# Knot Topology of Exceptional Point and Non-Hermitian No-Go Theorem

@inproceedings{Hu2021KnotTO, title={Knot Topology of Exceptional Point and Non-Hermitian No-Go Theorem}, author={Haiping Hu and Shuoxi Sun and Shu Chen}, year={2021} }

Exceptional points (EPs) are peculiar band singularities and play a vital role in a rich array of unusual optical phenomena and non-Hermitian band theory. In this paper, we provide a topological classification of isolated EPs based on homotopy theory. In particular, the classification indicates that an n-th order EP in two dimensions is fully characterized by the braid group Bn, with its eigenenergies tied up into a geometric knot along a closed path enclosing the EP. The quantized discriminant…

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