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Symmetry-protected exceptional and nodal points in non-Hermitian systems
by Sharareh Sayyad, Marcus Stålhammar, Lukas Rodland, Flore K. Kunst
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|Authors (as registered SciPost users):||Sharareh Sayyad · Marcus Stålhammar|
|Preprint Link:||scipost_202304_00017v2 (pdf)|
|Date submitted:||2023-09-13 12:39|
|Submitted by:||Sayyad, Sharareh|
|Submitted to:||SciPost Physics|
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.
Published as SciPost Phys. 15, 200 (2023)
Submission & Refereeing History
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Reports on this Submission
This is my second report on "Symmetry-protected exceptional and nodal points in non-Hermitian systems" by Sharareh Sayyad, Marcus Stålhammar, Lukas Rodland, Flore K. Kunst.
The authors have addressed my comments, and corrected the typos in their article. Given my previous report, I recommend the acceptance of this manuscript for publication in SciPost Physics.
Second report on "Symmetry-protected exceptional and nodal points in non-Hermitian systems" by Sharareh Sayyad, Marcus Stålhammar, Lukas Rodland, Flore K. Kunst.
The authors have addressed all my previous comments and their answers to the concerns of the other referees seems convincing. Therefore, I recommend the acceptance of this manuscript for publication in SciPost Physics.