Non-Hermitian morphing of topological modes

Topological modes (TMs) are usually localized at defects or boundaries of a much larger topological lattice(1,2). 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(3-6). 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 wave function 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.

Automated summary

The non-Hermitian skin effect (NHSE) is utilized to reshape the wavefunctions of topological modes (TMs) by delocalizing them from the boundary. The in-gap TMs become completely extended and form robust extended modes, protected by bulk-band topology, even against local disorders. Experimental realization in different topological lattices demonstrates the deformation of TMs into various shapes.