Probing Spin Dynamics of 2D Excitons with Twisted Light

Abstract

We propose a mechanism of intravalley spin–flip scattering in spin–valley-coupled two-dimensional (2D) systems by transferring the momentum of light into the exciton center of mass using optical vortex (OV) beams. By varying the dispersion of light using the topological charge of the OV beam, we demonstrate a unique approach to control the intravalley spin–flip scattering rate of excitons. From our photoluminescence measurements, we demonstrate that the intravalley scattering rate in W-based TMDs can be tuned externally by OV beams. Variation of photoluminescence intensity with topological charges shows a crossover temperature (>150 K), indicating competition among time scales involving radiative recombination, spin–flip scattering, and thermal relaxations. Our proposed technique utilizing a structured light beam can open up a new approach to exploring the physics of excitons in 2D systems.

Molecular and solid-state topological polaritons induced by population imbalance

“…TMDs, such as single-layer MoS 2 , display optically controllable valley polarization and could also be used in place of porphyrins [57][58][59] . Due to lack of inversion symmetry in these systems, the K and K' valleys are inequivalent; this results in optical selection rules that allow selective creation of excitons at K and K' valleys with σ + and σ − polarized light, respectively 60,61 .…”

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.…”

“…The fascinating attributes of TL have recently stimulated a few pioneering investigations concerning their interactions with BXs in 2D systems. 50 , 78 − 86 However, beyond scalar OV beams or TLs, the interplay between VVBs and excitons in 2D materials remains an appealing but largely unexplored area.…”