Plasmon dispersion relation of Au and Ag nanowires

Defect-induced activation of symmetry forbidden infrared resonances in individual metallic nanorods

“…For increasing incident angle, the coupling between the incident radiation and the dark modes becomes more efficient ͑up to a certain angle depending on the surrounding medium͒ while coupling to bright modes is less efficient. 15 We observe similar behavior for the IR antennas as shown in Fig. 3 where a quantitative comparison of extinction cross sections is given.…”

“…To identify clearly the effect of non-normal incidence of light on the appearance of the l = 2 mode, we tilted the sample to various angles ͑30°, 45°, and 60°with an error of about Ϯ5°͒ between the substrate normal and the direction of the incident light in air, which corresponds to angles of 13°, 19°, and 23°in ZnS according to Snell's law. As known from literature, 15,17,18 dark modes appear for such configurations because the incident electrical field is no longer constant along the length of the nanoantenna and phase shifts occur over the full nanorod length. For increasing incident angle, the coupling between the incident radiation and the dark modes becomes more efficient ͑up to a certain angle depending on the surrounding medium͒ while coupling to bright modes is less efficient.…”

“…At oblique incidence, symmetry-breaking arises due to retardation effects and excitation of the dark modes becomes possible because of the phase difference of the incoming wave at the two nanorod ends. Indeed, such behavior was observed in nanorods 14,15,17 and also in other metallic nanostructures. 18 In addition, dark modes are observed in spectroscopic studies of complex multimer structures.…”

“…Besides the strong fundamental ͑l =1͒ mode, such nanoantennas also exhibit multipolar ͑l Ͼ 1͒ resonances at res / l. 9,[12][13][14] Only multipolar modes with an antisymmetric charge distribution ͑odd l͒ can be optically excited at normal incidence of light because their total dipole moment does not vanish. 13,15 In contrast to these bright modes, plasmonic excitations with a centrosymmetric charge distribution ͑even l͒ ͑Ref. 16͒ cannot be excited under such conditions and are known as dark modes.…”

Design and implementation of plasmonic metamaterials and devices

“…Metal nanowires are known to support propagation of highly confined surface plasmons along their length [130,131] -a fact that is experimentally confirmed [132,133]-and when the surface plasmons reach the ends of a short nanowire, they can be reflected and form standing wave resonances [134][135][136] of different orders corresponding to different resonances. When a bent nanowire is used as a metamaterial metaatom, those resonances which show a virtual current loop can create an effective magnetization M eff and thus lead to a magnetic response [137], and those forming a dipolar distribution of charges can create a polarization P eff which leads to an electric response.…”