Classical higher-order topological insulators

TL;DR

This paper reviews the recent progress in higher-order topological insulators (HOTIs) for classical waves, highlighting their unique properties, experimental realizations, and potential applications across various wave-based systems.

Contribution

It provides a comprehensive overview of HOTIs in classical wave systems, covering principles, phenomena, and future challenges, thus advancing understanding in this emerging field.

Findings

Summary of physical properties of HOTIs

Overview of experimental realizations

Discussion of potential applications

Abstract

Topological states nurtures the emergence of devices with unprecedented functions in photonics, plasmonics, acoustics and phononics. As one of the recently discovered members, higher-order topological insulators (HOTIs) have been increasingly explored, featuring lower-dimensional topological boundary states, leading to rich mechanisms for topological manipulation, guiding and trapping of classical waves. Here, we provide an overview of current developments of HOTIs in classical waves including basic principles, unique physical properties, various experimental realizations, novel phenomena and potential applications. Based on these discussions, we remark on the trends and challenges in this field and the impacts of higher-order topology on other research fields.