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- Title
Symmetry-protected topological exceptional chains in non-Hermitian crystals.
- Authors
Zhang, Ruo-Yang; Cui, Xiaohan; Chen, Wen-Jie; Zhang, Zhao-Qing; Chan, C. T.
- Abstract
In non-Hermitian systems, defective band degeneracies called exceptional points can form exceptional lines (ELs) in 3D momentum space in the absence of any symmetries. However, whether the presence of symmetries can affect the EL configurations had rarely been discussed. Here we show that a natural orientation can be assigned to every EL according to the eigenenergy braiding around it, and we establish the source-free principle of ELs stating that the number of ELs ingoing and outgoing from the junction must be conserved. Based on this principle, we discover that three crystalline-symmetry-based mechanisms can stabilize the junction of ELs, resulting in the formation of various types of exceptional chains (ECs). We further demonstrate that ECs can be observed in prototypical non-Hermitian photonic crystals. Our results combine the effect of non-Hermitian spatiotemporal symmetry and topology to pave the way for understanding and manipulating the morphology of ELs in non-Hermitian crystalline systems. Exceptional points are of great importance to rationalize the topological properties of non-Hermitian systems. This study proposes a new class of non-Hermitian topological degeneracies named exceptional chains, and develops a general theory to understand such non-Hermitian crystalline system by merging non-Hermitian and topological fields.
- Subjects
HERMITIAN forms; TOPOLOGICAL fields; PHOTONIC crystals; MOMENTUM space; TOPOLOGICAL property; CRYSTALS
- Publication
Communications Physics, 2023, Vol 6, Issue 1, p1
- ISSN
2399-3650
- Publication type
Article
- DOI
10.1038/s42005-023-01291-0