Symmetry-protected quantization of complex Berry phases in non-Hermitian many-body systems

Abstract

We investigate the quantization of the complex-valued Berry phases in non-Hermitian quantum systems with certain generalized symmetries. In Hermitian quantum systems, the real-valued Berry phase is known to be quantized in the presence of certain symmetries, and this quantized Berry phase can be regarded as a topological order parameter for gapped quantum systems. In this paper, on the other hand, we establish that the complex Berry phase is also quantized in the systems described by a family of non-Hermitian Hamiltonians. Let $H(\theta )$ be a non-Hermitian Hamiltonian parameterized by $\theta$. Suppose that there exists a unitary and Hermitian operator $P$ such that $PH(\theta )P=H(-\theta )$ or $PH(\theta )P=H^{†}(-\theta )$. We prove that in the former case, the complex Berry phase $\gamma$ is ${\mathbb{Z}}_2$-quantized, while in the latter, only the real part of $\gamma$ is ${\mathbb{Z}}_2$-quantized. The operator $P$ can be viewed as a generalized symmetry for $H(\theta )$, and in practice, $P$ can be, for example, a spatial inversion. We also argue that this quantized complex Berry phase is capable of classifying non-Hermitian topological phases, and we demonstrate this in some one-dimensional strongly correlated systems.

6 pages, 4 figures

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• Topological phase transitions at finite temperature
• Fate of exceptional points under interactions: Reduction of topological classifications
• Complex Berry phase and imperfect non-Hermitian phase transitions
• Topological transitions in dissipatively coupled Su-Schrieffer-Heeger models
• Discriminant indicator with generalized rotational symmetry
• Topological analysis of the complex SSH model using the quantum geometric tensor
• A non-Hermitian Su-Schrieffer-Heeger model with the energy levels of free parafermions
• Hybrid Higher-Order Skin Topological Modes in the Two-Dimensional Su-Schrieffer-Heeger Model with Nonreciprocal Hoppings
• Non-orientable Exceptional Points in Twisted Boundary Systems