Strain control of hybridization between dark and localized excitons in a 2D semiconductor

Abstract

Mechanical strain is a powerful tuning knob for excitons, Coulomb-bound electron–hole complexes dominating optical properties of two-dimensional semiconductors. While the strain response of bright free excitons is broadly understood, the behaviour of dark free excitons (long-lived excitations that generally do not couple to light due to spin and momentum conservation) or localized excitons related to defects remains mostly unexplored. Here, we study the strain behaviour of these fragile many-body states on pristine suspended WSe2 kept at cryogenic temperatures. We find that under the application of strain, dark and localized excitons in monolayer WSe2—a prototypical 2D semiconductor—are brought into energetic resonance, forming a new hybrid state that inherits the properties of the constituent species. The characteristics of the hybridized state, including an order-of-magnitude enhanced light/matter coupling, avoided-crossing energy shifts, and strain tunability of many-body interactions, are all supported by first-principles calculations. The hybridized excitons reported here may play a critical role in the operation of single quantum emitters based on WSe2. Furthermore, the techniques we developed may be used to fingerprint unidentified excitonic states.

Interface engineering of charge-transfer excitons in 2D lateral heterostructures

“…the Supplementary material . The integrated intensity of the low-energy peak increases linearly with the excitation power, contrary to the saturating behaviour expected from defects 44 , 45 . In addition, we also observe a blue-shift of the peak with increasing excitation powers, similar to the behaviour of interlayer excitons, which blueshift due to dipole–dipole repulsion 46 .…”

Conversion of Classical Light Emission from a Nanoparticle‐Strained WSe2 Monolayer into Quantum Light Emission via Electron Beam Irradiation

“…[ 17–25 ] More recent work builds upon this idea and proposes that point defects, such as atomic vacancies, in addition to strain, are essential to form SPEs. [ 26–32 ] Under these conditions, it is hypothesized that SPEs originate from the hybridization of the strained dark exciton band and a valley symmetry‐breaking defect state. This model was recently supported in a study where the formation of SPEs was observed after applying both strain and electron beam (e − ‐beam) irradiation to WSe 2 .…”

Built-in tensile strain dependence on the lateral size of monolayer MoS2 synthesized by liquid precursor chemical vapor deposition

“…12,13 With regard to optical properties, local strain application can induce exciton funneling, 14,15 efficient exciton to trion conversion 16 or the formation of a new hybrid state of dark and localized excitons. 17…”