Near- and Far-Field Excitation of Topological Plasmonic Metasurfaces

Abstract

The breathing honeycomb lattice hosts a topologically non-trivial bulk phase due to the crystalline-symmetry of the system. Pseudospin-dependent edge states, which emerge at the interface between trivial and non-trivial regions, can be used for the directional propagation of energy. Using the plasmonic metasurface as an example system, we probe these states in the near- and far-field using a semi-analytical model. We provide the conditions under which directionality was observed and show that it is source position dependent. By probing with circularly-polarised magnetic dipoles out of the plane, we first characterise modes along the interface in terms of the enhancement of source emissions due to the metasurface. We then excite from the far-field with non-zero orbital angular momentum beams. The position-dependent directionality holds true for all classical wave systems with a breathing honeycomb lattice. Our results show that a metasurface in combination with a chiral two-dimensional material, could be used to guide light effectively on the nanoscale.

Higher-order topology in plasmonic kagome lattices

“…Starting at Γ the highest energy mode has a monopolar character and the two lowest energy modes are degenerate dipolar modes. At the light line, a strong polariton-like splitting occurs in the highest energy monopolar band due to the coupling to free photons; similar to effects in 1D 28 and other 2D plasmonic lattices [29][30][31] . Notably, the fully electrodynamical interactions remove the cusp at Γ observed in the QS…”

“…From the Poynting vector S , we see how the energy flow is confined to the interface, with direction given by the group velocity v g < 0 of the mode at k x > 0, while φ(E z ) and T z determine the propagation direction of modes upon excitation 30 . For example, beams with non-zero orbital angular momentum will excite a directional mode if the phase vortex of the beam matches the phase vortex in φ(E z ) of the edge eigenmode: this occurs at the centre of an expanded unit cell next to the interface and has been shown in a similar photonic crystal 36,37 .…”

Advances and Prospects in Topological Nanoparticle Photonics

“…This is due to a strong polariton-like splitting at the light line (see highest frequency band in Figure 6e) caused by coupling to free photons, and has been shown in 1D 33,123 and 2D plasmonic arrays. 124 As with the infinite long-range sums in the real space, the calculations for the finite lattice converge slowly with size. This implies that results from finite and periodic infinite lattices may differ, 125 and bulk-boundary correspondence is not so straightforward as with short-range interactions.…”

Exploiting oriented field projectors to open topological gaps in plasmonic nanoparticle arrays

“…Now we focus in arrays of plasmonic nanoparticles. Previously, optical response of metallic nanoparticles has been used to mimic topological condensed matter systems, as in zigzag chains [34,35], diatomic chains of nanospheres [36], or breathing Kagome [37] and breathing honeycomb plasmonic metasurfaces [38,39]. However, in these systems it has been shown that long-range interactions between nanoparticles must be considered, which have a striking effect on the topology of the system [18,19].…”