标题： 非厄米平坦带上的异常皮肤效应观测 显示英文标题

标题： Observation of the Exceptional Skin Effect on a Non-Hermitian Flat band

摘要： 平坦能带和非厄米性都是现代物理中的重要概念。 在本研究中，我们深入探讨了非厄米系统中平坦能带的行为，重点关注平坦能带与其色散对应物之间的相互作用，研究由它们共同形成的奇点（EPs），以及相应产生的非厄米皮肤效应（NHSE），我们将这种效应称为奇异皮肤效应（ESE）。 利用具有手征/亚晶格对称性的非厄米平坦能带，其中能量保持高度简并，我们探索了它们的独特性质。 与传统NHSE需要在布洛赫复数能谱中包围非零面积不同，平坦能带上的ESE可以通过仅包含一个点的布洛赫复数能谱生成，即不包围任何面积。 通过解析地调节非厄米参数，观察到复数能谱和黎曼面的变化，揭示了平坦能带与色散能带杂化形成EPs的过程，同时保持希尔伯特子空间的维度。 此外，在特定参数区域，平坦能带的波函数表现出ESE，这与现有框架相反。 通过使用具有主动调制的非厄米参数的弹性波系统进行实验验证，展示了对平坦能带态的影响，并确认了由于平坦能带-色散能带杂化而形成的ESE和相应的EPs。 这些结果为非厄米物理提供了新的见解，并为该领域的进一步研究和应用指明了潜在方向。 显示英文摘要

摘要： Flat band and non-Hermitian are both significant conceptions in modern physics. In this study, we delve into the behaviours of flat bands in non-Hermitian systems, focusing on the interplay between the flat band and its dispersive counterparts, investigating the exceptional points (EPs) formed by them together, and the non-Hermitian skin effect (NHSE) on the flat band correspondingly generated, which we name as the exceptional skin effect (ESE). Employing non-Hermitian flat band under chiral/sublattice symmetry, where energy remains highly degenerate, we explore their unique properties. Unlike traditional NHSE which requires the enclosing of a non-zero area in the Bloch complex energy spectrum, the ESE on flat band can be generated with a Bloch complex energy spectrum consisting of one single point, i.e. enclosing no area. By analytically tuning non-Hermitian parameters, changes in the complex energy spectrum and Riemann surfaces are observed, revealing the formation of EPs through the hybridization of flat and dispersive bands while maintaining the dimension of the Hilbert subspace. Additionally, the wave functions of flat band exhibit ESE in specific parameter regions, contrary to the existing frameworks. Experimental validation is conducted using an elastic wave system with actively modulated non-Hermitian parameters, showcasing the impact on flat-band states and confirming the formation of ESE due to flat band-dispersive bands hybridization and correspondingly formed EPs. These results offer novel insights into non-Hermitian physics and present potential directions for further researches and applications in this field.