Department of Physics, Hong Kong Baptist University, Kowloon Tong, Hong Kong, China.
Nature. 2022 Aug;608(7921):50-55. doi: 10.1038/s41586-022-04929-1. Epub 2022 Aug 3.
Topological modes (TMs) are usually localized at defects or boundaries of a much larger topological lattice. Recent studies of non-Hermitian band theories unveiled the non-Hermitian skin effect (NHSE), by which the bulk states collapse to the boundary as skin modes. Here we explore the NHSE to reshape the wavefunctions of TMs by delocalizing them from the boundary. At a critical non-Hermitian parameter, the in-gap TMs even become completely extended in the entire bulk lattice, forming an 'extended mode outside of a continuum'. These extended modes are still protected by bulk-band topology, making them robust against local disorders. The morphing of TM wavefunction is experimentally realized in active mechanical lattices in both one-dimensional and two-dimensional topological lattices, as well as in a higher-order topological lattice. Furthermore, by the judicious engineering of the non-Hermiticity distribution, the TMs can deform into a diversity of shapes. Our findings not only broaden and deepen the current understanding of the TMs and the NHSE but also open new grounds for topological applications.
拓扑模通常局限于较大拓扑晶格的缺陷或边界处。最近对非厄米带理论的研究揭示了非厄米表面效应（NHSE），即体态坍塌为边界的表面模。在这里，我们通过使它们从边界去局域化来探索 NHSE 对拓扑模波函数的重塑。在一个临界的非厄米参数下，带隙中的拓扑模甚至在整个体晶格中完全扩展，形成一个“连续体之外的扩展模”。这些扩展模仍然受到体带拓扑的保护，因此它们对局部无序具有鲁棒性。在一维和二维拓扑晶格以及更高阶拓扑晶格中的主动力学晶格中，实验上实现了拓扑模波函数的变形。此外，通过巧妙地设计非厄米分布，可以将拓扑模变形为各种形状。我们的发现不仅拓宽和深化了对拓扑模和 NHSE 的现有理解，也为拓扑应用开辟了新的道路。
