Current-induced motion of twisted skyrmions

Twisted skyrmions, whose helicity angles are different from those of Bloch and Néel skyrmions, have recently been demonstrated in experiments. In this work, we first discuss the origin and the topological properties of twisted skyrmions. Following that, we investigate the current-induced motion of twisted skyrmions by using micromagnetic simulations. It is found that the skyrmion Hall angle of twisted skyrmions driven by the spin Hall effect (SHE) varies continuously with the helicity, which means that the skyrmion Hall angle depends significantly upon the helicity in addition to the dissipative force tensor and the Gilbert damping. More importantly, we demonstrate that the trajectory of the twisted skyrmion can be controlled in a two-dimensional plane with a Gilbert damping gradient, which makes it possible to achieve the SHE-induced motion of twisted skyrmions with zero skyrmion Hall angle. At last, the simulation results demonstrate that the dynamics of twisted skyrmions driven by the spin transfer torque can be described by Thiele's equation, and they are essentially identical to the dynamics of Bloch and Néel skyrmions. Our results provide an understanding of the current-induced motion of twisted skyrmions, which may contribute to the applications of skyrmion-based racetrack memories.