Voltage-controlled long-range propagation of indirect excitons in van der Waals heterostructure

TL;DR

This study demonstrates long-range propagation of indirect excitons in van der Waals heterostructures, showing potential for high-temperature excitonic devices and control via gate voltage despite moiré superlattice effects.

Contribution

It provides experimental evidence of long-range indirect exciton propagation in TMD heterostructures and demonstrates voltage control of exciton flow.

Findings

IXs propagate up to 13 microns in MoSe2/WSe2 heterostructures.

Gate voltage can modulate IX luminescence signal by 40 times.

Long-range IX propagation is achievable despite moiré superlattice potentials.

Abstract

Indirect excitons (IXs), also known as interlayer excitons, can form the medium for excitonic devices whose operation is based on controlled propagation of excitons. A proof of principle for excitonic devices was demonstrated in GaAs heterostructures where the operation of excitonic devices is limited to low temperatures. IXs in van der Waals transition-metal dichalcogenide (TMD) heterostructures are characterized by high binding energies making IXs robust at room temperature and offering an opportunity to create excitonic devices operating at high temperatures suitable for applications. However, a characteristic feature of TMD heterostructures is the presence of moir\'e superlattice potentials, which are predicted to cause modulations of IX energy reaching tens of meV. These in-plane energy landscapes can lead to IX localization, making IX propagation fundamentally different in TMD and GaAs heterostructures and making uncertain if long-range IX propagation can be realized in TMD heterostructures. In this work, we realize long-range IX propagation with the $1/e$ IX luminescence decay distances reaching 13 microns in a MoSe$_2$/WSe$_2$ heterostructure. We trace the IX luminescence along the IX propagation path. We also realize control of the long-range IX propagation: the IX luminescence signal in the drain of an excitonic transistor is controlled within 40 times by gate voltage. These data show that the long-range IX propagation is possible in TMD heterostructures with the predicted moir\'e superlattice potentials.