Double Fano resonances in nanoring cavity dimers: The effect of plasmon hybridization between dark subradiant modes

Li-Yan Yin,Si-Tong Ning,Xia Wang,Shao-Ding Liu,Yun-Huan Huang

doi:10.1063/1.4890100

Abstract

Dark mode which is subradiant plays a key role in the generation of Fano effect. This study proposes that plasmon interaction between dark modes is a favorable method to generate multiple Fano resonances, where plasmon hybridization leads to the formation of a subradiant bonding and a subradiant antibonding combination. It demonstrates that a concentric ring/ring cavity dimer introduces interactions that render bonding quadrupolar ring mode dipole active, resulting in a pronounced Fano resonance. The corresponding antibonding quadrupolar ring mode is excited in a symmetry breaking nonconcentric cavity dimer, and double Fano resonances appear in the spectra.

Highlights

Localized surface plasmon resonances (LSPRs) in metallic nanostructures are promising for many applications including label-free biosensing.[1]
This study proposes that plasmon interaction between dark modes is a favorable method to generate multiple Fano resonances, where plasmon hybridization leads to the formation of a subradiant bonding and a subradiant antibonding combination
077113-7 Yin et al FIG. 5. (a) Extinction, and (b) absorption spectra of symmetry breaking cavity dimer versus the offset d, where the inset represents the geometry of the cavity dimer, and the two inner rings are moved to the same direction

Summary

INTRODUCTION

Localized surface plasmon resonances (LSPRs) in metallic nanostructures are promising for many applications including label-free biosensing.[1]. Plasmon hybridization between the dark modes leads to the formation of a bonding quadrupolar ring mode, and a Fano resonance appears in the spectra. It has been demonstrated that Fano resonances can only be generated in a nonconcentric ring/disk cavity, where the structure symmetry is breaking to excite the dark quadrupolar ring mode.[7,28] The structure symmetry is not breaking for the concentric cavity dimer, but there is a Fano resonance around 852 nm (Fig. 1(c)). The bonding quadrupolar ring mode overlaps with the bright superradiant mode, and the destructive interference between these two modes leads to the formation of the Fano resonance in the concentric ring/ring cavity dimer. It should be noted that in the presence of damping, there is a distinct spectral shift between the near-field and far-field response of plasmonic nanostructures, which has been conformed by theoretical and experimental results.[55,56,57] the spectra are broadening for both the bright and the dark modes, and near-field plots are taken at the extinction peaks and dips.[42]

PLASMON HYBRIDIZATION SCHEMES

CONCLUSION