Hierarchical Plasmonic Nanocavities for Simultaneously Probing Diverse Excitons in WSe2 at Room Temperature.

Two-dimensional transition metal dichalcogenides have emerged as promising candidates for optoelectronic applications because of their rich excitonic landscape featuring distinct spin-valley configurations. High-quality plasmonic nanocavities can dramatically enhance exciton-plasmon coupling through extreme optical field confinement. However, it has remained elusive to develop a robust nanocavity system for the manipulation of different excitons toward room-temperature excitonic devices. Herein we present a type of hierarchical plasmonic nanocavity constructed on a pyramid array for probing diverse excitons in WSe2 monolayer and multilayer at room temperature. Different excitons, including dark A, localized, and interlayer excitons, can be simultaneously detected and modulated within the plasmonic nanocavities. This hierarchical nanocavity platform utilizes sharp pyramid tips to introduce strain confinement and out-of-plane field enhancement for visualizing both localized and dark A excitons, whose emissions can be selectively modified by controlling the cavity dimensions. Different from classical bright A excitons, the valley-polarized emission enhancement of dark A excitons shows the opposite handedness to the excitation state. Our results offer an interesting cavity platform for the investigation of different excitonic systems and the development of quantum emitters.