Exceptional nexus with a hybrid topological invariant

Weiyuan Tang, Xue Jiang, Kun Ding*, Yi Xin Xiao, Zhao Qing Zhang, C. T. Chan, Guancong Ma*

*Corresponding author for this work

Research output: Contribution to journalJournal articlepeer-review

107 Citations (Scopus)


Branch-point singularities known as exceptional points (EPs), which carry a nonzero topological charge, can emerge in non-Hermitian systems. We demonstrate with both theory and acoustic experiments an "exceptional nexus" (EX), which is not only a higher-order EP but also the cusp singularity of multiple exceptional arcs (EAs). Because the parameter space is segmented by the EAs, the EX possesses a hybrid topological invariant (HTI), which consists of distinct winding numbers associated with Berry phases accumulated by cyclic paths on different complex planes. The HTI is experimentally characterized by measuring the critical behaviors of the wave functions. Our findings constitute a major advance in the fundamental understanding of non-Hermitian systems and their topology, possibly opening new avenues for applications.

Original languageEnglish
Pages (from-to)1077-1080
Number of pages4
Issue number6520
Publication statusPublished - 27 Nov 2020

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