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Discovery of a maximally charged Weyl point

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arXiv 2022年

作者： Chen, Qiaolu Chen, Fujia Yan, Qinghui Zhang, Li Gao, Zhen Yang, Shengyuan A. Yu, Zhi-Ming Chen, Hongsheng Zhang, Baile Yang, Yihao Interdisciplinary Center for Quantum Information State Key Laboratory of Modern Optical Instrumentation ZJU-Hangzhou Global Scientific and Technological Innovation Center Zhejiang University Hangzhou310027 China International Joint Innovation Center Key Lab. of Advanced Micro Nano Electronic Devices & Smart Systems of Zhejiang The Electromagnetics Academy Zhejiang University Zhejiang University Haining314400 China Jinhua Institute of Zhejiang University Zhejiang University Jinhua321099 China Department of Electrical and Electronic Engineering Southern University of Science and Technology Shenzhen518055 China Research Laboratory for Quantum Materials Singapore University of Technology and Design 487372 Singapore School of Physics Beijing Institute of Technology Beijing100081 China Beijing Key Laboratory of Nanophotonics and Ultrafine Optoelectronic Systems School of Physics Beijing Institute of Technology Beijing100081 China Division of Physics and Applied Physics School of Physical and Mathematical Sciences Nanyang Technological University 21 Nanyang Link 637371 Singapore Centre for Disruptive Photonic Technologies The Photonics Institute Nanyang Technological University 50 Nanyang Avenue 639798 Singapore

The hypothetical Weyl particles in high-energy physics have been discovered in three-dimensional crystals as collective quasiparticle excitations near two-fold degenerate Weyl points1-5. Such momentum-space Weyl particles carry quantized chiral charges, which can be measured by counting the number of Fermi arcs emanating from the corresponding Weyl points. It is known that merging unit-charged Weyl particles can create new ones with more charges6. However, only very recently has it been realised that there is an upper limit - the maximal charge number that a two-fold Weyl point can host is four - achievable only in crystals without spin-orbit coupling7-9. Here, we report the experimental realisation of such a maximally charged Weyl point in a three-dimensional photonic crystal. The four charges support quadruple-helicoid Fermi arcs, forming an unprecedented topology of two non-contractible loops in the surface Brillouin zone. The helicoid Fermi arcs also exhibit the long-pursued type-II van Hove singularities that can reside at arbitrary momenta. This discovery reveals a type of maximally charged Weyl particles beyond conventional topological particles in crystals. Copyright © 2022, The Authors. All rights reserved.

关键词： Topology

Enhanced Cherenkov radiation in twisted hyperbolic Van der Waals crystals

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InfoScience

InfoScience 2024年

作者： Hao Hu Xiao Lin Guangwei Hu Francisco J. Garcia-Vidal Yu Luo National Key Laboratory of Microwave Photonics Nanjing University of Aeronautics and Astronautics Nanjing China State Key Laboratory of Modern Optical Instrumentation Interdisciplinary Center for Quantum Information Zhejiang University Hangzhou China Key Laboratory of Advanced Micro/Nano Electronic Devices & Smart Systems of Zhejiang International Joint Innovation Center The Electromagnetics Academy at Zhejiang University Zhejiang University Haining China School of Electrical and Electronic Engineering Nanyang Technological University Singapore Singapore Departamento de Física Teórica de la Materia Condensada and Condensed Matter Physics Center (IFIMAC) Universidad Autónoma de Madrid Madrid Spain

Cherenkov radiation in artificial structures experiencing strong radiation enhancements promises important applications in free-electron quantum emitters, broadband light sources, miniaturized particle detectors, etc. However, the momentum matching condition between swift electrons and emitted photons generally restricts the radiation enhancement to a particular momentum. Efficient Cherenkov radiation over a wide range of momenta is highly demanded for many applications but still remains a challenging task. To this end, we explored the interaction between swift electrons and twisted hyperbolic Van der Waals crystals and observed enhanced Cherenkov radiation at the flatband resonance frequency. We show that, at the photonic magic angle of the twisted crystals, the electron momentum, once matching with that of the flatband photon, gives rise to a maximum energy loss (corresponding to the surface phonon generation), one-order of magnitude higher than that in conventional hyperbolic materials. Such a significant enhancement is attributed to the excitation of flatband surface phonon polaritons over a broad momentum range. Our findings provide a feasible route for highly directional free-electron radiation and radiation shaping.

关键词： free electron radiation metamaterials nanophotonics Van der Waals crystals

Photonic antiferromagnetic topological insulator with a single surface Dirac cone

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Science advances 2025年第22期11卷 eadu6230页

作者： Fujia Chen Ning Han Songyang Pu Rui Zhao Li Zhang Qiaolu Chen Yuze Hu Mingyu Tong Wenhao Li Junyao Wu Yudong Ren Xinrui Li Wenyan Yin Hongsheng Chen Rui-Xing Zhang Yihao Yang State Key Laboratory of Extreme Photonics and Instrumentation ZJU-Hangzhou Global Scientific and Technological Innovation Center Zhejiang University Hangzhou 310027 China. International Joint Innovation Center The Electromagnetics Academy at Zhejiang University Zhejiang University Haining 314400 China. Key Laboratory of Advanced Micro/Nano Electronic Devices & Smart Systems of Zhejiang Jinhua Institute of Zhejiang University Zhejiang University Jinhua 321099 China. College of Optical and Electronic Technology China Jiliang University Hangzhou 310018 China. Department of Physics and Astronomy The University of Tennessee Knoxville TN 37996 USA. Department of Materials Science and Engineering The University of Tennessee Knoxville TN 37996 USA.

Antiferromagnetism, characterized by alternating magnetic moments, has garnered renewed interest for its potential applications in spintronics and axion electrodynamics. Its synergy with topology may yield an exotic topological phase unique to a certain magnetic order, termed antiferromagnetic topological insulators (AF TIs). A hallmark signature of AF TIs is the presence of a single surface Dirac cone-a feature typically associated with strong three-dimensional (3D) topological insulators but lacking direct observation. Here, we theoretically and experimentally discover a 3D photonic AF TI protected by the combined symmetry of time reversal and half-lattice translation. By measuring both bulk and surface states, we directly observe the symmetry-protected single-Dirac-cone surface states and their remarkable robustness against random magnetic disorders. To our knowledge, our work constitutes the first realization of photonic AF TIs and photonic analogs of strong 3D topological insulators, opening a chapter for exploring topological photonic devices and phenomena incorporating additional magnetic degrees of freedom.

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Geometric Filterless Photodetectors for Mid-infrared Spin Light

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arXiv 2022年

作者： Wei, Jingxuan Chen, Yang Li, Ying Li, Wei Xie, Junsheng Lee, Chengkuo Novoselov, Kostya S. Qiu, Cheng-Wei Department of Electrical and Computer Engineering National University of Singapore Singapore117583 Singapore CAS Key Laboratory of Mechanical Behaviour and Design of Materials Department of Precision Machinery and Precision Instrumentation University of Science and Technology of China Hefei230026 China Interdisciplinary Center for Quantum Information State Key Laboratory of Modern Optical Instrumentation ZJU-Hangzhou Global Scientific and Technological Innovation Center Zhejiang University Hangzhou310027 China International Joint Innovation Center Key Lab of Advanced Micro/Nano Electronic Devices & Smart Systems of Zhejiang Zhejiang University Haining314400 China GPL Photonics Lab State Key Laboratory of Applied Optics Changchun Institute of Optics Fine Mechanics and Physics Chinese Academy of Sciences Changchun130033 China Center for Intelligent Sensors and MEMS National University of Singapore Singapore117608 Singapore Institute for Functional Intelligent Materials National University of Singapore Singapore117544 Singapore

Free-space circularly polarized light (CPL) detection, requiring polarizers and waveplates, has been well established, while such spatial degree of freedom is unfortunately absent in integrated on-chip optoelectronics. So far, those reported filterless CPL photodetectors suffer from the intrinsic small discrimination ratio, vulnerability to the non-CPL field components, and low responsivity. Here, we report a distinct paradigm of geometric photodetectors in mid-infrared exhibiting colossal discrimination ratio, close-to-perfect CPL-specific response, a zero-bias responsivity of 392 V/W at room temperature, and a detectivity of ellipticity down to 0.03o Hz−1/2. Our approach employs plasmonic nanostructures array with judiciously designed symmetry, assisted by graphene ribbons to electrically read their near-field optical information. This geometry-empowered recipe for infrared photodetectors provides a robust, direct, strict, and high-quality solution to on-chip filterless CPL detection and unlocks new opportunities for integrated functional optoelectronic devices. Copyright © 2022, The Authors. All rights reserved.

关键词： Photodetectors

Local orbital-angular-momentum dependent surface states with topological protection

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arXiv 2020年

作者： Chen, Menglin L.N. Jiang, Li Jun Lan, Zhihao Sha, Wei E.I. Department of Electrical and Electronic Engineering University of Hong Kong Hong Kong Department of Electronic and Electrical Engineering University College London United Kingdom Key Laboratory of Micro-Nano Electronic Devices and Smart Systems of Zhejiang Province College of Information Science and Electronic Engineering Zhejiang University Hangzhou310027 China

Chiral surface states along the zigzag edge of a valley photonic crystal in the honeycomb lattice are demonstrated. By decomposing the local fields into orbital angular momentum (OAM) modes, we find that the chiral surface states present OAM-dependent unidirectional propagation characteristics. Particularly, the propagation directivities of the surface states are quantified by the local OAM decomposition and are found to depend on the chiralities of both the source and surface states. These findings allow for the engineering control of the unidirectional propagation of electromagnetic energy without requiring an ancillary cladding layer. Furthermore, we examine the propagation of the chiral surface states against sharp bends. It turns out that although only certain states successfully pass through the bend, the unidirectional propagation is well maintained due to the topology of the structure. Copyright © 2020, The Authors. All rights reserved.

关键词： Topology

Coexistence of pseudospin- and valley-Hall-like edge states in a photonic crystal with C3v symmetry

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arXiv 2020年

作者： Chen, Menglin L.N. Jiang, Li Jun Lan, Zhihao Sha, Wei E.I. Department of Electrical and Electronic Engineering University of Hong Kong Hong Kong Department of Electronic and Electrical Engineering University College London United Kingdom Key Laboratory of Micro-nano Electronic Devices and Smart Systems of Zhejiang Province College of Information Science and Electronic Engineering Zhejiang University Hangzhou310027 China

We demonstrate the coexistence of pseudospin- and valley-Hall-like edge states in a photonic crystal with C3v symmetry, which is composed of three interlacing triangular sublattices with the same lattice constants. By tuning the geometry of the sublattices, three complete photonic band gaps with nontrivial topology can be created, one of which is due to the band inversion associated with the pseudospin degree of freedom at the Γ point and the other two due to the gapping out of Dirac cones associated with the valley degree of freedom at the K, K′ points. The system can support tri-band pseudospin- and valley-momentum locking edge states at properly designed domain-wall interfaces. Furthermore, to demonstrate the novel interplay of the two kinds of edge states in a single configuration, we design a four-channel system, where the unidirectional routing of electromagnetic waves against sharp bends between two routes can be selectively controlled by the pseudospin and valley degrees of freedom. Our work combines the pseudospin and valley degrees of freedom in a single configuration and may provide more flexibility in manipulating electromagnetic waves with promising potential for multiband and multifunctional applications. Copyright © 2020, The Authors. All rights reserved.

关键词： Landforms

Second-harmonic generation of structured light by transition-metal dichalcogenide metasurfaces

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Physical Review A 2020年第4期102卷 043508-043508页

作者： Ling Ling Meng Xiaoyan Y. Z. Xiong Tian Xia Qin S. Liu Li Jun Jiang Wei E. I. Sha Weng Cho Chew Department of Electrical and Computer Engineering University of Illinois at Urbana-Champaign Illinois 61820 USA Department of Electrical and Electronic Engineering University of Hong Kong Hong Kong China Key Laboratory of Micro-Nano Electronic Devices and Smart Systems of Zhejiang Province College of Information Science and Electronic Engineering Zhejiang University Hangzhou 310027 China School of Electrical and Computer Engineering Purdue University Indiana 47907 USA

Structured light characterized by spatially inhomogeneous optical fields found rich applications in optical communication, sensing, microscopy, manipulation, and quantum information. While generation of structured light has been extensively studied in linear optics, the nonlinear optical process, particularly in two-dimensional (2D) materials, is an emerging alternative for generating structured light at shorter wavelengths. In this work, we theoretically demonstrate that radially and azimuthally polarized beams and vortex beams carrying orbital angular momentum could be generated at second-harmonic frequencies by using 2D material-based metasurfaces comprising the same transition-metal dichalcogenide meta-atoms. Manipulation of translations and orientations of anisotropically nonlinear meta-atoms exhibiting a threefold rotation-symmetrical crystalline structure induces strong nonlinear spin-orbital coupling, which enables simultaneous control of spatial phase and polarization in second-harmonic generation. The nonlinear transition-metal dichalcogenide metasurface proposed is promising for on-chip integration of nonlinear generation of structured light.

关键词： Angular momentum of light Metamaterials Nonlinear optics

Coexistence of pseudospin- and valley-Hall-like edge states in a photonic crystal with C3v symmetry

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Physical Review Research 2020年第4期2卷 043148-043148页

作者： Menglin L. N. Chen Li Jun Jiang Zhihao Lan Wei E. I. Sha Department of Electrical and Electronic Engineering The University of Hong Kong Hong Kong Department of Electronic and Electrical Engineering University College London London WC1E 7JE United Kingdom Key Laboratory of Micro-nano Electronic Devices and Smart Systems of Zhejiang Province College of Information Science and Electronic Engineering Zhejiang University Hangzhou 310027 China

We demonstrate the coexistence of pseudospin- and valley-Hall-like edge states in a photonic crystal with C3v symmetry, which is composed of three interlacing triangular sublattices with the same lattice constants. By tuning the geometry of the sublattices, three complete photonic band gaps with nontrivial topology can be created, one of which is due to the band inversion associated with the pseudospin degree of freedom at the Γ point and the other two due to the gapping out of Dirac cones associated with the valley degree of freedom at the K,K′ points. The system can support triband pseudospin- and valley-momentum locking edge states at properly designed domain-wall interfaces. Furthermore, to demonstrate the novel interplay of the two kinds of edge states in a single configuration, we design a four-channel system, where the unidirectional routing of electromagnetic waves against sharp bends between two routes can be selectively controlled by the pseudospin and valley degrees of freedom. Our work combines the pseudospin and valley degrees of freedom in a single configuration and may provide more flexibility in manipulating electromagnetic waves with promising potential for multiband and multifunctional applications.

关键词： Optical & microwave phenomena Photonic crystals Topological effects in photonic systems

The Method of Locating Electromagnetic Radiation Source in Wire Bonded Ball Grid Array Package

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The Method of Locating Electromagnetic Radiation Source in W...

Workshop on Electromagnetic Compatibility of Integrated Circuits (EMC Compo)

作者： Guang-Lai Hu Hang Jin Tuo-Min Tao Er-Ping Li College of Information Science & Electronic Engineering The Key Laboratory of Advanced Micro/Nano Electronic Devices & Smart Systems and Applications Zhejiang University Hangzhou China

With the development of integrated circuit technology, electromagnetic interference (EMI) problems become more and more prominent, and finding the location of the radiation source has become increasingly critical. This paper proposes a method to accurately locate the radiation source of the wire bonded ball grid array (WB-BGA) package. Firstly, the potential radiation sources of WB-BGA package are investigated. Secondly, an accurate three-dimensional full-wave simulation model of WB-BGA package is established. Finally, 3-m far-field radiation of potential radiation sources is obtained by simulation, where the radiation source is the largest one.

关键词： Integrated circuit modeling Inductance System-on-chip Electromagnetic interference Substrates Dielectrics Electromagnetic compatibility