Surface plasmons on a thin film topological insulator

TL;DR

This paper extends the analysis of surface plasmons on topological insulators to thin films, accounting for multiple reflections and asymmetry, revealing how polarization and dispersion are affected.

Contribution

It provides a generalized analytic framework for surface plasmons on thin topological insulator films, including effects of multiple reflections and asymmetry.

Findings

Polarization rotation remains unchanged in symmetric thin films.

Dispersion relations are modified by interactions between surface layers.

An analytic expression for the resonance condition is derived.

Abstract

Recently it has been shown that surface plasmons supported by an interface between a 3+1 dimensional topological insulator and a metal or between a 3+1 dimensional topological insulator with residual bulk charge carriers and vacuum have a polarization that is rotated by an angle of order of the fine structure constant alpha compared to their topological trivial counterparts. In this work we generalize this analysis to the more realistic case of thin films, taking into account the effect of multiple reflections. In the symmetric case of a thin film surrounded by the same material on both sides the polarization of both allowed surface plasmon modes is unchanged from the single interface case, even though their dispersion relation is altered by the interactions between the two surface layers. In the general asymmetric case the angle is affected as well. We give a simple analytic expression for the resonance condition that determines the angle and solve it perturbatively for the case of a thin film between two media with almost identical permittivity.