We propose a mechanism of dark to bright exciton transitions in spin-valley coupled twodimensional 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 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 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.
Light–matter coupling in van der Waal’s materials holds significant promise in realizing bosonic condensation and superfluidity. The underlying semiconductor’s crystal asymmetry, if any, can be utilized to form anisotropic half-light half-matter quasiparticles. We demonstrate generation of such highly anisotropic exciton-polaritons at the interface of a biaxial layered semiconductor, stacked on top of a distributed Bragg reflector. The spatially confined photonic mode in this geometry couples with polarized excitons and their Rydberg states, creating a system of highly anisotropic polariton manifolds, displaying Rabi splitting of up to 68 meV. Rotation of the incident beam polarization is used to tune coupling strength and smoothly switch regimes from weak to strong coupling, while also enabling transition from one three-body coupled oscillator system to another. Light–matter coupling is further tunable by varying the number of weakly coupled optically active layers. Our work provides a versatile method of engineering devices for applications in polarization-controlled polaritonics and optoelectronics.
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.
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.
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