Near-Field Mapping and Modulation of Dark Exciton–Plasmon Hybrid States on Planar Open Cavity

The modulation of excitons via coupling with plasmon polaritons represents a crucial approach for controlling light-matter interactions in nanophotonics. However, nanoscale characterization and modulation of dark exciton-plasmon hybrid states remain largely unexplored. In this study, we demonstrate a near-field approach for probing and modulating dark exciton-plasmon hybrid states through planar plasmonic nanostructures at room temperature. The designed meta-structure from the hole array on Au films generates surface plasmon polariton (SPP) interference hotspots with precisely controlled out-of-plane electric fields, enabling direct access to dark exciton and coupled states in monolayer WSe₂. By integrating transmission-mode scanning near-field optical microscopy with in situ photoluminescence spectroscopy, we achieve simultaneous spatial mapping and spectral characterization of dark exciton-SPP hybrid states. We further propose the "<i>quantitative modulation via spacer thickness</i>" theory and approach, which quantifies the system's ultimate coupling capability and enables precise control over both the coupling strength and relative luminescence intensity of dark excitons. Our stress-free planar open cavity design provides a simple yet versatile platform for scalable excitonic devices, such as on-chip lasers and valleytronic systems. The modulation approach enables the multichannel excitonic information processing, which sets the foundation for advanced photonic devices, including optical switches, computing elements, and hybrid integrated circuits.