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Tunable quantum anomalous Hall effects in ferromagnetic van der Waals heterostructures

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National Science Review 2024年第3期11卷 100-107页

作者： Feng Xue Yusheng Hou Zhe Wang Zhiming Xu Ke He Ruqian Wu Yong Xu Wenhui Duan Beijing Academy of quantum Information Sciences State key laboratory of Low Dimensional quantum physics Department of Physics Tsinghua University guangdong provincial key laboratory of Magnetoelectric physics and Devices Center for Neutron Science and Technology School of Physics Sun Yat-sen University State key laboratory of Surface physics Key Laboratory of Computational Physical Sciences and Department of PhysicsFudan University Frontier Science Center for quantum Information Department of physics and astronomy University of California-Irvine Tencent quantum laboratory Tencent Technology(Shenzhen)Co.Ltd RIKEN Center for Emergent Matter Science(CEMS) Institute for Advanced Study Tsinghua University

The quantum anomalous Hall effect（QAHE） has unique advantages in topotronic applications, but it is still challenging to realize the QAHE with tunable magnetic and topological properties for building functional devices. Through systematic first-principles calculations, we predict that the in-plane magnetization induced QAHE with Chern numbers C = ±1 and the out-of-plane magnetization induced QAHE with high Chern numbers C = ±3 can be realized in a single material candidate, which is composed of van der Waals（vdW）coupled Bi and MnBi2Te4monolayers. The switching between different phases of QAHE can be controlled in multiple ways, such as applying strain or（weak） magnetic field or twisting the vdW materials. The prediction of an experimentally available material system hosting robust, highly tunable QAHE will stimulate great research interest in the field. Our work opens a new avenue for the realization of tunable QAHE and provides a practical material platform for the development of topological electronics.

关键词： quantum anomalous Hall effect topological quantum phase transition van der Waals heterostructures tunable Chern number high Chern number

Uncovering the magnetic response of open-shell graphene nanostructures on metallic surfaces at different doping levels

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Science China(physics,Mechanics & astronomy) 2024年第2期67卷 142-148页

作者： Zengfu Ou Jun Wang Jihai Zhang Yukang Ding Shenwei Chen Wenya Zhai Jingcheng Li Dingyong Zhong Donghui Guo school of physics Sun Yat-sen UniversityGuangzhou 510275China guangdong provincial key laboratory of Magnetoelectric physics and Devices School of PhysicsSun Yat-sen UniversityGuangzhou 510275China State key laboratory of Optoelectronic Materials and Technologies Sun Yat-sen UniversityGuangzhou 510275China College of Chemical Engineering Zhejiang University of TechnologyHangzhou 310014China

Open-shell graphene nanostructures(GNs)are promising candidates for future spintronics and quantum technologies.Recent progress based on on-surface synthetic approach has successfully created such GNs on metallic surfaces.Meanwhile,the doping effect of metallic surfaces is inevitably present and can significantly tune their electronic and magnetic properties.Here,we investigate the zigzag end states of open-shell 7-armchair graphene nanoribbons(7-AGNRs)on Au(111),Au(100)and Ag(111)surfaces.Combined with the manipulation of a scanning tunneling microscope,we demonstrate that the end states can be tuned from empty states to singly occupied states and to doubly occupied states by substrate doping.Furthermore,the singly occupied states can be finely tuned,with the occupancy number of the states and related magnetic behaviors uncovered by experiments at different temperatures and magnetic fields.Our results provide a comprehensive study of the magnetic response of open-shell GNs on metallic surfaces at different doping levels.

关键词： open-shell graphene nanostructures magnetic response metallic substrate doping Kondo resonance scanning tunneling microscopy/spectroscopy

Superexchange and charge transfer in the nickelate superconductor LaNiOunder pressure

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Science China(physics,Mechanics & astronomy) 2024年

作者： Wei Wu Zhihui Luo Dao-Xin Yao Meng Wang guangdong provincial key laboratory of Magnetoelectric physics and Devices Center for Neutron Science and Technology school of physics Sun Yat-sen University

Recently,a bulk nickelate superconductor La3Ni2O7is discovered at pressures with a remarkable high transition temperature Tc～80 K.Here,we study a Hubbard model with tight-binding parameters derived from ab initio calculations of La3Ni2O7,by employing large scale determinant quantum Monte Carlo and cellular dynamical mean-field theory.Our result suggests that the superexchange couplings in this system are comparable to that of cuprates.The system is a charge transfer insulator as the hole concentration becomes four per site at large Hubbard U.Upon hole doping,two low-energy spin-singlet bands emerge in the system exhibiting distinct correlation properties:while the one composed of the out-of-plane Ni-d3z2-r2and O-pzorbitals demonstrates strong antiferromagnetic correlations and narrow effective bandwidth,the in-plane singlet band consisting of the Ni-dx2-y2and O-px/pyorbitals is in general more itinerant.Over a broad range of hole doping,the doped holes occupy primarily the dx2-y2and px/pyorbitals,whereas the d3z2-r2and pzorbitals retain underdoped.We propose an effective t-J model to capture the relevant physics and discuss the implications of our result for comprehending the La3Ni2O7superconductivity.

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Structural transition, electric transport, and electronic structures in the compressed trilayer nickelate LaNiO

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Science China(physics,Mechanics & astronomy) 2024年

作者： Jingyuan Li Cuiqun Chen Chaoxin Huang Yifeng Han Mengwu Huo Xing Huang Peiyue Ma Zhengyang Qiu Junfeng Chen Xunwu Hu Lan Chen Tao Xie Bing Shen Hualei Sun Daoxin Yao Meng Wang Center for Materials of the Universe School of Molecular Sciences Arizona State University Center for Neutron Science and Technology Guangdong Provincial Key Laboratory of Magnetoelectric Physics and Devices School of Physics Sun Yat-sen University school of Sciences Sun Yat-sen University

Atomic structure and electronic band structure are fundamental properties for understanding the mechanism of superconductivity. Motivated by the discovery of pressure-induced high-temperature superconductivity at 80 K in the bilayer Ruddlesden-Popper nickelate La3Ni2O7, the atomic structure and electronic band structure of the trilayer nickelate La4Ni3O10under pressure up to 44.3 GPa are investigated. A structural transition from the monoclinic P21/a space group to the tetragonal I4/mmm around 12.6-13.4 GPa is identified, accompanied by a drop of resistance below 7 K. Density functional theory calculations suggest that the bonding state of Ni 3dz2orbital rises and crosses the Fermi level at high pressures, which may give rise to possible superconductivity observed in resistance under pressure in La4Ni3O10. The trilayer nickelate La4Ni3O10shows some similarities with the bilayer La3Ni2O7and has unique properties, providing a new platform to investigate the underlying mechanism of superconductivity in nickelates.

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Comprehensive study of the ultrafast photoexcited carrier dynamics in Sb2Te3–GeTe superlattices

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Chinese physics B 2024年第7期 391-398页

作者：叶之江金钻明蒋叶昕卢琦贾梦辉钱冬黄夏敏李舟彭滟朱亦鸣 Terahertz Technology Innovation Research Institute Terahertz Spectrum and Imaging Technology Cooperative Innovation CenterShanghai Key Laboratory of Modern Optical System University of Shanghai for Science and Technology Shanghai Institute of Intelligent Science and Technology Tongji University key laboratory of Artificial Structures and quantum Control (Ministry of Education) Shenyang National Laboratory for Materials ScienceSchool of Physics and Astronomy Shanghai Jiao Tong University State key laboratory of Precision Spectroscopy East China Normal University Tsung-Dao Lee Institute Shanghai Jiao Tong University GBA Branch of Aerospace Information Research Institute Chinese Academy of Sciences guangdong provincial key laboratory of Terahertz quantum Electromagnetics University of Chinese Academy of Sciences

Chalcogenide superlattices Sb2Te3-GeTe is a candidate for interfacial phase-change memory（iPCM） data storage devices.By employing terahertz emission spectroscopy and the transient reflectance spectroscopy together,we investigate the ultrafast photoexcited carrier dynamics and current transients in Sb2Te3-GeTe superlattices.Sample orientation and excitation polarization dependences of the THz emission confirm that ultrafast thermo-electric,shift and injection currents contribute to the THz generation in Sb2Te3-GeTe superlattices.By decreasing the thickness and increasing the number of GeTe and Sb2Te3layer,the interlayer coupling can be enhanced,which significantly reduces the contribution from circular photo-galvanic effect（CPGE）.A photo-induced bleaching in the transient reflectance spectroscopy probed in the range of～1100 nm to～1400 nm further demonstrates a gapped state resulting from the interlayer coupling.These demonstrates play an important role in the development of iPCM-based high-speed optoelectronic devices.

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New designed helical resonator to improve measurement accuracy of magic radio frequency

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Chinese physics B 2022年第9期31卷 268-272页

作者：郭天刘培亮李朝红 guangdong provincial key laboratory of quantum metrology and sensing&school of physics and astronomy Sun Yat-Sen University(Zhuhai Campus)Zhuhai 519082China State key laboratory of Optoelectronic Materials and Technologies Sun Yat-Sen University(Guangzhou Campus)Guangzhou 510275China

Based upon the new designed helical resonator,the resonant radio frequency(RF)for trapping ions can be consec-utively adjusted in a large range(about 12 MHz to 29 MHz)with high Q-factors(above 300).We analyze the helical resonator with a lumped element circuit model and find that the theoretical results fit well with the experimental data.With our resonator system,the resonant frequency near magic RF frequency(where the scalar Stark shift and the second-order Doppler shift due to excess micromotion cancel each other)can be continuously changed at kHz level.For ^(88)Sr^(+) ion,compared to earlier results,the measurement accuracy of magic RF frequency can be improved by an order of magnitude upon rough calculation,and therefore the net micromotion frequency shifts can be further reduced.Also,the differential static scalar polarizability △α0 of clock transition can be experimentally measured more accurately.

关键词： trapped ions helical resonator magic radio frequency precision measurements

Topological non-Hermitian skin effect

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Frontiers of physics 2023年第5期18卷 1-45页

作者： Rijia Lin Tommy Tai Linhu Li Ching Hua Lee guangdong provincial key laboratory of quantum metrology and sensing&school of physics and astronomy Sun Yat-Sen University(Zhuhai Campus)Zhuhai 519082China Department of physics Massachusetts Institute of TechnologyCambridgeMA 02139USA Department of physics National University of SingaporeSingapore117542Singapore

This article reviews recent developments in the non-Hermitian skin effect(NHSE),particularly on its rich interplay with topology.The review starts off with a pedagogical introduction on the modified bulk-boundary correspondence,the synergy and hybridization of NHSE and band topology in higher dimensions,as well as,the associated topology on the complex energy plane such as spectral winding topology and spectral graph topology.Following which,emerging topics are introduced such as non-Hermitian criticality,dynamical NHSE phenomena,and the manifestation of NHSE beyond the traditional linear non-interacting crystal lattices,particularly its interplay with quantum many-body interactions.Finally,we survey the recent demonstrations and experimental proposals of NHSE.

关键词： non-Hermitian skin effect topological phases

Topological properties of non-Hermitian Creutz ladders

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Chinese physics B 2022年第1期31卷 56-68页

作者：梁辉强李林虎 guangdong provincial key laboratory of quantum metrology and sensing&school of physics and astronomy Sun Yat-Sen University(Zhuhai Campus)Zhuhai 519082China

We study topological properties of the one-dimensional Creutz ladder model with different non-Hermitian asymmetric hoppings and on-site imaginary potentials,and obtain phase diagrams regarding the presence and absence of an energy gap and in-gap edge modes.The non-Hermitian skin effect(NHSE),which is known to break the bulk-boundary correspondence(BBC),emerges in the system only when the non-Hermiticity induces certain unbalanced non-reciprocity along the ladder.The topological properties of the model are found to be more sophisticated than that of its Hermitian counterpart,whether with or without the NHSE.In one scenario without the NHSE,the topological winding is found to exist in a two-dimensional plane embedded in a four-dimensional space of the complex Hamiltonian vector.The NHSE itself also possesses some unusual behaviors in this system,including a high spectral winding without the presence of long-range hoppings,and a competition between two types of the NHSE,with the same and opposite inverse localization lengths for the two bands,respectively.Furthermore,it is found that the NHSE in this model does not always break the conventional BBC,which is also associated with whether the band gap closes at exceptional points under the periodic boundary condition.

关键词： topological phases bulk-boundary correspondence non-Hermitian physics Creutz ladders

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非厄米赝能隙

Science Bulletin 2022年第7期67卷 685-690页

作者：李林虎 Ching Hua Lee guangdong provincial key laboratory of quantum metrology and sensing&school of physics and astronomy Sun Yat-sen University(Zhuhai Campus)Zhuhai 519082China Department of physics National University of SingaporeSingapore 117551Singapore

能隙是表征物态的重要概念之一.其中,能态密度极低但非零的区域被称为赝能隙,其出现与高温超导等现象有着重要的联系.本研究发现对于一些非厄米格点系统,引入开边界条件能够导致赝能隙的产生.这一现象通常在两个或更多不对称的非厄米泵... 详细信息

能隙是表征物态的重要概念之一.其中,能态密度极低但非零的区域被称为赝能隙,其出现与高温超导等现象有着重要的联系.本研究发现对于一些非厄米格点系统,引入开边界条件能够导致赝能隙的产生.这一现象通常在两个或更多不对称的非厄米泵浦通道相互影响时出现,并且没有厄米对应.非厄米赝能隙的出现同时也伴随着一些其他新奇的物理现象.与普通拓扑能隙类似,非厄米赝能隙中也能出现受对称性保护的隙间态,但这些隙间态具有扩展的空间分布,而不是局域在系统边缘,且对破坏对称性的扰动具有很高的敏感性.在传统的拓扑相变点处,非厄米赝能隙中同样可以存在与拓扑态类似的局域边界态,但并不直接对应相应赝能带的拓扑不变量:这些赝能带可能具有分数的拓扑数,甚至不具有良好定义的陈数.非厄米赝能隙的概念挑战了传统拓扑对应以及能带的概念,有望对分数陈绝缘体等多体现象产生重要的影响.

关键词：物理现象能态密度赝能隙高温超导拓扑不变量对称性