Hidden Real Topology and Unusual Magnetoelectric Responses in Monolayer Antiferromagnetic Cr$_2$Se$_2$O

TL;DR

This paper predicts that monolayer Cr2Se2O is a 2D antiferromagnetic real Chern insulator with topologically protected corner states, exhibiting switchable magnetization and unique magnetoelectric responses, broadening the scope of RCI materials.

Contribution

It identifies monolayer Cr2Se2O as the first 2D AFM real Chern insulator with unique corner states and spin-polarized corner modes, revealing new topological and magnetoelectric phenomena.

Findings

ML-CrSeO is a 2D AFM real Chern insulator with topological corner states.

Corner modes exhibit strong spin polarization and spin-corner coupling.

Magnetization can be electrostatically switched, leading to distinct magnetoelectric responses.

Abstract

Recently, the real topology has been attracting widespread interest in two dimensions (2D). Here, based on first-principles calculations and theoretical analysis, we reveal the monolayer Cr$_2$Se$_2$O (ML-CrSeO) as the first material example of a 2D antiferromagnetic (AFM) real Chern insulator (RCI) with topologically protected corner states. Unlike previous RCIs, we find that the real topology of the ML-CrSeO is rooted in one certain mirror subsystem of the two spin channels, and can not be directly obtained from all the valence bands in each spin channel as commonly believed. In particular, due to antiferromagnetism, the corner modes in ML-CrSeO exhibit strong corner-contrasted spin polarization, leading to spin-corner coupling (SCC). This SCC enables a direct connection between spin space and real space. Consequently, large and switchable net magnetization can be induced in the ML-CrSeO nanodisk by electrostatic means, such as potential step and in-plane electric field, and the corresponding magnetoelectric responses behave like a sign function, distinguished from that of the conventional multiferroic materials. Our work considerably broadens the candidate range of RCI materials, and opens up a new direction for topo-spintronics and 2D AFM materials research.