Article
Multidisciplinary Sciences
Shaojie Ma, Yangang Bi, Qinghua Guo, Biao Yang, Oubo You, Jing Feng, Hong-Bo Sun, Shuang Zhang
Summary: By constructing a system based on metamaterials with engineered electromagnetic properties, the research team observed new bulk and boundary topological effects, such as the linking of Weyl surfaces and surface Weyl arcs, via selected three-dimensional subspaces. The demonstrated photonic Weyl surfaces and Weyl arcs utilize the concept of higher-dimensional topology to control the propagation of electromagnetic waves in artificially engineered photonic media.
Article
Materials Science, Multidisciplinary
Jianhua Wang, Hongkuan Yuan, Wenhong Wang, Guangqian Ding, Xiao-Ping Li, Xiaotian Wang
Summary: In this study, a novel topological material, P6322-type BaNiIO6, with spin-polarized Weyl points and surface arcs is proposed. The material shows high stability under strain and interaction, making it a promising candidate for spintronics and topological physics applications.
Article
Physics, Multidisciplinary
Dylan Rees, Baozhu Lu, Yue Sun, Kaustuv Manna, Ruestem Oezguer, Sujan Subedi, Horst Borrmann, Claudia Felser, J. Orenstein, Darius H. Torchinsky
Summary: Researchers successfully measured the linear and circular photogalvanic effect currents derived from the Fermi arcs of a nonsymmorphic, chiral Weyl semimetal. They found that the direction of the surface photocurrent deviated from the theoretical expectation and observed an unexpected emergent mirror symmetry. This study provides important clues for understanding the electronic and optical properties of topological semimetals.
PHYSICAL REVIEW LETTERS
(2021)
Article
Physics, Multidisciplinary
Dennis Wawrzik, Jhih-Shih You, Jorge Facio, Jeroen van den Brink, Inti Sodemann
Summary: The study shows that Weyl Fermi arcs are generally accompanied by a divergence of the surface Berry curvature that scales as 1/k(2), relating to the distance to a hot line in the surface Brillouin zone connecting the projection of Weyl nodes with opposite chirality. The emergence of this surface Berry curvature is mainly determined by the velocity tilt of the bulk Weyl dispersion towards the surface of interest.
PHYSICAL REVIEW LETTERS
(2021)
Article
Multidisciplinary Sciences
Ruey-Lin Chern
Summary: This paper investigates the photonic topological phases in chiral metamaterials with diagonal chirality components. By introducing pseudospin states, the photonic system is described as two subsystems with spin-orbit Hamiltonians of spin 1, resulting in nonzero spin Chern numbers that determine the topological properties. Surface modes at the interface between vacuum and the chiral metamaterial are formulated by algebraic equations in the wave vector space. Specifically, the surface modes form a pair of spiral surface sheets wrapping around the Weyl cone, resembling the helicoid surface states in topological semimetals. At the Weyl frequency, the surface modes contain two Fermi arc-like states that concatenate to yield a straight line segment.
SCIENTIFIC REPORTS
(2023)
Article
Chemistry, Multidisciplinary
Weizhen Meng, Wei Liu, Xiaoming Zhang, Ying Liu, Xuefang Dai, Guodong Liu
Summary: The study reveals the presence of unique topological electronic properties in a 2D planar octagon TiB4 compound, including novel quadratic node, two types of nodal rings, and clear edge states. Under lattice strain and with consideration of spin-orbit coupling, the material exhibits rich topological phase transition characteristics.
Article
Materials Science, Multidisciplinary
Ikuma Tateishi, Viktor Koenye, Hiroyasu Matsuura, Masao Ogata
Summary: This study investigates the orbital magnetic susceptibility and the Hall conductivity of nodal-line materials, revealing their characteristic singular behaviors under certain conditions. These behaviors can serve as clear evidence for the presence of nodal-line materials and their orientation in experimental detection.
Article
Physics, Multidisciplinary
Dongyang Wang, Biao Yang, Mudi Wang, Ruo-Yang Zhang, Xiao Li, Z. Q. Zhang, Shuang Zhang, C. T. Chan
Summary: This study investigates a photon multiple nodal links system, where nodal lines of nonadjacent bands are examined through symmetry constraints on frame charges, and the existence of nodal lines between higher bands is predicted using an orthogonal nodal chain.
PHYSICAL REVIEW LETTERS
(2022)
Article
Physics, Multidisciplinary
Yang Li
Summary: Weyl semimetals, solid-state crystals with Fermi energy accurately located at Weyl points (WPs), have been extensively studied in condensed matter physics. In addition to theoretical and numerical predictions, Weyl quasiparticles have been observed in both electronic and bosonic regimes. This study reveals the coexistence of 12 single Weyl phonons with linear dispersion and six double Weyl phonons with quadratic dispersion in real material P4332 BaSi2. These phonons can form a Weyl complex phonon with a zero net chirality.
FRONTIERS IN PHYSICS
(2023)
Article
Materials Science, Multidisciplinary
Kuangyin Deng, John S. Van Dyke, Djordje Minic, J. J. Heremans, Edwin Barnes
Summary: Recent works suggest that an axial anomaly can occur in Weyl semimetals, leading to the electromagnetic response being governed by axion electrodynamics. Different versions of axion electrodynamics were considered, with consistent solutions found for certain conditions, particularly amplification of the magnetic field providing a detectable signature for experiments. Solutions were generally obtained for non-dynamical axions with linear chiral magnetic terms, while dynamical axions had consistent solutions only when the chiral magnetic term vanished. Nonlinear forms of the chiral magnetic term presented challenges in finding self-consistent solutions, with few special cases producing results.
Article
Chemistry, Multidisciplinary
Wenli Sun, Bingyang Li, Xiaorong Zou, Runhan Li, Baibiao Huang, Ying Dai, Chengwang Niu
Summary: This study theoretically demonstrates the existence of intrinsic ferromagnetic Weyl semimetals (WSMs) in BaCrSe2 with nontrivial nature, as confirmed by the Chern number and Fermi arc surface states analysis. Unlike previous WSMs, the WPs of BaCrSe2 have a long-distance distribution, indicating their high robustness against perturbations. These results not only advance the understanding of magnetic WSMs but also propose potential applications in topotronics.
Article
Physics, Multidisciplinary
Mudi Wang, Shan Liu, Qiyun Ma, Ruo-Yang Zhang, Dongyang Wang, Qinghua Guo, Biao Yang, Manzhu Ke, Zhengyou Liu, C. T. Chan
Summary: In this study, we designed phononic crystals with earring nodal links and experimentally observed two different types of earring nodal links. The experimental evidence supports the unique phenomena of non-Abelian band topology.
PHYSICAL REVIEW LETTERS
(2022)
Article
Physics, Applied
I Robredo, N. B. M. Schroeter, A. Reyes-Serrato, A. Bergara, F. de Juan, L. M. Schoop, M. G. Vergniory
Summary: In this study, the topological features of the metallic ferromagnetic pyrite CoS2 are investigated, revealing the presence of Weyl nodes, nodal lines, and a symmetry-protected fourfold fermion. The results suggest that CoS2 is a promising material for studying topological phenomena and spintronic applications.
JOURNAL OF PHYSICS D-APPLIED PHYSICS
(2022)
Article
Chemistry, Physical
Li Luo, Hai-Xiao Wang, Zhi-Kang Lin, Bin Jiang, Ying Wu, Feng Li, Jian-Hua Jiang
Summary: This study explores the existence of higher-order Weyl semimetals in phononic systems and demonstrates the presence of topologically protected boundary states in multiple dimensions. By realizing a chiral phononic crystal, the researchers observed topological boundary states linking projections of Weyl points in different dimensions and directions.
Article
Physics, Multidisciplinary
Yue Zheng, Wei Chen, Xiangang Wan, D. Y. Xing
Summary: One hallmark of Weyl semimetals is the emergence of Fermi arcs (FAs) in surface Brillouin zones, where FAs connect the projected Weyl nodes of opposite chiralities. We show that FAs can be simply modified by a surface gate voltage, resulting in a continuous deformation of the surface band. The Lifshitz transition of FAs can be probed by transport measurements in a magnetic field.
CHINESE PHYSICS LETTERS
(2023)
Article
Physics, Multidisciplinary
Qicheng Zhang, Yitong Li, Huanfa Sun, Xun Liu, Luekai Zhao, Xiling Feng, Xiying Fan, Chunyin Qiu
Summary: The topological features in ancient braiding and knotting arts have significant impacts on daily life and cutting-edge science. Recent efforts have been focused on the braiding topology of complex Bloch bands in non-Hermitian systems, surpassing the established classifications in Hermitian systems. In this study, the first acoustic realization of topological non-Hermitian Bloch braids was presented, using a two-band model that can easily achieve any desired knot structure. The non-Hermitian bands were synthesized using a simple binary cavity-tube system, enabling the direct visualization of various two-band braiding patterns and observation of highly elusive topological phase transitions.
PHYSICAL REVIEW LETTERS
(2023)
Review
Optics
Jian Wei You, Zhihao Lan, Qian Ma, Zhen Gao, Yihao Yang, Fei Gao, Meng Xiao, Tie Jun Cui
Summary: Metasurfaces are thin films with subwavelength structures that can control the polarization, phase, and amplitude of light. Recent developments in topological photonics have greatly expanded the design possibilities for metasurfaces in novel applications. This review summarizes recent progress in the field of topological metasurfaces, covering both passive and active systems in the classical and quantum regimes. It discusses passive topological phenomena and cutting-edge studies of active topological metasurfaces, as well as their potential applications in quantum information and many-body physics.
PHOTONICS RESEARCH
(2023)
Article
Physics, Applied
Yuanyuan Shen, Shengguo Guan, Chunyin Qiu
Summary: In this study, the experimental investigation on topological valley transport of spoof surface acoustic waves (SAWs) is reported. The valley pseudospins and valley Hall phase transition are achieved by adjusting the structural size of adjacent grooves. Aside from the direct visualization of the vortex chirality-locked beam splitting for the bulk valley states, valley-projected edge states are also observed in straight and bent interface channels formed by two topologically distinct valley Hall insulating phases. The experimental data are in good agreement with the numerical predictions. The topological transport of spoof SAWs, encoded with valley information, provides more possibilities in designing novel acoustic devices based on valley-contrasting physics.
JOURNAL OF APPLIED PHYSICS
(2023)
Article
Multidisciplinary Sciences
Haidong Tian, Xueshi Gao, Yuxin Zhang, Shi Che, Tianyi Xu, Patrick Cheung, Kenji Watanabe, Takashi Taniguchi, Mohit Randeria, Fan Zhang, Chun Ning Lau, Marc W. Bockrath
Summary: In a flat band superconductor, the charge carriers' velocity is extremely slow, leading to peculiar superconducting behavior. Using twisted bilayer graphene, the researchers investigate the effect of the slow velocity on the superconducting state. They find evidence for small Cooper pairs and discuss the unusual nature of ultra-strong coupling superconductivity in ultra-flat Dirac bands.
Article
Physics, Multidisciplinary
Zhenhang Pu, Hailong He, Licheng Luo, Qiyun Ma, Liping Ye, Manzhu Ke, Zhengyou Liu
Summary: Higher-order topological phases, characterized by topological boundary states with dimensions two or more less than the system bulk, have attracted widespread interest in various gapped and gapless phases. In this Letter, we report the first prediction and observation of a new type of hinge states, called bound hinge states in the continuum (BHICs), in a higher-order Weyl semimetal implemented in a phononic crystal. Unlike the hinge states in gaps, BHICs are identified by nontrivial surface polarization. This finding broadens our understanding of topological states and may inspire further research in other systems.
PHYSICAL REVIEW LETTERS
(2023)
Article
Physics, Multidisciplinary
Luohong Liu, Tianzi Li, Qicheng Zhang, Meng Xiao, Chunyin Qiu
Summary: We propose a simple but universal mirror-stacking approach to turn nontrivial bound states of any topological monolayer model into topological bound states with extraordinary robustness. By tuning the interlayer couplings, the topological bound state of one subspace can move into and out of the continuum of the other subspace continuously without hybridization. We construct one-dimensional first-order and two-dimensional higher-order topological bound states and demonstrate them unambiguously by acoustic experiments.
PHYSICAL REVIEW LETTERS
(2023)
Review
Multidisciplinary Sciences
Shaofan Yuan, Chao Ma, Ethan Fetaya, Thomas Mueller, Doron Naveh, Fan Zhang, Fengnian Xia
Summary: Geometry, as an ancient yet vibrant branch of mathematics, has significant and far-reaching impacts on various disciplines. In this article, we introduce a novel concept called geometric deep optical sensing, which is based on recent advancements in optical sensing and imaging. It involves the use of reconfigurable sensors to directly extract rich information from unknown incident light beams, including intensity, spectrum, polarization, spatial features, and angular momentum. We discuss the physical, mathematical, and engineering foundations of this concept, with a focus on classical and quantum geometry as well as deep neural networks. Furthermore, we explore the potential opportunities and challenges associated with this emerging scheme.
Article
Multidisciplinary Sciences
Huahui Qiu, Qicheng Zhang, Tingzhi Liu, Xiying Fan, Fan Zhang, Chunyin Qiu
Summary: Ideal acoustic metamaterials are used to construct a non-abelian braider, exploring non-abelian topological phases and phenomena in multi-gap systems.
NATURE COMMUNICATIONS
(2023)
Article
Optics
Jiazheng Li, Meng Xiao
Summary: Combining ODoF with higher-order topology is significant for exotic quantum states and solid-state materials. Experimental realization of a photonic p-orbital higher-order topological insulator can explore novel topological phases involving ODoF.
LIGHT-SCIENCE & APPLICATIONS
(2023)
Article
Physics, Multidisciplinary
Tianzi Li, Luohong Liu, Qicheng Zhang, Chunyin Qiu
Summary: Symmetry plays a key role in classifying topological phases. Recent theory shows that in the presence of gauge fields, the algebraic structure of crystalline symmetries needs to be projectively represented. This study reports the experimental realization of mirror Chern insulators in acoustic systems by exploiting the concept of projective symmetry.
COMMUNICATIONS PHYSICS
(2023)
Review
Physics, Applied
Meng Kang, Tao Liu, C. T. Chan, Meng Xiao
Summary: Bound states in the continuum (BICs) in photonics have unique properties, such as enhanced light confinement, sharp Fano resonances, and topological characteristics. They have potential applications in various fields, including lasing, nonlinear frequency conversion, and waveguiding. Moreover, BICs offer insights into emerging research frontiers like parity-time symmetric systems and higher-order topology.
NATURE REVIEWS PHYSICS
(2023)
Article
Physics, Multidisciplinary
Qicheng Zhang, Luekai Zhao, Xun Liu, Xiling Feng, Liwei Xiong, Wenquan Wu, Chunyin Qiu
Summary: The complex eigenenergy in non-Hermitian lattices gives rise to unique band topology. There has been recent interest in the winding and braiding topologies of non-Hermitian single and double bands. In this study, we explore the more complex multiband topology in non-Hermitian systems and experimentally characterize the three-band braid relations of an acoustic system. Using a tight-binding lattice model, we design a ternary cavity-tube structure with a controllable unidirectional coupler to reproduce the acoustic non-Hermitian Bloch bands in a synthetic space. We identify the non-Hermitian braid relations based on the global evolution of eigenvalues and acoustic states, including a noncommutative braid relation a1a2 =⠂ a2a1 and a swappable braid relation a1a2a1 = a2a1a2. These findings enhance our understanding of non-Hermitian Bloch band topology and have implications for designing practical devices for manipulating acoustic states.
PHYSICAL REVIEW RESEARCH
(2023)
Article
Materials Science, Multidisciplinary
Meng Xiao
Summary: A resonance transition occurs between two states under an oscillatory driving field with a proper frequency. The conventional belief that the frequency must match at the resonance transition is challenged when the system under driving has nontrivial band degeneracies. We study a kagome lattice under the modulation of an artificial gauge field and find the inequivalence between the modulation frequency and energy difference at transitions. The transitions exhibit chirality around the Dirac cone, and the fundamental one-photon transition is absent when the system Hamiltonian circles around a higher-order charged band degeneracy.
Article
Materials Science, Multidisciplinary
Han-Rong Xia, Meng Xiao
Summary: A chiral anomaly Landau level arises in the presence of an external magnetic field in a Weyl semimetal. It has been shown recently that similar chiral anomaly bulk states can exist in two-dimensional Dirac semimetals with appropriate boundary conditions. The dispersion of these chiral bulk states depends on both the boundary condition and chirality of the Dirac cone (whether it is at the K or K' point). This paper demonstrates that the slope (sign of group velocity) near the K and K' points can be reversed under a periodically staggered potential. The phenomenon is analyzed using a nearest-neighbor tight-binding model and a semi-analytical solution for the dispersion of the chiral anomaly bulk states is provided. It is further confirmed through full-wave simulations in a photonic crystal system.
