Elastic higher-order topological insulators with quantization of the quadrupole moments

TL;DR

This paper demonstrates the realization of higher-order topological insulators in 2D elastic phononic crystals, showcasing quantized quadrupole moments, topological edge and corner states, and potential for robust phononic circuits.

Contribution

It introduces a novel elastic phononic crystal design that exhibits higher-order topological insulator properties with quantized quadrupole moments and tunable topological states.

Findings

Visualization of 1D topological edge states

Visualization of 0D topological corner states

Robust localization of elastic wave energy

Abstract

We demonstrate that HOTIs with the quantization of the quadrupole moments can be realized in the two-dimensional elastic phononic crystals (PnCs). Both one-dimensional (1D) topological edge states and zero-dimensional (0D) topological corner states are visualized and can be transformed each other by tuning the crystalline symmetry in a hierarchical structure. The systematic band structure calculations indicate that elastic wave energy in the hierarchical structure can be localized with remarkable robustness, which is very promising for new generations of integrated solid-state phononic circuits with a great versatility.