title: Coexistence of Scattering Enhancement and Suppression by Plasmonic Cavity Modes in Loaded Dimer Gap-Antennas.
abstract: Plasmonic nanoantenna is of promising applications in optical sensing and detection, enhancement of optical nonlinear effect, surface optical spectroscopy, photoemission, etc. Here we show that in a carefully-designed dimer gap-antenna made by two metallic nanorods, the longitudinal plasmon antenna mode (AM) of bonding dipoles can compete with the transverse plasmonic cavity modes (CMs), yielding dramatically enhanced or suppressed scattering efficiency, depending on the CMs symmetry characteristics. More specifically, it is demonstrated that an appropriately loaded gap layer enables substantial excitation of toroidal moment and its strong interaction with the AM dipole moment, resulting in Fano- or electromagnetically induced transparency (EIT)-like profile in the scattering spectrum. However, for CMs with nonzero azimuthal number, the spectrum features a cumulative signature of the respective AM and CM resonances. We supply both detailed near-field and far-field analysis, showing that the modal overlap and phase relationship between the fundamental moments of different order play a crucial role. Finally, we show that the resonance bands of the AM and CMs can be tuned by adjusting the geometry parameters and the permittivity of the load. Our results may be useful in plasmonic cloaking, spin-polarized directional light emission, ultra-sensitive optical sensing, and plasmon-mediated photoluminescence.
authors.affiliation: College of Electronic and Information Engineering, Shenzhen Graduate School, Harbin Institute of Technology, Xili, Shenzhen 518055, China.
authors.forename: Qiang
authors.initials: Q
authors.lastname: Zhang
authors.affiliation: College of Electronic and Information Engineering, Shenzhen Graduate School, Harbin Institute of Technology, Xili, Shenzhen 518055, China.
authors.forename: Jun-Jun
authors.initials: JJ
authors.lastname: Xiao
authors.affiliation: College of Electronic and Information Engineering, Shenzhen Graduate School, Harbin Institute of Technology, Xili, Shenzhen 518055, China.
authors.forename: Meili
authors.initials: M
authors.lastname: Li
authors.affiliation: Department of Applied Physics, Chongqing University, Chongqing 400044, China.
authors.forename: Dezhuan
authors.initials: D
authors.lastname: Han
authors.affiliation: College of Physics, Optoelectronics and Energy of Soochow University, &Collaborative Innovation Center of Suzhou Nano Science and Technology, Soochow University, Suzhou 215006, China.|Jiangsu Key Laboratory of Thin Films, Soochow University, Suzhou 215006, China.
authors.forename: Lei
authors.initials: L
authors.lastname: Gao