Strain-Correlated Localized Exciton Energy in Atomically Thin Semiconductors

Single-photon emitters represent a key component for many quantum technologies, from quantum communication to computation. Atomically thin two-dimensional materials are promising hosts of quantum emitters, thanks to great freedom in assembling atomically precise heterostructures that are suitable for chip integration. Recent work showed that stable quantum emitters can be positioned deterministically by placing a 2D material over protrusions in a substrate. However, the origins of these emitters and their broad spectral distribution remain unclear. It has been suggested that the microscopic strain modulation near the protrusions plays a role because of local band gap modulation and band realignment, but the precise relationship between local strain and the transition energy of the quantum emitter remains elusive. To tackle this problem, we study free and localized excitons in a monolayer of WSe2 transferred onto microstructures. These measurements show positive correlation between the localized emission energies and the strain-modulated free-exciton energies. Moreover, their energy separation is larger than 42 meV, in agreement with recent theory suggesting that the quantum emitters originate from local strain-mediated mixing of dark exciton states and highly localized atomic defect states. Our results open the potential for deterministic positioning and spectral control of quantum emitters in 2D material heterostructures.