Enhanced valley polarization in WS$_2$/LaMnO$_3$ heterostructure

TL;DR

This study demonstrates significantly enhanced valley polarization in WS$_2$/LaMnO$_3$ heterostructures, achieving up to 80% at low temperature and maintaining high polarization at 160 K, through exciton-magnon coupling and ferromagnetic engineering.

Contribution

The paper introduces a novel heterostructure approach to greatly enhance valley polarization in monolayer WS$_2$ using LaMnO$_3$, revealing new mechanisms for valley control.

Findings

Valley polarization reaches 80% at 4.2 K in heterostructure.

High temperature valley polarization of 53% maintained at 160 K.

Observation of interlayer excitons with opposite valley polarizations.

Abstract

Monolayer transition metal dichalcogenides have attracted great attentions for potential applications in valleytronics. However, the valley polarization degree is usually not high because of the intervalley scattering. Here, we demonstrate a largely enhanced valley polarization up to 80\% in monolayer WS$_2$ under non-resonant excitation at 4.2 K using WS$_2$/LaMnO$_3$ thin film heterostructure, which is much higher than that for monolayer WS$_2$ on SiO$_2$/Si substrate with a valley polarization of 15\%. Furthermore, the greatly enhanced valley polarization can be maintained to a high temperature of about 160 K with a valley polarization of 53\%. The temperature dependence of valley polarization is strongly correlated with the thermomagnetic curve of LaMnO$_3$, indicating an exciton-magnon coupling between WS$_2$ and LaMnO$_3$. A simple model is introduced to illustrate the underlying mechanisms. The coupling of WS$_2$ and LaMnO$_3$ is further confirmed with an observation of two interlayer excitons with opposite valley polarizations in the heterostructure, resulting from the spin-orbit coupling induced splitting of the conduction bands in monolayer transition metal dichalcogenides. Our results provide a pathway to control the valleytronic properties of transition metal dichalcogenides by means of ferromagnetic van der Waals engineering, paving a way to practical valleytronic applications.