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Chinese Physics B 2024年第5期33卷 608-615页

作者：宋伟宾席国强潘昭刘锦叶旭斌刘哲宏王潇单鹏飞张林兴鲁年鹏樊龙龙秦晓梅龙有文 Department of Physics Shanghai Normal UniversityShanghai 200234China Beijing National Laboratory for condensed matter Physics Institute of PhysicsChinese Academy of SciencesBeijing 100190China Institute for Advanced Materials Technology University of Science and Technology BeijingBeijing 100083China Songshan Lake Materials Laboratory Dongguan 523808China Institute of High Energy Physics Chinese Academy of SciencesBeijing 100049China

Bi-based perovskite ferroelectric thin films have wide applications in electronic devices due to their excellent ferroelectric *** Bi-based perovskite thin films Bi(Cu_(1/2)Ti_(1/2))O_(3)–PbTiO_(3)(BCT–PT) are deposited on Pt(111)/Ti/SiO_(2)/Si substrates in the present study by the traditional sol–gel *** structures and related ferroelectric and fatigue characteristics are studied *** BCT–PT thin films exhibit good crystallization within the phase-pure perovskite structure,besides,they have a predominant(100) orientation together with a dense and homogeneous *** remnant polarization(2P_(r)) values at 30 μC/cm^(2) and 16 μC/cm^(2) are observed in 0.1BCT–0.9PT and 0.2BCT–0.8PT thin films,*** intriguingly,although the polarization values are not so high,0.2BCT–0.8PT thin films show outstanding polarization fatigue properties,with a high switchable polarization of 93.6% of the starting values after 10^(8) cycles,indicating promising applications in ferroelectric memories.

关键词： ferroelectric thin films perovskite PbTiO_(3)-BiMeO_(3)

Experimental determination of the Young’s modulus of individual single-walled carbon nanotubes with single chirality

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Nano Research 2024年第8期17卷 7522-7532页

作者： Jianlin Sun Xiao Zhang Yanchun Wang Mingming Li Xiaojun Wei Huaping Liu Weiya Zhou Beijing National Laboratory for condensed matter Physics and Institute of PhysicsChinese Academy of SciencesBeijing 100190China School of Physical Sciences and College of Materials Science and Optoelectronic Technology University of Chinese Academy of SciencesBeijing 100049China Songshan Lake Materials Laboratory Dongguan 523808China Beijing Key Laboratory for Advanced Functional Materials and Structure Research Beijing 100190China

One-dimensional carbon nanotube(CNT)exhibits excellent mechanical properties and is considered to be an ideal candidate material for the space ***,subtle changes in its chirality strongly affect its physical and chemical properties,including mechanical properties(such as Young's modulus,YM).Theoretical studies reveal that the YMs of perfect single-walled carbon nanotubes(SWCNTs)are in the order of TPa and related to their ***,due to the lack of SWCNTs samples with well-defined structures and the difficulties in mechanical tests on individual SWCNTs,the theoretical correlations between YM and structure of SWCNTs have not been verified and are still in debate,which directly influences the practical utilization of the excellent mechanical properties of *** this work,we have developed an experimental method to measure the YM of an individual micrometer-scale suspended CNT by atomic force microscopy.A distinct regularity is found between the YM and chirality(i.e.,chiral angle and diameter)of SWCNT in the experiment for the first *** comparing the YMs of SWCNTs with similar diameters and different chiral angles,it manifests that the SWCNT with a near zigzag configuration has a larger *** finding suggests that the effect of SWCNT’s structures on the YMs cannot be *** developed method of measuring YMs of SWCNTs will be valuable for further experimental research on the inherent physical and chemical properties of SWCNTs.

关键词： Young's modulus single-walled carbon nanotubes single chirality atomic force microscopy

Classification of high-ordered topological nodes towards Moiré flat bands in twisted bilayers

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Science China(Physics,Mechanics & Astronomy) 2024年第9期Mechanics & Astronomy) .卷 137-151页

作者： Fan Cui Congcong Le Qiang Zhang Xianxin Wu Jiangping Hu Ching-Kai Chiu Beijing National Laboratory for condensed matter Physics Institute of PhysicsChinese Academy of Sciences School of Physical Sciences University of Chinese Academy of Sciences RIKEN Interdisciplinary Theoretical and Mathematical Sciences(iTHEMS) CAS Key Laboratory of Theoretical Physics Institute of Theoretical PhysicsChinese Academy of Sciences Kavli Institute of Theoretical Sciences University of Chinese Academy of Sciences New Cornerstone Science Laboratory

At magic twisted angles, Dirac cones in twisted bilayer graphene(TBG) can evolve into flat bands, serving as a critical playground for the study of strongly correlated physics. When chiral symmetry is introduced, rigorous mathematical proof confirms that the flat bands are locked at zero energy in the entire Moiré Brillouin zone(BZ). Yet, TBG is not the sole platform that exhibits this absolute band flatness. Central to this flatness phenomenon are topological nodes and their specific locations in the BZ. In this study, considering twisted bilayer systems that preserve chiral symmetry, we classify various ordered topological nodes in base layers and all possible node locations across different BZs. Specifically, we constrain the node locations to rotational centers,such as Γ and M points, to ensure the interlayer coupling retains equal strength in all directions. Using this classification as a foundation, we systematically identify the conditions under which Moiré flat bands emerge. Additionally, through the extension of holomorphic functions, we provide proof that flat bands are locked at zero energy, shedding light on the origin of the band flatness. Remarkably, beyond Dirac cones, numerous twisted bilayer nodal platforms can host flat bands with a degeneracy number of more than two, such as four-fold, six-fold, and eight-fold. This multiplicity of degeneracy in flat bands might unveil more complex and enriched correlation physics.

关键词： twisted bilayer systems high-ordered topological nodes Morié flat bands high degeneracy

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Influence of exchange bias on spin torque ferromagnetic resonance for quantification of spin–orbit torque efficiency

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Chinese Physics B 2024年第5期33卷 688-694页

作者：赵乾张腾飞何斌李子木张森富于国强王建波刘青芳魏晋武 Key Laboratory for Magnetism and Magnetic Materials of the Ministry of Education Lanzhou UniversityLanzhou 730000China Beijing National Laboratory for condensed matter Physics Institute of PhysicsChinese Academy of SciencesBeijing 100190China Center of Materials Science and Optoelectronics Engineering University of Chinese Academy of SciencesBeijing 100049China Key Laboratory of Special Functional Materials and Structural Design Ministry of EducationLanzhou UniversityLanzhou 730000China

Antiferromagnet(AFM)/ferromagnet(FM)heterostructure is a popular system for studying the spin–orbit torque(SOT)of ***,the interfacial exchange bias field induces that the magnetization in FM layer is noncollinear to the external magnetic field,namely the magnetic moment drag effect,which further influences the characteristic of SOT *** this work,we study the SOT efficiencies of IrMn/NiFe bilayers with strong interfacial exchange bias by using spin-torque ferromagnetic resonance(ST-FMR)method.A full analysis on the AFM/FM systems with exchange bias is performed,and the angular dependence of magnetization on external magnetic field is determined through the minimum rule of free *** ST-FMR results can be well fitted by this *** obtained the relative accurate SOT efficiencyξ_(DL)=0.058 for the IrMn *** work provides a useful method to analyze the angular dependence of ST-FMR results and facilitates the accurate measurement of SOT efficiency for the AFM/FM heterostructures with strong exchange bias.

关键词： antiferromagnets spin-orbit torque exchange bias spin torque ferromagnetic resonance

High-performance terahertz modulators induced by substrate field in Te-based all-2D heterojunctions

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Light(Science & Applications) 2024年第3期13卷 577-586页

作者： Pujing Zhang Qihang Liang Qingli Zhou Jinyu Chen Menglei Li Yuwang Deng Wanlin Liang Liangliang Zhang Qinghua Zhang Lin Gu Chen Ge Kui-juan Jin Cunlin Zhang Guozhen Yang Department of Physics Key Laboratory of Terahertz OptoelectronicsMinistry of Educationand Beijing Advanced Innovation Center for Imaging Theory and TechnologyCapital Normal UniversityBeijing 100048China Beijing National Laboratory for condensed matter Physics Institute of PhysicsChinese Academy of SciencesBeijing 100190China Department of Materials Science and Engineering Beijing National Center for Electron Microscopy and Laboratory of Advanced MaterialsTsinghua UniversityBeijing 100084China

High-performance active terahertz modulators as the indispensable core components are of great importance for the next generation communication ***,they currently suffer from the tradeoff between modulation depth and ***,we introduce two-dimensional(2D)tellurium(Te)nanofilms with the unique structure as a new class of optically controlled terahertz modulators and demonstrate their integrated heterojunctions can successfully improve the device performances to the optimal and applicable levels among the existing all-2D broadband *** photoresponse measurements confirm the significant impact of the stacking *** first clarify the direction of the substrate-induced electric field through first-principles calculations and uncover the unusual interaction mechanism in the photoexcited carrier dynamics associated with the charge transfer and interlayer exciton *** advances the fundamental and applicative research of Te nanomaterials in high-performance terahertz optoelectronics.

关键词： performance field terahertz

Ultrathin Limit on the Anisotropic Superconductivity of Single-Layered Cuprate Films

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Chinese Physics Letters 2024年第2期41卷 94-101页

作者：冉峰陈潘李丁艺熊沛雨樊子鑫凌浩铭梁艳张坚地 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

Exploring dimensionality effects on cuprates is important for understanding the nature of high-temperature *** atomically layer-by-layer growth with oxide molecular beam epitaxy,we demonstrate that La_(2−x)Sr_(x)CuO_(4)(x=0.15)thin films remain superconducting down to 2 unit cells of thickness but quickly reach the maximum superconducting transition temperature at and above 4 unit *** fitting the critical magnetic field(μ0H_(c2)),we show that the anisotropy of the film’s superconductivity increases with decreasing film thickness,indicating that the superconductivity of the film gradually evolves from weak three-to two-dimensional *** results are helpful to gain more insight into the nature of high-temperature superconductivity with dimensionality.

关键词： dimensionality film evolve

Spontaneous unidirectional rotation of a symmetric gear driven by spherical active particles

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National Science Open 2024年第4期3卷 41-53页

作者： Chao Wang Wenchao Lian Huishu Li Wende Tian Kang Chen Center for Soft condensed matter Physics & Interdisciplinary Research School of Physical Science and Technology Soochow University School of Physics and Electronic Engineering Linyi University

Time reversal asymmetry and spatial anisotropy are considered two prerequisites for Brownian ratchet. An intriguing realization can be achieved by placing an asymmetric gear in the suspension of motile rod-like bacteria. Usually,alignment interactions caused by anisotropic collisions or hydrodynamics would boost the ratchet effect. Here, we are concerned with a perfectly isotropic system, i.e., symmetric gear immersed in a bath of spherical active Brownian particles. We find that, under certain conditions, kinetic symmetry-breaking arises spontaneously, i.e., the symmetric gear keeps rotating in one direction. Unexpectedly, such ratchet phenomenon does not rely on the direct many-particle interactions and moreover the introduction of alignment interaction would counterintuitively prevent it from happening! Further investigation reveals that such spontaneous symmetry-breaking phenomenon shares similarities with the equilibrium phase transition of the Ising *** results provide new insights and enhance our understanding of the fundamental aspects of active ratchet phenomena.

关键词： ratchet effect spontaneous symmetry breaking active brownian particles ising model hysteresis

Co-doped BaFe_(2)As_(2) Josephson junction fabricated with a focused helium ion beam

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Chinese Physics B 2024年第4期33卷 181-186页

作者：陈紫雯张焱马平徐中堂李宇龙王越路建明马衍伟甘子钊 Applied Superconductivity Research Center Peking UniversityBeijing 100871China State Key Laboratory for Artificial Microstructure and Mesoscopic Physics Peking UniversityBeijing 100871China Institute of condensed matter Physics School of PhysicsPeking UniversityBeijing 100871China Yangtze Delta Institute of Optoelectronics Peking UniversityBeijing 100871China Key Laboratory of Applied Superconductivity Institute of Electrical EngineeringChinese Academy of SciencesBeijing 100190China

Josephson junction plays a key role not only in studying the basic physics of unconventional iron-based superconductors but also in realizing practical application of thin-film based devices,therefore the preparation of high-quality iron pnictide Josephson junctions is of great *** this work,we have successfully fabricated Josephson junctions from Co-doped BaFe_(2)As_(2)thin films using a direct junction fabrication technique which utilizes high energy focused helium ion beam(FHIB).The electrical transport properties were investigated for junctions fabricated with various He^(+)irradiation *** junctions show sharp superconducting transition around 24 K with a narrow transition width of 2.5 K,and a dose correlated foot-structure resistance which corresponds to the effective tuning of junction properties by He^(+)*** J_c suppression by more than two orders of magnitude can be achieved by increasing the He^(+)irradiation dose,which is advantageous for the realization of low noise ion pnictide thin film *** Shapiro steps are observed under 10 GHz microwave *** above results demonstrate the successful fabrication of high quality and controllable Co-doped BaFe_(2)As_(2)Josephson junction with high reproducibility using the FHIB technique,laying the foundation for future investigating the mechanism of iron-based superconductors,and also the further implementation in various superconducting electronic devices.

关键词： focused helium ion beam Co doped BaFe_(2)As_(2) Josephson junction

DSAS:A new macromolecular substructure solution program based on the modified phase-retrieval algorithm

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Chinese Physics B 2024年第5期33卷 125-132页

作者：付兴科谭振希耿直刘茜丁玮 Beijing National Laboratory for condensed matter Physics Institute of PhysicsChinese Academy of SciencesBeijing 100190China Beijing Yunlu Technology Co. Ltd.Beijing 100161China Beijing Synchrotron Radiation Facility Institute of High Energy PhysicsChinese Academy of SciencesBeijing 100049China School of Physical Sciences University of Chinese Academy of SciencesBeijing 100049China Songshan Lake Materials Laboratory Dongguan 523808China

Considering the pivotal role of single-wavelength anomalous diffraction(SAD) in macromolecular crystallography,our objective was to introduce DSAS,a novel program designed for efficient anomalous scattering substructure *** stands out with its core components:a modified phase-retrieval algorithm and automated parameter *** software boasts an intuitive graphical user interface(GUI),facilitating seamless input of essential data and real-time *** testing on DSAS has involved diverse datasets,encompassing proteins,nucleic acids,and various anomalous scatters such as sulfur(S),selenium(Se),metals,and *** results confirm DSAS’s exceptional performance in accurately determining heavy atom positions,making it a highly effective tool in the field.

关键词： DSAS single-wavelength anomalous diffraction automated parameters settings phase-retrieval algorithm substructure determination

Purification of copper foils driven by single crystallization

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Chinese Physics B 2024年第2期33卷 506-511页

作者：寇金宗赵孟泽李兴光何梦林杨方友刘科海成庆秋任云龙刘灿付莹吴慕鸿刘开辉王恩哥 Songshan Lake Materials Laboratory Dongguan 523808China Beijing National Laboratory for condensed matter Physics Institute of PhysicsChinese Academy of SciencesBeijing 100190China Guangdong Provincial Key Laboratory of Quantum Engineering and Quantum Materials School of PhysicsSouth China Normal UniversityGuangzhou 510006China Guangdong–Hong Kong Joint Laboratory of Quantum matter Frontier Research Institute for PhysicsSouth China Normal UniversityGuangzhou 510006China State Key Laboratory for Mesoscopic Physics Frontiers Science Center for Nano-optoelectronicsSchool of PhysicsPeking UniversityBeijing 100871China Key Laboratory of Quantum State Construction and Manipulation(Ministry of Education) Department of PhysicsRenmin University of ChinaBeijing 100872China International Center for Quantum Materials Collaborative Innovation Center of Quantum MatterPeking UniversityBeijing 100871China School of Physics Liaoning UniversityShenyang 110036China

High-purity copper(Cu) with excellent thermal and electrical conductivity, is crucial in modern technological applications, including heat exchangers, integrated circuits, and superconducting magnets. The current purification process is mainly based on the zone/electrolytic refining or anion exchange, however, which excessively relies on specific integrated equipment with ultra-high vacuum or chemical solution environment, and is also bothered by external contaminants and energy consumption. Here we report a simple approach to purify the Cu foils from 99.9%(3N) to 99.99%(4N) by a temperature-gradient thermal annealing technique, accompanied by the kinetic evolution of single crystallization of *** success of purification mainly relies on(i) the segregation of elements with low effective distribution coefficient driven by grain-boundary movements and(ii) the high-temperature evaporation of elements with high saturated vapor *** purified Cu foils display higher flexibility(elongation of 70%) and electrical conductivity(104% IACS) than that of the original commercial rolled Cu foils(elongation of 10%, electrical conductivity of ~ 100% IACS). Our results provide an effective strategy to optimize the as-produced metal medium, and therefore will facilitate the potential applications of Cu foils in precision electronic products and high-frequency printed circuit boards.

关键词： purification copper foil thermal annealing technique single crystallization