Plasmons in Two-Dimensional Topological Insulators

TL;DR

This paper investigates collective excitations in two-dimensional topological insulators, revealing edge and bulk plasmons with unique properties depending on the topological phase, using the random phase approximation.

Contribution

It introduces a detailed analysis of plasmonic modes in 2D topological insulators, highlighting edge and bulk excitations and their dependence on topological phases.

Findings

Edge plasmons localized at boundaries in topologically non-trivial phase

Bulk plasmonic branches exhibit hardening and softening due to inter-band correlations

Chiral, uni-directional edge plasmons observed in Haldane Chern insulator nano-ribbons

Abstract

We analyze collective excitations in models of two-dimensional topological insulators using the random phase approximation. In a two-dimensional extension of the Su-Schrieffer-Heeger model, edge plasmonic excitations with induced charge-density distributions localized at the boundaries of the system are found in the topologically non-trivial phase, dispersing similarly as one-dimensional bulk plasmons in the conventional Su-Schrieffer-Heeger chain. For two-dimensional bulk collective modes, we reveal regimes of enhanced inter-band wave function correlations, leading to characteristic hardening and softening of inter- and intra-band bulk plasmonic branches, respectively. In the two-dimensional Haldane Chern insulator model, chiral, uni-directional edge plasmons in nano-ribbon architectures are observed, which can be characterized by an effective Coulomb interaction cross section. Bulk collective excitations in the two-dimensional Haldane model are shown to be originated by single-particle band structure details in different topological phases.