Regensburg 2019 – scientific programme
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MA: Fachverband Magnetismus
MA 25: Topological Semimetals - Theory (joint session TT/MA)
MA 25.4: Talk
Wednesday, April 3, 2019, 10:15–10:30, H22
Symmetry-Protected Nodal Phases in Non-Hermitian Systems — •Jan Carl Budich1, Johan Carlström2, Flore K Kunst2, and Emil J Bergholtz2 — 1Institute of Theoretical Physics, TU Dresden, 01062 Dresden, Germany — 2Department of Physics, Stockholm University, AlbaNova University Center, 106 91 Stockholm, Sweden
Non-Hermitian (NH) Hamiltonians have become an important asset for the effective description of various physical systems that are subject to dissipation. Motivated by recent experimental progress on realizing the NH counterparts of gapless phases such as Weyl semimetals, here we investigate how NH symmetries affect the occurrence of exceptional points (EPs), that generalize the notion of nodal points in the spectrum beyond the Hermitian realm. Remarkably, we find that the dimension of the manifold of EPs is generically increased by one as compared to the case without symmetry. This leads to nodal surfaces formed by EPs that are stable as long as a protecting symmetry is preserved, and that are connected by open Fermi volumes. We illustrate our findings with analytically solvable two-band lattice models in one and two spatial dimensions, and show how they are readily generalized to generic NH crystalline systems.