Observation of Topological Corner State Arrays in Photonic Quasicrystals

TL;DR

This paper experimentally demonstrates topological corner state arrays in photonic quasicrystals, revealing multiple TCSs per corner and introducing a new topological index, advancing the understanding of higher-order topological insulators.

Contribution

It provides the first experimental observation of TCS arrays in photonic quasicrystals and develops an improved theoretical framework with a new topological index.

Findings

HOTQIs possess TCS arrays with multiple TCSs

The multimer analysis method is improved for topological characterization

A new real-space topological index based on charge density differences

Abstract

Recently, the studies of topological corner states (TCSs) are extended from crystals to quasicrystals, which are referred to as higher-order topological quasicrystalline insulators (HOTQIs). However, the TCSs of complete quasi-periodic structure in photonic systems have yet to be demonstrated. Moreover, there is only one TCS in each corner region in higher-order topological insulators (HOTIs). Increasing the number of TCS is expected to increase application potential of TCSs. In this work, HOTQIs in photonic systems are experimentally observed. It is found that HOTQIs possess TCS arrays, and each TCS array contains several TCSs. Furthermore, the universal theoretical framework of the multimer analysis method is improved, and the difference in the average charge density is proposed as a real-space topological index. These results will open up new ideas for investigating highly integrated, multi-region localized TCSs and are expected to provide new ways to explore topological phenomena and the applications of photonic quasicrystals.