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

TL;DR

This study demonstrates how mechanical strain can tune and hybridize dark and localized excitons in monolayer WSe2, revealing new states with enhanced optical properties and potential applications in quantum emitters.

Contribution

We developed a cryogenic strain technique for pristine WSe2 and discovered strain-induced hybridization of dark and localized excitons, supported by first-principles calculations.

Findings

Dark and localized excitons are brought into resonance by strain.

Hybrid excitons exhibit enhanced light-matter coupling.

Strain allows tuning of many-body interactions in 2D semiconductors.

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 behavior 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 develop a technique capable of straining pristine suspended WSe2 kept at cryogenic temperatures up to 3\% to study the strain behavior of these fragile many-body states. 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 exciton 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