2021/07/22 by Mariano Pascale, Sander A. Mann, Pascale, Mariano +5
Engineering · Materials Science · Physics and Astronomy · #FOS: Physical sciences #Metamaterials and Metasurfaces Applications #Optics (physics.optics) #Photonic Crystals and Applications #Plasmonic and Surface Plasmon Research
paper · pdf · doi:10.48550/arxiv.2107.10770
openalex publication_date 2021/07/22 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
Plasmonic nanostructures with singular geometries can exhibit a broadband\nscattering response that at first glance appears to violate the lower bounds\nfor the radiation quality (Q) factor of small radiators, known as the Chu\nlimit. Here we explore this apparent contradiction, investigating the Q factor\nof the resonant modes supported by two nearly touching cylinders, and analyze\nhow their fractional bandwidth fares in relation to the Chu limit. We first\nderive lower bounds for the radiation Q factors of two-dimensional objects of\narbitrary cross-section. We then discuss the dissipation and radiation Q\nfactors associated with the plasmonic resonances of a cylinder dimer as a\nfunction of its gap size. We show that the radiation Q factor is always larger\nthan the minimum Q and, as long as the peaks in the scattering spectrum are\nwell separated, their bandwidth is equal to the inverse of their Q factor. In\nthe limit of touching cylinders, the resonance spectra transition from discrete\nto a continuum around an accumulation point, yielding a broadband response for\nany finite level of material loss. Within any given frequency interval, the\nresponse is the result of a multitude of plasmon resonances, each individually\nobeying the Chu limit. Nevertheless, the connection between the Q factor and\nthe overall bandwidth of the scattering response is lost. Our study sheds light\nonto the exotic resonant phenomena emerging when plasmonic materials are shaped\nin singular geometries, and outlines their opportunities and limitations for\nnanophotonics.\n