Quantum topological Hall effect and noncoplanar antiferromagnetism in K$_{0.5}$RhO$_2$

TL;DR

This paper predicts that K$_{0.5}$RhO$_2$ exhibits a three-dimensional quantum anomalous Hall phase driven by noncoplanar antiferromagnetic order, leading to a topological Hall effect without net magnetization or strong spin-orbit coupling.

Contribution

It introduces a novel prediction of a 3D QAH insulator in K$_{0.5}$RhO$_2$ caused by noncoplanar spin structure, expanding the understanding of topological phases in antiferromagnets.

Findings

K$_{0.5}$RhO$_2$ is a 3D QAH insulator with a large band gap.

The QAH phase arises from nonzero scalar spin chirality.

The phase exists without net magnetization or strong SOC.

Abstract

Quantum anomalous Hall (QAH) phase is a two-dimensional bulk ferromagnetic insulator with a nonzero Chern number in presence of spin-orbit coupling (SOC) but absence of applied magnetic fields. Associated metallic chiral edge states host dissipationless current transport in electronic devices. This intriguing QAH phase has recently been observed in magnetic impurity-doped topological insulators, {\it albeit}, at extremely low temperatures. Based on first-principles density functional calculations, here we predict that layered rhodium oxide K$_{0.5}$RhO$_2$ in noncoplanar chiral antiferromagnetic state is an unconventional three-dimensional QAH insulator with a large band gap and a Neel temperature of a few tens Kelvins. Furthermore, this unconventional QAH phase is revealed to be the exotic quantum topological Hall effect caused by nonzero scalar spin chirality due to the topological spin structure in the system and without the need of net magnetization and SOC.