Second-order photonic topological insulator with corner states

TL;DR

This paper introduces a new class of 2D second-order photonic topological insulators with corner and boundary states, expanding the understanding of topological phases in photonic systems.

Contribution

It proposes a novel design for 2D second-order photonic crystals exhibiting topologically non-trivial corner and boundary states, tunable through structural modifications.

Findings

Presence of zero-dimensional corner states in the proposed photonic crystals

Topological boundary states can be controlled by structural tuning

The approach can be extended to higher-dimensional systems

Abstract

Higher-order topological insulators (HOTIs) which go beyond the description of conventional bulk-boundary correspondence, broaden the understanding of topological insulating phases. Being mainly focused on electronic materials, HOTIs have not been found in photonic systems yet. In this article, we propose a type of two-dimensional second-order photonic crystals with zero-dimensional corner states and one-dimensional boundary states for optical frequencies. All of these states are topologically non-trivial and can be understood based on the theory of topological polarization. Moreover, by tuning the easily-fabricated structure of the photonic crystals, we can realize different topological phases with unique topological boundary states straightforwardly. Our result can be generalized to higher dimensions and provides unprecedented venues for higher-order photonic topological insulators and semimetals.