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Realization of ideal nodal-line fermions in doped Ni3In-based structures

Physical Review B 2024年第20期109卷 205103-205103页

作者： Ye Yang Rui Wang Xianhui Chen Department of Physics and CAS Key Laboratory of Strongly-Coupled Quantum Matter 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 CAS Center for Excellence in Quantum Information and Quantum Physics Hefei Anhui 230026 China and Collaborative Innovation Center of Advanced Microstructures Nanjing 210093 China

The discovery of the ideal topological semimetallic state in experimentally accessible materials is of both fundamental and technological interest. Here, based on first-principles calculations using the virtual crystal approximation method, we study the evolution of band structures in the Ni3In cubic structure by intercalating the doped C or N atoms, termed as Ni3InCxN(1–x). Through controlling the ratio of intercalated atoms, we calculate electronic structures of a series of doped samples. A distinctive feature of a nodal line occurring at the Fermi level is present at x=0.26, and the charge analysis indicates that the bond interaction between intercalated atoms and nickel atoms induces charge redistribution, giving rise to the rigidlike shift of bands. Within the spin-orbital coupling, the nodal line is gapped and thereby Ni3InCxN(1–x) transforms into topological insulators due to the spin-rotation symmetry breaking. Moreover, the nontrivial state is insensitive to the external strain and pressure, so one can expect exotic correlation physics of massless nodal-line fermions in the doped systems of Ni3InCxN(1–x). Our work provides a promising avenue to explore ideal topological massless quasiparticles in doped systems.

关键词： Electronic structure Fermi surface First-principles calculations Spin-orbit coupling Topological materials

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Liquid-gas phase transition of thermal nuclear matter and the in-medium balance between nuclear attraction and repulsion

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Physical Review C 2021年第1期103卷 014304-014304页

作者： Shen Yang (杨申) Xiang Dong Sun (孙向东) Jing Geng (耿晶) Bao Yuan Sun (孙保元) Wen Hui Long (龙文辉) School of Nuclear Science and Technology Lanzhou University Lanzhou 730000 China 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

Properties of the liquid-gas (LG) phase transition of thermal nuclear matter are investigated within the relativistic Hartree-Fock (RHF) theory, focusing on the role played by the in-medium balance between nuclear attraction and repulsion. Applying the RHF Lagrangian PKA1, rather different critical properties and LG phase diagrams are obtained in contrast to the other popular relativistic Lagrangians. Aiming at such notable model deviations, a series of testing parametrizations xκρ (κρ being the ρ-tensor coupling strength) are proposed to bridge PKA1 and other popular Lagrangians. Along the systematics from PKA1 to the xκρ series and further to other popular Lagrangians, it is illustrated that the in-medium balance of nuclear attraction and repulsion, manifested as various modeling of the nuclear in-medium effects, is essential for the van der Waals-like behaviors of thermal nuclear matter, in which the residual nuclear in-medium effects deduced from the dominant attractive and repulsive channels play a significant role. Our study paves a way to model the in-medium nuclear interactions from the thermal statistic aspects of nuclear systems, e.g., referring to the critical temperature from future delicate experiments.

关键词： Nuclear many-body theory Nuclear structure & decays Thermal & statistical models

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Ferromagnetic Weyl semimetal phase in a tetragonal structure

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Physical Review B 2017年第20期96卷 201102(R)-201102(R)页

作者： Y. J. Jin R. Wang Z. J. Chen J. Z. Zhao Y. J. Zhao H. Xu Department of Physics South University of Science and Technology of China Shenzhen 518055 People's Republic of China Institute for Structure and Function & Department of Physics Chongqing University Chongqing 400044 People's Republic of China Department of Physics South China University of Technology Guangzhou 510640 People's Republic of China Dalian Institute of Chemical Physics Chinese Academy of Sciences Dalian 116023 People's Republic of China

Magnetic topological semimetals have drawn significant interest since they can combine band topology with intrinsic magnetic order. Here, we propose that ideal Weyl semimetal features can coexist with a ferromagnetic (FM) ground state in a class of compounds with centrosymmetric tetragonal structures. In this magnetic system with inversion symmetry, the direction of magnetization is able to manipulate the symmetry protected band structures from a node-line type to a Weyl one in the presence of spin-orbital coupling. The FM node-line semimetal phase is protected by mirror symmetry with the reflection-invariant plane perpendicular to the magnetic order. Within mirror symmetry breaking due to magnetization along other directions, the gapless node-line loop will degenerate to only one pair of Weyl points protected by rotational symmetry along the magnetic axis, which is largely separated in momentum space. Such a FM Weyl semimetal phase offers a nice platform with a minimum number of Weyl points in a condensed matter system. These findings provide several realistic candidates for the investigation of topological semimetals with time-reversal symmetry breaking, especially demonstrating the use of system symmetry as a powerful recipe for discovering FM Weyl semimetals with attractive features.

关键词： Electronic structure Ferromagnetism Weyl semimetal First-principles calculations

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Berry-Curvature Engineering for Nonreciprocal Directional Dichroism in Two-Dimensional Antiferromagnets

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Physical Review Letters 2023年第25期131卷 256901-256901页

作者： Wenhao Liang Junjie Zeng Zhenhua Qiao Yang Gao Qian Niu International Centre for Quantum Design of Functional Materials CAS Key Laboratory of Strongly-Coupled Quantum Matter Physics and Department of Physics University of Science and Technology of China Hefei Anhui 230026 China Institute for Structure and Function Department of Physics and Chongqing Key Laboratory for Strongly Coupled Physics Chongqing University Chongqing 400044 China Hefei National Laboratory University of Science and Technology of China Hefei 230088 China

In two-dimensional antiferromagnets, we find that the mixed Berry curvature can be attributed as the geometrical origin of the nonreciprocal directional dichroism (NDD), which refers to the difference in light absorption between opposite propagation directions. This Berry curvature is closely related to the uniaxial strain in accordance with the symmetry constraint, leading to a highly tunable NDD, whose sign and strength can be tuned via strain direction. We choose the lattice model of MnBi2Te4 as a concrete example. The coupling between mixed Berry curvature and strain also suggests the magnetic quadrupole of the Bloch wave packet as the macroscopic order parameter probed by the NDD in two dimensions, which is distinct from the multiferroic order P×M or the spin toroidal and quadrupole order within a unit cell in previous studies. Our work paves the way for the Berry-curvature engineering for optical nonreciprocity in two-dimensional antiferromagnets.

关键词： Geometric & topological phases Non-reciprocal transmission Bilayer films Tight-binding model

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Photoinduced high-Chern-number quantum anomalous Hall effect from higher-order topological insulators

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Physical Review B 2024年第8期109卷 085148-085148页

作者： Xiaolin Wan Zhen Ning Dong-Hui Xu Rui Wang Baobing Zheng 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 College of Physics and Optoelectronic Technology Baoji University of Arts and Sciences Baoji 721016 People's Republic of China

Quantum anomalous Hall (QAH) insulators with high Chern number host multiple dissipationless chiral edge channels, which are of fundamental interest and promising for applications in spintronics and quantum computing. Here, we propose a dynamic approach for achieving high-Chern-number QAH phases in periodically driven two-dimensional higher-order topological insulators (HOTIs) irradiated by circularly polarized light (CPL). In particular, we consider two representative kinds of HOTIs which are characterized by a quantized quadruple moment and the second Stiefel-Whitney number, respectively. Using the Floquet formalism for periodically driven systems, we demonstrate that QAH insulators with tunable Chern numbers up to four can be achieved. Moreover, we show by first-principles calculations that the monolayer graphdiyne, a realistic HOTI, is an ideal material candidate. Remarkably, the irradiation of CPL does not destroy the quantized quadruple moment in periodically driven HOTIs, leading to an exotic mixed phase harboring both high Chern numbers and higher-order topology. Our work not only establishes a strategy for designing high-Chern-number QAH insulators in periodically driven HOTIs, but also provides a powerful approach to investigate exotic topological states in nonequilibrium cases.

关键词： Edge states First-principles calculations Photoinduced effect Topological insulators Topological materials Topological phase transition Topological phases of matter Bloch-Floquet theorem Density functional theory Second quantization Tight-binding model Wannier function methods k dot p method

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Symmetry-Protected Unpaired Weyl Phonons with Giant Arcs Spanning Full Surface Brillouin Zone

arXiv

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arXiv 2019年

作者： Wang, R. Xia, B.W. Chen, Z.J. Zheng, B.B. Zhao, Y.J. Xu, H. Department of Physics & Institute for Quantum Science and Engineering Southern University of Science and Technology Shenzhen518055 China Institute for Structure and Function Department of physics Chongqing University Chongqing400044 China Department of Physics South China University of Technology Guangzhou510640 China Center for Quantum Computing Peng Cheng Laboratory Shenzhen518055 China

Weyl points are often believed to appear in pairs with opposite chirality. In this work, we propose that the number of right-handed Weyl points is not equal to that of left-handed Weyl points in topological phonon systems. Using first-principles calculations and symmetry analysis, we show that single Weyl phonons with linear dispersion and double Weyl phonons with quadratic dispersion coexist in realistic materials with trigonal or hexagonal lattices. These phonon Weyl points are guaranteed to locate at high-symmetry points due to the screw rotational symmetry, forming a unique triangular Weyl complex. In sharp contrast to conventional Weyl systems with surface arcs terminated at the projections of a pair of collinear Weyl points with opposite chirality, the phonon surface arcs of the unconventional triangular Weyl complex connect the projections of one double Weyl point and two single Weyl points. Importantly, the phonon surface arcs originating from the triangular Weyl complex are extremely long and span the entire surface Brillouin-zone. Furthermore, there are only nontrivial phonon surface states across the iso-frequency surface, which facilitates their detection in experiments and further applications. This work paves an avenue to explore unpaired Weyl quasiparticles and their nontrivial properties. Copyright © 2019, The Authors. All rights reserved.

关键词： Phonons

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Tailoring quadrupole topological insulators with periodic driving and disorder

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Physical Review B 2022年第20期105卷 L201114-L201114页

作者： Zhen Ning Bo Fu Dong-Hui Xu Rui Wang Institute for Structure and Function and Department of Physics Chongqing University Chongqing 400044 People's Republic of China Chongqing Key Laboratory for Strongly Coupled Physics Chongqing University Chongqing 400044 People's Republic of China Department of Physics The University of Hong Kong Pokfulam Road Hong Kong China Center of Quantum Materials and Devices Chongqing University Chongqing 400044 People's Republic of China

The quadrupole topological insulator (QTI) has attracted intense studies as a prototype of symmetry-protected higher-order topological phases of matter with a quantized quadrupole moment. The realization of QTIs has been reported in various static settings with periodic structures. Here, we theoretically investigate topological phase transitions and establish the QTI phase in a periodically driven system with disorder. In the clean limit, the Floquet QTI phase emerges from a topologically trivial band structure driven by elliptically polarized irradiation. More strikingly, starting from a pure and static system with trivial topology, we unveil an intriguing QTI phase which necessitates the simultaneous presence of disorder and periodic driving. Furthermore, we reveal that particle-hole symmetry is sufficient to protect the QTI. Our work not only establishes a strategy to design QTIs but also enriches the symmetry-protected mechanism of higher-order topology.

关键词： Symmetry protected topological states Topological insulators Topological phases of matter

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Complete topological phase diagram and realization of minimum Weyl nodes in a sheared chiral crystal of elemental tellurium

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Physical Review B 2023年第23期108卷 235211-235211页

作者： Shuai Fan Botao Fu Da-Shuai Ma 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 College of Physics and Electronic Engineering Center for Computational Sciences Sichuan Normal University Chengdu 610068 People's Republic of China Center of Quantum Materials and Devices Chongqing University Chongqing 400044 People's Republic of China

Ideal Weyl semimetals, with minimum Weyl nodes located far away from each other in reciprocal space and near the Fermi level in the energy space, are considered to be crucial for revealing the intrinsic physical properties of Weyl semimetals. Based on first-principles calculations, we demonstrate that elemental tellurium, under application of a broad range of shear strain, is a candidate for realizing ideal Weyl semimetals. Particularly, the sheared elemental tellurium has only four Weyl nodes in the Brillioun zone, which is the minimum number of Weyl nodes that can be achieved by a system with time-reversal symmetry. More importantly, by adjusting the strength of the strain, we obtain abundant topological phases, i.e., Weyl semimetals, strong topological insulators, composite Weyl semimetals, and weak topological insulators in elemental tellurium. Notably, this paper proposes implementing a weak topological insulator phase in a space group with only time-reversal symmetry. The complete topological phase diagram of sheared tellurium is given and the topological properties of different topological nontrivial phases are characterized, respectively.

关键词： Electronic structure First-principles calculations Topological materials Topological phase transition

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Ideal type-III nodal-ring phonons

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Physical Review B 2020年第10期101卷 100303(R)-100303(R)页

作者： Baobing Zheng Bowen Xia Rui Wang Zhongjia Chen Jinzhu Zhao Yujun Zhao Hu Xu Department of Physics and Institute for Quantum Science and Engineering Southern University of Science and Technology Shenzhen 518055 People's Republic of China College of Physics and Optoelectronic Technology Baoji University of Arts and Sciences Baoji 721016 People's Republic of China School of Physics and Technology Wuhan University Wuhan 430072 People's Republic of China Institute for Structure and Function and Department of Physics Chongqing University Chongqing 400044 People's Republic of China Department of Physics South China University of Technology Guangzhou 510640 People's Republic of China

Type-III nodal ring associated with a flat band without dispersion, whose nodes are the critical states between type-I and type-II Dirac/Weyl nodes, is of great interest. Here, we propose a strategy to explore and design materials that can realize the type-III nodal-ring phonons by introducing two-dimensional (2D) lattices with ideal flat band. As a concrete example, we show by first-principles calculations that the Laves phase AB2 with C14 structure possesses ideal type-III nodal-ring phonons. The flat phonon band related to type-III nodal-ring phonons originates from their 2D triangular and kagome layers in the Laves phase AB2. The type-III nodal-ring phonons with nontrivial Berry phase lie on a reflection-invariant plane, which are protected by the inversion and time-reversal symmetries. In addition, the drumhead surface states and unique surface arcs are clearly visible, which facilitate experimental observations. Our work enriches the classification of topological quantum phases, and provides a feasible strategy in designing flat-band related topological phases.

关键词： Acoustic phonons Optical phonons Node-line semimetals Topological materials k dot p method

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Quantum transport evidence of boundary states and Lifshitz transition in Bi4Br4

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Physical Review B 2022年第7期106卷 075206-075206页

作者： Dong-Yun Chen Dashuai Ma Junxi Duan Dong Chen Haiwen Liu Junfeng Han Yugui Yao Centre for Quantum Physics Key Laboratory of Advanced Optoelectronic Quantum Architecture and Measurement Ministry of Education School of Physics Beijing Institute of Technology Beijing 100081 China Yangtze Delta Region Academy of Beijing Institute of Technology Jiaxing 314000 China Beijing Key Lab of Nanophotonics & Ultrafine Optoelectronic Systems School of Physics Beijing Institute of Technology Beijing 100081 China College of Physics Qingdao University Qingdao 266071 China Institute for Structure and Function & Department of Physics Chongqing University Chongqing 400044 China Center for Advanced Quantum Studies Department of Physics Beijing Normal University Beijing 100875 China

The quasi-one-dimensional van der Waals compound Bi4Br4 was recently found to be a promising high-order topological insulator with exotic electronic states. In this paper, we study the electrical transport properties of Bi4Br4 bulk crystals. Two electron-type samples with different electron concentrations are investigated. Both samples exhibit a saturation behavior of resistivity in low temperature. In the low-concentration sample, two-dimensional quantum oscillations are clearly observed in the magnetoresistance measurements, which are attributed to the band-bending-induced surface state on the (001) surface. In the high-concentration sample, the angular magnetoresistance exhibits two pairs of symmetrical sharp valleys with an angular difference close to the angle between the crystal planes (001) and (100). The additional valley can be explained by the contribution of the boundary states on the (100) facet. Besides, Hall measurements at low temperatures reveal an anomalous decrease of electron concentration with increasing temperature, which can be explained by the temperature-induced Lifshitz transition. These results shed light on the abundant boundary state transport signals and the temperature-induced Lifshitz transition in Bi4Br4.

关键词： Hall effect Magnetoresistance Surface states Topological insulators Quantum oscillation techniques

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