Twisted magnetic topological insulators

TL;DR

This paper investigates magnetic topological insulators, revealing how twisted spin interactions lead to complex magnetic orders like skyrmions, which influence surface electronic states and induce the anomalous Hall effect.

Contribution

It uncovers the role of Dzyaloshinskii-Moriya interactions in forming twisted magnetic states and their impact on topological surface states in magnetic topological insulators.

Findings

Twisted spin interactions induce complex magnetic orders.

Skyrmion lattices open gaps at the Dirac surface states.

Chiral modes around skyrmions contribute to anomalous Hall effect.

Abstract

Motivated by the discovery of the quantum anomalous Hall effect in Cr-doped \ce{(Bi,Sb)2Te3} thin films, we study the generic states for magnetic topological insulators and explore the physical properties for both magnetism and itinerant electrons. First-principles calculations are exploited to investigate the magnetic interactions between magnetic Co atoms adsorbed on the \ce{Bi2Se3} (111) surface. Due to the absence of inversion symmetry on the surface, there are Dzyaloshinskii-Moriya-like twisted spin interactions between the local moments of Co ions. These nonferromagnetic interactions twist the collinear spin configuration of the ferromagnet and generate various magnetic orders beyond a simple ferromagnet. Among them, the spin spiral state generates alternating counterpropagating modes across each period of spin states, and the skyrmion lattice even supports a chiral mode around the core of each skyrmion. The skyrmion lattice opens a gap at the surface Dirac point, resulting in the anomalous Hall effect. These results may inspire further experimental investigation of magnetic topological insulators.