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Capturing the non-equilibrium state in light–matter–free-electron interactions through ultrafast transmission electron microscopy

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Chinese Physics B 2024年第1期33卷 88-101页

作者：汪文韬孙帅帅李俊郑丁国黄思远田焕芳杨槐馨李建奇 Beijing National Laboratory for Condensed Matter Physics Institute of PhysicsChinese Academy of SciencesBeijing 100190China School of Physical Sciences University of Chinese Academy of SciencesBeijing 100049China Songshan Lake Materials Laboratory Dongguan 523808China yangtze River Delta Physics Research Center Co. Ltd.LiyangJiangsu 213300China

Ultrafast transmission electron microscope(UTEM) with the multimodality of time-resolved diffraction, imaging,and spectroscopy provides a unique platform to reveal the fundamental features associated with the interaction between free electrons and matter. In this review, we summarize the principles, instrumentation, and recent developments of the UTEM and its applications in capturing dynamic processes and non-equilibrium transient states. The combination of the transmission electron microscope with a femtosecond laser via the pump–probe method guarantees the high spatiotemporal resolution, allowing the investigation of the transient process in real, reciprocal and energy spaces. Ultrafast structural dynamics can be studied by diffraction and imaging methods, revealing the coherent acoustic phonon generation and photoinduced phase transition process. In the energy dimension, time-resolved electron energy-loss spectroscopy enables the examination of the intrinsic electronic dynamics of materials, while the photon-induced near-field electron microscopy extends the application of the UTEM to the imaging of optical near fields with high real-space resolution. It is noted that light–free-electron interactions have the ability to shape electron wave packets in both longitudinal and transverse directions, showing the potential application in the generation of attosecond electron pulses and vortex electron beams.

关键词： ultrafast transmission electron microscopy non-equilibrium structural dynamics photo-induced phase transition free-electron–photon interactions

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Structural phase transition, antiferromagnetism and two superconducting domes in LaFeAsO_(1-x)F_x(0

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Science China(Physics,Mechanics & Astronomy) 2018年第11期61卷 72-83页

作者： Jie yang Toshihide Oka Zheng Li huaixin yang JianQi Li GenFu Chen Guo-Qing Zheng Institute of Physics Chinese Academy of Sciences and Beijing National Laboratory for Condensed Matter Physics Department of Physics Okayama University

We report^(75) As nuclear magnetic resonance(NMR)/nuclear quadrupole resonance(NQR) and transmission electron microscopy(TEM) studies on LaFeAsO_(1-x)F_x. There are two superconducting domes in this material. The first one appears at 0.03 ≤ x ≤0.2 with T_c^(max) = 27 K, and the second one at 0.25 ≤x≤0.75 with T_c^(max) = 30 K. By NMR and TEM, we demonstrate that a C4-to-C2 structural phase transition(SPT) takes place above both domes, with the transition temperature T_s varying strongly with x. In the first dome, the SPT is followed by an antiferromagnetic(AF) transition, but neither AF order nor low-energy spin fluctuations are found in the second dome. By ^(75) As nuclear spin-lattice relaxation rate(1/T_1) measurements, we find that AF order and superconductivity coexist microscopically in LaFeAsO_(0.97) F_(0.03). In the coexisting region, 1/T_1 decreases at T_c but becomes proportional to T below 0.6 T_c, indicating gapless excitations. Therefore, in contrast to the early reports, the obtained phase diagram for x ≤ 0.2 is quite similar to the doped BaFe_2As_2 system. The electrical resistivity p in the second dome can be fitted by ρ = ρ0 + AT^n with n = 1 and a maximal coefficient A at around xopt = 0.5-0.55 at which T_s extrapolates to zero and Tc is the maximal, which suggests the importance of quantum critical fluctuations associated with the SPT. We have constructed a complete phase diagram of LaFeAsO_(1-x)F_x, which provides insight into the relationship between SPT, antiferromagnetism and superconductivity.

关键词：反铁磁性阶段转变超导性屋顶结构电子显微镜 SPT 转变温度

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为何俄乌冲突中的阴谋论叙事层出不穷?

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当代亚太 2024年第2期 84-106,159页

作者：梁怀新对外经济贸易大学国际关系学院对外经济贸易大学国家安全计算实验室

战略叙事历来是主权国家关注的焦点。一般而言,一国为实现既定目标,其战略叙事应以充足事实为依据,但我们也会发现,国际关系尤其是大国关系中还存在另一种以阴谋论为核心的战略叙事方式,此类叙事方式曾在美苏冷战时期大肆盛行。当前,大... 详细信息

战略叙事历来是主权国家关注的焦点。一般而言,一国为实现既定目标,其战略叙事应以充足事实为依据,但我们也会发现,国际关系尤其是大国关系中还存在另一种以阴谋论为核心的战略叙事方式,此类叙事方式曾在美苏冷战时期大肆盛行。当前,大国竞争背景下,阴谋论叙事死灰复燃,特别是俄乌冲突中,阴谋论叙事大量出现,不仅使俄乌冲突在“信息迷雾”中绵延至今,更动摇国际信任机制,加剧了国际社会对立。阴谋论叙事的作用机理体现为何?为何俄乌冲突中的阴谋论叙事层出不穷?现阶段学界对这一现象的专门研究还相对有限,为此,文章尝试从叙事场景和角色等角度进行了梳理,认为阴谋论叙事是一种独特的战略叙事策略,指重大国际突发事件发生后,“揭露者”运用阴谋论这一不合理的要素组织方式,通过影响“观众”的主观认知来实现打击“坏人”的既定目标,阴谋论叙事之所以会在特定历史阶段大量涌现,有着多重诱因。同时,文章对俄乌冲突中的阴谋论叙事进行了案例分析,并对阴谋论叙事的战略限度及应对策略提出了建议。该研究有助于加强学界对阴谋论叙事现象的理解,也对中国有效应对阴谋论叙事具有现实参考意义。

关键词：阴谋论战略叙事社会心理大国竞争俄乌冲突

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Orthorhombic-hexagonal Phase Transition in Na0.5CoO2 Crystals:A Raman Scattering Study

Orthorhombic-hexagonal Phase Transition in Na0.5CoO2 Crystal...

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第十三届全国光散射学术会议

作者： Liu Yulong Ding Shuo yang huaixin Shi Yougguo Wang Nanling Liu Jianqi Institute of Physics Chinese Academy of Sciences

Layered deintercalatable alkali metal oxides,such as LiCoO and NaCoO,have been a subject of an intense research activity in the past years owing to their potential technological applications as a battery electrodes and thermoelectric[1].Recently,further instabilities have been observed for non-hydrated(y=0)samples that show in transport,magnetic susceptibility and electron diffraction[2].Such effects could

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上海国际电影节“一带一路”电影周展映机制的有效性及其意义生产

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当代电影 2024年第1期 66-71页

作者：程波丁怀鑫上海大学上海电影学院不详

上海国际电影节“一带一路”电影周的设立与发展,受到新时代国际环境与社会文化的支撑,其基于政策语境与电影节展规律的项目执行背后有着明显的意义生产意味。对相关政策背景和其发展轨迹进行研究,并在对展映文本案例进行梳理的基础上,... 详细信息

上海国际电影节“一带一路”电影周的设立与发展,受到新时代国际环境与社会文化的支撑,其基于政策语境与电影节展规律的项目执行背后有着明显的意义生产意味。对相关政策背景和其发展轨迹进行研究,并在对展映文本案例进行梳理的基础上,分析“一带一路”电影周展映机制的有效性,可以发现其在影像叙事上的民族化特征,也能体现其在承载国家元素、全球视野、民族内容和跨文化表达上的价值,这对我们思考如何探索并构建一套适合国际传播的话语体系具有一定的参考作用。

关键词： “一带一路” 电影周上海国际电影节展映机制有效性意义生产

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Nonlocal Effects of Low-Energy Excitations in Quantum-Spin-Liquid Candidate Cu_(3)Zn(OH)_(6)FBr

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Chinese Physics Letters 2021年第9期38卷 96-100页

作者：魏源马肖燕冯子力张永朝张璐杨槐馨戚扬孟子杨王艳成石友国李世亮 Beijing National Laboratory for Condensed Matter Physics and Institute of PhysicsChinese Academy of SciencesBeijing 100190China School of Physical Sciences University of Chinese Academy of SciencesBeijing 100190China Institute for Solid State Physics University of TokyoKashiwa 277-8581Japan yangtze River Delta Physics Research Center Co. Ltd.Liyang 213300China State Key Laboratory of Surface Physics Department of PhysicsFudan UniversityShanghai 200433China Department of Physics and HKU-UCAS Joint Institute of Theoretical and Computational Physics The University of Hong KongPokfulam RoadHong KongChina School of Materials Science and Physics China University of Mining and TechnologyXuzhou 221116China Songshan Lake Materials Laboratory Dongguan 523808China

We systematically study the low-temperature specific heats for the two-dimensional kagome antiferromagnet,Cu_(3)Zn(OH)_(6)*** specific heat exhibits a T1.7 dependence at low temperatures and a shoulder-like feature above *** construct a microscopic lattice model of Z_(2) quantum spin liquid and perform large-scale quantum Monte Carlo simulations to show that the above behaviors come from the contributions from gapped anyons and magnetic ***,we find the entropy associated with the shoulder decreases quickly with grain size d,although the system is paramagnetic to the lowest *** this can be simply explained by a core-shell picture in that the contribution from the interior state disappears near the surface,the 5.9-nm shell width precludes any trivial *** a large length scale signifies the coherence length of the nonlocality of the quantum entangled excitations in quantum spin liquid candidate,similar to Pippard’s coherence length in *** approach therefore offers a new experimental probe of the intangible quantum state of matter with topological order.

关键词： temperature quantum trivial

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A density-wave-like transition in the polycrystalline V_(3)Sb_(2) sample with bilayer kagome lattice

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Chinese Physics B 2022年第1期31卷 15-23页

作者：王宁宁顾雨豪 M.A.McGuire Jiaqiang Yan 石利粉崔琦陈科宇王郁欣张华杨槐馨董晓莉蒋坤胡江平王铂森孙建平程金光 Beijing National Laboratory for Condensed Matter Physics and Institute of Physics Chinese Academy of SciencesBeijing 100190China School of Physical Sciences University of Chinese Academy of SciencesBeijing 100190China Materials Science and Technology Division Oak Ridge National LaboratoryOak RidgeTennessee 37831USA

Recently,transition-metal-based kagome metals have aroused much research interest as a novel platform to explore exotic topological quantum *** we report on the synthesis,structure,and physical properties of a bilayer kagome lattice compound V_(3)Sb_(2).The polycrystalline V_(3)Sb_(2) samples were synthesized by conventional solid-state-reaction method in a sealed quartz tube at temperatures below 850℃.Measurements of magnetic susceptibility and resistivity revealed consistently a density-wave-like transition at Tdw≈160 K with a large thermal hysteresis,even though some sample-dependent behaviors were observed presumably due to the different preparation *** cooling through Tdw,no strong anomaly in lattice parameters and no indication of symmetry lowering were detected in powder x-ray diffraction *** transition can be suppressed completely by applying hydrostatic pressures of about 1.8 GPa,around which no sign of superconductivity was observed down to 1.5 ***-heat measurements revealed a relatively large Sommerfeld coefficientγ=18.5 mJ·mol^(-1)·K^(-2),confirming the metallic ground state with moderate electronic *** functional theory calculations indicate that V_(3)Sb_(2) shows a non-trivial topological crystalline ***,our study makes V_(3)Sb_(2) a new candidate of metallic kagome compound to study the interplay between density-wave-order,nontrivial band topology,and possible superconductivity.

关键词： V_(3)Sb_(2) kagome metal charge density wave pressure effect

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Ultrafast electron microscopy in material science

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Chinese Physics B 2018年第7期27卷 32-43页

作者：杨槐馨孙帅帅张明李中文李子安徐鹏田焕芳李建奇 Beijing National Laboratory for Condensed Matter Physics Institute of Physics Chinese Academy of Sciences Collaborative Innovation Center of Quantum Matter

Recent advances in the ultrafast transmission electron microscope （UTEM）, with combined spatial and temporal resolutions, have made it possible to directly visualize the atomic, electronic, and magnetic structural dynamics of materials. In this review, we highlight the recent progress of UTEM techniques and their applications to a variety of material systems. It is emphasized that numerous significant ultrafast dynamic issues in material science can be solved by the integration of the pump-probe approach with the well-developed conventional transmission electron microscopy （TEM） techniques. For instance, UTEM diffraction experiments can be performed to investigate photoinduced atomic-scale dynamics, including the chemical reactions, non-equilibrium phase transition/melting, and lattice phonon coupling. UTEM imaging methods are invaluable for studying, in real space, the elementary processes of structural and morphological changes, as well as magnetic-domain evolution in the Lorentz TEM mode, at a high magnification. UTEM electron energy-loss spectroscopic techniques allow the examination of the ultrafast valence states and electronic structure dynamics, while photoinduced near-field electron microscopy extends the capability of the UTEM to the regime of electromagnetic-field imaging with a high real space resolution.

关键词： ultrafast transmission electron microscope (UTEM) structural dynamics electron diffraction ul-trafast imaging

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Superconductivity in an intermetallic oxide Hf_(3)Pt_(4)Ge_(2)O

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Chinese Physics B 2021年第7期30卷 507-514页

作者：徐程超王鸿田焕芳石友国李子安肖睿娟施洪龙杨槐馨李建奇 Beijing National Laboratory for Condensed Matter Physics Institute of PhysicsChinese Academy of SciencesBeijing 100190China School of Physical Sciences University of Chinese Academy of SciencesBeijing 100049China School of Science Minzu UniversityBeijing 100081China

Discovery of a new superconductor with distinct crystal structure and chemistry often provides great opportunity for further expanding superconductor material base,and also leads to better understanding of superconductivity ***,we report the discovery of superconductivity in a new intermetallic oxide Hf_(3)Pt_Ge_(2)O synthesized through a solid-state *** Hf_(3)Pt_Ge_(2)O crystallizes in a cubic structure(space group Fm-3 m)with a lattice constant of a=1.241 nm,whose stoichiometry and atomic structure are determined by electron microscopy and x-ray diffraction *** superconductivity at 4.1 K and type-II superconducting nature are evidenced by the electrical resistivity,magnetic susceptibility,and specific heat *** intermetallic oxide Hf_(3)Pt_Ge_(2)O system demonstrates an intriguing structural feature that foreign oxygen atoms can be accommodated in the interstitial sites of the ternary intermetallic *** also successfully synthesized a series of Hf_(3)Pt_Ge_(2)O1+δ(-0.25≤δ≤0.5),and found theδ-dependent superconducting transition temperature *** atomic structure and the electronic structure are also substantiated by first-principles *** results present an entirely new family of superconductors with distinct structural and chemical characteristics,and could attract research interest in further finding new superconductors and exploring novel physics pertaining to the 5 d-electron in these intermetallic compound systems.

关键词： superconductivity intermetallic oxide 5d-electron

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Robust Magnetism Against Pressure in Non-Superconducting Samples Prepared from Lutetium Foil and H2/N2 Gas Mixture

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Chinese Physics Letters 2023年第9期40卷 78-81页

作者：郭静蔡树王东束海云杨留响王鹏玉汪文韬田焕芳杨槐馨周亚洲赵金瑜韩金宇李建奇吴奇丁阳杨文革向涛毛河光孙力玲 Institute of Physics Chinese Academy of SciencesBeijing 100190China Center for High Pressure Science&Technology Advanced Research Beijing 100094China University of Chinese Academy of Sciences Beijing 100190China

We report the observation of a magnetic transition at the temperature about 56 K,through the high-pressure heat capacity and magnetic susceptibility measurements on the samples that have been claimed to be a nearroom-temperature superconductor[Dasenbrock-Gammon et *** 615,244(2023)].Our results show that this magnetic phase is robust against pressure up to 4.3 GPa,which covers the critical pressure of boosting the claimed superconductivity.

关键词： claimed magnetic superconductor

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