Edge states and corner modes in second-order topological phononic crystal plates

TL;DR

This paper demonstrates the realization of a second-order topological insulator in phononic crystal plates, exhibiting both edge and corner modes, which could enable advanced elastic wave control and trapping.

Contribution

It introduces a novel elastic second-order topological insulator in phononic crystals with controllable edge and corner states through symmetry breaking.

Findings

Observation of gapped edge states in phononic crystal plates.

Identification of zero-dimensional corner modes.

Control of topological phase transitions via symmetry breaking.

Abstract

We realize an elastic second-order topological insulator hosting both one-dimensional gapped edge states and zero-dimensional in-gap corner modes in the double-sided pillared phononic crystal plates with square lattice. Changing the width of two neighbor pillars breaks the inversion symmetry and induces the band inversion to emulate the quantum spin Hall effect where the gapless edge states are obtained. Further breaking the space-symmetry at interface, the gapless edge states are gapped and inducing the edge topological transitions and then giving rise to the zero-dimensional in-gap corner modes. Our work offers a novel way for elastic wave trapping and robustly guiding.