Abstract
In monolayer transition metal dichalcogenides (TMDs), the electron-hole exchange interaction couples exciton’s valley pseudospin to center-of-mass momentum, splitting the exciton dispersion into two branches of in-plane valley pseudospins, coupled to photons of linear polarization longitudinal and transverse branch to the exciton momentum, respectively. The Coulomb interaction is spatially modulated by placing on a periodic dielectric substrate, leading to renormalized dispersion and spatial texture featured wavefunction of the longitudinal excitons. At a lateral interface of different dielectric constant in the substrate, the transmission and reflection of exciton in the longitudinal branch obey the Snell-Descartes law of optical system, and total reflection can be exploited to realize excitonic waveguide using two parallel interfaces. When the monolayer is placed on a one-dimensional dielectric superlattice, the dispersion of the longitudinal branch is strongly renormalized, and the wavefunctions exhibit one-dimensional features. In two-dimensional (2D) dielectric superlattice case, we find the excitonic Bloch function features a spatial texture of valley polarization in the supercell, which is pattern locked to the propagation direction, enabling nano-optical excitation of directional exciton flow in the 2D plane. We also investigated exciton-polariton formed by layer hybridized exciton in TMDs heterobilayers. Placed in an optical cavity, the exciton-polariton can inherit the gauge structure from the photons, resulting in a spin/valley Hall effect, which presents electrical tunability through the control of exciton-cavity detuning.
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