Subgroup Decomposition of Plasmonic Resonances in Hybrid Oligomers: Modeling the Resonance Lineshape

• Published in: Nano letters Vol. 12; no. 4; pp. 2101 - 2106
• Main Authors: Rahmani, Mohsen, Lei, Dang Yuan, Giannini, Vincenzo, Lukiyanchuk, Boris, Ranjbar, Mojtaba, Liew, Thomas Yun Fook, Hong, Minghui, Maier, Stefan A
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 11.04.2012
• Subjects: Collective excitations (including excitons, polarons, plasmons and other charge-density excitations); Condensed matter: electronic structure, electrical, magnetic, and optical properties; Decomposition; Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures; Exact sciences and technology; General equipment and techniques; Instruments, apparatus, components and techniques common to several branches of physics and astronomy; Interference; Nanostructure; Oligomers; Particle shape; Physics; Plasmonics; Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing; Spectra; Spectral lines; Subgroups; Surface and interface electron states; plasmonic oligomers; subgroup decomposition; surface plasmons; Fano resonances; Subwavelength nanostructures; Nanocluster; Particle size; Calcium selenides; Line shape; Interference; Theoretical study; Line widths; Subgroup; Pentamer; Oligomers; Plasmons; Modelling; Resonance; Particle shape; Biosensors
• ISSN: 1530-6984; 1530-6992
• DOI: 10.1021/nl3003683

Plasmonic resonances with a Fano lineshape observed in metallic nanoclusters often arise from the destructive interference between a dark, subradiant mode and a bright, super-radiant one. A flexible control over the Fano profile characterized by its linewidth and spectral contrast is crucial for many potential applications such as slowing light and biosensing. In this work, we show how one can easily but significantly tailor the overall spectral profile in plasmonic nanocluster systems, for example, quadrumers and pentamers, by selectively altering the particle shape without a need to change the particle size, interparticle distance, or the number of elements of the oligomers. This is achieved through decomposing the whole spectrum into two separate contributions from subgroups, which are efficiently excited at their spectral peak positions. We further show that different strengths of interference between the two subgroups must be considered for a full understanding of the resulting spectral lineshape. In some cases, each subgroup is separately active in distinct frequency windows with only small overlap, leading to a simple convolution of the subspectra. Variation in particle shape of either subgroup results in the tuning of the overall spectral lineshape, which opens a novel pathway for shaping the plasmonic response in small nanoclusters.