures in equilibrium conditions [28,35,[50][51][52], however our work enables higher levels of dynamic control using low-intensity unstructured light. These advances add to the experimental toolkit available for controlling active behavior of solitons and promises new complex avenues and compelling possibilities for technological uses for LC skyrmions.…”

Higher-order topological solitonic insulators

“…where U j = R j − R 0 j is the displacement of the vortex core from the equilibrium position R 0 j , G = −4πQwM s /γ is the gyroscopic constant with Q = 1 4π dxdym · ( ∂m ∂x × ∂m ∂y ) being the topological charge [Q = −1/2 for the vortex configuration shown in Fig. 1(b)], m is the unit vector of magnetization, w is the thickness of nanodisk, M s is the saturation magnetization, γ is the gyromagnetic ratio, M is the effective mass of the magnetic vortex [50][51][52], and G 3 is the third-order gyroscopic coefficient [53][54][55]. The conservative force can be expressed as F j = −∂W/∂U j where W is the potential energy as a function of the vortex displacement: [49,56,57].…”