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Type-II nodal line fermions in the Z2 topological semimetals AV6Sb6 (A=K, Rb, and Cs) with a kagome bilayer

Physical Review B 2021年第24期104卷 245128-245128页

作者： Y. Yang R. Wang M.-Z. Shi Z. Wang Z. Xiang X.-H. Chen Hefei National Laboratory for Physical Sciences at Microscale and Department of Physics and Key Laboratory of Strongly-Couple Quantum Matter Physics Chinese Academy of Sciences University of Science and Technology of China Hefei Anhui 230026 China Institute for Structure and Function and Department of Physics and Center for Quantum Materials and Devices Chongqing University Chongqing 400044 China Chongqing Key Laboratory for Strongly Coupled Physics Chongqing 400044 China CAS Center for Excellence in Superconducting Electronics (CENSE) Shanghai 200050 China CAS Center for Excellence in Quantum Information and Quantum Physics Hefei Anhui 230026 China Collaborative Innovation Center of Advanced Microstructures Nanjing University Nanjing 210093 China

The recently discovered layered kagome metals AV3Sb5 (A=K, Rb, and Cs) attract intensive interest due to their intertwining with superconductivity, charge-density-wave state, and nontrivial band topology. In this work, we show by first-principles calculations and symmetry arguments that unconventional type-II Dirac nodal line fermions close to the Fermi level are present in another latest class of experimentally synthesized kagome compounds AV6Sb6 (A=K, Rb, and Cs). These compounds possess a unique kagome (V3Sb)2 bilayer that dominates their electronic and topological properties, instead of the kagome V3Sb monolayer in AV3Sb5. Crystal symmetry guarantees that the type-II Dirac nodal lines with quantized Berry phase lie in reflection-invariant planes of the Brillouin zone. We further reveal that the type-II Dirac nodal lines remain nearly intact in the presence of spin-orbital coupling and can be categorized as a Z2 classification. The findings establish AV6Sb6 as a class of new fascinating prototypes, which will extend the knowledge of interplay between unconventionally topological fermions and exotic quantum ordered states in kagome systems.

关键词： Electronic structure Symmetry protected topological states Topological insulators Topological materials Kagome lattice Node-line semimetals Semimetals Topological superconductors First-principles calculations Wannier function methods k dot p method

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Recipe for generating Weyl semimetals with extended topologically protected features

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Physical Review B 2017年第12期96卷 121104(R)-121104(R)页

作者： R. Wang J. Z. Zhao Y. J. Jin W. P. Xu L.-Y. Gan X. Z. Wu H. Xu S. Y. Tong Department of Physics South University of Science and Technology of China Shenzhen 518055 Peoples Republic of China Institute for Structure and Function & Department of Physics Chongqing University Chongqing 400044 Peoples Republic of China Dalian Institute of Chemical Physics Chinese Academy of Sciences 116023 Dalian Peoples Republic of China Key Laboratory of Advanced Technology of Materials (Ministry of Education) Superconductivity and New Energy R&D Center Southwest Jiaotong University Chengdu 610031 Sichuan Peoples Republic of China School of Science and Engineering The Chinese University of Hong Kong (Shenzhen) 518172 Shenzhen Peoples Republic of China

We present a recipe that leads to Weyl semimetals with extended topologically protected features. We show that compounds in a family that possess time-reversal symmetry and share a noncentrosymmetric cubic structure with the space group F−43m (no. 216) host robust Weyl fermions with extended and easily measurable protected features. The candidates in this family are compounds with different chemical formulas, AB2, ABC, ABC2, and ABCD, and their Fermi levels are predominantly populated by nontrivial Weyl fermions. Symmetry of the system requires that the Weyl nodes with opposite chirality are well separated in momentum space. Adjacent Weyl points have the same chirality; thus these Weyl nodes would not annihilate each other with respect to lattice perturbations. As Fermi arcs and surface states connect Weyl nodes with opposite chirality, the large separation of the latter in momentum space guarantees the appearance of very long arcs and surface states. This work demonstrates that the use of system symmetry by first-principles calculations is a powerful approach for discovering new Weyl semimetals with attractive features whose protected fermions may be candidates of many applications.

关键词： Topological materials Weyl semimetal k dot p method

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Symmetry-protected Dirac nodal lines and large spin Hall effect in a V6Sb4 kagome bilayer

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Physical Review B 2022年第15期105卷 155102-155102页

作者： Y. Yang R. Wang M.-Z. Shi Z. Wang Z. Xiang X.-H. Chen CAS Key Laboratory of Strongly-coupled Quantum Matter Physics Department of Physics University of Science and Technology of China Hefei Anhui 230026 China Institute for Structure and Function & Department of Physics Chongqing University Chongqing 400044 China Center of Quantum Materials and Devices Chongqing University Chongqing 400044 China Chongqing Key Laboratory for Strongly Coupled Physics Chongqing University Chongqing 400044 China CAS Center for Excellence in Superconducting Electronics (CENSE) Shanghai 200050 China CAS Center for Excellence in Quantum Information and Quantum Physics Hefei Anhui 230026 China Collaborative Innovation Center of Advanced Microstructures Nanjing University Nanjing 210093 China

Recently, a family of nonmagnetic kagome metals AV3Sb5 (A=K, Rb, and Cs) has attracted significant attention for realizing the intertwining of quantum order and nontrivial topology. However, these compounds have been identified to host complex band structures. Therefore, it is desirable to design and synthesize novel kagome materials with a simple band topology and good transport properties. In this study, using first-principles calculations, we present the electronic properties and the intrinsic spin Hall effect of V6Sb4, the latest experimentally synthesized vanadium-based compounds that form a kagome bilayer. In the absence of spin-orbital coupling (SOC), this compound is a Dirac nodal line semimetal with symmetry-protected nodal rings near the Fermi level. Within the SOC, the spin-rotation symmetry breaks the gaps of the nodal rings with a small band gap. Furthermore, based on the Wannier tight-binding approach and the Kubo formula, we reveal a large spin Hall effect in V6Sb4, which intrinsically originates from the spin Berry curvature. Our work further expands nonmagnetic kagome compounds for applications in spintronics accompanied by exotic quantum order.

关键词： Electrical conductivity First-principles calculations Topological materials Topological phases of matter Node-line semimetals Wannier function methods

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Photoinduced quantum anomalous hall states in the topological anderson insulator

arXiv

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arXiv 2021年

作者： Ning, Zhen Zheng, Baobing Xu, Dong-Hui Wang, Rui Institute for Structure and Function Department of Physics Chongqing University Chongqing400044 China Chongqing Key Laboratory for Strongly Coupled Physics Chongqing400044 China College of Physics and Optoelectronic Technology Advanced Titanium Alloys and Functional Coatings Cooperative Innovation Center Baoji University of Arts and Sciences Baoji721016 China Department of Physics Hubei University Wuhan430062 China Center for Quantum Materials and Devices Chongqing University Chongqing400044 China

The realization of the quantum anomalous Hall (QAH) effect without magnetic doping attracts intensive interest since magnetically doped topological insulators usually possess inhomogeneity of ferromagnetic order. Here, we propose a different strategy to realize intriguing QAH states aris- ing from the interplay of light and non-magnetic disorder in two-dimensional topologically trivial systems. By combining the Born approximation and Floquet theory, we show that a time-reversal invariant disorder-induced topological insulator, known as the topological Anderson insulator (TAI), would evolve into a time-reversal broken TAI and then into a QAH insulator by shining circularly polarized light. We utilize spin and charge Hall conductivities, which can be measured in experi- ments directly, to distinguish these three different topological phases. This work not only offers an exciting opportunity to realize the high-temperature QAH effect without magnetic orders, but also is important for applications of topological states to spintronics. Copyright © 2021, The Authors. All rights reserved.

关键词： Electric insulators

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Design monolayer iodinenes based on halogen bond and tiling theory

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Physical Review B 2024年第12期109卷 125423-125423页

作者： Kejun Yu Yichen Liu Botao Fu Run-Wu Zhang Da-shuai Ma Xiao-ping Li Zhi-Ming Yu Cheng-Cheng Liu Yugui Yao Centre for Quantum Physics Key Laboratory of Advanced Optoelectronic Quantum Architecture and Measurement (MOE) School of Physics Beijing Institute of Technology Beijing 100081 China Beijing Key Lab of Nanophotonics and Ultrafine Optoelectronic Systems School of Physics Beijing Institute of Technology Beijing 100081 China College of Physics and Electronic Engineering Center for Computational Sciences Sichuan Normal University Chengdu 610068 China Institute for Structure and Function and Department of Physics and Chongqing Key Laboratory for Strongly Coupled Physics Chongqing University Chongqing 400044 People's Republic of China Center of Quantum Materials and Devices Chongqing University Chongqing 400044 People's Republic of China School of Physical Science and Technology Inner Mongolia University Hohhot 010021 China

Xenes, two-dimensional (2D) monolayers composed of a single element, with graphene as a typical representative, have attracted widespread attention. Most of the previous Xenes, X from group-IIIA to group-VIA elements, have bonding characteristics of covalent bonds. In this paper, we unveil the pivotal role of a halogen bond, which is a distinctive type of bonding with interaction strength between that of a covalent bond and a van der Waals interaction, in 2D group-VIIA monolayers. Combing the ingenious non-edge-to-edge tiling theory and state-of-the-art ab initio method with refined local density functional M06-L, we provide a precise and effective bottom-up construction of 2D iodine monolayer sheets, iodinenes, primarily governed by halogen bonds, and successfully design a category of stable iodinenes encompassing herringbone, Pythagorean, gyrated truncated hexagonal, i.e., diatomic kagome, and gyrated hexagonal tiling patterns. These iodinene structures exhibit a wealth of properties, such as nontrivial topology, flat bands and fascinating optical characteristics, offering valuable insights and guidance for future experimental investigations. Our paper not only unveils the unexplored halogen bonding mechanism in 2D materials but also opens an avenue for designing other noncovalent bonding 2D materials.

关键词： Electronic structure Structural properties Topological materials 2-dimensional systems Two-dimensional electron system Density functional theory

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Transient Chaotic Dimensionality Expansion by Recurrent Networks

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Physical Review X 2021年第2期11卷 021064-021064页

作者： Christian Keup Tobias Kühn David Dahmen Moritz Helias Institute of Neuroscience and Medicine (INM-6) and Institute for Advanced Simulation (IAS-6) and JARA Institut Brain Structure-Function Relationships (INM-10) Jülich Research Centre Jülich Germany RWTH Aachen University Aachen Germany Laboratoire de Physique de l’ENS Laboratoire MSC de l’Université de Paris CNRS Paris France Department of Physics Faculty 1 RWTH Aachen University Aachen Germany

Neurons in the brain communicate with spikes, which are discrete events in time and value. functional network models often employ rate units that are continuously coupled by analog signals. Is there a qualitative difference implied by these two forms of signaling? We develop a unified mean-field theory for large random networks to show that first- and second-order statistics in rate and binary networks are in fact identical if rate neurons receive the right amount of noise. Their response to presented stimuli, however, can be radically different. We quantify these differences by studying how nearby state trajectories evolve over time, asking to what extent the dynamics is chaotic. Chaos in the two models is found to be qualitatively different. In binary networks, we find a network-size-dependent transition to chaos and a chaotic submanifold whose dimensionality expands stereotypically with time, while rate networks with matched statistics are nonchaotic. Dimensionality expansion in chaotic binary networks aids classification in reservoir computing and optimal performance is reached within about a single activation per neuron; a fast mechanism for computation that we demonstrate also in spiking networks. A generalization of this mechanism extends to rate networks in their respective chaotic regimes.

关键词： Fluctuations & noise Neural encoding Neuronal networks Statistical field theory Chaos & nonlinear dynamics Dynamical mean field theory Ising model Langevin equation

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Tensile Strain of Feni Alloy Coupled with Pyridinic-N Doping Carbon Layers for Activating Water and Urea Oxidation

SSRN

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SSRN 2022年

作者： Qian, Guangfu Chen, Wei Chen, Jinli Gan, Li Yong Yu, Tianqi Pan, Miaojing Zhuo, Xiaoyan Luo, Lin Yin, Shibin College of Chemistry and Chemical Engineering Guangxi Key Laboratory of Electrochemical Energy Materials State Key Laboratory of Processing for Non-Ferrous Metal and Featured Materials Guangxi University 100 Daxue Road Nanning530004 China Institute for Structure and Function Department of Physics Chongqing University Chongqing 400030 China

Exploitation of oxygen evolution reaction (OER) and urea oxidation reaction (UOR) catalysts with high activity and stability at large current density is a major challenge for energy-saving H2 production in water electrolysis. Herein, we successfully use the NiFe2O4 nanosheet to activate the tensile strain of FeNi alloy coupled with pyridinic-N doping carbon layers (FeNi/NiFe2O4@NC) for efficiently increasing the performance of water and urea oxidation. Due to the tensile strain effect on FeNi/NiFe2O4@NC, it provides a favorable modulation on the electronic properties of the active center, thus enabling amazing OER (η100=196 mV) and UOR (E10=1.32 V) intrinsic activity. Besides, the carbon-coated layers can be used as armor to prevent FeNi alloy from being corroded by the electrolyte to enhance the OER/UOR stability at large current density, showing high industrial practicability. This work thus provides a simple way to prepare high-efficiency catalyst for activating water and urea oxidation. © 2022, The Authors. All rights reserved.

关键词： Urea

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Pseudospin symmetry restoration and the in-medium balance between nuclear attractive and repulsive interactions

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Physical Review C 2019年第5期100卷 051301(R)-051301(R)页

作者： Jing Geng (耿晶) Jia Jie Li (李佳杰) Wen Hui Long (龙文辉) Yi Fei Niu (牛一斐) Shi Yao Chang (常士尧) School of Nuclear Science and Technology Lanzhou University Lanzhou 730000 China Institut für Theoretische Physik J.W. Goethe-Universität D-60438 Frankfurt am Main Germany Joint Department for Nuclear Physics Lanzhou University and Institute of Modern Physics CAS Lanzhou 730000 China Key Laboratory of Special Function Materials and Structure Design Ministry of Education Lanzhou 730000 China

The mechanism that restores pseudospin symmetry (PSS) is investigated under the relativistic Hartree-Fock (RHF) approach, by focusing on the in-medium balance between nuclear attractive and repulsive interactions. It is illustrated that the modelings of both the equilibrium of nuclear dynamics and the in-medium effects can be essentially changed by the ρ-tensor coupling that plays the role almost fully via the Fock terms, from which the model discrepancy on the PSS restoration is verified. Specifically, the largely different density-dependent behaviors of the isoscalar coupling strengths gσ and gω, deduced from the parametrization of the RHF Lagrangian PKA1, play an essential role in restoring the PSS of the high-l′ pseudospin doublets around the Fermi levels. Qualitatively, guidance is provided for the modeling of both the equilibrium of nuclear dynamics and the in-medium effects via the PSS restoration.

关键词： Nuclear forces Nuclear structure & decays Nuclear many-body theory

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Single pair of charge-two high-fold fermions with type-II van Hove singularities on the surface of ultralight chiral crystals

arXiv

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arXiv 2023年

作者： Xiao, Xiaoliang Jin, Yuanjun Ma, Da-Shuai Wei, Haoran Fan, Jing Wang, Rui Wu, Xiaozhi Institute for Structure and Function Department of Physics Chongqing University Chongqing400044 China Division of Physics and Applied Physics School of Physical and Mathematical Sciences Nanyang Technological University Singapore637371 Singapore Center of Quantum materials and devices Chongqing University Chongqing400044 China Center for Computational Science and Engineering Southern University of Science and Technology Shenzhen518055 China Chongqing Key Laboratory for Strongly Coupled Physics Chongqing400044 China

The realization of single-pair chiral fermions in Weyl systems remains challenging in topology physics, especially for the systems with higher chiral charges C. In this work, based on the symmetry analysis, low-energy effective model, and first-principles calculations, we identify the single-pair high-fold fermions in chiral cubic lattices. We first derive the minimal lattice model that exhibits a single pair of Weyl points with the opposite chiral charges of C = ±2. Furthermore, we show the ultralight chiral crystal P4332-type LiC2 and its mirror enantiomer as high-quality candidate materials, which exhibit large energy windows to surmount the interruption of irrelevant bands. Since two enantiomers are connected by the mirror symmetry, we observe the opposite chiral charges C and the reversal of the Fermi arc velocities, showing the correspondence of chirality in the momentum space and the real space. In addition, we also reveal type-II van Hove singularities on the helicoid surfaces, which may induce chirality-locked charge density waves on the crystal surface. Our work not only provides a promising platform for controlling the sign of topological charge through the structural chirality but also facilitates the exploration of electronic correlations on the surface of ultralight chiral crystals. Copyright © 2023, The Authors. All rights reserved.

关键词： Enantiomers

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Floquet valley-polarized quantum anomalous Hall state in nonmagnetic heterobilayers

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Physical Review B 2022年第8期105卷 L081115-L081115页

作者： Fangyang Zhan Zhen Ning Li-Yong Gan Baobing Zheng Jing Fan Rui Wang Institute for Structure and Function & Department of Physics Chongqing University Chongqing 400044 People's Republic of China Chongqing Key Laboratory for Strongly Coupled Physics Chongqing 400044 People's Republic of China Center for Computational Science and Engineering Southern University of Science and Technology Shenzhen 518055 People's Republic of China Center of Quantum Materials and Devices Chongqing University Chongqing 400044 People's Republic of China College of Physics and Optoelectronic Technology Baoji University of Arts and Sciences Baoji 721016 People's Republic of China

The valley-polarized quantum anomalous Hall (VQAH) state, which forwards a strategy for combining valleytronics and spintronics with nontrivial topology, attracts intensive interest in condensed-matter physics. So far, the exploration of VQAH states has still been limited to magnetic systems. Here, using the low-energy effective model and Floquet theorem, we propose an alternative mechanism to realize the Floquet VQAH state in nonmagnetic heterobilayers under light irradiation. We then realize this proposal via first-principles calculations in transition metal dichalcogenide heterobilayers, which initially possess the time-reversal invariant valley quantum spin Hall (VQSH) state. By irradiating circularly polarized light, the time-reversal invariant VQSH state can evolve into the VQAH state, behaving as an optically switchable topological spin-valley filter. These findings not only offer a rational scheme to realize the VQAH state in periodically driven nonmagnetic systems, but also pave a fascinating path for designing topological spintronic and valleytronic devices with high tunability. Our proposal can also be extended to design the general QAH effect without magnetic orders.

关键词： Chern insulators Edge states Photoinduced effect Spin filtering Topological materials Topological phase transition Topological phases of matter Valleytronics Transition metal dichalcogenides Bloch-Floquet theorem Density functional theory First-principles calculations Tight-binding model Wannier function methods k dot p method

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