Nov 13, 2020

Exceptional non-Hermitian topological edge mode and its application to active matter


Overview of the press release

Topological materials exhibit edge-localized scattering-free modes protected by their nontrivial bulk topology through the bulk-edge correspondence in Hermitian systems. While topological phenomena have recently been much investigated in non-Hermitian systems with dissipations and injections, the fundamental principle of their edge modes has not fully been established. Here, we reveal that, in non-Hermitian systems, robust gapless edge modes can ubiquitously appear owing to a mechanism that is distinct from bulk topology, thus indicating the breakdown of the bulk-edge correspondence. The robustness of these edge modes originates from yet another topological structure accompanying the branchpoint singularity around an exceptional point, at which eigenvectors coalesce and the Hamiltonian becomes nondiagonalizable. Their characteristic complex eigenenergy spectra are applicable to realize lasing wave packets that propagate along the edge of the sample. We numerically confirm the emergence and the robustness of the proposed edge modes in the prototypical lattice models. Furthermore, we show that these edge modes appear in a model of chiral active matter based on the hydrodynamic description, demonstrating that active matter can exhibit an inherently non-Hermitian topological feature. The proposed general mechanism would serve as an alternative designing principle to realize scattering-free edge current in non-Hermitian devices, going beyond the existing frameworks of non-Hermitian topological phases.

Figure: Non-Hermiticity can be utilized to realize an edge state (green curve) that connects the bulk bands (collection of blue curves) inside the sample. ​The parts between the exception points (red dot) are glued together so that they cannot be easily peeled off by disorder or impurities, making the edge state robust against them.


To read the full press release, please visit the website of the School of Engineering,The University of Tokyo.


Associate Professor Yuto Ashida (Department of Physics, Graduate School of Science) contributed to this research.


Publication details

Journal Nature Communications
Title Exceptional non-Hermitian topological edge mode and its application to active matter

Kazuki Sone*, Yuto Ashida, Takahiro Sagawa

DOI 10.1038/s41467-020-19488-0


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