Near- and Far-Field Excitation of Topological Plasmonic Metasurfaces

17 pags., 10 figs.
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 nearand 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.
M.P., R.V.C and P.A.H. acknowledge funding from the Leverhulme Trust. V.G. acknowledges the Spanish Ministerio de Economia y Competitividad for financial support through the grant NANOTOPO (FIS2017-91413-EXP) and also the Ministerio de Ciencia, Innovación y Universidades through the grant MELODIA (PGC2018-095777-B-C21). P.A.H. acknowledges financial support from Fundação para a Ciência e a Tecnologia and Instituto de Telecomunicações under projects UID/EEA/50008/2020 and the CEEC Individual program with reference CEECIND/03866/2017. S.A.M. acknowledges the Lee-Lucas Chair in Physics.