Chiral excitonics in monolayer semiconductors on patterned dielectric

TL;DR

This paper demonstrates how patterned dielectric substrates induce chiral excitonic states in monolayer semiconductors, enabling directional exciton flow controlled by light polarization and position, with potential for non-reciprocal optoelectronic devices.

Contribution

It introduces a novel method to engineer valley pseudospin textures and directional exciton flow in monolayer semiconductors using patterned dielectrics, revealing new chiral excitonic phenomena.

Findings

Spatial valley pseudospin textures are pattern-locked to exciton propagation.

Circular polarization controls exciton current directionality.

Exciton flow exhibits vortex patterns influenced by excitation location.

Abstract

Monolayer transition metal dichalcogenides feature tightly bound bright excitons at the degenerate valleys, where electron-hole Coulomb exchange interaction strongly couples the valley pseudospin to the momentum of exciton. Placed on periodically structured dielectric substrate, the spatial modulation of the Coulomb interaction leads to the formation of exciton Bloch states with real-space valley pseudospin texture displayed in a mesoscopic supercell. We find this spatial valley texture in the exciton Bloch function is pattern-locked to the propagation direction, enabling nano-optical excitation of directional exciton flow through the valley selection rule. The left-right directionality of the injected exciton current is controlled by the circular polarization of excitation, while the angular directionality is controlled by the excitation location, exhibiting a vortex pattern in a supercell. The phenomenon is reminiscent of the chiral light-matter interaction in nano-photonics structures, with the role of the guided electromagnetic wave now replaced by the valley-orbit coupled exciton Bloch wave in a uniform monolayer, which points to new excitonic devices with non-reciprocal functionalities.