Enhancing dark excitons in monolayer WSe₂ via strain-induced hybridization with defect states

Dark excitons in group VI transition metal dichalcogenides (TMDCs) have garnered significant interest due to their extended charge lifetime, spin lifetime, and diffusion length compared to bright excitons, presenting exciting opportunities for quantum communication and optoelectronic devices. However, their optical insensitivity poses challenges for investigation and manipulation. Here, we employ a strain engineering approach to introduce localized strain in monolayer WSe₂ using a substrate with prepatterned holes, resulting in the hybridization of dark excitons with bright defect states. This hybridization significantly enhances photoluminescence (PL) intensity and reduces the linewidths of dark excitons by orders of magnitude. Additionally, the hybridized states exhibit unique features in temperature-dependent and linearly polarized PL spectra, with stable localization across a broad excitation power range (up to 0.4 mW) and tunable circular polarization under a magnetic field (87% at −9 T). These findings underscore strain engineering as an effective method for enhancing dark excitons and provide new insights into exciton physics in TMDCs, paving the way for advanced optoelectronic technologies.