Electrical tuning of layer-polarized exciton gases in WSe2 bilayers

TL;DR

This study demonstrates the electrical tuning of layer-polarized excitons in WSe2 bilayers, achieving continuous polarity control, significant energy shifts, and extended exciton lifetimes, enabling the creation of dense exciton gases for advanced optoelectronic applications.

Contribution

We show for the first time that out-of-plane electric fields can continuously tune layer polarization in homo-bilayer WSe2, leading to long-lived, dense exciton gases.

Findings

Achieved continuous tuning of exciton layer polarity.

Observed a large linear Stark shift of ~100 meV.

Extended exciton lifetime to over 20 ns.

Abstract

Van der Waals heterostructures formed by stacking two-dimensional atomic crystals are a unique platform for exploring new phenomena and functionalities. Interlayer excitons, bound states of spatially separated electron-hole pairs in van der Waals heterostructures, have demonstrated potential for rich valley physics and optoelectronics applications, and been proposed to facilitate high-temperature superfluidity. Here, we demonstrate highly tunable layer-polarized excitons by an out-of-plane electric field in homo-bilayers of transition metal dichalcogenides. Continuous tuning from negative to positive layer polarity has been achieved, which is not possible in hetero-bilayers due to the presence of large built-in interfacial electric fields. A large linear field-induced redshift up to ~ 100 meV has been observed in the exciton resonance energy. The Stark effect is accompanied by an enhancement of the exciton recombination lifetime by more than two orders of magnitude to > 20 ns. The long recombination lifetime has allowed the creation of a layer-polarized exciton gas with density as large as 1.2*10^11 cm^-2 by moderate continuous-wave optical pumping. Our results have paved the way for realization of degenerate exciton gases in atomically thin semiconductors.