Plasmon-polaritonic quadrupole topological insulators

TL;DR

This paper proposes a design for plasmonic metamaterials that realize quadrupole topological insulators, enabling control over topological phases through nanocavity geometry, advancing the development of topological plasmonic devices.

Contribution

It introduces a novel lattice of plasmon-polaritonic nanocavities that achieves quadrupole topological insulators via geometry-dependent coupling sign-reversal.

Findings

The system exhibits multiple topological and trivial phases.

Topological phases are characterized by nested Wannier bands.

Topological quadrupole moment is tunable by nanocavity spacing.

Abstract

Quadrupole topological insulator is a symmetry-protected higher-order topological phase with intriguing topology of Wannier bands, which, however, has not yet been realized in plasmonic metamaterials. Here, we propose a lattice of plasmon-polaritonic nanocavities which can realize quadrupole topological insulators by exploiting the geometry-dependent sign-reversal of the couplings between the daisy-like nanocavities. The designed system exhibits various topological and trivial phases as characterized by the nested Wannier bands and the topological quadrupole moment which can be controlled by the distances between the nanocavities. Our study opens a pathway toward plasmonic topological metamaterials with quadrupole topology.