Correlation-driven topological and valley states in monolayer VSi$_{2}$P$_{4}$

TL;DR

This study explores how electronic correlations influence the magnetic, topological, and valley properties of monolayer VSi₂P₄, revealing multiple phase transitions and potential for magnetic control of valley polarization in 2D materials.

Contribution

It demonstrates the impact of correlation strength on the ground states and topological phases of monolayer VSi₂P₄, highlighting the emergence of quantum anomalous Hall and valley-polarized states.

Findings

Correlation strength induces various magnetic and topological phases.

Identification of a quantum anomalous Hall insulator with Chern number one.

Electron valley polarization can be controlled via magnetization reversal.

Abstract

Electronic correlations could have significant impact on the material properties. They are typically pronounced for localized orbitals and enhanced in low-dimensional systems, so two-dimensional (2D) transition metal compounds could be a good platform to study their effects. Recently, a new class of 2D transition metal compounds, the MoSi$_2$N$_4$-family materials, have been discovered, and some of them exhibit intrinsic magnetism. Here, taking monolayer VSi$_{2}$P$_{4}$ as an example from the family, we investigate the impact of correlation effects on its physical properties, based on the first-principles calculations. We find that different correlation strength can drive the system into a variety of interesting ground states, with rich magnetic, topological and valley features. With increasing correlation strength, while the system favors a ferromagnetic semiconductor state for most cases, the magnetic anisotropy and the band gap type undergo multiple transitions, and in the process, the band edges can form single, two or three valleys for electrons or holes. Remarkably, there is a quantum anomalous Hall (QAH) insulator phase, which has a unit Chern number. The boundary of the QAH phase correspond to the half-valley semimetal state with fully valley polarized bulk carriers. We further show that for phases with the out-of-plane magnetic anisotropy, the interplay between spin-orbit coupling and orbital character of valleys enable an intrinsic valley polarization for electrons but not for holes. This electron valley polarization can be switched by reversing the magnetization direction, providing a new route of magnetic control of valleytronics. Our result sheds light on the possible role of correlation effects in the 2D transition metal compounds, and it will open new perspectives for spintronic, valleytronic and topological nanoelectronic applications based on these materials.