Plasmon resonances and the plasmon-induced field enhancement in nanoring dimers

Abstract

Plasmon resonances and the plasmon-induced field enhancement (FE) in sodium nanoring dimers are investigated by time-dependent density functional theory. For larger separations, the optical absorption, the induced charge response and the frequency dependent current demonstrate that there are two capacitive coupling plasmon modes. One feature of FE is that, in the surface region of the nanoring, it has a very large maximum. Another feature of FE is that, along the perpendicular bisector of the line segment joining the two nanoring center points in the middle region of the nanoring dimers, it has maxima. With the decrease of the gap distance, because of the electrons tunneling across the dimer junction and screening, collective excitation modes are changed, and the charge transfer plasmon modes emerge in the nanoring dimers. FE induced by any plasmon modes decreases in the gap region. Moreover, corresponding to different gap distances, the high-energy plasmon resonance peak almost does not shift, because this plasmon mode is mainly the collective excitation as a result of interactions among degenerate individual electronic states.

Near-Field Mediated Plexcitonic Coupling and Giant Rabi Splitting in Individual Metallic Dimers

“…Several concepts such as hybridization, Fano resonances, and Rabi splitting have been successfully transferred from atomic and molecular physics to describe analogue phenomena seen in plasmonic systems. In the strong coupling regime, − ,− the coupling between a molecular exciton and a plasmonic cavity results in anticrossings of the hybrid plexciton dispersion curves and the formation of two hybrid energy states separated by a Rabi splitting energy. More recently, dynamic tuning , and ultrafast manipulation ,, of the plexcitonic coupling have been investigated in such hybrid nanostructures.…”

“…Previous studies have shown that coupling between elementary excitations can be mediated by the near-field and in particular by the highly enhanced electric field near the surfaces of plasmonic nanostructures, known as “hot spots”. − The strong and localized field in a plasmonic hot spot enhances the interaction between LSPRs and the local excitons, much as it enhances other molecular excitations. Plasmonic dimers are the canonical geometry for the generation of high-intensity hot spots, where the local field is sufficient to give rise to surface enhanced Raman spectroscopy at the single molecule level .…”