Moir\'e Potential Impedes Interlayer Exciton Diffusion in van der Waals Heterostructures

TL;DR

This study demonstrates that moiré superlattices in van der Waals heterostructures hinder interlayer exciton diffusion, with implications for designing 'twistronic' devices that utilize moiré patterns to tune material properties.

Contribution

The paper provides experimental evidence that moiré potentials impede interlayer exciton diffusion, highlighting the impact of twist angle and superlattice structure on exciton transport.

Findings

Moiré potential impedes interlayer exciton diffusion.

Diffusion length varies with twist angle and superlattice structure.

Commensurate heterostructures show minimal moiré effects on diffusion.

Abstract

The properties of van der Waals (vdW) heterostructures are drastically altered by a tunable moir\'e superlattice arising from periodic variations of atomic alignment between the layers. Exciton diffusion represents an important channel of energy transport in semiconducting transition metal dichalcogenides (TMDs). While early studies performed on TMD heterobilayers have suggested that carriers and excitons exhibit long diffusion lengths, a rich variety of scenarios can exist. In a moir\'e crystal with a large supercell size and deep potential, interlayer excitons may be completely localized. As the moir\'e period reduces at a larger twist angle, excitons can tunnel between supercells and diffuse over a longer lifetime. The diffusion length should be the longest in commensurate heterostructures where the moir\'e superlattice is completely absent. In this study, we experimentally demonstrate that the moir\'e potential impedes interlayer exciton diffusion by comparing a number of WSe2/MoSe2 heterostructures prepared with chemical vapor deposition and mechanical stacking with accurately controlled twist angles. Our results provide critical guidance to developing 'twistronic' devices that explore the moir\'e superlattice to engineer material properties.