Abstract
Motivated by recent progress on non-Hermitian topological band theories, we study the energy spectrum of a generic two-band non-Hermitian Hamiltonian. We prove rigorously that the complex energy spectrum of such a non-Hermitian Hamiltonian is restricted to the lower complex plane, provided that the parameters of the Hamiltonian satisfy a certain constraint. Furthermore, we consider one specific scenario where such a non-Hermitian Hamiltonian can arise, namely a two-band model coupled to an environment, and show that this aforementioned constraint originates from very general physical considerations. Using this construction we extract the real-space behaviour of the non-hermitian terms. Our findings are relevant in the definition of the energy gap in non-Hermitian topological band theories and also have implications on simulations of such theories using quantum systems.
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Midtgaard, J.M., Wu, Z. & Chen, Y. Constraints on the energy spectrum of non-Hermitian models in open environments. Eur. Phys. J. B 92, 260 (2019). https://doi.org/10.1140/epjb/e2019-100393-5
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DOI: https://doi.org/10.1140/epjb/e2019-100393-5