Collective Strong Light-Matter Coupling in Hierarchical Microcavity-Plasmon-Exciton Systems

Journal article, 2019

Polaritons are compositional light-matter quasiparticles that arise as a result of strong coupling between the vacuum field of a
resonant optical cavity and electronic excitations in quantum emitters. Reaching such a regime is often hard, as it requires materials
possessing high oscillator strengths to interact with the relevant optical mode. Two-dimensional transition metal dichalcogenides (TMDCs) have
recently emerged as promising candidates for realization of strong coupling regime at room temperature. However, these materials
typically provide coupling strengths in the range of 10−40 meV, which may be insufficient for reaching strong coupling with low quality factor
resonators. Here, we demonstrate a universal scheme that allows a straightforward realization of strong coupling with 2D materials and
beyond. By intermixing plasmonic excitations in nanoparticle arrays with excitons in a WS2 monolayer inside a resonant metallic
microcavity, we fabricate a hierarchical system with the collective microcavity−plasmon−exciton Rabi splitting exceeding ∼500
meV at room temperature. Photoluminescence measurements of the coupled systems show dominant emission from the lower
polariton branch, indicating the participation of excitons in the coupling process. Strong coupling has been recently suggested to
affect numerous optical- and material-related properties including chemical reactivity, exciton transport, and optical
nonlinearities. With the universal scheme presented here, strong coupling across a wide spectral range is within easy reach and
therefore exploration of these exciting phenomena can be further pursued in a much broader class of materials.