Topological Polaritons in a Quantum Spin Hall Cavity

TL;DR

This paper explores the topological properties of polaritons in a quantum spin Hall insulator within a photonic cavity, revealing protected edge states and a topological invariant under time reversal symmetry.

Contribution

It introduces a topological invariant for polaritons in a quantum spin Hall system and demonstrates the existence of protected helical edge states in this setting.

Findings

Existence of protected helical edge states below the polariton branch

Identification of a topological invariant under time reversal symmetry

Detection of uncoupled excitonic states via optical techniques

Abstract

We study the topological structure of matter-light excitations, so called polaritons, in a quantum spin Hall insulator coupled to photonic cavity modes. We identify a topological invariant in the presence of time reversal (TR) symmetry, and demonstrate the existence of a TR-invariant topological phase. We find protected helical edge states with energies below the lower polariton branch and characteristic uncoupled excitonic states, both detectable by optical techniques. Applying a Zeeman field allows us to relate the topological index to the double coverage of the Bloch sphere by the polaritonic pseudospin.