  We propose a mechanism of intravalley spin-flip scattering in spin-valley
coupled two dimensional systems by transferring momentum of light into exciton
center of mass using optical vortex (OV) beams. By varying the dispersion of
light using the topological charge of OV beam, we demonstrate a unique approach
to control the intra-valley spin-flip scattering rate of excitons. From our
photoluminescence measurements, we demonstrate that the intra-valley 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 competitions 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 explore the physics of excitons in 2D systems.
