Site-controlled coupling between plasomonic nanostructures and strain-localized excitons in nano-indented WSe₂

Localized excitons can be deterministically created in 2D transition metal dichalcogenides (TMDs) via strain engineering, which modifies the local band structure and gives rise to site-controlled single photon emission. This has led to recent interest in coupling these emitters to photonic structures to create on-chip-compatible platforms for quantum information and communications. Strong coupling to plasmonic nanostructures is a pathway to coherent control at room temperature. However, prior attempts to couple strain localized excitons in TMDs to plasmonic structures have remained in the weak coupling regime characterized by the Purcell effect.



Here we achieve site-controlled coupling between the localized surface plasmon resonance (LSPR) of Au discs and strain-localized excitons in WSe₂. We employ nano-indentation using an atomic force microscope (AFM) to create on-demand spatially localized excitons that display quantum emission. The exciton-plasmon coupling is characterized by mode-splitting of the scattering spectra, indicating fast energy exchange between the two systems. The LSPR wavelength is tuned via disc diameter in order to map the avoided crossing between the LSPR and exciton resonances. The observed coupling strength approaches the strong coupling regime at room temperature. Our results establish this system as a potential platform for novel quantum light sources in which to study coherent control as well as nonlinear exciton-plasmon polariton behavior.