Manipulating Coherent Plasmon–Exciton Interaction in a Single Silver Nanorod on Monolayer WSe₂

Abstract

Strong coupling between plasmons and excitons in nanocavities can result in the formation of hybrid plexcitonic states. Understanding the dispersion relation of plexcitons is important both for fundamental quantum science and for applications including optoelectronics and nonlinear optics devices. The conventional approach, based on statistics over different nanocavities, suffers from large inhomogeneities from the samples, owing to the nonuniformity of nanocavities and the lack of control over the locations and orientations of the excitons. Here we report the first measurement of the dispersion relationship of plexcitons in an individual nanocavity. Using a single silver nanorod as a Fabry-Pérot nanocavity, we realize strong coupling of plasmon in single nanocavity with excitons in a single atomic layer of tungsten diselenide. The plexciton dispersion is measured by in situ redshifting the plasmon energy via successive deposition of a dielectric layer. Room-temperature formation of plexcitons with Rabi splittings as large as 49.5 meV is observed. The realization of strong plasmon-exciton coupling by in situ tuning of the plasmon provides a novel route for the manipulation of excitons in semiconductors.

Strong Light–Matter Interactions Enabled by Polaritons in Atomically Thin Materials

“…The criteria for strong coupling have been widely discussed in the literature, and, broadly speaking, it is defined when the rate of coherent energy exchange exceeds any damping mechanisms (e.g., g ≫ Γ pl , Γ ex ). Although more than one criterion exists, a common approach to classify the strong coupling regime hinges on the fulfillment of the condition E R > (Γ pl + Γ ex )/2 [provided that (4 g ) 2 > (Γ pl − Γ ex ) 2 ] . An alternative approach—which is particularly useful in the presence of large losses typical of plasmonic cavities—is to make use of the formalism introduced in ref.…”

“…To illustrate this, in Figure we provide a cursory overview of a number of hybrid metal–TMDCs systems exhibiting strong plasmon–exciton interactions. In most cases, the experimental setup consists in hybrid systems composed by atomically thin TMDCs in conjunction with plasmonic resonators, such as metallic nanoparticles with various shapes, nanoparticle‐on‐a‐mirror (NPoM) geometries, plasmonic crystals, as well as plasmonic lattices . A significant number of such plasmonic cavities are based on chemically grown metallic nanoparticles; this is motivated by the high‐quality (up to the single‐crystalline level) and extremely low surface roughness presented by these nanoparticles, which naturally yield plasmonic resonances with smaller linewidths.…”

“…Since the first demonstration of strong coupling between LSPRs in metallic nanoparticles and excitons in 2D TMDCs, a growing number of experimental works have reported signatures of plasmon–exciton strong coupling probed by optical measurements. From the point of view of characterization techniques, many of the aforementioned experiments have used dark‐field scattering spectroscopy methods for determining the amplitude of the polariton anticrossing and infer from it wether the interaction is in the weak or strong coupling regime. However, as it has been recently pointed out by a number of theoretical and experimental works, the sole measurement of the scattering cross‐section is not sufficient to unambiguously conclude if the system is within strong‐coupling regime.…”

Recent Progress on Exciton Polaritons in Layered Transition‐Metal Dichalcogenides

“…The vertical line marks the exciton wavelength. c,d) Reproduced with permission . Copyright 2017, American Chemical Society.…”

Chiral Coupling of Valley Excitons and Light through Photonic Spin–Orbit Interactions

“…In the strong coupling regime, the energy exchanging between optical cavities and emitters compromise the dissipation, giving rise to hybridized states with both properties of light and matter. Excitons in 2D materials can serve as a good candidate for tuning the coupling strength owing to the well‐defined orientation and gate sensitive properties 77–80. Besides, distinct from traditional organic molecules, TMDCs are chemically robust and stable, which are highly desirable for practical photonic applications.…”