Long-range transport of 2D excitons with acoustic waves

Ruoming Peng,Huan Li,Yusen Ye,Kenji Watanabe,Adina Ripin,Takashi Taniguchi,Jiayi Zhu,Ting Cao,Mo Li,Seokhyeong Lee,Changming Wu,Xiaodong Xu

doi:10.1038/s41467-022-29042-9

Abstract

Excitons are elementary optical excitation in semiconductors. The ability to manipulate and transport these quasiparticles would enable excitonic circuits and devices for quantum photonic technologies. Recently, interlayer excitons in 2D semiconductors have emerged as a promising candidate for engineering excitonic devices due to their long lifetime, large exciton binding energy, and gate tunability. However, the charge-neutral nature of the excitons leads to weak response to the in-plane electric field and thus inhibits transport beyond the diffusion length. Here, we demonstrate the directional transport of interlayer excitons in bilayer WSe2 driven by the propagating potential traps induced by surface acoustic waves (SAW). We show that at 100 K, the SAW-driven excitonic transport is activated above a threshold acoustic power and reaches 20 μm, a distance at least ten times longer than the diffusion length and only limited by the device size. Temperature-dependent measurement reveals the transition from the diffusion-limited regime at low temperature to the acoustic field-driven regime at elevated temperature. Our work shows that acoustic waves are an effective, contact-free means to control exciton dynamics and transport, promising for realizing 2D materials-based excitonic devices such as exciton transistors, switches, and transducers up to room temperature.

Highlights

Excitons are elementary optical excitation in semiconductors
It was reported recently that the exciton energy of indirect excitons (IXs) in bilayer WSe2 could be modulated by an out-of-plane static field[29]
In conclusion, we have demonstrated that surface acoustic waves (SAW) is an efficient, contact-free approach to transport IXs in bilayer WSe2 over a distance far beyond the diffusion length

Summary

Introduction

Excitons are elementary optical excitation in semiconductors. The ability to manipulate and transport these quasiparticles would enable excitonic circuits and devices for quantum photonic technologies. Unlike electrons or holes, charge-neutral excitons experience no net force under uniform electric fields They can be dissociated by a moderately strong in-plane electric field if the binding energy is small, for example, in GaAs quantum well systems[7,8]. The indirect excitons (IXs) in bilayers and heterobilayers of TMDCs have additional desirable properties[27,29–32] Because these IXs consist of electrons and holes separated in different layers and valleys, their population lifetimes at low temperature are up to 100 s of nanoseconds[4], facilitating long-range transport before relaxation. Due to limited exciton mobility[38], diffusive and repulsive transport of IXs can only achieve a transport distance of a few μm using milliwatts of optical excitation power at a low temperature[39]. Such diffusive transport is non-directional, challenging to realize functional excitonic circuits, which entail transporting excitons in a controlled direction over a long distance

Methods

Results

Conclusion