Excitonic Quantum Anomalous Hall Effect in Collinear Magnets Without Spin-Orbit Coupling

TL;DR

This paper proposes a novel exciton-condensation mechanism to realize the quantum anomalous Hall effect in collinear magnets without relying on spin-orbit coupling, expanding potential material candidates.

Contribution

It introduces a new excitonic mechanism for QAH effect in magnets with negligible SOC, involving spin-splitting bands and triplet exciton condensation, applicable to ferromagnets and altermagnets.

Findings

Electron-phonon coupling induces noncollinear spin textures.

First-principles calculations identify V2SeTeO as a candidate material.

Mechanism does not require strong spin-orbit coupling.

Abstract

Spin-orbit coupling (SOC) is thought to be necessary in realizing quantum anomalous Hall (QAH) insulators in magnetic materials. In this Letter, we propose an exciton-condensation mechanism to realize QAH effect in collinear magnets with negligible spin-orbit coupling. This mechanism is realized by two steps: first prepare a spin-splitting nodal-ring band structure, and then gap out the nodal-ring via triplet exciton condensation. A nonzero Chern number can be obtained if the in-plane spin texture resulting from the triplet exciton condensation is noncollinear in momentum space. We show that the electron-phonon coupling can switch the spin texture from a colinear pattern to a noncolinear one and plays an essential role in realizing QAH effect. The above mechanism is not only suitable for ferrogmagnets but also applicable for altermagnets. Finally, through first-principles calculations we propose the bilayer material V2SeTeO to be a promising candidate of excitonic QAH insulator.