Photo-induced Vortex States in the Transition Metal Dichalcogenides

The response of the low-energy quasiparticles in transition metal dichalcogenides (TMDs), such as MoS₂, to circularly polarized light leads to valley-dependent optical phenomena such as valley-selective dichroism [1]. In addition to the spin angular momentum resulting from light polarization, optical vortex beams carry orbital angular momentum resulting from the space modulation of their wavefronts. Our work explores the effects of the interaction between low-energy electrons in TMDs and light vortex beams. Using the Floquet formalism, we determine the light polarizations that conserve the total angular momentum and derive the orbital, valley, spin, and pseudo-spin dependence of electron-photon states. Within the one-photon approximation, we show that the reduced Floquet Hamiltonian is equivalent to a model for an s-wave superconductor with multiple vortices. The mapping allows us to determine the spectra, number, and valley dependence of the low-energy vortex states in the irradiated system. We also numerically diagonalize the total Floquet Hamiltonian using Bessel decomposition methods that reveal the emerging photon-dressed electronic vortex states. This approach fully characterizes each state's valley-spin dependence and its real-space distribution.

[1] Di Xiao, et al., PRL 108, 196802 (2012)