Wide-area Topological Corner Modes in Heterostructured Kagome Phononic Crystal

Topological phononic crystals (TPnCs) have attracted increasing attention due to their robust boundary modes against defects, disorders, and bends with nearly zero energy dissipation. Especially, higher-order topological state (HOTS) appearing at lower dimension in TPnCs is expected to enrich the functionality of elastic devices to store elastic energy at a designated region. However, HOTS is only available at narrow boundaries hindering its use in devices where the energy carried by phonon is converted to electrical one. Here, we propose a heterostructured TPnC that has wide-area HOTSs. To broaden the area of topological corner modes, we design a heterostructure composed of three domains, formed with Kagome lattices. The domain with the same widths of intra- and inter-bonds of the lattice is sandwiched between trivial and nontrivial domains. We numerically demonstrate that corner modes are broadened in the corner region of the mid-domain. We also show the energy is stored at the extended corners more efficiently than at the corners of the conventional structure. This study may open new strategies for efficient elastic energy storage and/or energy harvesting.