Robustness of the Rabi splitting under nonlocal corrections in plexcitonics

TL;DR

This paper theoretically investigates how nonlocal effects in metals influence the strong coupling between excitons and plasmons, finding that nonlocality has limited impact on Rabi splitting in typical nanoscale structures.

Contribution

It provides a detailed theoretical analysis showing that nonlocal corrections have minimal effect on Rabi splitting, clarifying their role in plexcitonics.

Findings

Nonlocal effects minimally affect Rabi splitting width.

Hybrid modes remain well distinguishable despite nonlocal corrections.

Analytic Mie theory solutions support the limited influence of nonlocality.

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.