Finite-dimensional bistable topological insulators: From small to large

TL;DR

This paper investigates finite-sized photonic topological insulators, demonstrating how topological properties develop with increasing size, and explores bistability and selective excitation of edge states in polariton microcavity arrays.

Contribution

It provides the first detailed analysis of topological edge states in small, finite polariton insulators, including effects of dissipation, bistability, and novel excitation mechanisms.

Findings

Topological edge states emerge as the system size increases.

Bistability enables selective excitation of edge states.

Vortex pump can excite different edge currents based on topological charge.

Abstract

Photonic topological insulators supporting unidirectional topologically protected edge states represent attractive platform for realization of disorder- and backscattering-immune transport of edge excitations in both linear and nonlinear regimes. In many realizations of topological insulators structured periodic materials are used, since they may admit specific Dirac degeneracy in the spectrum, around which unidirectional edge states appear under the action of physical effects breaking time-reversal symmetry. While properties of the edge states at unclosed interfaces of two bulk media with different topology are known, the existence of the edge states in practical finite-dimensional topological insulators fully immersed in nontopological environment remains largely unexplored. In this work using as an example realistic polariton topological insulators built from small-size honeycomb arrays of microcavity pillars, we illustrate how topological properties of the system build up upon gradual increase of its dimensionality. To account for dissipative nature of polariton condensate forming in the array of microcavity pillars, we consider the impact of losses and resonant pump leading to rich bistability effects in this system. We describe the mechanism in accordance with which trivial-phase pump "selects" and excites specific nonlinear topological edge states circulating along the periphery of the structure in the azimuthal direction dictated by the direction of the external applied magnetic field. We also show the possibility of utilization of vortex pump with different topological charges for selective excitation of different edge currents.