An elastic higher-order topological insulator based on kagome phononic crystals

Recently, the novel bulk-edge-corner correspondence of higher-order topological states had attracted increasing attention. Past research studies on higher-order topological insulators, however, have mainly concentrated on the topological multipole states within the low-frequency bandgap for airborne sound waves. In this paper, we propose a higher-order topological insulator with kagome symmetry based on two-dimensional elastic phononic crystals (PNCs), which can operate in the high-frequency bandgap. Topological corner and edge states are both achieved in well-designed finite PNCs. In addition, we demonstrate the robust characteristics of elastic topological corner and edge states in PNCs with different defects (e.g., cavities, disorders, and bends). As the analog counterpart for classical waves, the proposed PNCs provide an alternative scheme for research into the topological phases of matter in macroscopic systems.