Pseudospin induced topological corner state at intersecting sonic lattices

Inspired by the discoveries of electronic topological phases and topological insulators, topologically protected boundary states in classical wave-based systems have attracted considerable interest in the last decade. Most recently, acoustic higher-order topological insulators and Kekulé-distorted sonic lattices have been proposed to support topological corner states and zero-dimensional bound states. Here, we demonstrate a domain wall induced topological corner state that is bound at the crossing point among finite acoustic graphenelike crystals. The approach is based on designing multipolar pseudospin resonances, which give rise to topologically trivial and nontrivial transitions across the domain walls that flank this unusual corner excitation toward the crossing point. By deliberately adding a substantial amount of defects into the cavities of the sonic lattice, we find that the pseudospin induced topological corner state remains entirely unaffected and pinned spectrally to the complete audible band gap. Our findings may thus have the potential to broaden the possibilities for sound confinement and focusing.