In-Plane Plasmon Coupling in Topological Insulator Bi$_2$Se$_3$ Thin Films

TL;DR

This paper investigates in-plane coupling of Dirac plasmon polaritons in Bi$_2$Se$_3$ thin films, revealing dipole-dipole interactions in stripe arrays and potential for TI-based metasurface applications.

Contribution

It is the first to demonstrate in-plane DPP coupling in topological insulator stripe arrays, showing dipole-dipole interactions and their dependence on lattice spacing.

Findings

In-plane DPP coupling observed in TI stripe arrays.

Coupling strength diminishes when lattice constant exceeds ~2.8 times stripe width.

Results comparable to metallic nanoparticle and graphene plasmon coupling.

Abstract

The surface states of the 3D topological insulator (TI), Bi$_2$Se$_3$, are known to host two-dimensional Dirac plasmon polaritons (DPPs) in the terahertz spectral range. In TI thin films, the DPPs excited on the top and bottom surfaces couple, leading to an acoustic and an optical plasmon mode. Vertical coupling in these materials is therefore reasonable well-understood, but in-plane coupling among localized TI DPPs has yet to be investigated. In this paper, we demonstrate in-plane DPP coupling in TI stripe arrays and show that they exhibit dipole-dipole type coupling. The coupling becomes negligible with the lattice constant is greater than approximately 2.8 times the stripe width, which is comparable to results for in-plane coupling of localized plasmons excited on metallic nanoparticles or graphene plasmon polaritons. This understanding could be leveraged for the creation of TI-based metasurfaces.