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A quasi-particle dictionary:exhaustive classification of energy band crossing in time-reversal-invariant systems

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Science Bulletin 2022年第4期67卷 345-346,M0003页

作者： xiangang wan Ational Laboratory of Solid State Microstructures and School of Physics Nanjing UniversityNanjing 210093China Collaborative Innovation Center of Advanced Microstructures Nanjing UniversityNanjing 210093China

The topological properties of electronic bands have received significant attention since the 1980s,and recently one of the most important progress in condensed matter systems is the discovery of the topological insulator(TI)[1].It had been found that insulators can be classified by a topological invariant that takes different values for TI and ordinary insulators[1],and the topological invariant cannot be changed without closing the energy gap of the *** usually people believe the gapless system cannot have interesting topological features.

关键词：时间反转 topological 准粒子

Competition of Quantum Anomalous Hall States and Charge Density Wave in a Correlated Topological Model

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Chinese Physics Letters 2022年第7期39卷 63-68页

作者： Xin Gao Jian Sun xiangang wan Gang Li School of Physical Science and Technology ShanghaiTech UniversityShanghai 201210China National Laboratory of Solid State Microstructures and School of Physics Nanjing UniversityNanjing 210093China Collaborative Innovation Center of Advanced Microstructures Nanjing UniversityNanjing 210093China ShanghaiTech Laboratory for Topological Physics ShanghaiTech UniversityShanghai 201210China

We investigate the topological phase transition driven by non-local electronic correlations in a realistic quantum anomalous Hall model consisting of d_(xy)–d_(x^(2)-y^(2)) orbitals. Three topologically distinct phases defined in the noninteracting limit evolve to different charge density wave phases under correlations. Two conspicuous conclusions were obtained: The topological phase transition does not involve gap-closing and the dynamical fluctuations significantly suppress the charge order favored by the next nearest neighbor interaction. Our study sheds light on the stability of topological phase under electronic correlations, and we demonstrate a positive role played by dynamical fluctuations that is distinct to all previous studies on correlated topological states.

关键词： Quantum Competition of Quantum Anomalous Hall States and Charge Density Wave in a Correlated Topological Model

Determination of the Range of Magnetic Interactions from the Relations between Magnon Eigenvalues at High-Symmetry k Points

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Chinese Physics Letters 2021年第11期38卷 53-58页

作者： Di wang Jihai Yu Feng Tang Yuan Li xiangang wan National Laboratory of Solid State Microstructures and School of Physics Nanjing UniversityNanjing 210093China Collaborative Innovation Center of Advanced Microstructures Nanjing UniversityNanjing 210093China International Center for Quantum Materials School of PhysicsPeking UniversityBeijing 100871China Collaborative Innovation Center of Quantum Matter Beijing 100871China

Magnetic exchange interactions(MEIs) define networks of coupled magnetic moments and lead to a surprisingly rich variety of their magnetic properties. Typically MEIs can be estimated by fitting experimental ***, how many MEIs need to be included in the fitting process for a material is unclear a priori,which limits the results obtained by these conventional methods. Based on linear spin-wave theory but without performing matrix diagonalization, we show that for a general quadratic spin Hamiltonian, there is a simple relation between the Fourier transform of MEIs and the sum of square of magnon energies(SSME). We further show that according to the real-space distance range within which MEIs are considered relevant, one can obtain the corresponding relationships between SSME in momentum space. By directly utilizing these characteristics and the experimental magnon energies at only a few high-symmetry k points in the Brillouin zone, one can obtain strong constraints about the range of exchange path beyond which MEIs can be safely neglected. Our methodology is also generally applicable for other Hamiltonian with quadratic Fermi or Boson operators.

关键词： Hamiltonian Determination of the Range of Magnetic Interactions from the Relations between Magnon Eigenvalues at High-Symmetry k Points

Concepts of the half-valley-metal and quantum anomalous valley Hall effect

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npj Computational Materials 2020年第1期6卷 588-594页

作者： He Hu Wen-Yi Tong Yu-Hao Shen xiangang wan Chun-Gang Duan State Key Laboratory of Precision Spectroscopy and Key Laboratory of Polar Materials and Devices Ministry of EducationDepartment of ElectronicsEast China Normal University200241 ShanghaiChina Department of Physics and National Laboratory of Solid State Microstructures Nanjing University210093 NanjingChina Collaborative Innovation Center of Extreme Optics Shanxi UniversityTaiyuan 030006 ShanxiChina

Valley,the energy extrema in the electronic band structure at momentum space,is regarded as a new degree of freedom of electrons,in addition to charge and *** studies focused on valley degree of freedom now form an emerging field of condensed-matter physics,i.e.,valleytronics,whose development is exactly following that of spintronics,which focuses on the spin degree of freedom.

关键词： quantum momentum exactly

Observations of nodal lines in the topological semimetal ZrSnTe

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Science China(Physics,Mechanics & Astronomy) 2020年第2期63卷 111-116页

作者： Bo Chen Bo Zhang JiHai Yu FuCong Fei Muhammad Naveed Yi Zhang Zhe Sun xiangang wan FengQi Song National Laboratory of Solid State Microstructure School of PhysicsNanjing UniversityNanjing 210093China National Synchrotron Radiation Laboratory University of Science and Technology of ChinaHefei 230029China Collaborative Innovation Center of Advanced Microstructures Nanjing UniversityNanjing 210093China

Performing angle-resolved photoemission spectroscopy(ARPES) and theoretical calculations for ZrSnTe, we find a nodal line in the kx-ky plane with a tiny gap and two nodal lines without gaps along the kzdirection. The constant energy contours are plotted in the kx-ky plane at a photon energy of 30 e V to examine the gapping feature of the nodal line. In addition, we depict the band dispersions along the Γ-M and Γ-X directions from the ARPES images at photon energies ranging from 24 to 40 e V. The kz mapping confirms the presence of stable Dirac points with obvious kzdependences along the M-A and X-R directions. In this paper, we report the two types of nodal lines associated with the theoretical local-density approximation calculations, broadening the horizons of nodal-line semimetal research.

关键词： nodal-line semimetals ZrSnTe ARPES

Pressure engineering of intertwined phase transitions in lanthanide monopnictide NdSb

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Science China(Physics,Mechanics & Astronomy) 2022年第8期65卷 140-147页

作者： Ying Zhou Xuliang Chen Yonghui Zhou Jihai Yu Xiangde Zhu Chao An Changyong Park xiangang wan Xiaoping Yang Zhaorong Yang Institutes of Physical Science and Information Technology Anhui UniversityHefei230601China Anhui Province Key Laboratory of Condensed Matter Physics at Extreme Conditions High Magnetic Field LaboratoryHFIPSChinese Academy of SciencesHefei230031China High Magnetic Field Laboratory of Anhui Province Hefei230031China National Laboratory of Solid State Microstructures School of PhysicsCollaborative Innovation Center of Advanced MicrostructuresNanjing UniversityNanjing210093China HPCAT X-ray Science DivisionArgonne National LaboratoryArgonneIL60439USA

Coexistence of non-trivial band topology and intrinsic magnetic order not only leads to emergent phenomena but also allows for the tunability of the exotic properties from different degrees of freedom. By performing transport measurements at synergetic extreme conditions, here we report on pressure engineering of intertwined structural, magnetic, and topological phase transitions in an antiferromagnetic Dirac semimetal NdSb. We show that the original antiferromagnetic state is strengthened in the lowpressure region while destabilized upon further compression close to the critical pressure where a structural transition from Fm-3m phase to P4/mmm phase takes place at P~18 GPa, forming a yurt-shaped evolution in response to magnetic field,pressure and temperature. Concomitant with the structural transition, NdSb simultaneously carries on a magnetic transition to the ferromagnetic state. Moreover, theoretical calculations unravel that the ferromagnetic tetragonal phase presents nontrivial features of Weyl fermions. These findings offer new important insight into the microscopic interplay among lattice, spin, and relativistic fermions in lanthanide monopnictides.

关键词： synergetic extreme conditions high pressure NdSb magnetic topological semimetal phase transition

Effective models for nearly ideal Dirac semimetals

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Frontiers of physics 2019年第4期14卷 63-69页

作者： Feng Tang xiangang wan National Laboratory of Solid State Microstructures and School of Physics Nanjing University Nanjing 210093 China Collaborative Innovation Center of Advanced Microstructures Nanjing University Nanjing 210093 China

Topological materials (TMs) have gained intensive attention due to their novel behaviors compared with topologically trivial materials. Among various TMs, Dirac semimetal (DSM) has been studied extensively. Although several DSMs have been proposed and verified experimentally, the suitable DSM for realistic applications is still lacking. Thus finding ideal DSMs and providing detailed analyses to them are of both fundamental and technological importance. Here, we sort out 8 (nearly) ideal DSMs from thousands of topological semimetals in Nature 566(7745), 486 (2019). We show the concrete positions of the Dirac points in the Brillouin zone for these materials and clarify the symmetryprotection mechanism for these Dirac points as well as their low-energy effective models. Our results provide a useful starting point for future study such as topological phase transition under strain and transport study based on these effective models. These DSMs with high mobilities are expected to be applied in fabrication of functional electronic devices.

关键词： Dirac semimetal symmetry effective model

Plasmonic evolution of atomically size-selected Au clusters by electron energy loss spectrum

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National Science Review 2021年第12期8卷 20-28页

作者： Siqi Lu Lin Xie Kang Lai Runkun Chen Lu Cao Kuojuei Hu Xuefeng wang Jinsen Han xiangang wan Jianguo wan Qing Dai Fengqi Song Jiaqing He Jiayu Dai Jianing Chen Zhenlin wang Guanghou wang National Laboratory of Solid State Microstructures Collaborative Innovation Center of Advanced Microstructures and School of PhysicsNanjing University Department of Physics Southern University of Science and Technology Department of Physics National University of Defense Technology Institute of Physics Chinese Academy of Sciences and Beijing National Laboratory for Condensed Matter Physics School of Physical Sciences University of Chinese Academy of Sciences School of Electronic Science and Engineering and Collaborative Innovation Center of Advanced Microstructures Nanjing University Division of Nanophotonics CAS Center for Excellence in Nanoscience National Center for Nanoscience and Technology Songshan Lake Materials Laboratory

The plasmonic response of gold clusters with atom number(N) = 100–70 000 was investigated using scanning transmission electron microscopy-electron energy loss spectroscopy. For decreasing N, the bulk plasmon remains unchanged above N = 887 but then disappears, while the surface plasmon firstly redshifts from 2.4 to 2.3 e V above N = 887 before blueshifting towards 2.6 e V down to N = 300, and finally splitting into three fine features. The surface plasmon’s excitation ratio is found to follow N0.669, which is essentially R2. An atomically precise evolution picture of plasmon physics is thus demonstrated according to three regimes: classical plasmon(N = 887–70 000), quantum confinement corrected plasmon(N = 300–887)and molecule related plasmon(N < 300).

关键词： atomically precise gold cluster plasmonic response electron energy loss spectroscopy full-scale evolution

Electron-Correlation-Induced Charge Density Wave in FeGe

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Chinese Physics Letters 2023年第11期40卷 93-99页

作者：武琳胡雅婷樊东泽王棣万贤纲 National Laboratory of Solid State Microstructures and School of Physics Nanjing UniversityNanjing 210093China Collaborative Innovation Center of Advanced Microstructures Nanjing UniversityNanjing 210093China

As the first magnetic kagome material to exhibit the charge density wave(CDW)order,FeGe has attracted much attention in recent *** to AV_(3)Sb_(5)(A=K,Cs,Rb),FeGe exhibits the CDW pattern with an in-plane 2×2 structure and the existence of van Hove singularities near the Fermi ***,sharply different from AV_(3)Sb_(5)which has phonon instability at M point,all the theoretically calculated phonon frequencies in FeGe remain *** on first-principles calculations,we surprisingly find that the maximum of nesting function is at K point instead of M *** Fermi pockets with Fe-d_(xz)and Fe-d_(x^(2)-y^(2))/d_(xy)orbital characters have large contribution to the Fermi nesting,which evolve significantly with k_(z),indicating the highly three-dimensional(3D)feature of FeGe in contrast to AV_(3)Sb_(5).Considering the effect of local Coulomb interaction,we reveal that the instability at K point is significantly suppressed due to the sublattice interference ***,the wave functions nested by vector M have many ingredients located at the same Fe site,thus the instability at M point is *** indicates that the electron correlation,rather than electron-phonon interaction,plays a key role in the CDW transition at M point.

关键词： mechanism phonon Fermi