Strong Coupling between Surface Phonon-Polaritons and Surface Plasmon-Polaritons

Resonantly excited plasmonic nanostructures confine electromagnetic radiation on the nanoscale and therefore enhance the light-matter interaction, which can be used to increase the signature of excitations in the infrared. Here we discuss the coupling between surface phonon-polaritons and localized surface plasmon-polaritons. We perform IR spectroscopy of metal nanoantennas placed on SiO₂ layers of different thickness. Due to strong coupling between the plasmonic excitation of the antennas and the surface phonon-polaritons of the thin SiO₂ layers a splitting of the plasmonic resonance is found. Although the phonon-polaritons themselves are dark excitations under normal illumination, they strongly interact with plasmon-polaritons as we detail for a planar SiO₂ layer beneath the nanostructures. The observed splitting can result in a transparency window, corresponding to suppression of antenna scattering, respectively “cloaking” of the antenna. Furthermore, we investigate the coupling of localized surface plasmon-polaritons to localized surface phonon polaritons of SiO₂ ultra-fine dust particles. Our studies demonstrate the potential of plasmonic nanostructures for specific identification of ultra-fine dust particles and guide the way toward dust sensing devices based on SEIRA.