Topological Surface-plasmon-polariton Modes on Biharmonic Metal-dielectric Gratings*

The area of topological plasmonics is a relatively new and rather unploughed field. The majority of progress thus far has been in constructing crystal structures whose atomic sites take the form of an array of metallic nanoparticles. Such nanoparticles are capable of hosting localised plasmon-polariton modes, which form the basis upon which a tight-binding model may be generated. Through this model, the topological character of the lattice may be probed. A similar result may be arrived at by considering surface-plasmon-polariton resonances on biharmonic metal-dielectric gratings. In such a case, provided that the surface is smooth and has a parabolic profile, the amplitude of the SPP mode may be described by an emergent 1D Schrödinger equation. This equation may then be made to mimic the SSH model through a suitable manipulation of the physical parameters of the system. Then topological states may be observed within the basic scattering formalism, whose existance and character are then confirmed through a tight-binding model.