[Prof. Kyoung-Duck Park] Tip-Enhanced Dark Exciton Nanoimaging and Loc…

caption. (a) Topography, (b) strain, (c) bright exciton intensity, and (d) dark exciton XD intensity across a 200 × 200 nm2 scan area of monolayer WSe2. Averaged cross sections of intensities and strain (e) for blue dotted regions in (c) and (d) and correspondingly (f) for red dotted regions.

[Prof. Kyoung-Duck Park] Tip-Enhanced Dark Exciton Nanoimaging and Local Strain Control in Monolayer WSe2 

Dark excitons in transition-metal dichalcogenides, with their long lifetimes and strong binding energies, provide potential platforms from photonic and optoelectronic applications to quantum information science even at room temperature. However, their spatial heterogeneity and sensitivity to strain is not yet understood. Here, we combine tip-enhanced photoluminescence spectroscopy with atomic force induced strain control to nanoimage dark excitons in WSe2 and their response to local strain. Dark exciton emission is facilitated by out-of-plane picocavity Purcell enhancement giving rise to spatially highly localized emission, providing for higher spatial resolution compared to bright exciton nanoimaging. Further, tip–antenna-induced dark exciton emission is enhanced in areas of higher strain associated with bubbles. In addition, active force control shows dark exciton emission to be more sensitive to strain with both compressive and tensile lattice deformation facilitating emission. This interplay between localized strain and Purcell effects provides novel pathways for nanomechanical exciton emission control.