Long-range transport of 2D excitons in dynamic acoustic lattice

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 long lifetime, large exciton binding energy, and gate tunability. However, the charge-neutral nature of the excitons leads to a 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 dynamic potential lattice 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 a distance at least ten times longer than the diffusion length, only limited by the device size. Temperature-dependent measurement reveals the transition from the diffusion-limited regime at low temperature to an 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.

Molding 2D Exciton Flux toward Room Temperature Excitonic Devices

“…d–f) Reproduced under the terms of a Creative Commons Attribution International 4.0 License (CC BY). [ 175 ] Copyright 2021, The Authors.…”

“…The IXs possessing longer lifetime and out‐of‐plane dipole moment provide promising route to realize long‐range directional transport by vertical electric field. [ 37 ] The propagating surface acoustic waves (SAW) on piezoelectric substrate that can generate a large out‐of‐plane piezoelectric field ( E z ) on the order of 10 7 V m −1 at 1 mW µm −1 of acoustic power, [ 175 ] were exploited to manipulate IXs flux in QW system at cryogenic. [ 176–178 ] As shown in Figure 1b of ref.…”

“…[ 176–178 ] As shown in Figure 1b of ref. [175], the SAW can drive IXs in TMDC bilayer move along the propagating direction for a long distance. [ 175 ] The exciton diffusion is relatively weak because of the low diffusion coefficient for SAW is OFF (Figure 2a of ref.…”

“…[ 175 ] The exciton diffusion is relatively weak because of the low diffusion coefficient for SAW is OFF (Figure 2a of ref. [175]). When SAW is turned ON, as the velocity of the SAW (≈3000 m s −1 ) is much smaller than the thermal velocity of excitons (10 4 –10 5 m s −1 ), the IXs will drift along the gradient of E z and thus be carried by the SAW with identical velocity, like surfing on a wave.…”