Regensburg 2025 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 53: Topology: Other Topics
TT 53.3: Vortrag
Freitag, 21. März 2025, 10:00–10:15, H32
Topological Order in the Spectral Riemann Surfaces of Non-Hermitian Systems — •Anton Montag1,2, Alexander Felski1, and Flore Kiki Kunst1,2 — 1Max Planck Institute for the Science of Light, 91058 Erlangen, Germany — 2Department of Physics, Friedrich-Alexander-Universität Erlangen-Nürnberg, 91058 Erlangen, Germany
We show topologically ordered states in the complex-valued spectra of non-Hermitian systems. These arise when the distinctive exceptional points in the energy Riemann surfaces of such models are annihilated after threading them across the boundary of the Brillouin zone. This process results in a non-trivially closed branch cut that can be identified with a Fermi arc. Building on an analogy to Kitaev’s toric code, these cut lines form non-contractible loops, which parallel the defect lines of the toric-code ground states. Their presence or absence establishes topological order for fully non-degenerate non-Hermitian systems. Excitations above these ground-state analogs are characterized by the occurrence of additional exceptional points. We illustrate the characteristics of the topologically protected states in a non-Hermitian two-band model and provide an outlook toward experimental realizations in metasurfaces and single-photon interferometry.
Keywords: Non-Hermitian topology; Riemann surfaces; Fermi arcs; Branch cuts; Exceptional points