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Symmetry-protected exceptional and nodal points in non-Hermitian systems
Max Planck Institute for the Science of Light, Staudtstraße 2, 91058 Erlangen, Germany.
Nordita SU; Department of Physics, Stockholm University, AlbaNova University Center, 106 91 Stockholm, Sweden.
Department of Physics, Stockholm University, AlbaNova University Center, 106 91 Stockholm, Sweden.
Max Planck Institute for the Science of Light, Staudtstraße 2, 91058 Erlangen, Germany.
2023 (English)In: SciPost Physics, E-ISSN 2542-4653, Vol. 15, no 5, article id 200Article in journal (Refereed) Published
Abstract [en]

One of the unique features of non-Hermitian (NH) systems is the appearance of NH degeneracies known as exceptional points (EPs). The extensively studied defective EPs occur when the Hamiltonian becomes non-diagonalizable. Aside from this degeneracy, we show that NH systems may host two further types of non-defective degeneracies, namely, non-defective EPs and ordinary (Hermitian) nodal points. The non-defective EPs manifest themselves by i) the diagonalizability of the NH Hamiltonian at these points and ii) the non-diagonalizability of the Hamiltonian along certain intersections of these points, resulting in instabilities in the Jordan decomposition when approaching the points from certain directions. We demonstrate that certain discrete symmetries, namely parity-time, parity-particle-hole, and pseudo-Hermitian symmetry, guarantee the occurrence of both defective and non-defective EPs. We extend this list of symmetries by including the NH time-reversal symmetry in two-band systems. Two-band and four-band models exemplify our findings. Through an example, we further reveal that ordinary nodal points may coexist with defective EPs in NH models when the above symmetries are relaxed.

Place, publisher, year, edition, pages
Stichting SciPost , 2023. Vol. 15, no 5, article id 200
National Category
Control Engineering
Identifiers
URN: urn:nbn:se:kth:diva-340969DOI: 10.21468/SciPostPhys.15.5.200ISI: 001110706300002Scopus ID: 2-s2.0-85178085861OAI: oai:DiVA.org:kth-340969DiVA, id: diva2:1820282
Note

QC 20231218

Available from: 2023-12-18 Created: 2023-12-18 Last updated: 2024-02-29Bibliographically approved

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CiteExportLink to record
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Citation style
  • apa
  • ieee
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  • Other style
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  • de-DE
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