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Superexchange and charge transfer in the nickelate superconductor La_(3)Ni_(2)O_(7) under pressure

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Science China(physics,Mechanics & Astronomy) 2024年第11期67卷 1-8页

作者： Wéi Wú Zhihui Luo Dao-Xin Yao Meng Wang Center for Neutron Science and Technology Guangdong Provincial Key Laboratory of Magnetoelectric Physics and DevicesSchool of PhysicsSun Yat-sen UniversityGuangzhou 510275China

Recently, a bulk nickelate superconductor La_(3)Ni_(2)O_(7) is discovered at pressures with a remarkable high transition temperature T_(c)~ 80 K. Here, we study a Hubbard model with tight-binding parameters derived from ab initio calculations of La_(3)Ni_(2)O_(7),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-d_(3z^(2)-r^(2)) and O-p_(z) orbitals demonstrates strong antiferromagnetic correlations and narrow effective bandwidth, the in-plane singlet band consisting of the Ni-d_(x^(2)-y^(2)) and O-p_(x)/p_(y) orbitals is in general more itinerant. Over a broad range of hole doping, the doped holes occupy primarily the d_(x^(2)-y^(2)) and p_(x)/p_(y) orbitals, whereas the d_(3z^(2)-r^(2)) and p_(z) orbitals retain underdoped. We propose an effective t-J model to capture the relevant physics and discuss the implications of our result for comprehending the La_(3)Ni_(2)O_(7) superconductivity.

关键词： superconductivity nickelate superconductors Hubbard model superexchange charge transfer insulator quantum Monte Carlo

Detecting bulk and edge exceptional points in non-Hermitian systems through generalized Petermann factors

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Frontiers of physics 2024年第2期19卷 169-177页

作者： Yue-Yu Zou Yao Zhou Li-Mei Chen Peng Ye School of physics State Key Laboratory of Optoelectronic Materials and Technologiesand Guangdong Provincial Key Laboratory of Magnetoelectric Physics and DevicesSun Yat-sen UniversityGuangzhou 510275China

Non-orthogonality in non-Hermitian quantum systems gives rise to tremendous exotic quantum phenomena,which can be fundamentally traced back to *** this paper,we introduce an interesting quantity(denoted asη)as a new variant of the Petermann factor to directly and efficiently measure non-unitarity and the associated non-Hermitian *** tuning the model parameters of underlying non-Hermitian systems,we find that the discontinuity of bothηand its first-order derivative(denoted as■η)pronouncedly captures rich physics that is fundamentally caused by *** concretely,in the 1D non-Hermitian topological systems,two mutually orthogonal edge states that are respectively localized on two boundaries become non-orthogonal in the vicinity of discontinuity ofηas a function of the model parameter,which is dubbed"edge state transition".Through theoretical analysis,we identify that the appearance of edge state transition indicates the existence of exceptional points(EPs)in topological edge *** the discontinuity of■η,we investigate a two-level non-Hermitian model and establish a connection between the points of discontinuity of■ηand EPs of bulk *** studying this connection in more general lattice models,we find that some models have discontinuity of■η,implying the existence of EPs in bulk states.

关键词： non-Hermitian Su−Schrieffer−Heeger(SSH)model exceptional point

A Simple Urea Approach to N-Dopedα-Mo_(2)C with Enhanced Superconductivity

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Chinese physics Letters 2024年第10期41卷 103-111页

作者： Longfu Li Lei Shi Lingyong Zeng Kuan Li Peifeng Yu Kangwang Wang Chao Zhang Rui Chen Zaichen Xiang Yunwei Zhang Huixia Luo School of Materials Science and Engineering State Key Laboratory of Optoelectronic Materials and TechnologiesGuangdong Provincial Key Laboratory of Magnetoelectric Physics and DevicesKey Lab of Polymer Composite&Functional MaterialsSun Yat-Sen UniversityGuangzhou 510275China School of physics Guangdong Provincial Key Laboratory of Magnetoelectric Physics and DevicesSun Yat-Sen UniversityGuangzhou 510275China

Chemical doping is a critical factor in the development of new superconductors or optimizing the superconducting transition temperature(T_(c))of the parent superconducting ***,a new simple urea approach is developed to synthesize the N-dopedα-Mo_(2)*** from the simple urea method,a broad superconducting dome is found in the Mo_(2)C1−xNx(0≤x≤0.49)compositions.X-ray diffraction results show that the structure of𝛼α-Mo_(2)C remains unchanged and there is a variation of lattice parameters with nitrogen ***,magnetic susceptibility,and heat capacity measurement results confirm that T_(c)was strongly increased from 2.68K(x=0)to 7.05K(x=0.49).First-principles calculations and our analysis indicate that increasing nitrogen doping leads to a rise in the density of states at the Fermi level and doping-induced phonon softening,which enhances electron–phonon *** results in an increase in𝑇T_(c)and a sharp rise in the upper critical *** findings provide a promising strategy for fabricating transition metal carbonitrides and provide a material platform for further study of the superconductivity of transition metal carbides.

关键词： softening doping critical

Evolution of anomalous Hall effect in ferromagnetic Weyl semimetal Nb_(x)Zr_(1-x)Co_(2)Sn

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Chinese physics B 2024年第8期33卷 491-496页

作者：陈博文沈冰 Center for Neutron Science and Technology Guangdong Provincial Key Laboratory of Magnetoelectric Physics and DevicesSchool of PhysicsSun Yat-Sen UniversityGuangzhou 510275China State key laboratory of Optoelectronic Materials and Technologies Sun Yat-Sen UniversityGuangzhou 510275China

Magnetic topological semimetal can host various topological non-trivial states leading to exotic novel transport *** we report the systematic magneto-transport studies on the Heusler alloy Nb_(x)Zr_(1-x)Co_(2)Sn considered as a ferromagnetic(FM)Weyl *** cusp anomaly of temperature-dependent resistivity and large isotropic negative magneto-resistivity(MR)emerge around the FM transition consistent with the theoretical half-metallic *** prominent anomalous Hall effect(AHE)has the same behavior with the applied field along various crystal *** Nb doping introduces more disorder resulting in the enhancement of the upturn for the temperature-dependent resistivity in low *** Nb doping,the AHE exhibits systemic evolution with the Fermi level *** the doping level of x=0.25,the AHE mainly originates from the intrinsic contribution related to non-trivial topological Weyl states.

关键词： anomalous Hall effect magnetic Weyl semimetal ferromagnetism

Angular and planar transport properties of antiferromagnetic V5S8

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Chinese physics B 2024年第2期33卷 83-88页

作者：吴晓凯王彬吴德桐陈博文弭孟娟王以林沈冰 Center for Neutron Science and Technology and School of physics Guangdong Provincial Key Laboratory of Magnetoelectric Physics and Devicesand Key Laboratory of Optoelectronic Materials and Technologies Sun Yat-Sen University School of Integrated Circuits Shandong Technology Center of Nanodevices and Integration State Key Laboratory of Crystal MaterialsShandong University

Systemically angular and planar transport investigations are performed in layered antiferromagnetic(AF) V5S8. In this AF system, obvious anomalous Hall effect(AHE) is observed with a large Hall angle of 0.1 compared to that in ferromagnetic(FM) system. It can persist to the temperatures above AF transition and exhibit strong angular field *** phase diagram reveals various magnetic states by rotating the applied field. By analyzing the anisotropic transport behavior, magnon contributions are revealed and exhibit obvious angular dependence with a spin-flop vanishing line. The observed prominent planar Hall effect and anisotropic magnetoresisitivity exhibit two-fold systematical angular dependent oscillations. These behaviors are attributed to the scattering from spin–orbital coupling instead of nontrivial topological origin. Our results reveal anisotropic interactions of magnetism and electron in V5S8, suggesting potential opportunities for the AF spintronic sensor and devices.

关键词： antiferromagnetism planar Hall effect magnetic and topological properties

Magnetic Interactions with Strain Gradient in Ultrathin Pr_(0.67)Sr_(0.33)MnO_(3) Films

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Engineering 2024年第9期40卷 158-165页

作者： Bangmin Zhang Ping Yang Jun Ding Jingsheng Chen Gan Moog Chow guangdong provincial key laboratory of magnetoelectric physics and devices School of PhysicsSun Yat-sen UniversityGuangzhou 510275China Singapore Synchrotron Light Source National University of SingaporeSingapore 117603Singapore Department of Materials Science and Engineering National University of SingaporeSingapore 117575Singapore

Strain gradient is a normal phenomenon around a heterostructural interface in ultrathin film,and it is important to determine its effect on magnetic interactions to understand interfacial *** this work,ultrathin Pr_(0.67)Sr_(0.33)MnO_(3)(PSMO)films on different substrates are *** PSMO film under different in-plane strain conditions,the saturated magnetization and Curie temperature can be qualitatively explained by double-exchange interaction and the Jahn-Teller ***,the difference in the saturated magnetization with zero field cooling and 5 T field cooling is proportional to the strain ***-gradient-induced structural disorder is proposed to enhance phonon-electron antiferromagnetic interactions and the corresponding antiferromagnetic-to-ferromagnetic phase transition via a strong magnetic field during the field cooling process.A non-monotonous structural transition of the MnO_(6) octahedral rotation can enlarge the strain gradient in PSMO film on a SrTiO_(3) *** work demonstrates the existence of the flexomagnetic effect in ultrathin manganite film,which should be applicable to other complex oxide systems.

关键词： Strain gradient Manganite film Octahedral rotation Flexomagnetic Magnetic interactions Phase transition

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 *** progress based on on-surface synthetic approach has successfully created such GNs on metallic ***,the doping effect of metallic surfaces is inevitably present and can significantly tune their electronic and magnetic ***,we investigate the zigzag end states of open-shell 7-armchair graphene nanoribbons(7-AGNRs)on Au(111),Au(100)and Ag(111)*** 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 ***,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 *** 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

Normal and Superconducting Properties of La3Ni2O7

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Chinese physics Letters 2024年第7期41卷 145-156页

作者：王猛闻海虎吴涛姚道新向涛 guangdong provincial key laboratory of magnetoelectric physics and devices School of PhysicsSun Yat-Sen University National laboratory of Solid State Microstructures and Department of physics Collaborative Innovation Center of Advanced Microstructures Nanjing University Hefei National Research Center for Physical Sciences at the Microscale University of Science and Technology of China Institute of physics Chinese Academy of Sciences School of physics University of Chinese Academy of Sciences

This review provides a comprehensive overview of current research on the structural,electronic,and magnetic characteristics of the recently discovered high-temperature superconductor La3Ni2O7under high *** present the experimental results for synthesizing and characterizing this material,derived from measurements of transport,thermodynamics,and various spectroscopic techniques,and discuss their physical implications.

关键词： Nickel compounds

Structural transition,electric transport,and electronic structures in the compressed trilayer nickelate La_(4)Ni_(3)O_(10)

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Science China(physics,Mechanics & Astronomy) 2024年第11期67卷 9-15页

作者： Jingyuan Li Cui-Qun 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 Dao-Xin Yao Meng Wang Center for Neutron Science and Technology Guangdong Provincial Key Laboratory of Magnetoelectric Physics and DevicesSchool of PhysicsSun Yat-sen UniversityGuangzhou 510275China Center for Materials of the Universe School of Molecular SciencesArizona State UniversityTempe 85287USA School of Sciences Sun Yat-sen UniversityShenzhen 518107China

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 La_(3)Ni_(2)O_(7), the atomic structure and electronic band structure of the trilayer nickelate La_(4)Ni_(3)O_(10) under pressure up to 44.3 GPa are investigated. A structural transition from the monoclinic P2_(1)/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 3d_(z^(2)) orbital rises and crosses the Fermi level at high pressures, which may give rise to possible superconductivity observed in resistance under pressure in La_(4)Ni_(3)O_(10). The trilayer nickelate La_(4)Ni_(3)O_(10) shows some similarities with the bilayer La_(3)Ni_(2)O_(7) and has unique properties, providing a new platform to investigate the underlying mechanism of superconductivity in nickelates.

关键词： La_(4)Ni_(3)O_(10) high pressure synchrotron X-ray diffraction structural transition DFT calculations