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arXiv · 2312.03054

Braids and Higher-order Exceptional Points from the Interplay Between Lossy Defects and Topological Boundary States

Zi-Jian Li·Gabriel Cardoso·Emil J. Bergholtz·Qing-Dong Jiang
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Abstract

We show that the perturbation of the Su-Schrieffer-Heeger chain by a localized lossy defect leads to higher-order exceptional points (HOEP). Depending on the location of the defect, third- and fourth- order exceptional points (EP3 \& EP4) appear in the space of Hamiltonian parameters. On the one hand, they arise due to the non-Abelian braiding properties of exceptional lines (EL) in parameter space. Namely, the HOEPs lie at intersections of mutually non-commuting ELs. On the other hand, we show that such special intersections happen due to the fact that the delocalization of edge states, induced by the non-Hermitian defect, hybridizes them with defect states. These can then coalesce together into an EP3. When the defect lies at the midpoint of the chain, a special symmetry of the full spectrum can lead to an EP4. In this way, our model illustrates the emergence of interesting non-Abelian topological properties in the multiband structure of non-Hermitian perturbations of topological phases.

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Zi-Jian Li, Gabriel Cardoso, Emil J. Bergholtz, Qing-Dong Jiang. 2023-12-05. Braids and Higher-order Exceptional Points from the Interplay Between Lossy Defects and Topological Boundary States. https://doi.org/10.1103/physrevresearch.6.043023

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