Complex bound and leaky modes in chains of plasmonic nanospheres

Abstract

Bound and leaky modes with complex wavenumber in chains (linear arrays) of plasmonic nanospheres are characterized for both longitudinal and transverse polarization states (with respect to the array axis). The proposed method allows for the description of each mode evolution when varying frequency. As a consequence, full characterization of the guided modes with complex wavenumber is provided in terms of propagation direction, guidance or radiance, proper or improper, and physical or nonphysical conditions. Each nanosphere is modeled according to the single dipole approximation, and the metal permittivity is described by the Drude model. Modal wavenumbers are obtained by computing the complex zeroes of the homogeneous equation characterizing the field in the one dimensional periodic array. The required periodic Green's function is analytically continued into the complex wavenumber space by using the Ewald method. Furthermore, a parametric analysis of the mode wavenumbers is performed with respect to the geometrical parameters of the array.

Hyperbolic metamaterial as super absorber for scattered fields generated at its surface

“…The curve shows that the wave propagating inside the HM is backward because β z α z < 0. 20,21 The −k z solution, with β z < 0 and α z > 0, would be the equivalent solution decaying in the + z direction. We note that similar diagrams are preserved at other frequencies as well (see the discussion in Sec.…”

Exceptional points of degeneracy andPTsymmetry in photonic coupled chains of scatterers

“…In this study, we are only interested in the guided (bound) modes. An alternative representation of the fields can be accomplished via a combination of both spectral and spatial GFs, such as in the Ewald method for linear arrays [59][60][61][62].…”

“…Furthermore, such additional radiation losses (at high frequencies) could be manipulated and engineered to produce effects related to EPDs, such as loss-induced transmission [39]. Here, the analysis of lossy chains of infinite length is omitted because it would require the use of an infinitely periodic GF [59][60][61][62], whereas our main scope is to provide a simple but intuitive analysis based on the nearest-neighbor approximation, that resembles the TB approach used in [48,50,64,65]. We consider an example of a chain in vacuum (i.e., These values approximately satisfy (19) because of the lowfrequency choice for this EPD to occur.…”

Overcoming the adverse effects of substrate on the waveguiding properties of plasmonic nanoparticle chains

“…Dispersion relations and transient processes (wave packet transmission) in plasmonic chains have also been studied in detail. 19,20,[27][28][29] In particular, it was found that chains of spherical particles cannot support propagation of well-formed wave packets due to the flatness of the corresponding dispersion curves. This, in particular, has motivated our interest in chains of non-spherical particles such as prolate or oblate spheroids, 20,21 which can serve as broadband SPP waveguides.…”