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Intrinsic freedom of dislocation structures and Peierls stress oscillation

Physical Review B 2022年第9期105卷 094113-094113页

作者： Shaofeng Wang Institute for Structure and Function Department of Physics Chongqing University Chongqing 401331 China

When the continuous translation symmetry breaks, a continuous mode splits into two distinct discrete modes with different energies. Based on the fully discrete Peierls model, it is found that stability of such discrete modes for dislocations can be tuned by the stacking fault energy of a slip system. As the stacking fault energy changes continuously, the stable dislocation structure transforms periodically and the Peierls stress varies oscillatorily. Furthermore, at the transformation point, the lattice resistance nearly vanishes and thus the dislocation can almost move freely.

关键词： Defects Disclinations & dislocations Plasticity Stacking faults Stress

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Circularly polarized light irradiated ferromagnetic MnBi2Te4: A possible ideal Weyl semimetal

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Physical Review B 2024年第12期110卷 125204页

作者： Shuai Fan Shengpu Huang Zhuo Chen Fangyang Zhan Xian-Yong Ding Da-Shuai Ma Rui Wang Institute for Structure and Function Department of Physics and Chongqing Key Laboratory for Strongly Coupled Physics Center of Quantum Materials and Devices

The interaction between light and nontrivial energy band topology allows for the precise manipulation of topological quantum states, which has attracted intensive interest in condensed-matter physics. In this work, using first-principles calculations, we studied the topological transition of ferromagnetic (FM) MnBi2Te4 upon irradiation with circularly polarized light (CPL). We revealed that the MnBi2Te4 can be driven from an FM insulator to a Weyl semimetal with a minimum number of Weyl points, i.e., two Weyl points (WPs) in systems without time-reversal symmetry. More importantly, in FM MnBi2Te4 with an out-of-plane easy magnetization axis, we found that the band dispersion of the WP evolves from type-II to type-III and finally to type-I when the light intensity increases. Moreover, we show that the profile of the characteristic Fermi arc of the Weyl semimetal phase is sensitive to changes in light intensity, which enables efficient manipulation of the Fermi arc length of FM MnBi2Te4 in experiments. In addition, for FM MnBi2Te4 with an in-plane easy magnetization axis, the system becomes a type-I Weyl semimetal under CPL irradiation. With controllable band dispersion, the length of the Fermi arc, and a minimum number of WPs, our results indicate that CPL-irradiated FM MnBi2Te4 is an ideal platform for the study of novel transport phenomena in Weyl semimetals with distinct band dispersion.

关键词： Electronic structure First-principles calculations Topological materials Weyl semimetal

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Core structure and Peierls stress of the 90°dislocation and the 60°dislocation in aluminum investigated by the fully discrete Peierls model

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Chinese physics B 2022年第8期31卷 517-529页

作者： Hao Xiang Rui Wang Feng-Lin Deng Shao-Feng Wang Department of Physics and Institute for Structure and Function Chongqing UniversityChongqing 401331China CAS Key Laboratory of Magnetic Materials and Devices Ningbo Institute of Materials Technology and EngineeringChinese Academy of SciencesNingbo 315201China Zhejiang Province Key Laboratory of Magnetic Materials and Application Technology Ningbo Institute of Materials Technology and EngineeringChinese Academy of SciencesNingbo 315201China

The core structure,Peierls stress and core energy,*** comprehensively investigated for the 90°dislocation and the 60°dislocation in metal aluminum using the fully discrete Peierls model,and in particular thermal effects are included for temperature range 0≤T≤900 *** the 90°dislocation,the core clearly dissociates into two partial dislocations with the separating distance D~12?,and the Peierls stress is very smallσp<1 k *** nearly vanishing Peierls stress results from the large characteristic width and a small step length of the 90°*** 60°dislocation dissociates into 30°and 90°partial dislocations with the separating distance D~*** Peierls stress of the 60°dislocation grows up from1 MPa to 2 MPa as the temperature increases from 0 K to 900 *** influence on the core structures is weak for both the 90°dislocation and the 60°*** core structures theoretically predicted at T=0 K are also confirmed by the first principle simulations.

关键词： dislocation temperature effect aluminum

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Perspective: Floquet engineering topological states from effective models towards realistic materials

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Quantum Frontiers 2024年第1期3卷 1-21页

作者： Zhan, Fangyang Chen, Rui Ning, Zhen Ma, Da-Shuai Wang, Ziming Xu, Dong-Hui Wang, Rui Institute for Structure and Function & amp Department of Physics & amp Chongqing Key Laboratory for Strongly Coupled Physics Chongqing University Chongqing 400044 China Center of Quantum Materials and Devices Chongqing University Chongqing 400044 China Department of Physics Hubei University Wuhan 430062 China

With significant advances in classifying and cataloguing topological matter, the focus of topological physics has shifted towards quantum control, particularly the creation and manipulation of topological phases of matter. Floquet engineering, the concept of tailoring a system by periodic fields, offers a powerful tool to manipulate electronic properties of condensed systems, and even to create exotic non-equilibrium topological states that are impossibly present in equilibrium scenarios. In this perspective, we give a brief review of recent progress in theoretical investigations of Floquet engineering topological states from effective models towards realistic materials. We show that light irradiation can realize various desired topological states through the introduction of symmetry breaking, such as first- and higher-order Weyl fermions, quadrupole topological insulator with periodic driving and disorder, quantum anomalous Hall effects with a tunable Chern number, as well as beyond. Moreover, based on first-principles calculations and Floquet theorem, we show several realistic material candidates proposed as potential hosts for promising Floquet topological states, facilitating their verification in experiments. We believe that our perspective on Floquet engineering of topological states will advance further studies of rich exotic light-induced phenomena in condensed matter physics. © The Author(s) 2024.

关键词： Effective models First-principles calculations Floquet engineering Topological states

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Two-dimensional double kagome lattice nitrogene: A direct band gap semiconductor with nontrivial corner state

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Physical Review B 2024年第12期110卷 125428页

作者： Wenzhang Li Qin He Xiao-Ping Li Da-Shuai Ma Botao Fu College of Physics and Electronic Engineering Center for Computational Sciences School of Physical Science and Technology Institute for Structure and Function and Department of Physics

The kagome lattice, characterized by its flat band and Dirac electrons, continues to attract enduring attention in condensed matter physics as an ideal structure for studying electron correlation and various quantum phases. Despite recent experimental advances, two-dimensional (2D) kagome-structured materials with significant flat-band characteristics still remain rare. Based on first-principles calculations, we predict that nitrogen atoms can assemble into a single-layer double kagome lattice (DKL), which possesses the characteristics of an intrinsic direct band gap semiconductor, boasting a substantial band gap of 3.460 eV. The DKL structure results in a flat valence band with a high effective mass and a conduction band with a small effective mass that comes from Dirac electrons. These distinctive band edges lead to a significant disparity in carrier mobilities, with electron mobility being four orders of magnitude higher than that of holes. The presence of a flat band in DKL-nitrogene can be further discerned through the enhanced optical absorption and correlated effects as exemplified by hole-induced ferromagnetism. Interestingly, DKL-nitrogene exhibits inherent second-order topological states, confirmed by a nontrivial second Stiefel-Whitney number and the presence of 1D floating edge states and 0D corner states within the bulk band gap. Additionally, the robust N-N bonds and the lattice's bending structure ensure thermodynamic stability and mechanical stiffness. These attributes make it exceptionally stable for potential applications in nanodevices.

关键词： Electronic structure First-principles calculations Flat bands Magnetism Optoelectronics

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Multiple PD sources separation of oil-paper insulation using S transform based similarity

Multiple PD sources separation of oil-paper insulation using...

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2012 International Conference on High Voltage Engineering and Application, ICHVE 2012

作者： Wang, Ke Liao, Ruijin Yang, Lijun Li, Shaorong Qi, Chaoliang State Key Laboratory of Power Transmission Equipment and System Security and New Technology Chongqing University Chongqing China Institute for Structure and Function Department of Physics Chongqing University Chongqing China

ISBN: (纸本)9781467347464

A new algorithm for multiple partial discharge sources separation is proposed in this paper. ST is firstly employed to obtain the time-frequency representation of original PD pulses. Then, PD pulses similarity matrix is computed based on ST amplitude matrix. By using the pulses similarity matrix, affinity propagation clustering is applied to perform the automatic separation of PD pulses. The proposed algorithm is tested by multiple PD sources generated by manually combining pulses from different single sources. It is shown that the successful rates of pulses separation 99.63% and 98.35% are obtained in two application cases. Results demonstrate that it is feasible to apply ST and APC to realize multiple PD source separation. © 2012 IEEE.

关键词： Partial discharges

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Anharmonicity-induced phonon hardening and anomalous thermal transport in ScZn

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Physical Review B 2024年第5期110卷 054304-054304页

作者： Xianyong Ding Xin Jin Zheng Chang Dengfeng Li Xiaoyuan Zhou Xiaolong Yang Rui Wang Institute for Structure and Function & Department of Physics Center of Quantum materials and devices College of Physics and Electronic Engineering School of Naval Architecture and Maritime School of Science

Phonon anharmonicity plays a crucial role in the lattice dynamics and lattice thermal conductivity κL of solids. Here, by combining first-principles calculations with the linearized Boltzmann transport equation, we unveil that phonon anharmonicity can make an unexpected contribution to κL and thereby lead to anomalous thermal transport behavior in the intermetallic compound ScZn, a recently theoretically predicted topological phonon material. We explicitly consider phonon renormalization, four-phonon (4ph), and phonon-electron scattering to predict the κL of ScZn. The results show that anharmonic phonon renormalization due to quartic anharmonicity gives rise to significant phonon hardening, especially for heat-carrying acoustic phonons. We also reveal that anharmonic effects largely decrease the fourth-order force constants, causing the dramatic suppression of 4ph scattering on κL. The incorporation of renormalization-induced phonon hardening and the decrease of quartic force constants makes a consequence of an almost twofold increase in the κL compared to the conventional harmonic treatment, from 3.9 to 7.6 W/mK at room temperature. This is enabled by the suppressed phonon scattering phase space and weakened fourth-order lattice anharmonicity due to the temperature-induced phonon renormalization effect. Moreover, it is found that the electronic contribution κe always plays a dominating role on the thermal conductivity; however, the lattice contribution is still considerable, leading to the substantial deviation of Lorenz number from the Sommerfeld value. This work provides a fundamental understanding of the thermal transport in ScZn and highlights the importance of anharmonic effects on the phonon energies and thermal conductivity of metals.

关键词： Anharmonic lattice dynamics Electrical conductivity Electron thermal conductivity Electronic structure Lattice thermal conductivity Thermal conductivity

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Temperature-dependent and magnetism-controlled Fermi surface changes in magnetic Weyl semimetals

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Physical Review Research 2023年第2期5卷 L022013-L022013页

作者： Nan Zhang Xianyong Ding Fangyang Zhan Houpu Li Hongyu Li Kaixin Tang Yingcai Qian Senyang Pan Xiaoliang Xiao Jinglei Zhang Rui Wang Ziji Xiang Xianhui 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 and Center for Quantum Materials and Devices Chongqing University Chongqing 400044 China High Magnetic Field Laboratory Chinese Academy of Sciences Hefei Anhui 230031 China Collaborative Innovation Center of Advanced Microstructures Nanjing University Nanjing 210093 China

The coupling between band structure and magnetism can lead to intricate Fermi surface modifications. Here we report on the comprehensive study of the Shubnikov–de Haas (SdH) effect in two rare-earth-based magnetic Weyl semimetals, NdAlSi and CeAlSi0.8Ge0.2. The results show that the temperature evolution of topologically nontrivial Fermi surfaces strongly depends on magnetic configurations. In NdAlSi, the SdH frequencies vary with temperature in both the paramagnetic state and the magnetically ordered state with a chiral spin texture, but become temperature independent in the high-field fully polarized state. In CeAlSi0.8Ge0.2, SdH frequencies are temperature dependent only in the ferromagnetic state with magnetic fields applied along the axis. First-principles calculations suggest that the notable temperature and magnetic-configuration dependence of Fermi surface morphology can be attributed to strong exchange coupling between the conduction electrons and local magnetic moments.

关键词： Fermi surface First-principles calculations High magnetic fields Landau levels Magnetotransport Topological materials Transport phenomena Ferromagnets Weyl semimetal Quantum oscillation techniques Resistivity measurements Shubnikov-de Haas effect

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Obstructed atomic insulators with robust corner modes

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Physical Review B 2023年第10期108卷 L100101-L100101页

作者： Da-Shuai Ma Kejun Yu Xiao-Ping Li Xiaoyuan Zhou Rui Wang Institute for Structure and Function & Department of Physics & 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 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 School of Physical Science and Technology Inner Mongolia University Hohhot 010021 China

Higher-order topological insulators (HOTIs), that are classified as obstructed atomic insulators (OAIs) in the topological quantum chemistry (TQC) theory, attract great interest owning to the lower-dimensional topological boundary states. However, the boundary states in HOTIs reported so far are often fragile, manifested as strongly depending on crystalline symmetries and cleavage terminations in the disk or cylinder geometry. Here, using the TQC theory, we propose an intuitive strategy to establish the connection between the obstructed Wannier charge centers of OAIs and the emergence of robust corner states in two-dimensional systems. Based on first-principles calculations and real space invariant theory, we extend the concept of OAIs to phonon systems and thereby predict that the robust corner states can be realized in the phonon spectra of MX3 (M = Bi, Sb, As, Sc, Y; X = I, Br, Cl) monolayers. The phonon corner modes in different shapes of nanodisks are investigated, and their robustness facilitates the detection in experiments and further applications. This work suggests a promising avenue to explore more attractive features of higher-order band topology beyond the existing paradigm.

关键词： Edge states First-principles calculations Phonons Topological materials Topological phases of matter 2-dimensional systems Topological insulators High-throughput calculations Wannier function methods

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Topological corner states in graphene by bulk and edge engineering

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Physical Review B 2022年第20期106卷 L201407-L201407页

作者： Junjie Zeng Chen Chen Yafei Ren Zheng Liu Wei Ren Zhenhua Qiao CAS Key Laboratory of Strongly-Coupled Quantum Matter Physics and Department of Physics University of Science and Technology of China Hefei Anhui 230026 China Chongqing Key Laboratory for Strongly Coupled Physics and Institute for Structure and Function Department of Physics Chongqing University Chongqing 401331 China International Center for Quantum and Molecular Structures Materials Genome Institute Physics Department and Shanghai Key Laboratory of High Temperature Superconductors Shanghai University Shanghai 200444 China Department of Materials Science and Engineering University of Washington Seattle Washington 98195 USA ICQD Hefei National Laboratory for Physical Sciences at Microscale University of Science and Technology of China Hefei Anhui 230026 China

Two-dimensional higher-order topology is usually studied in (nearly) particle-hole symmetric models, so that an edge gap can be opened within the bulk one. But more often the edge anticrossing deviates even into the bulk, where corner states are difficult to pinpoint. We address this problem in a graphene-based Z2 topological insulator with spin-orbit coupling and in-plane magnetization both originating from substrates through a Slater-Koster multiorbital model. The gapless helical edge modes cross inside the bulk, where the magnetization-induced edge gap is also located. After demonstrating its second-order nontriviality in bulk topology by a series of evidence, we show that a difference in bulk-edge on-site energy can adiabatically tune the position of the crossing/anticrossing of the edge modes to be inside the bulk gap. This can help unambiguously identify two pairs of topological corner states with nonvanishing energy degeneracy for a rhombic flake. We further find that the obtuse-angle pair is more stable than the acute-angle one.

关键词： Edge states Spin-orbit coupling Topological phases of matter Graphene Topological insulators

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