Creation and Manipulation of Higher-Order Topological States by Altermagnets

TL;DR

This paper demonstrates how heterojunctions of 2D topological insulators and altermagnets can host and control higher-order topological states with tunable corner modes, using symmetry analysis, effective theory, and first-principles calculations.

Contribution

It introduces a novel method to create and manipulate higher-order topological states via altermagnets with unique spin properties, expanding topological control in 2D heterostructures.

Findings

Higher-order topological states can be induced by altermagnets with specific symmetries.

Adjusting the Ne9el vector allows control over the position of topological corner states.

First-principles calculations confirm the feasibility of the proposed heterojunctions.

Abstract

We propose to implement tunable higher-order topological states in a heterojunction consisting of a two-dimensional (2D) topological insulator and the recently discovered altermagnets, whose unique spin-polarization in both real and reciprocal space and null magnetization are in contrast to conventional ferromagnets and antiferromagnets. Based on symmetry analysis and effective edge theory, we show that the special spin splitting in altermagnets with different symmetries, such as $d$-wave, can introduce Dirac mass terms with opposite signs on the adjacent boundaries of the topological insulator, resulting in the higher-order topological state with mass-domain bound corner states. Moreover, by adjusting the direction of the N\'{e}el vector, we can manipulate such topological corner states by moving their positions. By first-principles calculations, taking a 2D topological insulator bismuthene with a square lattice on an altermagnet MnF$_2$ as an example, we demonstrate the feasibility of creating and manipulating the higher-order topological states through altermagnets. Finally, we discuss the experimental implementation and detection of the tunable topological corner states, as well as the potential non-Abelian braiding of the Dirac corner fermions.