Effect of Symmetry Breaking on Plasmonic Coupling in Nanoring Dimers
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Effect of Symmetry Breaking on Plasmonic Coupling in Nanoring Dimers Bereket Dalga Dana 1 & Alemayehu Nana Koya 2 & Xiaowei Song 1 & Jingquan Lin 1 Received: 2 September 2019 / Accepted: 4 May 2020 # Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract Breaking the morphological and compositional symmetries of metallic nanoparticle (NP) dimers provides a novel approach to modulate plasmon coupling between the NPs. In this study, we theoretically investigate the effect of symmetry breaking on the plasmonic coupling in morphologically asymmetric Au nanoring-nanodisk (NR-ND) dimer, compositionally heterogeneous AuAg nanoring dimer, and compositionally as well as morphologically asymmetric Au-Ag NR-ND heterodimers. It has been found that when the inner radii of symmetrical Au NR dimer is decreased, the scattering spectral intensity of coupled bonding mode and higher-order coupled bonding mode drastically decreases and increases, respectively. Besides, the effect of aspect ratio on the plasmon resonance modes is investigated. Furthermore, with fixed geometric parameters of one NR and by morphing the shape of the other NR into ND through inner radius, we show the generation and modification of a Fano resonance. As a result of introducing morphological and compositional asymmetry separately, single Fano-type spectral feature is observed in the scattering spectra. We demonstrate that the double Fano resonances can be easily achieved in compositionally and morphologically asymmetric heterodimer with double symmetry breaking. These dual modes are caused by the interference of dipolar bright mode (localized LSPR modes) of Ag NP with the quadrupole and hexapole modes (interband transitions) of the Au NP. Finally, at optimum asymmetric heterodimers, we discussed the effect of refractive index on the Fano-type resonance. These new and simple designs provide a novel insight to modulate optical response and the generation of higher-order Fano resonances, which have many potential applications such as in photonics and refractive index sensing. Keywords Plasmon coupling . Symmetry breaking . Fano resonances . Refractive index sensing
Introduction Localized surface plasmon resonance (LSPR) arises in the noble metal nanostructures due to the collective oscillation of conduction band electrons in response to external electromagnetic field [1, 2]. These resonance properties are highly dependent on the shape, size, material composition, and the refractive index of the surrounding medium of the nanostructures [3–5]. Moreover, it has attracted extensive research interest because of many promising applications in areas such as
* Xiaowei Song [email protected] * Jingquan Lin [email protected] 1
School of Science, Changchun University of Science and Technology, Changchun 130022, China
2
Istituto Italiano di Tecnologia, via Morego 30, 16163 Genoa, Italy
chemical and biological sensing [6], negative index materials [7], plasmonic waveguiding [8, 9], and information technology [1]. Apart from numerous LS
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