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arXiv · 2509.15102

Zero Indirect Band Gap in Non-Hermitian Systems

S Rahul·Giandomenico Palumbo
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Abstract

Zero indirect gaps in band models are typically viewed as unstable and achievable only through fine-tuning. Recent works, however, have revealed robust semimetallic phases in Hermitian systems where the indirect gap remains pinned at zero over a finite parameter range. Here, we extend this paradigm to non-Hermitian lattice models by studying a one-dimensional diamond-like system with gain and loss. We show that the zero indirect band gap in the real part of the spectrum remains stable in the presence of non-Hermitian perturbations and identify the parameter regime in which this robustness persists. We find that the appearance of the zero indirect gap coincides with the suppression of the non-Hermitian skin effect. Our results reveal new connections between indirect gaps, exceptional points and non-Hermitian skin effect, opening avenues for experimental realizations.

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S Rahul, Giandomenico Palumbo. 2025-09-18. Zero Indirect Band Gap in Non-Hermitian Systems. https://doi.org/10.1063/5.0308387

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