Topological Corner Modes by Composite Wannier States in Glide-Symmetric Photonic Crystal

TL;DR

This paper demonstrates second-order topological insulators in a glide-symmetric photonic crystal, revealing corner modes linked to Wannier states and confirmed through simulations and experiments, with implications for photonics applications.

Contribution

It introduces a new method to realize higher-order topological insulators using nonsymmorphic glide symmetry and Wannier band inversion in photonic crystals.

Findings

Identification of topological corner modes via hybridized Wannier functions.

Confirmation of second-order topology through simulations and microwave experiments.

Unique modal symmetries of corner states due to Wannier band inversion.

Abstract

Second-order topological insulators can be characterized by their bulk polarization, which is believed to be intrinsically connected to the center of the Wannier function. In this study, we demonstrate the existence of second-order topological insulators that feature a pair of partially degenerate photonic bands. These arise from the nonsymmorphic glide symmetry in an all-dielectric photonic crystal. The center of the maximally localized Wannier function (MLWF) is consistently located at the origin but is not equivalent with respect to the sum of constituent polarizations. As a result, topological corner modes can be identified by the distinctly hybridized MLWFs that truncate at the sample boundary. Through full-wave numerical simulations paired with microwave experiments, the second-order topology is clearly confirmed and characterized. These topological corner states exhibit notably unique modal symmetries, which are made possible by the inversion of the Wannier bands. Our results provide an alternative approach to explore higher-order topological physics with significant potential for applications in integrated and quantum photonics.