Kapitza-resistance-like exciton dynamics in atomically flat MoSe$_{2}$-WSe$_{2}$ lateral heterojunction

TL;DR

This paper demonstrates that atomically sharp MoSe₂-WSe₂ lateral heterostructures can control exciton flow directionality, introducing the concept of exciton Kapitza resistance and showing how transport can be tuned via near-field engineering.

Contribution

It introduces the concept of exciton Kapitza resistance at TMD heterojunctions and shows how exciton transport can be controlled over large distances using structural and optical modifications.

Findings

Discontinuity in exciton density at the heterojunction interface.

Unidirectional exciton flow induced by the heterostructure.

Transport properties are tunable via near-field engineering and laser power.

Abstract

Being able to control the neutral excitonic flux is a mandatory step for the development of future room-temperature two-dimensional excitonic devices. Semiconducting Monolayer Transition Metal Dichalcogenides (TMD-ML) with extremely robust and mobile excitons are highly attractive in this regard. However, generating an efficient and controlled exciton transport over long distances is a very challenging task. Here we demonstrate that an atomically sharp TMD-ML lateral heterostructure (MoSe$_{2}$-WSe$_{2}$) transforms the isotropic exciton diffusion into a unidirectional excitonic flow through the junction. Using tip-enhanced photoluminescence spectroscopy (TEPL) and a modified exciton transfer model, we show a discontinuity of the exciton density distribution on each side of the interface. We introduce the concept of exciton Kapitza resistance, by analogy with the interfacial thermal resistance referred to as Kapitza resistance. By comparing different heterostructures with or without top hexagonal boron nitride (hBN) layer, we deduce that the transport properties can be controlled, over distances far greater than the junction width, by the exciton density through near-field engineering and/or laser power density. This work provides a new approach for controlling the neutral exciton flow, which is key toward the conception of excitonic devices.