Enhanced Valley Polarization in WS /LaMnO Heterostructure.

Monolayer transition metal dichalcogenides have attracted great attention for potential applications in valleytronics. However, the valley polarization degree is usually not high because of the intervalley scattering. Here, a largely enhanced valley polarization up to 80% in monolayer WS under nonresonant excitation at 4.2 K is demonstrated using WS /LaMnO thin film heterostructure, which is much higher than that for monolayer WS on SiO /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 , indicating an exciton-magnon coupling between WS and LaMnO . A simple model is introduced to illustrate the underlying mechanisms. The coupling of WS and LaMnO 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. The 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.