Mode imaging and selection in strongly coupled nanoantennas

TL;DR

This paper demonstrates direct imaging and selective excitation of bonding and antibonding modes in symmetric nanoantennas, crucial for advanced plasmonic device functionalities and sensing applications.

Contribution

It introduces a method for direct imaging and selective excitation of specific plasmon modes in strongly coupled nanoantennas, advancing mode control in complex nanostructures.

Findings

Antibonding mode exhibits a two-lobed pattern in imaging.

Excitation of antibonding mode is forbidden at symmetric feedgap.

Mode energy splitting suppresses bonding mode excitation.

Abstract

The number of eigenmodes in plasmonic nanostructures increases with complexity due to mode hybridization, raising the need for efficient mode characterization and selection. Here we experimentally demonstrate direct imaging and selective excitation of the bonding and antibonding plasmon mode in symmetric dipole nanoantennas using confocal two-photon photoluminescence mapping. Excitation of a high-quality-factor antibonding resonance manifests itself as a two-lobed pattern instead of the single spot observed for the broad bonding resonance, in accordance with numerical simulations. The two-lobed pattern is observed due to the fact that excitation of the antibonding mode is forbidden for symmetric excitation at the feedgap, while concomitantly the mode energy splitting is large enough to suppress excitation of the bonding mode. The controlled excitation of modes in strongly coupled plasmonic nanostructures is mandatory for efficient sensors, in coherent control as well as for implementing well-defined functionalities in complex plasmonic devices.