Robustness of the Rabi Splitting under Nonlocal Corrections in Plexcitonics

Abstract

We explore theoretically how nonlocal corrections in the description of the metal affect the strong coupling between excitons and plasmons in typical examples where nonlocal effects are anticipated to be strong, namely small metallic nanoparticles, thin metallic nanoshells or dimers with narrow separations, either coated with or encapsulating an excitonic layer. Through detailed simulations based on the generalised nonlocal optical response theory, which simultaneously accounts both for modal shifts due to screening and for surface-enhanced Landau damping, we show that, contrary to expectations, the influence of nonlocality is rather limited, as in most occasions the width of the Rabi splitting remains largely unaffected and the two hybrid modes are well distinguishable. We discuss how this behaviour can be understood in view of the popular coupled-harmonic-oscillator model, while we also provide analytic solutions based on Mie theory to describe the hybrid modes in the case of matryoshka-like single nanoparticles. Our analysis provides an answer to a so far open question, that of the influence of nonlocality on strong coupling, and is expected to facilitate the design and study of plexcitonic architectures with ultrafine geometrical details.

Mie excitons: Understanding strong coupling in dielectric nanoparticles

“…Since this is practically impossible, we focus here on a NP with similar linewidth and resonance position of its lower-energy mode before coupling -in plasmonics, this is of course ian electric dipolar mode. To tune the plasmon mode at 1.76 eV, we consider silica-gold nanoshells (ε silica = 2.13) instead of homogeneous gold spheres, and introduce plasmon hybridisation as a mode shifting mechanism [48,49]. For a silica core of radius 19.5 nm, total nanoshell radius (R 1 in the previous context) 25 nm, and D = 20 nm, the extinction spectrum of Fig.…”

Plasmonic quantum effects on single-emitter strong coupling

“…In fact, although similar systems have already been investigated by some of the authors of this article [70], this result has not been observed before. On the contrary, Tserkezis et al [56,71] have demonstrated robustness of strong coupling against nonlocal corrections, when collective emitters are considered. As we will see later, however, this behavior is hindered in the vicinity of noble metal systems, since photon emission spectra are strongly affected by d-band transitions.…”

“…The closer they are to a nanoplasmonic system, the more efficiently their fields can probe nonlocal and quantum effects in the metal response [1][2][3][4]. Recent studies have highlighted the impact of nonlocality on single-emitter weak coupling [53][54][55], as well as in plasmon-exciton systems in the strong coupling regime [56]. Quantum effects have also been investigated in metals, in plasmon-exciton systems [57], and in molecules, beyond the point-dipole approximation [21].…”

Tunable Fano Resonance and Plasmon–Exciton Coupling in Single Au Nanotriangles on Monolayer WS2 at Room Temperature

“…Thus an extended criterion is demanded. When the detuning is smaller than ω ex , the splitting of plexcitonic states can be approximately expressed in the form of ℏΩ 0 through the classic description of strong coupling . When ℏΩ 0 > ℏ W ′ ex + ℏ W ′ pl , the system with δ not equating to 0 achieves the strong coupling regime.…”