Valley Dependence of Photo-induced Vortex States in Transition Metal Dichalcogenides

Subjecting transition metal dichalcogenides (TMDs), such as Molybdenum Disulfide (MoS₂), to a monochromatic circularly polarized light leads to the observation of interesting optically induced phenomena such as valley-selective circular dichroism and a valley-selective optical Stark shift. Traditionally, light polarization, frequency, and amplitude have been used to tune phases of matter via Floquet engineering. However, additional degrees of tunability can arise from the spatial control of optical beams. Light-vortex beams are examples of such radiation sources since, in addition to polarization, they carry orbital angular momentum. Considering a monolayer TMD subjected to a monochromatic vortex-light beam, we analyze the possible appearance of valley-polarized quantum-vortex states in these systems. We obtain the Floquet Hamiltonian of the space-dependent system by identifying the light polarization and frequencies for which a total angular momentum characterizes the Floquet states, and we diagonalize the one-dimensional radial problem. We present our findings on the valley-dependent electronic vortex states and analyze their spin textures, topological properties, and real space extension.