Light-Emitting Plexciton: Exploiting Plasmon–Exciton Interaction in the Intermediate Coupling Regime

TLDR

The interaction between plasmons in metal nanostructures and excitons in layered materials is of recent interest because it combines tunable spectral and spatial properties from plasmons with large optical nonlinearity and light‑emitting properties from excitons. This study demonstrates light‑emitting plexcitons formed by coupling neutral excitons in monolayer WSe₂ with highly confined nanocavity plasmons in a nanocube‑over‑mirror system. The hybrid system achieves strong confinement by shrinking the hot spot within the gap between the nanocube and the metal film, enabling coupling between the excitons and plasmons. An anticrossing dispersion and a 1700‑fold photoluminescence enhancement were observed, attributed to increased local density of states, and numerical simulations confirmed the interaction, demonstrating a compact room‑temperature platform for quantum cavity electromagnetics at deep subwavelength scales.

Abstract

The interaction between plasmons in metal nanostructures and excitons in layered materials attracts recent interests due to its fascinating properties inherited from the two constituents, e.g., the high tunability on its spectral or spatial properties from the plasmonic component, and the large optical nonlinearity or light emitting properties from the excitonic counterpart. Here, we demonstrate light-emitting plexcitons from the coupling between the neutral excitons in monolayer WSe2 and highly confined nanocavity plasmons in the nanocube-over-mirror system. We observe, simultaneously, an anticrossing dispersion curve of the hybrid system in the dark-field scattering spectrum and a 1700 times enhancement in the photoluminescence. We attribute the large photoluminescence enhancement to the increased local density of states by both the plasmonic and excitonic constituents in the intermediate coupling regime. In addition, increasing the confinement of the hybrid systems is achieved by shrinking down the size of the hot spot within the gap between the nanocube and the metal film. Numerical calculations reproduce the experimental observations and provide the effective number of excitons taking part in the interaction. This highly compact system provides a room temperature testing platform for quantum cavity electromagnetics at the deep subwavelength scale.