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Structure and optical properties of the Ge and Sn quantum-dots

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nuclear Science and Techniques 2000年第2期11卷 119-123页

作者： HAN Zhao-Hui ZHAO Zi-Qiang(Institute of Heavy Ion physics, Technical physics Depariment, peking university,beijing 100871) 北京大学北京 100871

Embedded cluster samples Ge:CaF2 and Sn:CaF2 with different sizes less than 8nm were produced and their optical properties were *** diffraction reveals that the clusters’ structures are crystallites and compared with the bulk Germanium and Stannum, lattice constants expand about 4.7% in the case of Ge:CaF2 and 5.2% of Sn:CaF2. Optical absorption and photoluminescence spectra of these samples show good agreement with the Quantum-Confinement-Effect(QCE) theory. With the decreasing of the cluster’s size, the energy gap broadens and the absorption edge blueshift is observed, and the absorption edge also shifts with the changing of the fraction of Sn and Ge. The XPS results show that in the cluster state,the binding energy becomes higher.

关键词：锗微晶锡微晶半导体 X射线光电子能谱结构光学性质电子衍射氟化钙

Absence of state Collapse and Revival in a Superconducting Charge Qubit

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Communications in Theoretical physics 2007年第12期48卷 1029-1032页

作者： HUO Wen-Yi~1 and LONG Gui-Lu~(1,2,3)~1 department of physics amd key laboratory for Quantum Information and Measurements,Tsinghua university,beijing100084,china~2 key laboratory for Atomic and Molecular Nanosciences,Tsinghua university,beijing 100084,china~3 National laboratory for Information Science and technology,Hsinghua university,beijing 100084,china department of physics amd key laboratory for Quantum Information and Measurements Tsinghua University Beijing 100084 China key laboratory for Atomic and Molecular Nanosciences Tsinghua University Beijing 100084 China National laboratory for Information Science and technology Hsinghua University Beijing 100084 China

The Hamiltonian of a superconducting charge qubit with a configuration of dc SQUID contains an interac-tion between the LC oscillator part and charge *** interaction may leads to quantum state collapse and revivalwhich degrades the charge qubits and leads to serious *** analysis shows that the existing charge qubitparameters do not lead to this phenomenon,which is very good for the superconducting charge

关键词： quantum computer superconducting charge qubit absence and revival

Order-disorder Transformation for TiAl with L1_0 Structure at Stoichiometrical Composition

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Rare Metals 2001年第3期20卷 147-151页

作者： Timothé e Nsongo, Xiaodong Ni,Guoliang Chen,Keh-Minn Chan 1) state key laboratory for Advanced Metals and Materials, university of Science and technology beijing, beijing 100083, china 2) Faculty of Science (physics department, P.O. Box 69 Brazzaville, 北京科技大学新金属材料国家重点实验室北京 100083 West-Virginia university 美国

The embedded atom method (EAM) was used to study the order-disorder transformation in gamma -TiAl alloy with L1(0). structure at stoichiometrical composition, and the effect of lattice constants was also investigated. It was found that the gamma -TiAl alloy at stoichiometrical composition exhibits a second-order transition, and the relations between lattice constants a, c and the long-range order sigma are not linear. The lattice constant a decreases whereas c increases with the increase of the long-range order parameter. In this case the ordering induces the transformation from cubic to tetragonal. The change of the lattice constant during the ordering processes can be interpreted in terms of bond length.

关键词： order-disorder transformation TiAl long-range order intermetallic

Entropy product measure for multipartite pure states

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Science china(physics,Mechanics & Astronomy) 2006年第5期49卷 606-615页

作者： CAO Wancang1,2, LIU Dan2, PAN Feng3 & LONG Guilu2,4 1. department of physics, Chifeng College, Chifeng 024001, china 2. key laboratory for Quantum Information and Measurements, department of physics, Tsinghua university, beijing 100084, china 3. department of physics, Liaoning Normal university, Dalian 116029, china 4. key laboratory for Atomic and Molecular Nano-Sciences, Tsinghua university, beijing 100084, china Correspondence should be addressed to Long Guilu department of physics Chifeng College Chifeng China key laboratory for Quantum Information and Measurements Department of Physics Tsinghua University Beijing China department of physics Liaoning Normal University Dalian China key laboratory for Atomic and Molecular Nano-Sciences Tsinghua University Beijing China

An entanglement measure for multipartite pure states is formulated using the product of the von Neumann entropy of the reduced density matrices of the constituents. Based on this new measure, all possible ways of the maximal entanglement of the triqubit pure states are studied in detail and all types of the maximal entanglement have been compared with the result of ‘the average entropy’. The new measure can be used to calculate the degree of entanglement, and an improvement is given in the area near the zero entropy.

关键词： multipartite pure state von Neumann entropy entanglement measure

Intermediate processes and critical phenomena: Theory, method and progress of fractional operators and their applications to modern mechanics

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Science china(physics,Mechanics & Astronomy) 2006年第3期49卷 257-272页

作者： XU Mingyu1 & TAN Wenchang2 1. Institute of Applied Mathematics, School of Math & System Science, Shandong university, Jinan 250100, china 2. state key laboratory of Turbulence and Complex Systems & department of Mechanics and Engineering Science, peking university, beijing 100871, china Institute of Applied Mathematics School of Math & System Science Shandong University Jinan China state key laboratory of Turbulence and Complex Systems & department of Mechanics and Engineering Science Peking University Beijing China

From point of view of physics, especially of mechanics, we briefly introduce fractional operators (with emphasis on fractional calculus and fractional differential equa- tions) used for describing intermediate processes and critical phenomena in physics and mechanics, their progress in theory and methods and their applications to modern me- chanics. Some authors’ researches in this area in recent years are included. Finally, prospects and evaluation for this subject are made.

关键词： fractional operators,intermediate processes,critical phenomena,modern mechanics

A Self-consistent Calculation and an Anisotropic Wavelength Cut off Energy of Spin-wave Spectrumin Magnetic Tunnel Junctions

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Journal of Materials Science & technology 2001年第2期17卷 197-202页

作者： Xiufeng HAN state key laboratory of Magnetism, Institute of physics, Chinese Academy of Sciences, beijing 100080, china Terunobu Miyazaki department of Applied physics, Graduate School of Engineering, Tohoku university, Aoba-yama 08, Sendai 980-8579, Japa state key Lab. of Magnetism Inst. of Phys. Chinese Acad. of Sci. Beijing 100080 China

Temperature dependence of tunnel magnetoresistance (TMR) ratio, resistance, and coercivity from 4.2 K to room temperature (RT), applied de bias voltage dependence of the TMR ratio and resistances at 4.2 K and RT, tunnel current I and dynamic conductance dI/dV as functions of the de bias voltage at 4.2 K, and inelastic electron tunneling (IET) spectroscopy, d(2)I/dV(2) versus V, at 4.2 K for a tunnel junction of Ta(5 nm)/Ni79Fe21(25 nm)/Ir22Mn78(12 nm)/Co75Fe25(4 nm)/Al(0.8 nm)-oxide/Co75Fe25(4 nm)/Ni79Fe21(25 nm)/Ta(5 nm) were systematically investigated. High TMR ratio of 59.2% at 4.2 K and 41.3% at RT were observed for this junction after annealing at 275 degreesC for an hour. The temperature dependence of TMR ratio and resistances from 4.2 to 300 K at 1.0 mV bias and the de bias voltage dependence of TMR ratio at 4.2 K from 0 to 80 mV can be evaluated by a comparison of self-consistent calculations with the experimental data based on the magnon-assisted inelastic excitation model and theory. An anisotropic wavelength cutoff energy of spin-wave spectrum in magnetic tunnel junctions (MTJs) was suggested, which is necessary for self-consistent calculations, based on a series of IET spectra observed in the MTJs.

关键词： off TMR A Self-consistent Calculation and an Anisotropic Wavelength Cut Energy of Spin-wave Spectrumin Magnetic Tunnel Junctions wave Figure than

Electron dynamics in collisionless magnetic reconnection with a PIC simulation

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Chinese Science Bulletin 2009年第3期54卷 456-460页

作者： GUO Jun1,2 1 School of Mathematics and physics, Qingdao university of Science and technology, Qingdao 266042, china 2 state key laboratory of Space Weather, Chinese Academy of Sciences, beijing 100080, china School of Mathematics and physics Qingdao University of Science and Technology Qingdao China state key laboratory of Space Weather Chinese Academy of Sciences Beijing China

Two-dimensional particle-in-cell (PIC) simulation is used to investigate electron dynamics in colli- sionless magnetic reconnection, and the proton/electron mass ratio is taken to be mi /me = 256. The results show that the presence of a strong initial guide field will change the direction of the electron flow. The electron density cavities and the parallel electric field can be found in the electron inflow re- gion along the separatrix, and the electron inflow and density cavities only appear in the second and fourth quadrants. What is different from the results with a smaller mass ratio is that new structures appear in the diffusion region near the X line: (1) Narrow regions of density enhancement and density cavities can be found synchronously in this region; and (2) corresponding to the electron density changes near the X line, the strong parallel electric fields are found to occur in the first and third quadrants. These electric fields perhaps play a more important role in acceleration and heating electrons than those fields located in the density cavities.

关键词： PIC模仿磁链接导向场电子动力学

A computational investigation on random packings of sphere-spherocylinder mixtures

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Science china(physics,Mechanics & Astronomy) 2010年第12期53卷 2284-2292页

作者： LU Peng, LI ShuiXiang , ZHAO Jian & MENG LingYi state key laboratory for Turbulence and Complex Systems, department of Mechanics & Aerospace Engineering, College of Engineering, peking university, beijing 100871, china state key laboratory for Turbulence and Complex Systems Department of Mechanics & Aerospace Engineering College of Engineering Peking University Beijing China

Random packings of binary mixtures of spheres and spherocylinders with the same volume and the same diameter were simulated by a sphere assembly model and relaxation algorithm. Simulation results show that, independently of the component volume fraction, the mixture packing density increases and then decreases with the growth of the aspect ratio of spherocylinders, and the packing density reaches its maximum at the aspect ratio of 0.35. With the same volume particles, results show that the dependence of the mixture packing density on the volume fraction of spherocylinders is approximately linear. With the same diameter particles, the relationship between the mixture packing density and component volume fraction is also roughly linear for short spherocylinders, but when the aspect ratio of spherocylinders is greater than 1.6, the curves turn convex which means the packing of the mixture can be denser than either the sphere or spherocylinder packing alone. To validate the sphere assembly model and relaxation algorithm, binary mixtures of spheres and random packings of spherocylinders were also simulated. Simulation results show the packing densities of sphere mixtures agree with previous prediction models and the results of spherocylinders correspond with the simulation results in literature.

关键词： packing binary mixture sphere spherocylinder packing density aspect ratio

Propagation of interplanetary shock excited ultra low frequency (ULF) waves in magnetosphere-ionosphere-atmosphere——Multi-spacecraft “Cluster” and ground-based magnetometer observations

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Science china(Technological Sciences) 2010年第9期53卷 2528-2534页

作者： WANG ChengRui1,2,ZONG QiuGang1,3 & WANG YongFu1 1 Institute of Space physics and Applied technology,peking university,beijing 100871,china 2 Sate key laboratory of Space Weather,Chinese Academy of Sciences,beijing 100190,china 3 Center for Atmospheric Research,600 Suffolk Street,university of Massachusetts Lowell,MA 01854,USA Institute of Space physics and Applied technology Peking University Beijing China Sate key laboratory of Space Weather Chinese Academy of Sciences Beijing China Center for Atmospheric Research University of Massachusetts Lowell USA

The ultra low frequency (ULF) wave in magnetosphere can act as an important means for solar wind energy inward *** paper quantitatively analyzes the propagation process of the ULF wave triggered by the interplanetary shock propagating from inner magnetosphere equatorial plane along magnetic field lines to the top of the ionosphere and below ionosphere propagating process and establishes a relatively complete magnetosphere-ionosphere-atmosphere propagation model which can be used to study the relationship between the amplitude of the ULF waves triggered by the interplanetary shock wave in magnetospheric space and the magnetic effect caused by the ULF *** a comparison with recent observations,we found that: in the event during November 7,2004 that an interplanetary shock wave interacted with the magnetosphere,Cluster satellites observed that electric field fluctuations and the band-pass filtered result of ground stations meridional component had similar *** with the geomagnetic measurement near the footprints,we found that the electric field disturbance in the magnetosphere spread along the ground magnetic field lines in the form of the ULF waves and changed into geomagnetic *** result reveals that the ULF wave is in contact with the ground geomagnetic *** ULF waves couple with ionized components in ionosphere and spread to the ground in the form of electromagnetic *** this research,we believe that the magnetosphere,ionosphere and ground magnetic effects caused by interplanetary shock wave are the same physical phenomena responding in different *** on the overall consideration of entire electromagnetic response to the interplanetary shock wave,we found that the correlation between CLUSTER multi-satellite observation and geomagnetic station observation is due to the ULF wave propagated in magnetosphere-ionosphere-atmosphere system,and we quantitatively interpreted this response process

关键词： ultra low frequency (ULF) wave magnetic storm ionosphere IRI model interplanetary shock