Large Intrinsic Valley Polarization and High Curie Temperature in Stable Two-dimensional Ferrovalley YX$_2$(X=I,Br and Cl)

TL;DR

This study predicts that 2D YX$_2$ materials are stable ferromagnetic semiconductors with large intrinsic valley polarization and high Curie temperatures, making them promising for valleytronic applications.

Contribution

First-principles calculations reveal YX$_2$ monolayers as stable, high-temperature ferromagnetic semiconductors with large valley polarization and tunable valley physics under strain.

Findings

YX$_2$ are dynamically and thermally stable 2D ferromagnetic semiconductors.

Large spontaneous valley polarizations are predicted in YX$_2$ monolayers.

Valley polarization and ferromagnetism can be tuned by biaxial strain.

Abstract

Ferrovalley materials with spontaneous valley polarization are crucial to valleytronic application. Based on first-principles calculations, we demonstrate that two-dimensional (2D) YX$_2$(X= I, Br,and Cl) in 2H structure constitute a series of promising ferrovalley semiconductors with large spontaneous valley polarization and high Curie temperature. Our calculations reveal that YX$_2$ are dynamically and thermally stable 2D ferromagnetic semiconductors with a Curie temperature above 200 K. Due to the natural noncentrosymmetric structure, intrinsic ferromagnetic order and strong spin orbital coupling, the large spontaneous valley polarizations of 108.98, 57.70 and 22.35 meV are also predicted in single-layer YX$_2$(X = I, Br and Cl),respectively. The anomalous valley Hall effect is also proposed based on the valley contrasting Berry curvature. Moreover, the ferromagnetism and valley polarization are found to be effectively tuning by applying a biaxial strain. Interestingly, the suppressed valley physics of YBr$_2$ and YCl$_2$ can be switched on via applying a moderate compression strain. The present findings promise YX$_2$ as competitive candidates for the further experimental studies and practical applications in valleytronics.