Design of a room-temperature topological exciton-polariton laser in a ZnO/TiO$_2$-photonic crystal slab

TL;DR

This paper proposes a theoretical design for a room-temperature 2D topological exciton-polariton laser using a photonic crystal slab with a ZnO layer and a TiO2 lattice, supporting protected topological lasing modes.

Contribution

It introduces a novel photonic crystal structure supporting topological exciton-polariton lasing modes at room temperature, with detailed numerical analysis of the mode properties and topological characteristics.

Findings

Supports counter-propagating, topologically protected modes in the gap

Modes are orthogonally polarized and resistant to back-scattering

Suitable for room-temperature topological lasing with localized excitation

Abstract

We propose theoretically a scheme to get a room-temperature 2D topological exciton-polariton laser with propagating topological lasing modes. The structure uses guided modes in a photonic crystal slab. A ZnO layer provides strong excitonic resonances stable at room temperature. It is capped by a TiO$_2$ layer pierced by a triangular lattice. The exciton-polariton modes of the 3D structure are computed by solving numerically Maxwell's equations including the excitonic response. The designed triangular lattice shows a transverse electric gap. The triangular lattice is shown to be the limit of a staggered honeycomb lattice when one of the sub-lattices vanishes. Its topology can be characterized by symmetry indicators. The interface between two shifted triangular lattices supports two counter-propagating modes lying in the gap of the bulk modes. The interface states are analogous to quantum pseudospin Hall interface states. These modes show orthogonal polarizations. They can be selectively excited using polarized excitation and are well-protected from back-scattering. These modes can benefit from the exciton-polariton gain at room temperature because of their sufficiently large exciton fraction and favorable position in energy. The strong localization of these propagating modes makes them suitable to host topological lasing triggered by a non-resonant pump localized on the interface.