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We study the emergence of non-Hermitian band topology in a two-dimensional metal with planar spiral magnetism due to a momentum-dependent relaxation rate. A sufficiently strong momentum dependence of the relaxation rate leads to exceptional…

Strongly Correlated Electrons · Physics 2021-11-17 Johannes Mitscherling , Walter Metzner

The most intriguing properties of non-Hermitian systems are found near the exceptional points (EPs) at which the Hamiltonian matrix becomes defective. Due to the complex topological structure of the energy Riemann surfaces close to an EP…

Classical Physics · Physics 2018-06-19 Xu-Lin Zhang , Shubo Wang , Bo Hou , C. T. Chan

Even in the linear limit, the topology of multifold (also called higher-order) exceptional points across the Brillouin zone has lacked a general characterization, leaving the doubling theorem essentially limited to two-fold exceptional…

Mesoscale and Nanoscale Physics · Physics 2026-04-02 Tsuneya Yoshida

Exceptional points (EPs) are non-Hermitian degeneracies, where both eigenvalues and eigenvectors coalesce, which are fundamentally distinct from their Hermitian counterparts. In this study, we investigate the influence of hexagonal warping…

Mesoscale and Nanoscale Physics · Physics 2026-01-13 Md Afsar Reja , Awadhesh Narayan

Non-Hermitian systems exhibit a variety of unique features rooted in the presence of exceptional points (EP). The distinct topological structure in the proximity of an EP gives rise to counterintuitive behaviors absent in Hermitian systems,…

Quantum Physics · Physics 2025-05-13 He Zhang , Tong Liu , Zhongcheng Xiang , Kai Xu , Heng Fan , Dongning Zheng

Non-Hermitian systems distinguish themselves from Hermitian systems by exhibiting a phase transition point called an exceptional point (EP), which is the point at which two eigenstates coalesce under a system parameter variation. Many…

Mesoscale and Nanoscale Physics · Physics 2016-04-20 Kun Ding , Guancong Ma , Meng Xiao , Z. Q. Zhang , C. T. Chan

Non-Hermitian systems with parity-time (PT) symmetric complex potentials can exhibit a phase transition when the degree of non-Hermiticity is increased. Two eigenstates coalesce at a transition point, which is known as the exceptional point…

Optics · Physics 2016-01-07 Kun Ding , Z. Q. Zhang , C. T. Chan

Current progress in electro-optical modulation within silicon integrated photonics, driven by the unique capabilities of advanced functional materials, has led to significant improvements in device performance. However, inherent constraints…

Optics · Physics 2025-10-30 Shahab Ramezanpour , Amr Helmy

The existence of exceptional points (EPs) ${-}$ where both eigenvalues and eigenvectors converge ${-}$ is a key characteristic of non-Hermitian physics. A newly-discovered class of magnets ${-}$ termed as altermagnets (AMs) ${-}$ are…

Mesoscale and Nanoscale Physics · Physics 2024-12-04 Md Afsar Reja , Awadhesh Narayan

In non-Hermitian systems, the defective band degeneracies, so-called exceptional points (EPs), can form robust exceptional lines (ELs) in 3D momentum space in the absence of any symmetries. Here, we show that a natural orientation can be…

Optics · Physics 2022-12-13 Ruo-Yang Zhang , Xiaohan Cui , Wen-Jie Chen , Zhao-Qing Zhang , C. T. Chan

Non-Hermitian systems can produce branch singularities known as exceptional points (EPs). Different from singularities in Hermitian systems, the topological properties of an EP can involve either the winding of eigenvalues that produces a…

Quantum Physics · Physics 2021-07-21 Weiyuan Tang , Kun Ding , Guancong Ma

Exceptional points (EPs) with their intriguing spectral topology have attracted considerable attention in a broad range of physical systems, with potential sensing applications driving much of the present research in this field. Here we…

Optics · Physics 2026-01-29 Jan Wingenbach , Stefan Schumacher , Xuekai Ma

Non-conservative physical systems admit a special kind of spectral degeneracy, known as exceptional point (EP), at which eigenvalues and eigenvectors of the corresponding non-Hermitian Hamiltonian coalesce. Dynamical parametric encircling…

Mesoscale and Nanoscale Physics · Physics 2019-10-21 Alexey Galda , Valerii M. Vinokur

Exceptional points (EPs) are distinct characteristics of non-Hermitian Hamiltonians that have no counterparts in Hermitian systems. In this study, we focus on EPs in continuous systems rather than discrete non-Hermitian systems, which are…

Quantum Physics · Physics 2025-05-13 Y. T. Wang , R. Wang , X. Z. Zhang

Exceptional points (EPs) are central to non-Hermitian physics because of their unique properties and broad application prospects. While extensively studied in parity-time ($\mathcal{P}\mathcal{T}$)-symmetric systems and under Markovian…

Optics · Physics 2026-01-15 H. Z. Shen , X. C. Zhang , L. Y. Ning , Zhi-Guang Lu , Yan-Hui Zhou , Cheng Shang

Exceptional points (EPs) are special points in non-Hermitian systems where both eigenvalues and eigenvectors coalesce. In open quantum systems, these points are typically analyzed using effective non-Hermitian Hamiltonians or Liouvillian…

Quantum Physics · Physics 2025-07-23 Wai Chun Wong , Bei Zeng , Jensen Li

We establish a novel mechanism for topological transitions in non-Hermitian systems that are controlled by the system size. Based on a new paradigm known as exceptional-bound (EB) band engineering, its mechanism hinges on the unique…

Other Condensed Matter · Physics 2026-03-10 Mengjie Yang , Ching Hua Lee

We classify gapped phases and characteristic nodal points of non-Hermitian band structures on two-dimensional nonorientable parameter spaces. Such spaces arise in a wide range of physical systems in the presence of nonsymmorphic parameter…

Mesoscale and Nanoscale Physics · Physics 2026-03-30 J. Lukas K. König , Kang Yang , André Grossi Fonseca , Sachin Vaidya , Marin Soljačić , Emil J. Bergholtz

Exceptional points (EPs) have recently attracted considerable attention in the study of non-Hermitian systems and in applications such as sensors and mode switching. In particular, nontrivial topological structures of EPs have been studied…

Quantum Physics · Physics 2022-08-17 Kyu-Won Park , Jinuk Kim , Kabgyun Jeong

We have investigated the exceptional points (EPs) which are degeneracies of a non-Hermitian Hamiltonian, in the case that three modes are interacting with each other. Even though the parametric evolution of the modes cannot be uniquely…

Quantum Physics · Physics 2015-05-30 Jung-Wan Ryu , Soo-Young Lee , Sang Wook Kim