Polariton $\mathbb{Z}$ Topological Insulator

TL;DR

This paper demonstrates that honeycomb arrays of microcavity pillars can act as optical 2D topological insulators, with topologically protected edge states arising from photonic spin-orbit coupling and magnetic field effects.

Contribution

It introduces a new optical-frequency 2D topological insulator model based on microcavity arrays with spin-orbit coupling and Zeeman splitting.

Findings

Non-trivial band gap with Chern numbers ±2

Formation of topologically protected one-way edge states

Potential for optical topological devices

Abstract

Recent search for optical analogues of topological phenomena mainly focuses on mimicking the key feature of quantum Hall and quantum spin Hall effects (QHE and QSHE): edge currents protected from disorder. QHE relies on time-reversal symmetry breaking, which can be realised in photonic gyromagnetic crystals. In the optical range, the weak magneto-optical activity may be replaced with helical design of coupled waveguides, converting light propagation into a time-dependent perturbation. Finally, optical QHE due to artificial gauge fields was predicted in microcavity lattices. Here, we consider honeycomb arrays of microcavity pillars as an alternative optical-frequency 2D topological insulator. We show that the interplay between the photonic spin-orbit coupling natively present in this system and the Zeeman splitting of exciton-polaritons in external magnetic fields leads to the opening of a non-trivial gap characterised by $C=\pm 2$ set of band Chern numbers and to the formation of topologically protected one-way edge states.