Bifurcation of a Topological Skyrmion String

TL;DR

This paper demonstrates that a bifurcation of 3D skyrmion strings, induced by spin-orbit torque, can be controlled to produce various shapes, offering a new method to manipulate topological objects for spintronic applications.

Contribution

It reveals the mechanism of skyrmion string bifurcation in layered frustrated systems and shows how different bifurcation geometries can be achieved via current injection.

Findings

Bifurcation occurs at minimal topological charge Q=2.

Different current geometries produce I-, Y-, X-, and O-shaped skyrmion strings.

Bifurcated strings can spontaneously merge into isolated skyrmions.

Abstract

Manipulation of three-dimensional (3D) topological objects is of both fundamental interest and practical importance in many branches of physics. Here, we show by spin dynamics simulations that the bifurcation of a 3D skyrmion string in a layered frustrated system could be induced by the dampinglike spin-orbit torque. The bifurcation of a skyrmion string happens when the skyrmion string carries a minimal topological charge of $Q=2$. We demonstrate that three types of bifurcations could be realized by applying different current injection geometries, which lead to the transformation from I-shaped skyrmion strings to Y-, X-, and O-shaped ones. Besides, different branches of a bifurcated skyrmion string may merge into an isolated skyrmion string spontaneously. The mechanism of bifurcation should be universal to any skyrmion strings with $Q\geq 2$ in the layered frustrated system and could offer a general approach to manipulate 3D stringlike topological objects for spintronic functions.