Higher-order valley vortices enabled by synchronized rotation in a photonic crystal

TL;DR

This paper introduces a novel design of higher-order topological insulators in photonic crystals using synchronized unit cell rotation, enabling control over valley-dependent corner and edge states with chiral vortex features.

Contribution

The work demonstrates a new approach to realize HOTIs with synchronized rotation in photonic lattices, supporting valley-dependent corner and edge states with chiral vortex properties.

Findings

Supports zero-dimensional corner states and one-dimensional edge states

Corner states exhibit chiral orbital angular momentum locked by valleys

Valley topological states emerge at both edges and corners simultaneously

Abstract

Synchronized rotation of unit cells in a periodic structure provides a novel design perspective for manipulation of band topology. We then design a two-dimensional version of higher-order topological insulators (HOTI), by such rotation in a triangular photonic lattice with $\mathcal{C}_3$ symmetry. This HOTI supports the hallmark zero-dimensional corner states and simultaneously the one-dimensional edge states. We also find that our photonic corner states carry chiral orbital angular momenta locked by valleys, whose wavefunctions are featured by the phase vortex (singularity) positioned at the maximal Wyckoff points. Moreover, when excited by a fired source with various frequencies, the valley topological states of both one-dimensional edges and zero-dimensional corners emerge simultaneously. Extendable to higher or synthetic dimensions, our work provides access to a chiral vortex platform for HOTI realisations in the THz photonic system.