Probing Spin Dynamics of 2D Excitons with Twisted Light

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