A steady state approach for studying valley relaxation using optical vortex beam

TL;DR

This paper introduces a steady-state optical vortex beam method to control and measure valley relaxation dynamics in monolayer transition metal dichalcogenides, revealing exciton momentum-dependent valley depolarization.

Contribution

It presents a novel steady-state approach using optical vortex beams to tune exciton center of mass momentum and study valley relaxation in 2D materials.

Findings

Valley depolarization depends on exciton COM controlled by vortex beams.

Steady-state measurement reveals valley decoherence timescales.

Method enables new exploration of exciton physics in 2D systems.

Abstract

Spin-valley coupling in monolayer transition metal dichalcogenides gives rise to valley polarization and coherence effect, limited by intervalley scattering caused by exciton-phonon, exciton-impurity, and electron-hole exchange interaction (EHEI). We explore an approach to tune the EHEI by controlling excitons center of mass momentum (COM) utilizing the photon distribution of higher-order optical vortex beam. By virtue of this, we have observed excitons COM-dependent valley depolarization and decoherence which gives us the ability to measure the timescale associated with valley dynamics in the steady-state measurement. Our steady-state technique to probe the valley dynamics can open up a new paradigm to explore the physics of excitons in two-dimensional systems.