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engineering a Spin-Orbital Magnetic Insulator by Tailoring Superlattices

Physical Review Letters 2015年第24期114卷 247209-247209页

作者： J. Matsuno K. Ihara S. Yamamura H. Wadati K. Ishii V. V. Shankar Hae-Young Kee H. Takagi RIKEN Advanced Science Institute Wako Saitama 351-0198 Japan Department of Advanced Materials Science University of Tokyo Kashiwa Chiba 277-8561 Japan Department of Applied Physics and Quantum-Phase Electronics Center (QPEC) University of Tokyo Hongo Tokyo 113-8656 Japan Institute for Solid State Physics University of Tokyo Kashiwa Chiba 277-8581 Japan SPring-8 Japan Atomic Energy Agency Sayo Hyogo 679-5148 Japan Department of Physics University of Toronto Toronto Ontario M5S 1A7 Canada Canadian Institute for Advanced Research Toronto Ontario M5G 1Z8 Canada Department of Physics University of Tokyo Hongo Tokyo 113-0033 Japan

In 5d Ir oxides with an interplay of spin-orbit coupling and electron correlations, we have tailored a spin-orbital magnetic insulator out of a semimetal SrIrO3 by tuning the structure through superlattices [(SrIrO3)m, SrTiO3] (m=1,2,3,4, and ∞). We observed the systematic decrease of the magnetic ordering temperature and the resistivity as a function of m. The transition from the semimetal to the insulator is found to be closely linked to the appearance of magnetism at m≃3. Long range magnetic ordering was realized even in the m=1 single layer superlattice, implying that the design and realization of novel electronic phases is feasible at the level of a single atomic layer in complex Ir oxides.

关键词： SPIN-orbit coupling IRIDIUM oxide ELECTRIC insulators & insulation SUPERLATTICES TEMPERATURE MAGNETISM MAGNETIC insulators

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Broadband tunable liquid crystal terahertz waveplates driven with porous graphene electrodes

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Light:science & Applications 2015年第1期4卷 e253页

作者： Wang Lei Lin Xiaowen Hu Wei Shao Guanghao Chen Peng Liang Lanju Jin Biaobing Wu Peiheng Qian Hao Lu Yinong Liang Xiao Zheng Zhigang Lu Yanqing College of Engineering and Applied Sciences Nanjing University National Laboratory of Solid State Microstructures Collaborative Innovation Center of Advanced Microstructures Nanjing 210093 Research Institute of Superconductor Electronics (RISE) School of Electronic Science and Engineering Nanjing University Nanjing 210093 College of Materials Science and Engineering Nanjing Tech University State Key Laboratory of Materials Oriented Chemical Engineering Nanjing 210009 Department of Chemistry Tsinghua University Beijing 100084

Versatile devices, especially tunable ones, for terahertz imaging, sensing and high-speed communication, are in high demand. Liquid crystal based components are perfect candidates in the optical range; however, they encounter significant challenges in the terahertz band, particularly the lack of highly transparent electrodes and the drawbacks induced by a thick cell. Here, a strategy to overcome all these challenges is proposed: Few-layer porous graphene is employed as an electrode with a transmittance of more than 98%. A subwavelength metal wire grid is utilized as an integrated high-efficiency electrode and polarizer. The homogeneous alignment of a high-birefringence liquid crystal is implemented on both frail electrodes via a non-contact photo-alignment technique. A tunable terahertz waveplate is thus obtained. Its polarization evolution is directly demonstrated. Furthermore, quarter-wave plates that are electrically controllable over the entire testing range are achieved by stacking two cells. The proposed solution may pave a simple and bright road toward the development of various liquid crystal terahertz apparatuses.

关键词： liquid crystal porous graphene terahertz waveplate

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Defect-induced magnetism in SiC: Interplay between ferromagnetism and paramagnetism

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Physical Review B 2015年第17期92卷 174409-174409页

作者： Yutian Wang Yu Liu Elke Wendler René Hübner Wolfgang Anwand Gang Wang Xuliang Chen Wei Tong Zhaorong Yang Frans Munnik Gregor Bukalis Xiaolong Chen Sibylle Gemming Manfred Helm Shengqiang Zhou Helmholtz-Zentrum Dresden-Rossendorf Institute of Ion Beam Physics and Materials Research Bautzner Landstr. 400 01328 Dresden Germany Technische Universität Dresden 01062 Dresden Germany Research & Development Center for Functional Crystals Beijing National Laboratory for Condensed Matter Physics Institute of Physics Chinese Academy of Sciences Beijing 100190 China Institut für Festkörperphysik Friedrich-Schiller Universität Jena 07743 Jena Germany Helmholtz-Zentrum Dresden-Rossendorf Institute of Radiation Physics Bautzner Landstr. 400 01328 Dresden Germany Key Laboratory of Materials Physics Institute of Solid State Physics Chinese Academy of Sciences Hefei 230031 People's Republic of China High Magnetic Field Laboratory Hefei Institutes of Physical Science Chinese Academy of Sciences Hefei 230031 People's Republic of China Helmholtz-Zentrum Berlin für Materialien und Energie GmbH Abteilung F-A1 Hahn-Meitner-Platz 1 14109 Berlin Germany Faculty of Science Technische Universität Chemnitz 09107 Chemnitz Germany Center for Advancing Electronics Dresden Technische Universität Dresden 01314 Dresden Germany

Defect-induced ferromagnetism has triggered a lot of investigations and controversies. The major issue is that the induced ferromagnetic signal is so weak that it can be sufficiently accounted for by trace contamination. To resolve this issue, we studied the variation of the magnetic properties of SiC after neutron irradiation with fluence covering four orders of magnitude. A large paramagnetic component has been induced and scales up with defect concentration, which can be well accounted for by uncoupled divacancies. However, the ferromagnetic contribution is still weak and only appears in the low fluence range of neutrons or after annealing treatments. First-principles calculations hint towards a mutually exclusive role of the concentration of defects: A higher defect concentration favors a larger magnetic interaction at the expense of spin polarization. Combining both experimental and first-principles calculation results, the defect-induced ferromagnetism can probably be understood as a local effect which cannot be scaled up with the volume.

关键词： SILICON carbide FERROMAGNETISM CRYSTAL defects SPIN polarization PARAMAGNETISM NEUTRON irradiation

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Anomalous elastic hardening in Fe-Co alloys at high temperature

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Physical Review B 2014年第18期89卷 184107-184107页

作者： Hualei Zhang Xiaoqing Li Stephan Schönecker Henrik Jesperson Börje Johansson Levente Vitos Center of Microstructure Science Frontier Institute of Science and Technology Xi'an Jiaotong University Xi'an 710054 China Applied Materials Physics Department of Materials Science and Engineering Royal Institute of Technology Stockholm SE-100 44 Sweden Uddeholms AB SE-683 85 Hagfors Sweden Department of Physics and Astronomy Division of Materials Theory Uppsala University Box 516 SE-75120 Uppsala Sweden Wigner Research Center for Physics Research Institute for Solid State Physics and Optics Budapest H-1525 P.O. Box 49 Hungary

The elastic moduli of Fe1−cCoc (c≤0.2) alloys are found to decrease strongly with increasing temperature, but show very weak alloying effects for both low-temperature ferromagnetic and high-temperature paramagnetic states. For temperatures slightly below and around the Curie temperature of Fe, Co addition significantly increases the elastic moduli. The variation of the tetragonal shear elastic constant upon 20% Co addition increases from a small negative value to more than 135% as the temperature rises from 0 to 1200 K. The expected elastic softening in the case of Al doping is not confirmed. Both anomalous trends are ascribed to the interplay between intrinsic chemical effects, magnetism, and temperature.

关键词： ELASTICITY PARAMAGNETIC materials HIGH temperature physics FERROMAGNETIC materials SHEAR (Mechanics) CURIE temperature

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Avian photoreceptor patterns represent a disordered hyperuniform solution to a multiscale packing problem

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Physical Review E 2014年第2期89卷 022721-022721页

作者： Yang Jiao Timothy Lau Haralampos Hatzikirou Michael Meyer-Hermann Joseph C. Corbo Salvatore Torquato Princeton Institute of the Science and Technology of Materials Princeton University Princeton New Jersey 08540 USA Materials Science and Engineering Arizona State University Tempe Arizona 85287 USA Department of Pathology and Immunology Washington University School of Medicine St. Louis Missouri 63110 USA Department of Systems Immunology Helmholtz Centre for Infection Research Braunschweig Germany Center for Advancing Electronics Dresden TU Dresden 01062 Dresden Germany Department of Chemistry Department of Physics Program in Computational and Applied Mathematics Princeton University Princeton New Jersey 08544 USA

Optimal spatial sampling of light rigorously requires that identical photoreceptors be arranged in perfectly regular arrays in two dimensions. Examples of such perfect arrays in nature include the compound eyes of insects and the nearly crystalline photoreceptor patterns of some fish and reptiles. Birds are highly visual animals with five different cone photoreceptor subtypes, yet their photoreceptor patterns are not perfectly regular. By analyzing the chicken cone photoreceptor system consisting of five different cell types using a variety of sensitive microstructural descriptors, we find that the disordered photoreceptor patterns are “hyperuniform” (exhibiting vanishing infinite-wavelength density fluctuations), a property that had heretofore been identified in a unique subset of physical systems, but had never been observed in any living organism. Remarkably, the patterns of both the total population and the individual cell types are simultaneously hyperuniform. We term such patterns “multihyperuniform” because multiple distinct subsets of the overall point pattern are themselves hyperuniform. We have devised a unique multiscale cell packing model in two dimensions that suggests that photoreceptor types interact with both short- and long-ranged repulsive forces and that the resultant competition between the types gives rise to the aforementioned singular spatial features characterizing the system, including multihyperuniformity. These findings suggest that a disordered hyperuniform pattern may represent the most uniform sampling arrangement attainable in the avian system, given intrinsic packing constraints within the photoreceptor epithelium. In addition, they show how fundamental physical constraints can change the course of a biological optimization process. Our results suggest that multihyperuniform disordered structures have implications for the design of materials with novel physical properties and therefore may represent a fruitful area for future research

关键词： PHOTORECEPTORS ARRAY processing BIRDS MULTISCALE modeling SAMPLING (Signal processing) EPITHELIUM

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Optimization for MEMS Filter to Reduce Feed-Through and an Analysis Method Based on Polar Diagram

Optimization for MEMS Filter to Reduce Feed-Through and an A...

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The Second International Conference on Micro Nano Devices,Structure and Computing Systems(MNDSCS 2013)

作者： Guowei Han Chaowei Si Jing Ning Yongmei Zhao Guosheng Sun Fuhua Yang Research Center of Engineering for Semiconductor Integrated Technology Institute of Semiconductors Chinese Academy of Sciences State Key Laboratory of Transducer Technology Department of Electronics Engineer Tsinghua University Key Laboratory of Semiconductor Materials Science Institute of Semiconductors Chinese Academy of Sciences

This paper presents an optimization of polysilicon based RF MEMS filter to improve electric isolation and minimize the feed-through, raising the stop-band reject above 20 dB from the original 0.2 dB, and proposes a performance analysis methodology based on polar diagram, which could simplify and visualize the analysis. Intrinsic feed-through of the device is minimized by optimization of substrate in fabrication process, differing from the characterization method reported previously, which is simple and effective.

关键词： MEMS filter feed-through cancellation performance enhancement polar diagram

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Ideal strength of random alloys from first principles

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Physical Review B 2013年第21期87卷 214203-214203页

作者： Xiaoqing Li Stephan Schönecker Jijun Zhao Börje Johansson Levente Vitos Applied Materials Physics Department of Materials Science and Engineering Royal Institute of Technology Stockholm SE-10044 Sweden School of Physics and Optoelectronic Technology and College of Advanced Science and Technology Dalian University of Technology Dalian 116024 People's Republic of China Key Laboratory of Materials Modification by Laser Electron and Ion Beams Dalian University of Technology Ministry of Education Dalian 116024 People's Republic of China Department of Physics and Astronomy Division of Materials Theory Uppsala University Box 516 Uppsala SE-75120 Sweden Research Institute for Solid State Physics and Optics Wigner Research Center for Physics P.O. Box 49 Budapest H-1525 Hungary

The all-electron exact muffin-tin orbitals method in combination with the coherent-potential approximation was employed to investigate the ideal tensile strengths of elemental V and Mo solids, and V- and Mo-based random solid solutions. Under uniaxial [001] tensile loading, the ideal tensile strength of V is 11.6 GPa and the lattice fails by shear. Assuming isotropic Poisson contraction, the ideal tensile strengths are 26.7 and 37.6 GPa for V in the [111] and [110] directions, respectively. The ideal strength of Mo is 26.7 GPa in the [001] direction and decreases when a few percent of Tc is introduced in Mo. For the V-based alloys, Cr increases and Ti decreases the ideal tensile strength in all principal directions. Adding the same concentration of Cr and Ti to V leads to ternary alloys with similar ideal strength values as that of pure V. The alloying effects on the ideal strength are explained using the electronic band structure.

关键词： ALLOYS ELECTRONS MUFFIN pans TENSILE strength solid solutions

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Lead-free and lead-based ABO3 perovskite relaxors with mixed-valence A-site and B-site disorder: Comparative neutron scattering structural study of (Na1/2Bi1/2)TiO3 and Pb(Mg1/3Nb2/3)O3

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Physical Review B 2013年第17期88卷 174115-174115页

作者： Wenwei Ge Christopher P. Devreugd D. Phelan Qinhui Zhang Muhtar Ahart Jiefang Li Haosu Luo Lynn A. Boatner Dwight Viehland Peter M. Gehring Department of Materials Science and Engineering Virginia Polytechnic Institute and State University Blacksburg Virginia 24061 USA NIST Center for Neutron Research National Institute of Standards and Technology Gaithersburg Maryland 20899-6100 USA Shanghai Institute of Ceramics Chinese Academy of Sciences Shanghai 201800 China Geophysical Laboratory Carnegie Institution of Washington Washington D.C. 20015 USA Solid State Division Oak Ridge National Laboratory Oak Ridge Tennessee 37831 USA

We report the results of neutron elastic-scattering measurements made between −250 °C and 620 °C on the lead-free relaxor (Na1/2Bi1/2)TiO3 (NBT). Strong, anisotropic, elastic diffuse scattering intensity decorates the (100), (110), (111), (200), (210), and (220) Bragg peaks at room temperature. The wave-vector dependence of this diffuse scattering is compared to that in the lead-based relaxor Pb(Mg1/3Nb2/3)O3 (PMN) to determine if any features might be common to relaxors. Prominent ridges in the elastic diffuse scattering intensity contours that extend along ⟨110⟩ are seen that exhibit the same zone dependence as those observed in PMN and other lead-based relaxors. These ridges disappear gradually on heating above the cubic-to-tetragonal phase transition temperature TCT = 523 °C, which is also near the temperature at which the dielectric permittivity begins to deviate from Curie-Weiss behavior. We thus identify the ⟨110⟩-oriented ridges as a relaxor-specific property. The diffuse scattering contours also display narrower ridges oriented along ⟨100⟩ that are consistent with the x-ray results of Kreisel et al. [Phys. Rev. B 68, 014113 (2003)]; these vanish near 320 °C, indicating that they have a different physical origin. The ⟨100⟩-oriented ridges are not observed in PMN. We observe no equivalent relaxor-specific elastic diffuse scattering from the homovalent relaxor analogues K0.95Li0.05TiO3 (A-site disordered) and KTa0.95Nb0.05O3 (B-site disordered). This suggests that the ⟨110⟩-oriented diffuse scattering ridges are correlated with the presence of strong random electric fields and invites a reassessment of what defines the relaxor phase. We find that doping NBT with 5.6% BaTiO3, a composition close to the morphotropic phase boundary with enhanced piezoelectric properties, increases the room-temperature correlation length along [11¯0] from 40 to 60 Å while doubling the associated integrated diffuse scattering. Similar behavior was reported by Matsuura et al. [Phys.

关键词： NEUTRON scattering PEROVSKITE analysis RELAXOR ferroelectrics ELECTRIC fields INDUCTIVELY coupled plasma atomic emission spectrometry

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The structural and optical properties of GaSb/inGaAs type-II quantum dots grown on inP (100) substrate

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Nanoscale research Letters 2012年第1期7卷 1-6页

作者： Shuhui, Zhang Lu, Wang Zhenwu, Shi Yanxiang, Cui Haitao, Tian Huaiju, Gao Haiqiang, Jia Wenxin, Wang Hong, Chen Liancheng, Zhao School of Materials Science and Engineering Harbin Institute of Technology Harbin 150001 China National Laboratory for Condensed Matter Physics Institute of Physics Chinese Academy of Sciences Beijing 100190 China Engineering Research Center of Solid-State Lighting School of Electrical Engineering and Automation Tianjin Polytechnic University Tianjin 300160 China

We have investigated the structural and optical properties of type-II GaSb/InGaAs quantum dots [QDs] grown on InP (100) substrate by molecular beam epitaxy. Rectangular-shaped GaSb QDs were well developed and no nanodash-like structures which could be easily found in the InAs/InP QD system were formed. Low-temperature photoluminescence spectra show there are two peaks centered at 0.75eV and 0.76ev. The low-energy peak blueshifted with increasing excitation power is identified as the indirect transition from the InGaAs conduction band to the GaSb hole level (type-II), and the high-energy peak is identified as the direct transition (type-I) of GaSb QDs. This material system shows a promising application on quantum-dot infrared detectors and quantum-dot field-effect transistor. © 2012 Shuhui et al.

关键词： III-V semiconductors

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Formation and rotation of skyrmion crystal in the chiral-lattice insulator Cu2OSeO3

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Physical Review B 2012年第22期85卷 220406(R)-220406(R)页

作者： S. Seki J.-H. Kim D. S. Inosov R. Georgii B. Keimer S. Ishiwata Y. Tokura Department of Applied Physics and Quantum Phase Electronics Center (QPEC) University of Tokyo Tokyo 113-8656 Japan Max Planck Institute for Solid State Research Heisenbergstraße 1 D-70569 Stuttgart Germany Forschungsneutronenquelle Heinz Maier-Leibnitz (FRM II) Technische Universität München D-85748 Garching Germany Cross-Correlated Materials Research Group (CMRG) and Correlated Electron Research Group (CERG) RIKEN Advanced Science Institute Wako 351-0198 Japan Multiferroics Project ERATOJapan Science and Technology Agency (JST) Tokyo 113-8656 Japan

Small-angle neutron scattering experiments were performed on a bulk single crystal of chiral-lattice multiferroic insulator Cu2OSeO3. In the absence of an external magnetic field, helical spin order with magnetic modulation vector q∥〈001〉 was identified. When a magnetic field is applied, a triple-q magnetic structure emerges normal to the field in the A phase just below the magnetic ordering temperature Tc, which suggests the formation of a triangular lattice of skyrmions. Notably, the favorable q direction in the A phase changes from q∥〈110〉 to q∥〈001〉 upon approaching Tc. Near the phase boundary between these two states, the external magnetic field induces a 30∘ rotation of the skyrmion lattice. This suggests a delicate balance between the magnetic anisotropy and the spin texture near Tc, such that even a small perturbation significantly affects the ordering pattern of the skyrmions.

关键词： SKYRME model CRYSTAL lattices CHIRALITY ELECTRIC insulators & insulation COPPER compounds NEUTRON scattering SMALL-angle scattering MAGNETIC fields

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