Multiple corner states and particle trapping in higher-order topological waterborne acoustic crystals

Long-range coupling is usually much weaker than nearest-neighbor coupling, and achieving stronger long-range coupling is challenging. Recently, a unique topological phase induced by strong long-range coupling has been proposed and experimentally demonstrated in quadrupole topological insulators with both positive and negative couplings. Here, we propose a new higher-order topological insulator protected by the multipole chiral number in a two-dimensional Su-Schrieffer-Heeger model by introducing strong third-nearest-neighbor couplings and requiring only positive couplings. We design and fabricate a waterborne acoustic crystal, which consists of through holes and grooves in a copper plate, to realize this topological material. The near-field response spectra and pressure field distributions provide evidence for the existence of multiple zero-dimensional topological corner states within the bulk gap. Interestingly, as an application, we further demonstrate the trapping of polystyrene particles by utilizing the highly localized pressure fields of the multiple corner states. Our work offers a feasible acoustic topological device to manipulate corner states as well as particles and is expected to have potential applications in acoustic sensing and acoustic tweezers.