Buffering plasmons in nanoparticle waveguides at the virtual-localized transition

TL;DR

This paper investigates plasmonic energy transfer in nanoparticle chains, revealing that maximum excitation occurs at the virtual-localized transition due to slow group velocity, offering new insights for plasmonic control.

Contribution

It introduces an analytical framework to distinguish resonant, localized, and virtual states in nanoparticle waveguides, highlighting the significance of the virtual-localized transition for energy transfer.

Findings

Maximum excitation transfer occurs at the virtual-localized transition.

Slow group velocity at the transition enhances excitation buffering.

Transition sensitivity offers new plasmonic control tools.

Abstract

We study the plasmonic energy transfer from a locally excited nanoparticle (LE-NP) to a linear array of small NPs and we obtain the parametric dependence of the response function. An analytical expression allows us to distinguish the extended resonant states and the localized ones, as well as an elusive regime of virtual states. This last appears when the resonance width collapses and before it becomes a localized state. Contrary to common wisdom, the highest excitation transfer does not occur when the system has a well defined extended resonant state but just at the virtual-localized transition, where the main plasmonic modes have eigenfrequencies at the passband edge. The slow group velocity at this critical frequency enables the excitation buffering and hence favors a strong signal inside the chain. A similar situation should appear in many other physical systems. The extreme sensitivity of this transition to the waveguide and LE-NP parameters provides new tools for plasmonics.