Observation of Z<sub>2</sub> Non-Hermitian Skin Effect in Projective Mirror-Symmetric Acoustic Metamaterials.

Liu, Tingzhi; Li, Yuzeng; Zhang, Qicheng; Qiu, Chunyin · Adv Mater · 2025

basic_science · Level V

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Abstract

Non-Hermitian skin effect (NHSE), where eigenstates localize at the boundary of non-Hermitian lattices, has gained significant attention in various fields. This phenomenon, driven by the point-gap topology of complex energy bands, occurs even without special symmetries. Nevertheless, additional symmetry may significantly enrich the NHSE. Notably, time-reversal symmetry protects a Z<sub>2</sub> NHSE, featuring oppositely accumulated skin modes. Here, a 1D bilayer Z<sub>2</sub> NHSE model based on projective mirror symmetry is proposed, making Z<sub>2</sub> NHSE possible in spinless systems. Experimentally, both uniform and bidirectional Z<sub>2</sub> NHSEs are observed in acoustic metamaterials, where the necessary non-Hermitian elements-gain and loss-are achieved through active feedback circuits. These findings open new avenues for exploring symmetry-enriched non-Hermitian topological phenomena and pave the way for potential applications in wave manipulation, sensing, and beyond.