Higher-order Non-Hermitian skin effect in an acoustic lattice

Non-Hermitian physical systems offer a distinct band topology that gives rise to the interesting phenomenon known as the non-Hermitian skin effect (NHSE). However, the exploration of higher-order NHSE in classical wave systems by leveraging non-reciprocity has been largely unexplored. In this study, we introduce a novel approach to experimentally realize the higher-order NHSE in a two-dimensional non-reciprocal breathing acoustic Kagome lattice. This lattice is composed of acoustic cavities with non-reciprocal coupling achieved through electrically controlled active acoustic elements. We successfully observed second-order corner modes using a 3 × 3 lattice, which manifest as localized pressure distributions at specific frequencies in both parallelogram and triangular topological acoustic lattices. We delve into the underlying mechanisms and their implications, thereby paving the way for a deeper understanding of higher-order NHSE and potentially innovative applications rooted in the acoustic non-reciprocity.