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arXiv 2020年

作者： Zou, Runling Zhan, Fangyang Zheng, Baobing Wu, Xiaozhi Fan, Jing Wang, Rui Institute for Structure and Function Department of Physics Chongqing University Chongqing400044 China College of Physics and Optoelectronic Technology Nonlinear Research Institute Baoji University of Arts and Sciences Baoji721016 China Center for Computational Science and Engineering Southern University of Science and Technology Shenzhen518055 China

A van der Waals heterostructure combined with intrinsic magnetism and topological orders have recently paved attractive avenues to realize quantum anomalous Hall effects. In this work, using first-principles calculations and effective model analysis, we propose that the robust quantum anomalous Hall states with sizable band gaps emerge in the van der Waals heterostructure of germanene/Cr2Ge2Te6. This heterostructure possesses high thermodynamic stability, thus facilitating its experimental fabrication. Furthermore, we uncover that the proximity effect enhances the coupling between the germanene and Cr2Ge2Te6 layers, inducing the nontrivial band gaps in a wide range from 29 meV to 72 meV. The chiral edge states inside the band gap, leading to Hall conductance quantized to −e2/h, are clearly visible. This findings provide an ideal candidate to detect the quantum anomalous Hall states and realize further applications to nontrivial quantum transport at a high temperature. Copyright © 2020, The Authors. All rights reserved.

关键词： Van der Waals forces

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Stability and thermoelectric performance of the two-dimensional rare-earth compounds RTeCl (R=La,Pr,Nd)

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Physical Review Applied 2024年第5期21卷 054026-054026页

作者： Haoran Wei Xin Jin Xiaoliang Xiao Li Shi Yuanhao Duan Jing Fan Rui Wang Xiaozhi Wu Institute for Structure and Function & Department of Physics Chongqing University Chongqing 400044 China College of Physics and Electronic Engineering Chongqing Normal University Chongqing 401331 China Center for Computational Science and Engineering Southern University of Science and Technology Shenzhen 518055 China Center of Quantum Materials and Devices Chongqing University Chongqing 400044 China Chongqing Key Laboratory for Strongly Coupled Physics Chongqing 400044 China

Thermoelectric conversion technology is increasingly important for sustainable energy, particularly in transforming waste heat into electricity. In this study, we explore the thermoelectric properties of three novel two-dimensional materials, monolayer RTeCl (with R=La,Pr,Nd), using density-functional theory and semiclassical Boltzmann transport theory. These materials are stable and can be easily exfoliated from bulk structures due to their low cleavage energy. Notably, monolayer RTeCl materials have high power factors ((2.04--4.48)×104μWm−1K−2), attributed to multiple valleys in their valence-band maximum. Their complex crystal structures and the presence of two heavy elements contribute to an ultralow lattice thermal conductivity ((2.42--4.58)Wm−1K−1) at room temperature. Impressively, the figure of merit (ZT) values of monolayer RTeCl range from 0.4 to 1.2 at 300 K. Across the temperature range of 300 to 700 K, the average ZT value and thermoelectric conversion efficiency reach 1.32--2.75 and 15.3%--22.6%, respectively. Our results indicate that monolayer RTeCl is a promising candidate for nanoelectronics and low-dimensional thermoelectric devices, offering a new avenue for high-performance thermoelectric materials.

关键词： Phonons Thermoelectric effects 2-dimensional systems Semiconductor compounds Thermoelectrics Ab initio molecular dynamics Boltzmann theory Density functional calculations

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Symmetry-Protected Topological Triangular Weyl Complex

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Physical Review Letters 2020年第10期124卷 105303-105303页

作者： R. Wang B. W. Xia Z. J. Chen B. B. Zheng Y. J. Zhao H. Xu Department of Physics & Institute for Quantum Science and Engineering Southern University of Science and Technology Shenzhen 518055 People’s Republic of China Institute for Structure and Function & Department of Physics & Center for Quantum Materials and Devices Chongqing University Chongqing 400044 People’s Republic of China Department of Physics South China University of Technology Guangzhou 510640 People’s Republic of China Guangdong Provincial Key Laboratory of Computational Science and Material Design Southern University of Science and Technology Shenzhen 518055 People’s Republic of China

Weyl points are often believed to appear in pairs with opposite chirality. In this work, we show by first-principles calculations and symmetry analysis that single Weyl phonons with linear dispersion and double Weyl phonons with quadratic dispersion are simultaneously present between two specific phonon branches 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 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 isofrequency surface, which facilitates their detection in experiments and further applications. Our work not only offers the promising triangular phonon Weyl complex but also provides guidance for exploring triangular Weyl bosons in both phononic and photonic systems.

关键词： Phonons Symmetry protected topological states Topological materials Weyl semimetal

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Topological insulator path toward efficient hydrogen evolution catalysts in the Li2Pt family

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Physical Review B 2023年第23期107卷 235414-235414页

作者： Yu-Hao Wei Da-Shuai Ma Hong-Kuan Yuan Xiaotian Wang 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 & 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 Institute for Superconducting and Electronic Materials (ISEM) University of Wollongong Wollongong 2500 Australia

Topological materials, such as topological semimetals and topological insulators, with robust topological surface states have bright application prospects in electrochemical catalysis. Here, the first-principles calculations indicate the strong topological insulator Li2Pt family promotes efficient catalytic response to the hydrogen evolution reaction. For Li2Pt and Li2Pd, the calculated Gibbs free energy ΔGH* of the bridge site is 0.054 eV and 0.041 eV, while that for the top site is 0.187 eV and 0.641 eV, respectively. The better hydrogen evolution reaction performance of the bridge site can ascribe to H hybridizes with the dxy+dx2−y2 orbital, which donates the nontrivial topological surface states, while H hybridizes with the dz2 orbital that withholds contribution to topological surface states for the top site. Noticeably, the ΔGH* of the bridge site for Li2Pt (0.054 eV) and Li2Pd (0.041 eV) is nearly half of the value of Pt (0.09 eV), indicating an excellent hydrogen evolution reaction activity. This work uncovers the hybridization between adsorbate and topological surface states plays a vital role in enhancing the hydrogen evolution reaction performance and provides a promising route to design topological quantum catalysts.

关键词： Chemical kinetics, dynamics & catalysis Electronic structure Hydrogen energy Topological insulators First-principles calculations

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Weyl nodes with higher-order topology in an optically driven nodal-line semimetal

arXiv

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arXiv 2021年

作者： Du, Xiu-Li Chen, Rui Wang, Rui Xu, Dong-Hui Department of Physics Hubei University Wuhan430062 China Shenzhen518055 China Institute for Structure and Function Department of Physics Chongqing University Chongqing400044 China Chongqing Key Laboratory for Strongly Coupled Physics Chongqing400044 China Center for Quantum Materials and Devices Chongqing University Chongqing400044 China

Creating and manipulating topological states is a key goal of condensed matter physics. Periodic driving offers a powerful method to manipulate electronic states, and even to create topological states in solids. Here, we investigate the tunable Floquet states in a periodically driven higher-order nodal line semimetal with both spatial inversion and time-reversal symmetries. We found that the Floquet Weyl semimetal states, which support both one-dimensional hinge Fermi arc and two-dimensional surface Fermi arc states, can be induced in the higher-order nodal-line semimetal by shining circularly polarized light. Moreover, we show that the location of Weyl nodes and the curvature of surface Fermi arcs can be tuned by adjusting the propagation direction and incident angle of light. © 2021, CC BY.

关键词： Topology

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Photoinduced High-Chern-Number Quantum Anomalous Hall Effect from Higher-Order Topological Insulators

arXiv

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arXiv 2023年

作者： Wan, Xiaolin Ning, Zhen Xu, Dong-Hui Zheng, Baobing Wang, Rui Institute for Structure and Function Department of Physics Chongqing Key Laboratory for Strongly Coupled Physics Chongqing University Chongqing400044 China Center of Quantum Materials and Devices Chongqing University Chongqing400044 China College of Physics and Optoelectronic Technology Baoji University of Arts and Sciences Baoji721016 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. However, only a limited number of high-Chern-number QAH insulators have been reported to date. Here, we propose a dynamic approach for achieving high-Chern-number QAH phases in periodically driven two-dimensional higher-order topological insulators (HOTIs). 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 number 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. 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. Copyright © 2023, The Authors. All rights reserved.

关键词： Electric insulators

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Abundant surface-semimetal phases in three-dimensional obstructed atomic insulators

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Physical Review B 2023年第8期108卷 085135-085135页

作者： Xianyong Ding Xin Jin Zhuo Chen Xuewei Lv Da-Shuai Ma Xiaozhi Wu Rui Wang Institute for Structure and Function & Department of 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 Electronic Engineering Chongqing Normal University Chongqing 401331 China College of Materials Science and Engineering Chongqing University Chongqing 400044 China

Three-dimensional obstructed atomic insulators (OAIs) are characterized by the appearance of floating surface states (FSSs) at specific surfaces. Benefiting from this feature, our study here shows the presence of abundant surface-semimetal phases in 3D OAIs. The symmetries of obstructed Wannier charge centers ensure the degeneracy of such FSSs at high-symmetry points or invariant lines in the surface Brillouin zone. Utilizing topological quantum chemistry theory, we identify a carbon allotrope with a body-centered tetragonal structure, named bct−C20, as an ideal candidate for realizing different kinds of surface-semimetal phases. For the (001) surface of bct−C20, there are four in-gap FSSs, and these four FSSs form two kinds of surface Dirac cones, i.e., topological Dirac cones with linear dispersion and symmetry-enforced quadratic Dirac cones. The band topology of a surface Dirac cone is captured by the effective surface Hamiltonian and the emergence of hinge states. Moreover, the existence of the surface-nodal-line state is also discussed. This work reports an approach to obtain d-dimensional semimetal phases from the surface states of (d+1)-dimensional systems, which is of great significance for the studies in revealing topological states and their practical applications in high-dimensional crystals.

关键词： Electronic structure Surface states Topological materials Carbon-based materials Discrete symmetries in condensed matter

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Three-Dimensional Dirac Phonons with Inversion Symmetry

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Physical Review Letters 2021年第18期126卷 185301-185301页

作者： Z. J. Chen R. Wang B. W. Xia B. B. Zheng Y. J. Jin Yu-Jun Zhao H. Xu Department of Physics South China University of Technology Guangzhou 510640 People’s Republic of China Department of Physics and Institute for Quantum Science and Engineering Southern University of Science and Technology Shenzhen 518055 People’s Republic of China Guangdong Provincial Key Laboratory of Computational Science and Material Design Southern University of Science and Technology Shenzhen 518055 People’s Republic of China Institute for Structure and Function and Department of Physics and Center for Quantum Materials and Devices Chongqing University Chongqing 400044 People’s Republic of 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 nonsymmorphic 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.

关键词： Acoustic phonons Phonons Symmetry protected topological states Topological phases of matter Dirac semimetal Topological materials First-principles calculations k dot p method

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

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Physical Review B 2023年第20期108卷 205139-205139页

作者： Ruoning Ji Xianyong Ding Fangyang Zhan Xiaoliang Xiao Jing Fan Zhen Ning Rui Wang 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 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

The precise control of Weyl physics in realistic materials offers a promising avenue to construct accessible topological quantum systems, and thus draws widespread attention in condensed-matter physics. Here, based on first-principles calculations, the maximally localized Wannier function 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 irradiation of a linearly polarized light. We show that the positions of Weyl nodes and Fermi arcs can be accurately controlled by changing the 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 the Weyl physics, but also paves a reliable pathway for designing accessible topological states under light irradiation.

关键词： Electrical properties Electronic structure First-principles calculations Photoinduced effect Topological materials Weyl semimetal Bloch-Floquet theorem Density functional theory Tight-binding model Wannier function methods

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

arXiv

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arXiv 2023年

作者： Li, Wenzhang He, Qin Li, Xiao-Ping Ma, Da-Shuai Fu, Botao College of Physics and Electronic Engineering Center for Computational Sciences Sichuan Normal University Chengdu610068 China School of Physical Science and Technology Inner Mongolia University Hohhot010021 China Institute for Structure and Function Department of Physics Chongqing University Chongqing400044 China

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 high effective mass and a conduction band with small effective mass 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 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 non-trivial 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 nano-devices. © 2023, CC BY.

关键词： Energy gap

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