# Exciting Pseudospin Dependent Edge States in Plasmonic Metasurfaces

## TL;DR

This paper investigates plasmonic metasurfaces supporting pseudospin dependent edge states, revealing their properties, propagation behavior, and optical responses, with potential implications for topological photonics.

## Contribution

It introduces a detailed analysis of pseudospin dependent edge states in plasmonic metasurfaces considering full electrodynamic effects, expanding understanding beyond idealized models.

## Key findings

- Edge states exhibit pseudospin dependence influenced by electromagnetic spin angular momentum.
- Propagation direction is determined by local spin angular momentum sign.
- Radiation and retardation significantly affect the optical response of the metasurface.

## Abstract

We study a plasmonic metasurface that supports pseudospin dependent edge states confined at a subwavelength scale, considering full electrodynamic interactions including retardation and radiative effects. The spatial symmetry of the lattice of plasmonic nanoparticles gives rise to edge states with properties reminiscent of the quantum spin Hall effect in topological insulators. However, unlike the spin-momentum locking characteristic of topological insulators, these modes are not purely unidirectional and their propagation properties can be understood by analysing the spin angular momentum of the electromagnetic field, which is inhomogenous in the plane of the lattice. The local sign of the spin angular momentum determines the propagation direction of the mode under a near-field excitation source. We also study the optical response under far-field excitation and discuss in detail the effects of radiation and retardation.