Ferro-Valleytricity with In-Plane Magnetization

TL;DR

This paper introduces a new mechanism for ferro-valleytricity in 2D materials with in-plane magnetization, expanding the understanding of valley polarization phenomena beyond out-of-plane magnetized systems.

Contribution

It proposes a theoretical model and demonstrates, via first-principles calculations, that in-plane magnetization can induce ferro-valleytricity, with controllable valley polarization in 2D materials.

Findings

Mirror symmetry is essential for valley polarization.

Valley polarization can be reversed by modulating in-plane magnetization.

Electric fields can switch valley polarization via ferroelectricity.

Abstract

Ferro-valleytricity, a fundamental phenomenon that manifests spontaneous valley polarization, is generally considered to occur in two-dimensional (2D) materials with out-of-plane magnetization. Here, we propose a mechanism to realize ferro-valleytricity in 2D materials with in-plane magnetization, wherein the physics correlates to non-collinear magnetism in triangular lattice. Our model analysis provides comprehensive ingredients that allows for in-plane ferro-valleytricity, revealing that mirror symmetry is required for remarkable valley polarization and time-reversal-mirror joint-symmetry should be excluded. Through modulating in-plane magnetization offset, the valley polarization could be reversed. Followed by first-principles, such mechanism is demonstrated in a multiferroic triangular lattice of single-layer W3Cl8. We further show that the reversal of valley polarization could also be driven by applying electric field that modulates ferroelectricity. Our findings greatly enrich the valley physics research and significantly extend the scope for material classes of ferro-valleytricity.