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Ferromagnetic Dirac-Nodal Semimetal Phase of Stretched Chromium Dioxide

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arXiv 2017年

作者： Wang, R. Zhao, J.Z. Jin, Y.J. Du, Y.P. Zhao, Y.X. Xu, H. Tong, S.Y. Department of Physics South University of Science and Technology of China Shenzhen518055 China Institute for Structure and Function Department of physics Chongqing University Chongqing400044 China Dalian Institute of Chemical Physics Chinese Academy of Sciences Dalian116023 China Department of Applied Physics Nanjing University of Science and Technology NanjingJiangsu210094 China Department of Physics and Center of Theoretical and Computational Physics University of Hong Kong Pokfulam Road Hong Kong Hong Kong Shenzhen518172 China

We show by first-principles calculations that the Dirac nodal-line semimetal phase can co-exist with the ferromagnetic order at room temperature in chromium dioxide, a widely used material in magnetic tape applications, under small tensile hydrostatic strains. An ideally flat Dirac nodal ring close to the Fermi energy is placed in the reflection-invariant boundary of the Brillouin zone perpendicular to the magnetic order, and is topologically protected by the unitary mirror symmetry of the magnetic group D4h(C4h), which quantizes the corresponding Berry phase into integer multiples of π. The symmetry-dependent topological stability is demonstrated through showing that only the topologically protected nodal ring can persistently exist under small anisotropic stains preserving the symmetry D4h(C4h), while the other seeming band touching points are generically gapped. Our work provides a practical platform for the investigation of novel physics and potential applications of the Dirac nodal-line and drumhead fermions, in particular those related to ferromagnetic properties. Copyright © 2017, The Authors. All rights reserved.

关键词： Chromium compounds

Hybrid Nodal-chain Semimetal State in MgCaN2

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arXiv 2023年

作者： Wu, Hongbo Ma, Da-Shuai Fu, Botao College of Physics Hebei Key Laboratory of Photophysics Research and Application Hebei Normal University Shijiazhuang050024 China Institute for Structure and Function & Department of Physics Chongqing University Chongqing400044 China College of Physics and Electronic Engineering Center for Computational Sciences Sichuan Normal University Chengdu610068 China

The distinct over-tilting of band crossings in topological semimetal generates the type-I and type-II classification of Dirac/Weyl and nodal-line fermions, accompanied by the exotic electronic and magnetic transport properties. In this work, we propose a concept of hybrid nodal-chain semimetal, which is identified by the linked type-I and type-II nodal rings in the Brillouin zone. Based on first-principles calculations and swarm-intelligence structure search technique, a new ternary nitride MgCaN2 crystal is proposed as the first candidate to realize a novel 3D hybrid nodal-chain state. Remarkably, a flat band is emergent as a characteristic signature of such a hybrid nodal-chain along certain direction in the momentum space, thereby serving a platform to explore the interplay between topological semimetal state and flat band. Moreover, the underlying protection mechanism of the hybrid nodal-chain is revealed by calculating the mirror Z2 invariant and developing a k·p effective Hamiltonian. Additionally, considerable drumhead-like surface states with unique connection patterns are illustrated to identify the non-trivial band topology, which may be measured by future *** Codes hybrid Nodal-chain semimetal, band tilting effect, flat-band, first-principles calculations © 2023, CC BY.

关键词： Crystal structure

Single pair of charge-2 high-fold fermions with surface type-II Van Hove singularities in ultralight chiral crystals

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Physical Review B 2024年第16期109卷 165136-165136页

作者： Xiaoliang Xiao Yuanjun Jin Da-Shuai Ma Haoran Wei Jing Fan Rui Wang Xiaozhi Wu Institute for Structure and Function & Department of Physics Chongqing University Chongqing 400044 China Guangdong Basic Research Center of Excellence for Structure and Fundamental Interactions of Matter Guangdong Provincial Key Laboratory of Quantum Engineering and Quantum Materials School of Physics South China Normal University Guangzhou 510006 China Center of Quantum Materials and Devices Chongqing University Chongqing 400044 China Center for Computational Science and Engineering Southern University of Science and Technology Shenzhen 518055 China Chongqing Key Laboratory for Strongly Coupled Physics Chongqing 400044 China

The realization of the single-pair fermions in electronic systems remains challenging in topology physics, especially for the systems with larger chiral charges C. In this work, based on the symmetry analysis, low-energy effective models, and first-principles calculations, we identify the single-pair charge-two chiral fermions in 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 Fermi-arc connections, 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 chiral charge through structural chirality but also facilitates the exploration of electronic correlations on the surface of ultralight chiral crystals.

关键词： Crystal symmetry Fermions Symmetry protected topological states 3-dimensional systems Crystal structures Electronic structure Weyl semimetal High-throughput calculations Tight-binding model Wannier function methods k dot p method

Three-dimensional dirac phonons with inversion symmetry

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arXiv 2021年

作者： Chen, Z.J. Wang, R. Xia, B.W. Zheng, B.B. Jin, Y.J. Zhao, Yu-Jun Xu, H. Department of Physics South China University of Technology Guangzhou510640 China Department of Physics & Institute for Quantum Science and Engineering Southern University of Science and Technology Shenzhen518055 China Guangdong Provincial Key Laboratory of Computational Science and Material Design Southern University of Science and Technology China Institute for Structure and Function Department of physics & Center for Quantum Materials and Devices Chongqing University Chongqing400044 China

Dirac semimetals associated with bulk Dirac fermions are well-known in topological electronic systems. In sharp contrast, three-dimensional (3D) Dirac phonons in crystalline solids are still unavailable. Here we perform symmetry arguments and first-principles calculations to systematically investigate 3D Dirac phonons in all space groups with inversion symmetry. The results show that there are two categories of 3D Dirac phonons depending on their protection mechanisms and positions in momentum space. The first category originates from the four-dimensional irreducible representations at the high symmetry points. The second category arises from the phonon branch inversion, and the symmetry guarantees Dirac points to be located along the high symmetry lines. Furthermore, we reveal that non-symmorphic symmetries and the combination of inversion and time-reversal symmetries play essential roles in the emergence of 3D Dirac phonons. Our work not only offers a comprehensive understanding of 3D Dirac phonons but also provides significant guidance for exploring Dirac bosons in both phononic and photonic systems. Copyright © 2021, The Authors. All rights reserved.

关键词： Phonons

Higher-Order Band Topology in Twisted Bilayer Kagome Lattice

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arXiv 2024年

作者： Wan, Xiaolin Zeng, Junjie Zhu, Ruixiang Xu, Dong-Hui Zheng, Baobing 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 Baoji University of Arts and Sciences Baoji721016 China Center of Quantum Materials and Devices Chongqing University Chongqing400044 China

Topologically protected corner states serve as a key indicator for two-dimensional higher-order topological insulators, yet they have not been experimentally identified in realistic materials. Here, by utilizing the effective tight-binding model and symmetry arguments, we establish a connection between higher-order topological insulators and twisted bilayer kagome lattices. We find that the topologically nontrivial bulk band gap arises in the twisted bilayer kagome lattice system due to twist-induced intervalley scattering, leading to the emergence of higher-order topological insulators with a range of commensurate twist angles, and the higher-order band topology is verified by the second Stiefel-Whitney number and fractionally quantized corner charges. Moreover, we investigate the influence of disorder and charge density wave order on the stability of higher-order topological insulator phases. The results show that the corner states of twisted bilayer kagome lattice systems are robust with respect to disorder and charge density wave. Our work not only provides a feasible approach to realize the readily controllable higher-order topological insulator phases by employing a simple twist technique, but also demonstrates that the twisted bilayer kagome lattice systems exhibit the robustness of higher-order band topology, making it feasible to check above prediction in experiments. Copyright © 2024, The Authors. All rights reserved.

关键词： Charge density waves

In-plane canted ferromagnetism, intrinsic Weyl fermions, and large anomalous Hall effect in the kagome semimetal Rh3Sn2S2

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Physical Review B 2023年第17期108卷 174430-174430页

作者： Meng-Xin Wu Yu-Hao Wei Da-Shuai Ma Peng Wang Nan Gao Shao-Yi Wu Min-Quan Kuang Chongqing Key Laboratory of Micro & Nano Structure Optoelectronics and School of Physical Science and Technology Southwest University Chongqing 400715 People's Republic of China Institute for Structure and Function 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 Material Science and Engineering Taizhou University Taizhou 318000 People's Republic of China Department of Applied Physics School of Physics University of Electronic Science and Technology of China Chengdu 611731 People's Republic of China

Magnetic Weyl semimetals can reveal a renowned electronic transport phenomenon, i.e., the anomalous Hall effect due to the intrinsic Berry curvature promoted by the Weyl fermions. Here, the layered kagome compound Rh3Sn2S2 is identified as a ferromagnetic Weyl semimetal by first-principles calculations. When the spin-orbit coupling is absent, three sets of nontrivial Weyl nodal lines emerge in the spin-up channel, while the spin-down bands are fully gapped. The obtained magnetocrystalline anisotropy energy indicates that Rh3Sn2S2 has an in-plane canted magnetic order with a 30∘ angle to the a axis. As a consequence, the spin-orbit coupling breaks the time-reversal symmetry, and the broken Weyl nodal lines give birth to one pair of Weyl points near the Fermi level. The chiral Weyl nodes, protected by the space inversion and the C3z-rotation symmetry, act as the monopole source and sink of the Berry curvature and boost a large anomalous Hall conductivity approaching 580 Ω−1cm−1. This work unveils the magnetic, electronic, and topological properties as well as the anomalous Hall effect of Rh3Sn2S2, which will facilitate future research on the unexplored topological phenomena in Rh3Sn2S2.

关键词： Anomalous Hall effect Ferromagnetism Kagome lattice Weyl semimetal Electronic structure First-principles calculations Symmetries

Strongly Ideal Robust Weyl Semimetals in Cubic Symmetry with Spatial-Inversion Breaking

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arXiv 2017年

作者： Wang, R. Zhao, J.Z. Jin, Y.J. Xu, W.P. Gan, L.-Y. Wu, X.Z. Xu, H. Tong, S.Y. Department of Physics South University of Science and Technology of China Shenzhen518055 China Institute for Structure and Function Department of physics Chongqing University Chongqing400044 China Dalian Institute of Chemical Physics Chinese Academy of Sciences Dalian116023 China Superconductivity and New Energy R&D Center Southwest Jiaotong University ChengduSichuan610031 China Shenzhen518172 China

We show that compounds in a family that possess time-reversal symmetry and share a non-centrosymmetric cubic structure with the space group F-43m (No. 216) host robust ideal Weyl semi-metal fermions with desirable topologically 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 the use of system symmetry by first-principles calculations as a powerful recipe for discovering new Weyl semi-metals with attractive features whose protected fermions may be candidates of many applications. Copyright © 2017, The Authors. All rights reserved.

关键词： Chirality

Inventory of high-quality flat-band van der Waals materials

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arXiv 2022年

作者： Duan, Jingyi Ma, Da-Shuai Zhang, Run-Wu Zhang, Zeying Cui, Chaoxi Jiang, Wei Yu, Zhi-Ming Yao, Yugui School of Physics Beijing Institute of Technology Beijing100081 China Beijing Key Lab of Nanophotonics and Ultrafine Optoelectronic Systems School of Physics Beijing Institute of Technology Beijing100081 China Institute for Structure and Function Department of Physics Chongqing University Chongqing400044 China College of Mathematics and Physics Beijing University of Chemical Technology Beijing100029 China College of Physics and Optoelectronic Engineering Shenzhen University Shenzhen518060 China

More is left to do in the field of flat bands besides proposing theoretical models. One unexplored area is the flat bands featured in the van der Waals (vdW) materials. Exploring more flat-band material candidates and moving the promising materials toward applications have been well recognized as the cornerstones for the next-generation high-efficiency devices. Here, we utilize a powerful high-throughput tool to screen desired vdW materials based on the Inorganic Crystal structure Database. Through layers of filtration, we obtained 861 potential mono-layers from 4997 vdW materials. Significantly, it is the first example to introduce flat-band electronic properties in the vdW materials and propose three families of representative flat-band materials by mapping two-dimensional (2D) flat-band lattice models. Unlike existing screening schemes, a simple, universal rule, i.e., 2D flat-band score criterion, is first proposed to efficiently identify 229 high-quality flat-band candidates, and guidance is provided to diagnose the quality of 2D flat bands. All these efforts to screen experimental available flat-band candidates will certainly motivate continuing exploration towards the realization of this class of special materials and their applications in material science. Copyright © 2022, The Authors. All rights reserved.

关键词： Van der Waals forces

Controllable Weyl nodes and Fermi arcs in a light-irradiated carbon allotrope

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arXiv 2023年

作者： Ji, Ruoning Ding, Xianyong Zhan, Fangyang Xiao, Xiaoliang Fan, Jing Ning, Zhen Wang, Rui Institute for Structure and Function Department of Physics Chongqing Key Laboratory for Strongly Coupled Physics Chongqing University Chongqing400044 China Center for Computational Science and Engineering Southern University of Science and Technology Shenzhen518055 China Center of Quantum materials and devices Chongqing University Chongqing400044 China

The precise control of Weyl physics in realistic materials offers a promising avenue to construct accessible topological quantum systems, and thus draw widespread attention in condensed-matter physics. Here, based on first-principles calculations, maximally localized Wannier functions based tight-binding model, and Floquet theorem, we study the light-manipulated evolution of Weyl physics in a carbon allotrope C6 crystallizing a face-centered orthogonal structure (fco-C6), an ideal Weyl semimetal with two pairs of Weyl nodes, under the irradiation of a linearly polarized light (LPL). We show that the positions of Weyl nodes and Fermi arcs can be accurately controlled by changing light intensity. Moreover, we employ a low-energy effective k · p model to understand light-controllable Weyl physics. The results indicate that the symmetry of light-irradiated fco-C6 can be selectively preserved, which guarantees that the light-manipulated Weyl nodes can only move in the high-symmetry plane in momentum space. Our work not only demonstrates the efficacy of employing periodic driving light fields as an efficient approach to manipulate Weyl physics, but also paves a reliable pathway for designing accessible topological states under light irradiation. Copyright © 2023, The Authors. All rights reserved.

关键词： Carbon