Control of the exciton valley dynamics in van der Waals heterostructures

TL;DR

This paper investigates how the dielectric environment influences exciton valley dynamics in van der Waals heterostructures, showing that encapsulation can significantly extend valley polarization lifetime.

Contribution

It provides a theoretical analysis of dielectric effects on long-range exchange interactions and valley dynamics in transition metal dichalcogenide monolayers.

Findings

Encapsulation in hexagonal boron nitride modifies exciton splitting.

Dielectric environment significantly enhances valley polarization lifetime.

Long-range exchange interaction governs exciton valley relaxation.

Abstract

The exciton valley dynamics in van der Waals heterostructures with transition metal dichalcogenides monolayers is driven by the long-range exchange interaction between the electron and the hole in the exciton. It couples the states active in the opposite circular polarizations resulting in the longitudinal-transverse splitting of excitons propagating in the monolayer plane. Here we study theoretically the effect of the dielectric environment on the long-range exchange interaction and demonstrate how the encapsulation in the hexagonal boron nitride modifies the exciton longitudinal-transverse splitting. We calculate the exciton spin/valley polarization relaxation due to the long-range exchange interaction and demonstrate that the variation of the monolayer environment results in significant, up to five-fold, enhancement of the exciton valley polarization lifetime.