Tracking intrinsic non-Hermitian skin effects in lossy lattices

Non-Hermitian skin effect (NHSE), characterized by a majority of eigenstates localized at open boundaries, is one of the most iconic phenomena in non-Hermitian lattice systems. Despite notable experimental studies, most of them witness only certain signs of the NHSE rather than the intrinsic exponential localization inherent in eigenstates, owing to the ubiquitous background loss. Here, we propose a dual-test approach to eliminate the undesired loss effect and track the intrinsic NHSEs that are irrelevant to background loss. The approach is then experimentally validated in non-Hermitian acoustic lattices, which are skillfully constructed by coordinating passive air cavity-tube structures and active unidirectional couplers. Apart from observing the pure NHSE in the prototypical Hatano-Nelson lattice, we precisely capture the intrinsic characteristics of defect-related NHSE, symmetry-enriched NHSE, and high-dimensional interface NHSE. Our study provides conclusive experimental evidence for the fundamental NHSEs in lossy lattices, and showcases the applicability and robustness of our approach across different lattice structures and random perturbations.