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Self-propulsion is a quintessential aspect of biological systems, which can induce nonequilibrium phenomena that have no counterparts in passive systems. Motivated by biophysical interest together with recent advances in experimental…

Soft Condensed Matter · Physics 2026-02-26 Kazuki Sone , Kazuki Yokomizo , Kyogo Kawaguchi , Yuto Ashida

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

Symmetry is one of the cornerstones of modern physics and has profound implications in different areas. In symmetry-protected topological systems, symmetries are responsible for protecting surface states, which are at the heart of the…

Mesoscale and Nanoscale Physics · Physics 2024-05-10 E. Slootman , W. Cherifi , L. Eek , R. Arouca , E. J. Bergholtz , M. Bourennane , C. Morais Smith

One dimensional topological insulators are characterized by edge states with exponentially small energies. According to one generalization of topological phases to non-Hermitian systems, a finite system in a non-trivial topological phase…

Quantum Physics · Physics 2017-12-06 Lorenzo Campos Venuti , Zhengzhi Ma , Hubert Saleur , Stephan Haas

The metallic surface state of a topological insulator (TI) is not only topologically protected, but exhibits a remarkable property of inducing an effective vector potential on curved surfaces. For an electron in the surface state of a…

Mesoscale and Nanoscale Physics · Physics 2013-05-08 Ken-Ichiro Imura , Yositake Takane

The application of topology in optics has led to a new paradigm in developing photonic devices with robust properties against disorder. Although significant progress on topological phenomena has been achieved in the classical domain, the…

Energy bands of non-Hermitian crystalline systems are described in terms of the generalized Brillouin zone (GBZ) having unique features which are absent in Hermitian systems. In this paper, we show that in one-dimensional non-Hermitian…

Mesoscale and Nanoscale Physics · Physics 2020-10-20 Kazuki Yokomizo , Shuichi Murakami

The current understanding of the role of topology in non-Hermitian (NH) systems and its far-reaching physical consequences observable in a range of dissipative settings are reviewed. In particular, how the paramount and genuinely NH concept…

Mesoscale and Nanoscale Physics · Physics 2021-03-03 Emil J. Bergholtz , Jan Carl Budich , Flore K. Kunst

Topological states of light represent counterintuitive optical modes localized at boundaries of finite-size optical structures that originate from the properties of the bulk. Being defined by bulk properties, such boundary states are…

Topological states of light represent counterintuitive optical modes localized at boundaries of finite-size optical structures that originate from the properties of the bulk. Being defined by bulk properties, such boundary states are…

Sub-symmetry (SubSy) protected topological states represent a concept that goes beyond the conventional framework of symmetry-protected topological (SPT) phases, demonstrating that topological boundary states can remain robust even when the…

Broadband and continuous frequency tuning is central to the versatility of semiconductor lasers, yet existing approaches typically rely on external moving components, limiting scalability and integration. Here we demonstrate broadband…

Topological insulators are a new class of materials which have gapped spectra in the bulk, but are accompanied by topologically protected gapless excitations at the surface (edge) of the system. These phenomena have a close relationship…

Mesoscale and Nanoscale Physics · Physics 2015-11-30 Taro Kimura

Topological modes (TMs) are typically localized at boundaries, interfaces and dislocations, and exponentially decay into the bulk of a large enough lattice. Recently, the non-Hermitian skin effect has been leveraged to delocalize the…

Quantum Physics · Physics 2024-02-13 Kai Bai , Jia-Zheng Li , Tian-Rui Liu , Liang Fang , Duanduan Wan , Meng Xiao

Topological insulators exhibit boundary states protected by bulk band topology, a principle first established in quantum systems and later extended to classical waves, including phononics. Conventionally, an $n$-dimensional bulk with…

Mesoscale and Nanoscale Physics · Physics 2025-11-26 Joel R. Pyfrom , Kai Sun , Jihong A. Ma

Topological phenomena in non-Hermitian systems have recently become a subject of great interest in the photonics and condensed-matter communities. In particular, the possibility of observing topologically-protected edge states in…

Mesoscale and Nanoscale Physics · Physics 2020-04-02 Pablo Reséndiz-Vázquez , Konrad Tschernig , Armando Perez-Leija , Kurt Busch , Roberto de J. León-Montiel

Electromagnetic waves propagating, at finite speeds, in conventional wave-guiding structures are reflected by discontinuities and decay in lossy regions. In this Letter, we drastically modify this typical guided-wave behavior by combining…

Optics · Physics 2018-09-12 S. Ali Hassani Gangaraj , Francesco Monticone

Topological concepts open many new horizons for photonic devices, from integrated optics to lasers. The complexity of large scale topological devices asks for an effective solution of the inverse problem: how best to engineer the topology…

Optics · Physics 2018-03-09 Laura Pilozzi , Francis A. Farrelly , Giulia Marcucci , Claudio Conti

In a topological semimetal with Dirac or Weyl points, the bulk edge correspondence principle predicts a gapless edge mode if the essential symmetry is still preserved at the surface. The detection of such topological surface state has been…

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