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The topological classification of energy bands has laid the groundwork for the discovery of various topological phases of matter in recent decades. While this classification has traditionally focused on real-energy bands, recent studies…

Mesoscale and Nanoscale Physics · Physics 2025-11-18 Yang Long , Haoran Xue , Baile Zhang

We proposed a framework for the topological classification of non-Hermitian systems. Different from previous $K$-theoretical approaches, our approach is a homotopy classification, which enables us to see more topological invariants.…

Mesoscale and Nanoscale Physics · Physics 2022-06-09 Zhi Li , Roger S. K. Mong

Machine learning has been used to identify phase transitions in a variety of physical systems. However, there is still a lack of relevant research on non-Bloch energy braiding in non-Hermitian systems. In this work, we study non-Bloch…

Mesoscale and Nanoscale Physics · Physics 2024-12-31 Shuwei Shi , Shibing Chu , Yuee Xie , Yuanping Chen

Topological features embedded in ancient braiding and knotting arts endow significant impacts on our daily life and even cutting-edge science. Recently, fast growing efforts are invested to the braiding topology of complex Bloch bands in…

Mesoscale and Nanoscale Physics · Physics 2023-01-18 Qicheng Zhang , Yitong Li , Huanfa Sun , Xun Liu , Luekai Zhao , Xiling Feng , Xiying Fan , Chunyin Qiu

Non-Hermitian matrices are ubiquitous in the description of nature ranging from classical dissipative systems, including optical, electrical, and mechanical metamaterials, to scattering of waves and open quantum many-body systems. Seminal…

Mesoscale and Nanoscale Physics · Physics 2024-07-08 Kang Yang , Zhi Li , J. Lukas K. König , Lukas Rødland , Marcus Stålhammar , Emil J. Bergholtz

The complex energy bands of non-Hermitian systems braid in momentum space even in one dimension. Here, we reveal that the non-Hermitian braiding underlies the Hermitian topological physics with chiral symmetry under a general framework that…

Mesoscale and Nanoscale Physics · Physics 2023-10-09 W. B. Rui , Y. X. Zhao , Z. D. Wang

We show that distinct topological phases of the band structure of a non-Hermitian Hamiltonian can be classified with elements of the braid group. As the proof of principle, we consider the non-Hermitian evolution of the statistics of…

Mesoscale and Nanoscale Physics · Physics 2013-05-23 Jie Ren , N. A. Sinitsyn

We revisit the problem of classifying topological band structures in non-Hermitian systems. Recently, a solution has been proposed, which is based on redefining the notion of energy band gap in two different ways, leading to the so-called…

Mathematical Physics · Physics 2020-05-20 Charles C. Wojcik , Xiao-Qi Sun , Tomáš Bzdušek , Shanhui Fan

The non-Hermiticity of the system gives rise to distinct knot topology that has no Hermitian counterpart. Here, we report a comprehensive study of the knot topology in gapped non-Hermitian systems based on the universal dilation method with…

Quantum Physics · Physics 2023-11-14 Yang Wu , Yunhan Wang , Xiangyu Ye , Wenquan Liu , Chang-Kui Duan , Ya Wang , Xing Rong , Jiangfeng Du

Knots have a twisted history in quantum physics. They were abandoned as failed models of atoms. Only much later was the connection between knot invariants and Wilson loops in topological quantum field theory discovered. Here we show that…

Mesoscale and Nanoscale Physics · Physics 2021-01-08 Haiping Hu , Erhai Zhao

Knots and links represent a fundamental motif of non-local connectivity that permeates the physical sciences from string theory to protein folds. While spectral braiding has been explored in two-band non-Hermitian models across various…

Quantum Physics · Physics 2026-04-30 Truman Yu Ng , Yuzhu Wang , Wei Jie Chan , Ruizhe Shen , Tianqi Chen , Ching Hua Lee

Non-Hermitian systems host band degeneracies that are fundamentally distinct from those in Hermitian systems, most notably exceptional points (EPs) where both eigenvalues and eigenvectors coalesce. In three dimensional (3D) non-Hermitian…

Mesoscale and Nanoscale Physics · Physics 2026-03-12 Bin Jiang , Aolong Guo , Qilin Cai , Jian-Hua Jiang

The integration of artificial intelligence (AI) into fundamental science has opened new possibilities to address long-standing scientific challenges rooted in mathematical limitations. For example, topological invariants are used to…

Mesoscale and Nanoscale Physics · Physics 2025-11-18 Yang Long , Haoran Xue , Baile Zhang

We develop the topological band theory for systems described by non-Hermitian Hamiltonians, whose energy spectra are generally complex. After generalizing the notion of gapped band structures to the non-Hermitian case, we classify "gapped"…

Mesoscale and Nanoscale Physics · Physics 2018-04-11 Huitao Shen , Bo Zhen , Liang Fu

We present a study of complex energy braiding in a 1D non-Hermitian system with $n$th order long range asymmetrical coupling. Our work highlights the emergence of novel topological phenomena in such systems beyond the conventional…

Quantum Physics · Physics 2024-07-08 S. M. Rafi-Ul-Islam , Zhuo Bin Siu , Md. Saddam Hossain Razo , Mansoor B. A. Jalil

In the band theory for non-Hermitian systems, the energy eigenvalues, which are complex, can exhibit non-trivial topology which is not present in Hermitian systems. In one dimension, it was recently noted theoretically and demonstrated…

Optics · Physics 2022-10-19 Charles C. Wojcik , Kai Wang , Avik Dutt , Janet Zhong , Shanhui Fan

There has been much recent interest and progress on topological structures of the non-Hermitian Bloch bands. Here, we study the topological structures of non-Bloch bands of non-Hermitian multiband quantum systems under open boundary…

Mesoscale and Nanoscale Physics · Physics 2024-09-10 Yongxu Fu , Yi Zhang

Non-Hermitian nodal knot metals (NKMs) contains intricate complex-valued energy bands gives rise to knotted exceptional loops and new topological surface states. We introduce a formalism that connects the algebraic, geometric, and…

Mesoscale and Nanoscale Physics · Physics 2021-03-02 Xiao Zhang , Guangjie Li , Yuhan Liu , Tommy Tai , Ronny Thomale , Ching Hua Lee

The study of topological properties by machine learning approaches has attracted considerable interest recently. Here we propose machine learning the topological invariants that are unique in non-Hermitian systems. Specifically, we train…

Computational Physics · Physics 2021-01-27 Ling-Feng Zhang , Ling-Zhi Tang , Zhi-Hao Huang , Guo-Qing Zhang , Wei Huang , Dan-Wei Zhang

Non-Hermitian topological phases have gained widespread interest due to their unconventional properties, which have no Hermitian counterparts. In this work, we propose to use machine learning to identify and predict non-Hermitian…

Mesoscale and Nanoscale Physics · Physics 2021-02-11 Brajesh Narayan , Awadhesh Narayan
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