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Bulletin of the Chinese Academy of Sciences 2022年第2期36卷 106-107页

作者： luo huiqian 不详

In unconventional superconductors,the major challenge on the mechanism research is to reveal how the electrons form Cooper pairs and collectively condense to a superconducting state under both interactions from charge and spin.The ironbased superconductors are similar to those copper oxide and heavy fermion superconductors;they also exhibit strong spin fluctuations,which likely promote the superconducting pairing by acting as the bosonic“pairing glue”.Such argument is supported by a spin resonance mode with a peak energy universally linear scaling with Tc.However,it is still unknown whether in such multi-orbital systems the spin system may have some preferred fluctuating directions that is coupled to the orbital degree of freedom.

关键词： superconductors orbital collective

Planckian dissipation and non-Ginzburg-Landau type upper critical field in Bi2201

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Science China(Physics,Mechanics & Astronomy) 2023年第3期66卷 147-155页

作者： Qihao Zang Zhengyan Zhu Zuyu Xu Shichao Qi Haoran Ji Yiwen Li Jian Wang Huiqian Luo Hua-Bing Wang Hai-Hu Wen National Laboratory of Solid State Microstructures and Department of Physics Collaborative Innovation Center of Advanced MicrostructuresNanjing UniversityNanjing 210093China Research Institute of Superconductor Electronics Nanjing UniversityNanjing 210093China International Center for Quantum Materials School of PhysicsPeking UniversityBeijing 100871China Institute of Physics Chinese Academy of SciencesBeijing 100190China Purple Mountain Laboratories Nanjing 211111China

Resistivity and Hall effect measurements have been carried out on a micro-fabricated bridge of Bi2201 single crystal at low temperatures down to 0.4 K under high magnetic fields.When superconductivity is crashed by a high magnetic field,the recovered "normal state" resistivity still shows a linear temperature dependence in the low temperature region.Combining with the effective mass and the charge carrier density,we get a linear scattering rate 1/τ=αkBT/h with 0.77 <α <1.16,which gives a strong evidence of the Planckian dissipation.Furthermore,our results reveal a new type of temperature dependence of the upper critical field,H_(c2)(T)=H*■,which is totally different from the expectation of the Ginzburg-Landau theory,and suggests the existence of uncondensed Cooper pairs above H_(c2)(T) line.

关键词： cuprates scattering rate Planckian dessipation anomalous upper critical field

Stability of superconducting Nd_(0.8)Sr_(0.2)NiO_(2) thin films

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Science China(Physics,Mechanics & Astronomy) 2022年第6期65卷 123-130页

作者： Xiang Ding Shengchun Shen Huaqian Leng Minghui Xu Yan Zhao Junrui Zhao Xuelei Sui Xiaoqiang Wu Haiyan Xiao Xiaotao Zu Bing Huang Huiqian Luo Pu Yu Liang Qiao School of Physics University of Electronic Science and Technology of ChinaChengdu 610054China Department of Physics Tsinghua UniversityBeijing 100084China Beijing Computational Science Research Center Beijing 100193China School of Mechanical Engineering Chengdu UniversityChengdu 610106China Beijing National Laboratory for Condensed Matter Physics Institute of PhysicsChinese Academy of SciencesBeijing 100190China Songshan Lake Materials Laboratory Dongguan 523808China

The discovery of superconducting states in the nickelate thin film with infinite-layer structure has paved a new way for studying unconventional superconductivity.So far,research in this field is still very limited due to difficulties in sample preparation.Here we report the successful preparation of the superconducting state of Nd_(0.8)Sr_(0.2)NiO_(2)thin film(T_(c)=8.0-11.1 K)and study the stability of such films in the ambient environment,water,and under electrochemical conditions.Our work demonstrates that the superconducting state of Nd_(0.8)Sr_(0.2)NiO_(2)is remarkably stable,which can last for at least 47-day continuous exposure to air at 20°C and 35%relative humidity.We also show that the superconductivity disappears after being immersed in de-ionized water at room temperature for 5 h.Surprisingly,it can also survive under ionic liquid gating conditions with an applied voltage of about 4 V,which is even more stable than conventional perovskite complex oxides.

关键词： nickelate superconductor stability ionic liquid gating

Anisotropic magnetoelastic response in the magnetic Weyl semimetal Co_(3)Sn_(2)S_(2)

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Science China(Physics,Mechanics & Astronomy) 2021年第5期64卷 82-90页

作者： Chang Liu ChangJiang Yi XingYu Wang JianLei Shen Tao Xie Lin Yang Tom Fenne Uwe Stuhr ShiLiang Li HongMing Weng YouGuo Shi EnKe Liu Huiqian Luo Beijing National Laboratory for Condensed Matter Physics Institute of PhysiesChinese Academy of SciencesBeijing 100190China School of Physical Sciences University of Chinese Academy of SciencesBejing 100190China Laboratory for Neutron Scattering and Imaging Paul Scherrer InstituteVlligen CH-5232Switzerland Songshan Lake Materials Laboratory Dongguan 523808China SCAS Centre for Excelence in Topological Quantum Computation Bejing 100190China Physical Science Laboratory Huairou National Comprehensive Science CenterBeijing 101400China

Co_(3)Sn_(2)S_(2) is a recently identified magnetic Weyl semimetal in Shandite compounds. Upon cooling, Co_(3)Sn_(2)S_(2) undergoes a ferromagnetic transition with c-axis polarized moments(0.3 μ_(B)/Co) around T_(C)= 175 K, followed by another magnetic anomaly around T_(A)≈ 140 K. A large intrinsic anomalous Hall effect is observed in the magnetic state below TC with a maximum of anomalous Hall angle near T_(A). Here, we report an elastic neutron scattering on the crystalline lattice of Co_(3)Sn_(2)S_(2) in a magnetic field up to 10 T. A strongly anisotropic magnetoelastic response is observed, while only a slight enhancement of the Bragg peaks is observed when B//c. The in-plane magnetic field(B//ab) dramatically suppresses the Bragg peak intensity probably by tilting the moments and lattice toward the external field direction. The in-plane magnetoelastic response commences from T_(C), and as it is further strengthened below T_(A), it becomes nonmonotonic against the field between T_(A) and T_(C) because of the competition from another in-plane magnetic order. These results suggest that a magnetic field can be employed to tune the Co_(3)Sn_(2)S_(2) lattice and its related topological states.

关键词： Weyl semimetal magneto-elastic coupling topological materials elastic neutron scattering ferromagnetism

Surface morphology and electronic structure in stoichiometric superconductor CaKFe_(4)As_(4) robed by scanning tunneling microscopy/spectroscopy

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Science China(Physics,Mechanics & Astronomy) 2021年第12期64卷 144-150页

作者： Xiaodong Yu Zhongxu Wei Zhanyi Zhao Tao Xie Chang Liu Ge He Qihong Chen Lei Shan Huiqian Luo Qing Huan Jie Yuan Kui Jin 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 Walther Meissner Institute Bayerische Akademie der WissenschaftenGarching 85748Germany Key Laboratory of Structure and Functional Regulation of Hybrid Materials of Ministry of Education Institutes of Physical Science and Information TechnologyAnhui UniversityHefei 230601China Songshan Lake Materials Laboratory Dongguan 523808China

CaKFe_(4)As_(4) is a new-type superconductor with a relatively high transition temperature of 35 K among stoichiometric iron-based superconductors. Based on scanning tunneling microscopy/spectroscopy, the surface morphology and electronic structure of CaKFe_(4)As_(4) single crystal were systematically investigated. The cleaved CaKFe_(4)As_(4) showed various morphologies, such as atomically resolved 1×1, 1×2, and √2×√2 lattices. By analyzing the geometrical correlations of these morphologies, the 1×1 and 1×2 lattices were identified as the original and reconstructed As layers, respectively, whereas the √2×√2 lattice was distinguished as the reconstructed alkaline-earth-metal or alkali-metal layer. The superconducting energy gap of 7.3 me V and bosonic mode of 12.7 me V were resolved in the scanning tunneling spectra. In addition, the superconducting energy gaps measured on different terminations were identical and consistent with the values obtained by bulk-sensitive techniques, indicating that the electronic structures of CaKFe_(4)As_(4) were insensitive to the surface reconstructions. Our study clarifies the relationships between complex surface reconstructions and surface terminations and preliminarily presents that there is no obvious effect of surface reconstructions on electronic states.

关键词： CaKFe_(4)As_(4) scanning tunneling microscopy surface reconstructions superconductivity

Spin excitations and spin wave gap in the ferromagnetic Weyl semimetal Co3Sn2S2

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Science China(Physics,Mechanics & Astronomy) 2021年第1期64卷 3-9页

作者： Chang Liu JianLei Shen JiaCheng Gao ChangJiang Yi Di Liu Tao Xie Lin Yang Sergey Danilkin GuoChu Deng WenHong Wang ShiLiang Li YouGuo Shi HongMing Weng EnKe Liu Huiqian Luo Beijing National Laboratory for Condensed Matter Physics Institute of PhysicsChinese Academy of SciencesBeijing100190China School of Physical Sciences University of Chinese Academy of SciencesBeijing100190China Australian Centre for Neutron Scattering Australian Nuclear Science and Technology OrganizationLucas HeightsNSW2234Australia Songshan Lake Materials Laboratory Dongguan523808China Physical Science Laboratory Huairou National Comprehensive Science CenterBeijing101407China

We report a comprehensive neutron scattering study on the spin excitations in the magnetic Weyl semimetal Co3Sn2S2 with a quasi-two-dimensional structure.Both in-plane and out-of-plane dispersions of the spin waves were revealed in the ferromagnetic state.Similarly,dispersive but damped spin excitations were found in the paramagnetic state.The effective exchange interactions were estimated using a semi-classical Heisenberg model to consistently reproduce the experimental TCand spin stiffness.However,a full spin wave gap below Eg=2.3 meV was observed at T=4 K.This value was considerably larger than the estimated magnetic anisotropy energy(~0.6 meV),and its temperature dependence indicated a significant contribution from the Weyl fermions.These results suggest that Co3Sn2S2 is a three-dimensional correlated system with a large spin stiffness,and the low-energy spin dynamics can interplay with the topological electron states.

关键词： magnetic Weyl semimetal topological materials spin excitations neutron scattering

Stability of superconducting Nd;Sr;NiO;thin films

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Science China(Physics,Mechanics & Astronomy) 2022年

作者： Xiang Ding Shengchun Shen Huaqian Leng Minghui Xu Yan Zhao Junrui Zhao Xuelei Sui Xiaoqiang Wu Haiyan Xiao Xiaotao Zu Bing Huang Huiqian Luo Pu Yu Liang Qiao School of Physics University of Electronic Science and Technology of China Department of Physics Tsinghua University Beijing Computational Science Research Center School of Mechanical Engineering Chengdu University Beijing National Laboratory for Condensed Matter Physics Institute of Physics Chinese Academy of Sciences Songshan Lake Materials Laboratory

The discovery of superconducting states in the nickelate thin film with infinite-layer structure has paved a new way for studying unconventional superconductivity. So far, research in this field is still very limited due to difficulties in sample preparation. Here we report the successful preparation of the superconducting state of Nd;Sr;NiO;thin film （T;= 8.0-11.1 K） and study the stability of such films in the ambient environment, water, and under electrochemical conditions. Our work demonstrates that the superconducting state of Nd;Sr;NiO;is remarkably stable, which can last for at least 47-day continuous exposure to air at 20°C and 35% relative humidity. We also show that the superconductivity disappears after being immersed in de-ionized water at room temperature for 5 h. Surprisingly, it can also survive under ionic liquid gating conditions with an applied voltage of about 4 V,which is even more stable than conventional perovskite complex oxides.

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超导与诺贝尔奖

自然杂志 2017年第6期39卷 427-436页

作者：罗会仟中国科学院物理研究所北京100190

超导作为凝聚态物理前沿领域之一,百余年来长盛不衰,相关研究促成了至少5次诺贝尔物理学奖,获奖人数至少10人。随着超导研究的不断发展,中国科学家在其中的贡献也越来越重要,特别是在铁基超导领域已经引领世界前沿。本文将从各位诺奖得... 详细信息

超导作为凝聚态物理前沿领域之一,百余年来长盛不衰,相关研究促成了至少5次诺贝尔物理学奖,获奖人数至少10人。随着超导研究的不断发展,中国科学家在其中的贡献也越来越重要,特别是在铁基超导领域已经引领世界前沿。本文将从各位诺奖得主的经历,主要介绍超导研究及其重要性,并探讨未来超导领域可能产生诺奖之处。

关键词：超导诺贝尔奖铁基超导凝聚态物理

Low temperature specific heat in BaFe_(1.9)Ni_(0.1)As_2 single crystals

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Science China(Physics,Mechanics & Astronomy) 2010年第7期53卷 1221-1224页

作者： ZENG Bin MU Gang luo huiqian WEN HaiHu National Laboratory for Superconductivity Institute of PhysicsChinese Academy of SciencesBeijing 100190China Beijing National Laboratory for Condensed Matter Physics Institute of PhysicsChinese Academy of SciencesBeijing 100190China

Low-temperature specific heat was measured on the BaFe1.9Ni0.1As2 single crystals with critical transition temperature Tc = 20.1 K.A clear specific heat jump with the value ΔC/T|Tc ≈ 23 mJ/mol K2 was observed.In addition,a roughly linear magnetic field dependence of the electronic specific heat coefficient Δγ(H) was found in the zero-temperature limit,suggesting that at least one Fermi pocket,probably the hole derivative one,was fully gapped with a small anisotropy in the present sample.A slight curvature of the curve Δγ(H) may suggest a complex gap structure(anisotropic gap or nodes) at other Fermi surfaces.

关键词： specific heat BaFe1.9Ni0.1As2 nodeless gap

Characterization of nanometer tungsten powders

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Rare Metals 2008年第2期27卷 197-200页

作者： LI huiqian LIN Tao SHAO Huiping WU Chengyi GUO Zhimeng luo Ji School of Materials Science and Engineering University of Science and Technology Beijing Beijing 100083 China

Three types of tungsten powders were prepared by hydrogen reduction of three precursor powders at low temperature, which were used as samples, and were then characterized by Brunauer-Emmer-Teller （BET） method, scanning electron microscopy （SEM）, transmission electronic microscopy （TEM）, small angle X-ray scattering （SAXS）, and field-emission scanning election microscopy （FESEM） respectively. The results showed that although BET and SEM could not characterize the particle size of nanometer powders, they were important means of assistance to exclude non-nanometer powders. TEM and FESEM could directly measure the particle size of nanometer powders, but this needs a lot of time, to count the average particle size and particle size distribution. SAXS could not describe the state of agglomeration. By the combination of FESEM and SAXS, the particle size, particle size distribution, and particle shape of nanometer powders could be precisely characterized.

关键词： nanometer tungsten powder particle size particle size distribution