Higher-order topological states in photonic Thue-Morse quasicrystals: quadrupole insulator and a new origin of corner states

TL;DR

This paper investigates higher-order topological states in two-dimensional Thue-Morse photonic quasicrystals, revealing new corner states with different origins and demonstrating their potential for robust photonic applications.

Contribution

It introduces the first systematic study of higher-order topological insulators in photonic quasicrystals, discovering new types of corner states and analyzing their origins.

Findings

Identification of topological phase transitions in TM-PQCs

Discovery of new corner states due to complex quasicrystal structure

Analysis of corner states' origins using tight-binding models

Abstract

Corner states (CSs) in higher-order topological insulators (HOTIs) have recently been of great interest in both crystals and quasicrystals. In contrast to electronic systems, HOTIs have not been found in photonic quasicrystals (PQCs). Here, we systemically study the higher-order topology in the two-dimensional Thue-Morse photonic quasicrystals (TM-PQCs). Not only the topological phase transition and the non-trivial CSs with fractional charge induced by multipole moments, but also a new type of CSs are found due to the complex structure of TM-PQCs near corners. The different origins of these CSs are also analyzed based on the tight-binding model. Our work opens the door to explore richer HOT physics beyond photonic crystals and the robustness of CSs in PQC shows the potential for applications.