A higher-order topological insulator with wide bandgaps in Lamb-wave systems

We demonstrate that higher-order topological insulators with C-4 symmetry can be realized in two-dimensional elastic phononic crystals. Both one-dimensional topological edge states and zero-dimensional topological corner states are visualized and can transform each other by tuning the crystalline symmetry in a hierarchical structure. The systematic band structure calculations indicate that elastic wave energy in the hierarchical structures can be localized with remarkable robustness, which is very promising for new generations of integrated solid-state phononic circuits with a great versatility. In addition, the corner states residing in a much wider bandgap greatly increase the signal-to-noise ratio of topological devices. Published under license by AIP Publishing.