From individual to strongly coupled metallic nanocavities

TL;DR

This paper demonstrates that metallic nanocavities can exhibit very strong coupling mediated by propagating surface plasmons, even at distances hundreds of nanometers apart, leading to significant changes in their optical symmetry and response.

Contribution

It introduces a new regime of strong coupling between nanocavities in metal films driven by surface plasmons, extending interaction ranges and altering optical properties.

Findings

Strong coupling observed at hundreds of nanometers distance

Nanocavities lose individual symmetry and behave as a single dipolar system

A quantitative model describes the transition from individual to coupled states

Abstract

Localized plasmonic modes of metallic nanoparticles may hybridize like those of atoms forming a molecule. However, the rapid decay of the plasmonic fields outside the metal severely limits the range of these interactions to tens of nanometers. Herein, we demonstrate very strong coupling of nanocavities in metal films, sparked by propagating surface plasmons and evident even at much larger distances of hundreds of nanometers for the properly selected metal/wavelength combination. Such strong coupling drastically changes the symmetry of the charge distribution around the nanocavities making it amenable to probing by the nonlinear optical response of the medium. We show that when strongly coupled, equilateral triangular nanocavities lose their individual three-fold symmetry to adopt the lower symmetry of the coupled system and then respond like a single dipolar entity. A quantitative model is suggested for the transition from individual to strongly coupled nanocavities.