A Steady-State Approach for Studying Valley Relaxation Using an Optical Vortex Beam

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 interactions (EHEIs). We explore an approach to tune the EHEI by controlling the exciton center of mass momentum (COM) utilizing the photon distribution of higher-order optical vortex beams. By virtue of this, we have observed exciton-COM-dependent valley depolarization and decoherence, which gives us the ability to probe the valley relaxation time scale in a 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.

Probing Spin Dynamics of 2D Excitons with Twisted Light

“…Thus, any contribution from intervalley dark excitons 11,38 may not alter the interpretation of PL intensity variation that we observe with l. Consequently, the effect of matrix B only becomes important to understand the valley depolarization and decoherence effect, which we have investigated in detail in monolayer WSe 2 . 39 The solution of bright exciton intensity can be written as…”

Enhanced Photo-excitation and Angular-Momentum Imprint of Gray Excitons in WSe2 Monolayers by Spin–Orbit-Coupled Vector Vortex Beams

“…Notably, GXs have recently garnered significant attention due to their possession of both advantages from BXs as well as DXs, i.e., long lifetime and brightness. , These characteristics are highly desirable for future exciton-based quantum technologies and devices. , Nevertheless, optically accessing the GX states remains a nontrivial task and usually needs the additional aid of external fields or postprocessed structures of samples, such as in-plane magnetic fields, ,, plasmonic fields, or photonic crystals in close proximity. , Despite the out-of-plane dipole and the expected light emission along the plane of 2D materials, direct observation of GXs in TMD-MLs has been shown to be achievable by using high numerical aperture objectives in both regular photoluminescence (PL) spectroscopies , where the detectors are set in the normal direction to the 2D materials, and angle-resolved optical spectroscopies. The fascinating attributes of TL have recently stimulated a few pioneering investigations concerning their interactions with BXs in 2D systems. ,− However, beyond scalar OV beams or TLs, the interplay between VVBs and excitons in 2D materials remains an appealing but largely unexplored area.…”