Twist‐Induced All‐Flat‐Band Higher‐Order Acoustic Topological Insulator

ABSTRACT Twisted Moiré superlattices (TMSs) exhibit unique geometric periodicity and interlayer Bragg scattering effects, which have been widely exploited for flat‐band engineering. However, to date, no report has directly addressed the mechanism of achieving all‐flat‐band topology with the intrinsic eigenmodes of Moiré periodicity. In this work, by introducing periodic strong localized resonances into the superlattices, a novel acoustic flat‐band higher‐order topological insulator is proposed. Based on the standing‐wave effect of multipolar Mie resonances, varied‐frequency edge states and high‐quality (high‐Q) corner states are observed in the topological all‐flat‐bandgaps. More interestingly, owing to the operational simplicity of acoustic TMS, it can be readily stacked into a 3D configuration, yielding out‐of‐phase topological hinge states. This study unveils a simple strategy to construct acoustic all‐flat‐band topological insulators, providing new potential for applications such as energy harvesting and sensing.