2D Exciton Lensing: Collimation, Focusing and Trapping

Controlling the motion of neutral excitons in optically active media is a mandatory development to enable the conception of advanced circuits and devices for applications in excitronics, quantum photonics, and optoelectronics. Recently, a proof of unidirectional exciton transport from high- to low-band-gap material has been evidenced using a high-quality lateral heterostructure separating transition metal dichalcogenide monolayers (TMD-MLs). In this paper, by combining room-temperature micro-photoluminescence far-field imaging with a statistical description of exciton transport, we unveil the underlying excitonic local distribution and fluxes taking place near lateral heterojunctions. We study the complex 2D excitonic transport properties found near a linear interface separating WSe$_2$ from MoSe$_2$ TMD-MLs and reveal two distinct diffusion regimes profoundly affecting the effective diffusion length. Then, we show that combining two and three of these interfaces, allows advanced in-plane control of the excitonic distribution and flux over large distances. We demonstrate exciton focalization and trapping, allowing an increase in the local exciton density up to three orders of magnitude. Finally, we achieve flux collimation with the formation of parallel current lines extending a few micrometers away from the source. We believe that the deterministic shaping and positioning of the exciton distribution and flux here will be a key towards the conception of realistic excitronic devices.