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Volume 19 Issue 7
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Original Articles
Bifurcation, Bi-instability and Area Principle for the Solitary Waves of the Nonlinear Wave Equation with Quartic Polynomial Potential
HUA Cun-Cai, LIU Yan-Zhu
Chin. Phys. Lett. 2002, 19 (7): 885-888 .  
Abstract   PDF(pc) (330KB) ( 416 )
For the nonlinear wave equation with quartic polynomial potential, bifurcation, bi-instability and solitary waves are investigated. An area principle based on the bifurcation diagram is found for the existence of bright and dark solitary waves and shock waves. The simple forms of solitary wave solutions are given by an approximate analytic method.
New Three-Mode Charge-Related Entangled State Representation
FAN Hong-Yi, CHEN Jun-Hua
Chin. Phys. Lett. 2002, 19 (7): 889-892 .  
Abstract   PDF(pc) (226KB) ( 520 )
We construct a new kind of three-mode charge-related entangled state |q,k;n >θ in three-mode Fock space, which possess the completeness relation and orthogonal property. It can describe when photons emitted by two energy levels simultaneously are absorbed by the third energy level. The relation between |q,k;n >θ and the tripartite entangled state |q,k;n >θ [Chin. Phys. Lett. 18 (2001) 1301] is pointed out.
A Theoretical Scheme for Multi-user Quantum Key Distribution with N Einstein-Podolsky-Rosen Pairs on a Passive Optical Network
DENG Fu-Guo, LIU Xiao-Shu, MA Ying-Jun, Xiao Li, LONG Gui-Lu, ,
Chin. Phys. Lett. 2002, 19 (7): 893-896 .  
Abstract   PDF(pc) (308KB) ( 783 )
We propose a theoretical scheme for any-to-any multi-user quantum key distribution on a passive optical network with ordered N Einstein-Podolsky-Rosen pairs. This scheme is safe and more efficient than those with single photons. Its efficiency approaches 100% in the limit that the number of pairs used in eavesdropping check becomes negligible. It also has high capacity and is convenient for users.
Wentzel-Kremers-Brilouin Approximation for Dynamic Systems with Kinetic Coupling in Entangled State Representations
FAN Hong-Yi
Chin. Phys. Lett. 2002, 19 (7): 897-900 .  
Abstract   PDF(pc) (193KB) ( 607 )
We study the Wentzel-Kramers-Brillouin (WKB) approaximation for dynamic systems with kinetic couplings in entangled state
representations. The result shows that the kinetic coupling will affects the position of classical turning points where the condition of using the WKB approximation breaks down. The modified WKB approximation formula is derived in the entangled state representation, for example, the common eigenvector of relative coordinate and total momentum of two particles. The corresponding Bohr-Sommerfeld quantization rule is also derived.
Crisis of Transient Chaos
WANG Wen-Xiu, LU Yun-Qing, CHEN He-Sheng, MA Ming-Quan, ZHU You-Zhang, HE Da-Ren
Chin. Phys. Lett. 2002, 19 (7): 901-903 .  
Abstract   PDF(pc) (365KB) ( 499 )
A new kind of crisis, which is marked by a sudden change of a strange repeller, is observed in an electronic relaxation oscillator. Firstly, by its simplified piecewise linear model, we show analytically that a strange repeller appears after a hole-induced crisis, and that the fractal dimension of the strange repeller and the averaged lifetime of the iterations in the region occupied by the original attractor suddenly change at the critical parameter value when the repeller disappears. Our numerical investigation convinces us that the corresponding phenomenon can be found in the original electronic relaxation oscillator.
Phase Space Prediction Model Based on the Chaotic Attractor
LI Ke-Ping, CHEN Tian-Lun
Chin. Phys. Lett. 2002, 19 (7): 904-907 .  
Abstract   PDF(pc) (328KB) ( 344 )
A new prediction technique is proposed for chaotic time series. The usefulness of the technique is that it removes some false neighbouring points which are not suitable for the local estimation of the dynamics systems. We use a feedforward neural network to approximate the local dominant Lyapunov exponent, and choose the neighbouring points by the exponent. The model is tested for the convection amplitude of the Lorenz model, and the results indicate that this prediction technique can improve the prediction of chaotic time series.
Darboux Transformation Method for Solving the Sine-Gordon Equation in a Laboratory Reference
CAI Hao, SHI Jing, TIAN De-Cheng, HUANG Nian-Ning
Chin. Phys. Lett. 2002, 19 (7): 908-911 .  
Abstract   PDF(pc) (202KB) ( 487 )
The sine-Gordon equation is solved in a laboratory reference using the method of Darboux transformation. Using the Liouville theorem, explicit expressions of the single soliton solution and the breather solution are derived from the Darboux matrix in the case of null spectral parameter.
Colour Conductivity of a Quark Plasma at Finite Chemical Potential
ZHANG Chao, ZHENG Xiao-Ping, LI Jia-Rong
Chin. Phys. Lett. 2002, 19 (7): 912-914 .  
Abstract   PDF(pc) (203KB) ( 336 )
We apply non-Abelian transport theory to a low- temperature case, and discuss the colour electric dynamics of cold-dense quark matter at large chemical potential. Finally, at leading logarithmic accuracy, the color conductivity dependence on chemical potential is obtained.
Development of On-Line Perturbed Angular Correlation
ZHU Sheng-Yun, ZHU Jia-Zheng, T. Minamisono, K. Matsuta, XU Yong-Jun, M. Fukuda, M. Mihara, WANG Zhi-Qiang, CUI Bao-Qun, RONG Chao-Fan, CHU Cheng-Jie, CHEN Jun, LUO Hai-Long, ZHENG Yong-Nan, ZHOU Dong-Mei
Chin. Phys. Lett. 2002, 19 (7): 915-916 .  
Abstract   PDF(pc) (332KB) ( 361 )
The on-line time differential perturbed angular correlation technique has been developed for the first time. The quadrupole interaction of 19F in Cd was measured.
Isotopic Distributions of the 18N Fragmentation Products in Coincidence with Neutrons on Targets 197Au and 9Be
LI Xiang-Qing, JIANG Dong-Xing, YE Yan-Lin, HUA Hui, CHEN Tao, LI Zhi-Huan, GE Yu-Cheng, WANG Quan-Jin, WU He-Yu, JIN Gen-Ming, DUAN Li-Min, XIAO Zhi-Gang, WANG Hong-Wei, LI Zhu-Yu, WANG Su-Fang
Chin. Phys. Lett. 2002, 19 (7): 917-920 .  
Abstract   PDF(pc) (531KB) ( 376 )
We present the experimental isotopic distributions of the 18N projectile fragmentation products Li, Be, B, and C in coincidence with neutrons, as well as the inclusive ones on 197Au and 9Be targets. In the framework of the abrasion-ablation model, these distributions are calculated for various nucleon density distributions of the projectile. The comparison with the experimental isotopic distributions of the projectile-like fragments in coincidence with neutrons shows that the information on the nucleon density distribution of the 18N projectile can be extracted.
Quasi-elastic Scattering of a Secondary 6He Beam on a 9Be Target at 25MeV/Nucleon
CHEN Tao, YE Yan-Lin, LI Zhi-Huan, JIANG Dong-Xing, HUA Hui, LI Xiang-Qing, WANG Quan-Jing, GE Yu-Cheng, PANG Dan-Yang, DI Zhen-Yu, JIN Gen-Ming, XIAO Guo-Qing, GUO Zhong-Yan, XIAO Zhi-Gang, WANG Hong-Wei, ZHANG Bao-Guo, WU He-Yu, LI Jia-Xing, SUN Zhi-Yu, ZHAN Wen-Long
Chin. Phys. Lett. 2002, 19 (7): 921-922 .  
Abstract   PDF(pc) (357KB) ( 392 )
The quasi-elastic scattering of a secondary 6He beam (25 MeV/n) on a 9Be target has been measured for the first time by applications of a sophisticated tracking detector system. The angular distribution is reported. A phenomenological optical potential is obtained by fitting the experimental data, which encourages more accurate experiment measurements.
Dilepton Production in a Chemically Equilibrating Quark--Gluon Matter
HE Ze-Jun, JIANG Wei-Zhou, ZHANG Jia-Ju, ZHANG Wei, LIU Bo
Chin. Phys. Lett. 2002, 19 (7): 923-925 .  
Abstract   PDF(pc) (293KB) ( 1026 )
We have studied dilepton production in a chemically equilibrating quark-gluon matter produced at RHIC energies. We find that the dilepton yield is no longer a monotonously decreasing function of the initial quark chemical potential. therefore, the dilepton suppression may not be useful as a signature for quark-gluon matter formation.
Transverse Flow of Kaons in Heavy-Ion Collisions
ZHENG Yu-Ming, CHU Zi-Li, FUCHS Christian, FAESSLER Amand, XIAO Wu, HUA Da-Ping, YAN Yu-Peng
Chin. Phys. Lett. 2002, 19 (7): 926-928 .  
Abstract   PDF(pc) (265KB) ( 390 )
The transverse flow of positive charged kaons from heavy-ion collisions at intermediate energy is investigated within the framework of the quantum molecular dynamics model. The calculated results show that the experimental data are only consistent with the ones including the kaon mean-field potential from the chiral Lagrangian. This indicates that the transverse flow pattern of kaons is an useful probe of the kaon potential in a nuclear medium.
Great Scintillating Properties of a YAP:Ce Crystal
GOU Quan-Bu, DONG Xiao-Li, LI Zu-Hao, ZHU Guo-Yi, HE Jing-Tang, TANG Xiao-Wei
Chin. Phys. Lett. 2002, 19 (7): 929-930 .  
Abstract   PDF(pc) (353KB) ( 524 )
We study the decay time constants and light output of an 18 x 18 x 1 mm3 YAP (YAlO3) crystal doped with cerium. The result shows that the light pulse is composed of fast and a slow components. The fast component has a decay time constant of 24.05±0.15 ns with an intensity of 81.57±0.97% and the slow one has a decay time constant of 87.67±2.49 ns with an intensity of 18.51±1.34%. The measured light output is 3608±80 photoelectrons/MeV without the correction for the quantum efficiency of the photomultiplier tube XP2262B.
Monte Carlo Simulation of Opacities of Hot and Dense Au Plasma in the Unresolved Transition Array Approximation
CHENG Xin-Lu, YANG Li, ZHANG Hong, YANG Xiang-Dong
Chin. Phys. Lett. 2002, 19 (7): 931-933 .  
Abstract   PDF(pc) (255KB) ( 433 )
The opacity, and its Planck and Rosseland mean values, of the hot and dense Au plasma in local thermodynamics equilibrium are studied by the Monte Carlo method based on unresolved transition array (UTA) approximation. The average ion model and the Saha equation is used to determine the atomic level populations. The result gives a more detailed structure for frequency-dependent opacity than the popularly used super transition array or UTA in the photon energy range of 500 eV to 2000 eV. The Monte Carlo method can give a result better than that of UTA, with almost the same computation effort.
Average Distribution of Ionic Charges and Ionizability for the Au Plasma System
YANG Tian-Li, JIANG Gang, ZHU Zheng-He
Chin. Phys. Lett. 2002, 19 (7): 934-936 .  
Abstract   PDF(pc) (306KB) ( 338 )
Using relativistic multi-configuration Dirac-Fock theory, we calculate the transition data of 3dj-nfj' (n = 5,6,7) for the M-shell from an Ni-like Au ion to an As-like Au ion by the GRASP programme with the core-polarization, quantum electrodynamical effect and Breit correction. Based on the present calculation results and the experiment of Xingguang-II laser facilities, the average distribution of ionic charge and the ionizability have been derived. The average ionization degree of Au plasma Z* is 49.06±0.5, which is comparable with the result of the Lawrence Livemore National Laboratory.
A Proposal for Realizing an Array of Bose-Einstein Condensates
YIN Jian-Ping, GAO Wei-Jian, HU Jian-Jun
Chin. Phys. Lett. 2002, 19 (7): 937-940 .  
Abstract   PDF(pc) (668KB) ( 651 )
We propose one-dimensional (1D) and two-dimensional (2D) arrays of magnetic surface microtraps for cold alkali atoms using some arrays of current-carrying wires and calculate the spatial distributions of magnetic fields from the 1D and 2D arrays of current-carrying wires. The field gradients and curvatures from a single magnetic microtrap are analysed, and some interesting and periodic magnetic-well microstructures are found. The result shows that the magnetic-field gradient greater than 2.4 x 105G/cm and the field curvature greater than 4.05 x 108G/cm2 can be generated in our array of magnetic microraps, which can be used to realize the 1D and 2D arrays of Bose-Einstein condensations (or 1D and 2D arrays of Bose clusters) by rf-induced evaporative cooling, and then to form 1D and 2D atomic magnetic lattices, even to prepare 1D and 2D photonic crystals.
A Discharge-Excited SrBr2 Vapor Laser
PAN Bai-Liang, YAO Zhi-Xin, CHEN Gang
Chin. Phys. Lett. 2002, 19 (7): 941-943 .  
Abstract   PDF(pc) (277KB) ( 731 )
A new-style discharge tube for a metal vapor laser has been designed and built. SrBr2 was successfully used to replace metal Strontium as a working medium, and multi-line laser oscillations from resonance to metastable transition of strontium atoms (6.45μm), ions (1.03μm/1.09μm) and from strontium ion recombination (416.2 nm/430.5 nm) have been obtained through longitudinal pulsed discharge. The problem of an incompatibility reaction between metallic strontium and the discharge tube in the strontium vapor laser was solved. Some proposals are presented for further developments of strontium halide lasers.
Blue Generation in a Periodically Poled LiTaO3 by Frequency Tripling an 1342 nm Nd:YVO4 Laser
HE Jing-Liang, LIU Jie, LUO Guo-Zhen, JIA Yu-Lei, DU Jian-Xin, GUO Cheng-Shan, ZHU Shi-Ning
Chin. Phys. Lett. 2002, 19 (7): 944-946 .  
Abstract   PDF(pc) (266KB) ( 405 )
We report on an efficient blue light generation in a periodically poled LiTaO3 by the frequency tripling of a quasi-continuous 1342 nm Nd:YVO4 laser. The period of the sample was 14.778μm. Blue light with an average power of 138 mW was generated from a 18 mm long crystal in a single-pass process under an averaged fundamental power of 713 mW. The internal conversion efficiency was 19.3%.
Effects of Charge Transfer Agents on the Holographic Parameters of a Photopolymer
YAO Hua-Wen, HUANG Ming-Ju, CHEN Zhong-Yu, GAN Fu-Xi
Chin. Phys. Lett. 2002, 19 (7): 947-949 .  
Abstract   PDF(pc) (284KB) ( 330 )
The principle of charge transfer agents was investigated experimentally. There is a compensation effect between triethanolamine (TEA) and diphenyliodonium hexafluorophosphate (DPI) in the polymerization process of photopolymer. The experimental results illustrated that TEA has a stronger effect in the initial stage of exposure, and DPI has a stronger effect during the propagation stage of the polymerization process. We explain the main contributions of DPI in the superadditive photopolymer kinetics that results in an obvious increase of sensitivity.
Stress Wave Propagation in a Gradient Elastic Medium
ZHAO Ya-Pu, ZHAO Han, HU Yu-Qun,
Chin. Phys. Lett. 2002, 19 (7): 950-952 .  
Abstract   PDF(pc) (253KB) ( 400 )
The gradient elastic constitutive equation incorporating the second gradient of the strains is used to determine the monochromatic elastic plane wave propagation in a gradient infinite medium and thin rod. The equation of motion, together with the internal material length, has been derived. Various dispersion relations have been determined. We present explicit expressions for relationship among various wave speeds, wavenumber and internal material length.
A Pseudo Detailed Term Accounting Method for Radiative Opacity of Laser-Produced Plasmas
MENG Xu-Jun, SUN Yong-Sheng, ZHANG Ben-Ai
Chin. Phys. Lett. 2002, 19 (7): 953-955 .  
Abstract   PDF(pc) (457KB) ( 351 )
A statistical method is introduced to deal with the two-electron energies of a configuration in the detailed term accounting (DTA) approximation for the spectral line absorption in the radiative opacity of laser-produced plasmas in local thermodynamics equilibrium. The relativistic Hartree-Fock-Slater self-consistent field average atom model is used to select the reference ion with most-probability and providing basically atomic data. In this way, fully frequency-dependent and spectral resolved opacity for heavy element can be obtained readily for the primary design of radiation transfer in the inertial confinement fusion simulation. Opacities of Au plasmas are given.
Generation of Hot Electron at Higher Temperature from Solid Plasma with a Moderate-Intensity Femtosecond Laser
TAO Ye-Zheng, LI Ye-Jun, TANG Xiu-Zhang, ZHANG Hai-Feng, SHAN Yu-Sheng, WANG Nai-Yan
Chin. Phys. Lett. 2002, 19 (7): 956-958 .  
Abstract   PDF(pc) (279KB) ( 395 )
We experimentally investigate the generation of hot electrons from the interaction of a moderate-intensity (1016W/cm2) pre-pulsed-free femtosecond laser (6 mJ, 120 fs, at 744 nm) with a solid target. The temperature of the hot electrons is inferred from the hard x-ray ( > 30 keV) continuum. The measured hard x-ray continuum is fitted by the Maxwellian distribution with two hot-electron temperatures of 45 and 85 keV. Electrons with the lower temperature were accelerated by “vacuum heating”. However it is necessary to carry out an accurate numerical simulation to explain the generation of hot electrons at higher temperature.

Generation of Helical and Axial Magnetic Fields by the Relativistic Laser Pulses in Under-dense Plasma: Three-Dimensional Particle-in-Cell Simulation
ZHENG Chun-Yang, ZHU Shao-Ping, HE Xian-Tu
Chin. Phys. Lett. 2002, 19 (7): 959-961 .  
Abstract   PDF(pc) (350KB) ( 406 )
The quasi-static magnetic fields created in the interaction of the relativistic laser pulses with under-dense plasmas have been investigated by three-dimensional particlein-cell (PIC) simulation. The relativistic ponderomotive force can drive an intense electron current in the laser propagation direction, which is responsible for the generation of a helical magnetic field. The axial magnetic field results from a difference beat of wave-wave, which drives a solenoidal current. In particular, the physical significance of the kinetic model for the generation of the axial magnetic field is discussed.
Quantum Effects on the Coulomb Logarithm for Energetic Ions During the Initial Thermalization Phase
DENG Bai-Quan, YAN Jian-Cheng, DENG Mei-Gen, PENG Li-Lin
Chin. Phys. Lett. 2002, 19 (7): 962-963 .  
Abstract   PDF(pc) (180KB) ( 501 )
We have discussed the quantum mechanical effects for the energetic charged particles produced in D - He3 fusion reactions. Our results show that it is better to use the proper coulomb logarithm at the high-energy end in describing the thermalization process, because the quantum mechanical effects on the coulomb logarithm are not negligible, based on an assumption of binary collision.
Improvement of Stress Anisotropy in Circular Planar Magnetron Sputter Deposited Molybdenum Films with Annealing
WU Yong-Gang, GU Chun-Shi, CAO Er-Hua, WANG Zhan-Shan, WEI Jun-Ming, TANG Wei-Xing, CHEN Ling-Yan
Chin. Phys. Lett. 2002, 19 (7): 964-966 .  
Abstract   PDF(pc) (480KB) ( 433 )
As part of the programme to develop a free-standing thin-film filter for soft x-ray optics applications, stress anisotropy in molybdenum films deposited by dc circular planar magnetron sputtering has been studied by off-normal x-ray diffraction as a function of sputtering argon gas pressure over a range of 0.8-1.5 Pa. The stresses are found to be more compressive in the center area than in the edge area, and more compressive in the tangential direction than in the radial direction. The highest stress anisotropy exists in the film deposited at 1.5 Pa gas pressure. Annealing the films in vacuum is effective in reducing both the tensile stress and stress anisotropy in the tensile stressed films.
Improved Luminescence Properties and Thermal Stability of ZnS Quantum Dots by Organic and Inorganic Passivation
Hatim Mohamed El-Khair, XU Ling, CHEN Kun-Ji, MA Yi, ZHANG Yu, LI Ming-Hai, HUANG Xin-Fan
Chin. Phys. Lett. 2002, 19 (7): 967-969 .  
Abstract   PDF(pc) (355KB) ( 454 )
ZnS quantum dots (QDs) synthesized in water and ethanol solutions were coated with polystyrene (PS) and SiO2 shells, respectively. The band edge emission was enhanced by nearly five times after PS coating and about 13 times after SiO2 coating, because the surface trap states were removed. From the photoluminescence properties of ZnS QDs coated with PS and SiO2 shells we have detected the improvement of thermal stability. This is due to the fact that the surface passivation can prevent the further growth of the ZnS QDs and the diffusion of oxygen on the surface of ZnS QDs during thermal oxidation.
Localization of Surface-Exciton Polaritons
WANG Qing-Song, CHENG Ze
Chin. Phys. Lett. 2002, 19 (7): 970-973 .  
Abstract   PDF(pc) (347KB) ( 322 )
We develop a numerical model to investigate the localization of surface-exciton polaritons in the presence of random roughness and spatial dispersion. It is found that the localization occurs in a limited frequency range near the maximum frequency of surface-exciton polaritons. The decaying length in the extended region is much larger than that in the localized region. The localization of surface-exciton polaritons is due to the destructive interference between waves scattered from the rough surface.
Polarons with Spatially Dependent Mass in a Finite Parabolic Quantum Well
ZHAO Feng-Qi, LIANG Xi-Xia
Chin. Phys. Lett. 2002, 19 (7): 974-977 .  
Abstract   PDF(pc) (357KB) ( 430 )
We study the energy levels of an electron (or hole) polaron in a parabolic quantum well structure, including the spatial dependence of the effective mass. We also consider the two-mode behaviour of longitudinal optical phonon modes of the ternary mixed crystals in the structure, in the calculation of the effect of the electron-phonon interaction. We calculate the ground state, the first excited state and the transition energy of an electron (or hole) in the GaAs/AlxGa1-xAs parabolic quantum well structure. The numerical results show that the electron-phonon interaction obviously affects the energy levels of the electron (hole), which are in agreement with experimental results.
Transition of the True Ground State in a Coupled Three-Layer Quantum Dot
ZHANG Zhan-Jun, LI Bai-Wen, RAO Jian-Guo, BAO Cheng-Guang
Chin. Phys. Lett. 2002, 19 (7): 978-980 .  
Abstract   PDF(pc) (351KB) ( 311 )
Low-lying states of a vertically coupled three-layer quantum-dot system are studied. Each layer contains one electron, and the tunnelling of electrons between layers is neglected. Effects of the interlayer separation d and the external magnetic field B are evaluated by numerical calculations. In the strong coupling case (i.e., d is small), as in a single dot, transitions of the angular momentum L of the true ground states occur when B increases, whereas in the weak coupling case the transition does not occur and the L remains zero. Furthermore, it is found that the variation of d may also induce the L-transition. As a result, a phase diagram of L of the true ground state is given in the d - B plane.
Dynamic Localization of a One-Dimensional Quantum Dot Array in an ac Electric Field
LUO Ying, DUAN Su-Qing, FAN Wen-Bin, ZAO Xian-Geng, WANG Li-Min, MA Ben-Kun
Chin. Phys. Lett. 2002, 19 (7): 981-984 .  
Abstract   PDF(pc) (323KB) ( 468 )
We investigate the dynamics of two interaction electrons confined to one-dimensional quantum dot array in an ac electric field. We find that initially localized electrons will maintain localized in the absence of Coulomb interaction if the ratio of the ac field magnitude to the frequency is a root of the ordinary zero-order Bessel function. In contrast to the case without Coulomb interaction, no matter what the value is, the electrons are delocalized and the delocalization effect depends on the ratio U/ω and eaE/ω, where U is the strength of Coulomb interaction, a is the lattice constant, and E and ω are the ac field amplitude and frequency, respectively.

Zero-Point Energy in a Mesoscopic Nonlinear Inductance-Capacitance Circuit
ZHANG Shou, UM Chung-In, YEON Kyu-Hwang
Chin. Phys. Lett. 2002, 19 (7): 985-987 .  
Abstract   PDF(pc) (234KB) ( 489 )
The zero-point energy of mesoscopic nonlinear inductance-capacitance (L-C) circuit is obtained by making use of the variation method. This is somewhat less than that of simple harmonic oscillator.

Period Halving of Persistent Currents in Mesoscopic Möbius Ladders
DENG Wen-Ji, XU Ji-Huan, LIU Ping
Chin. Phys. Lett. 2002, 19 (7): 988-990 .  
Abstract   PDF(pc) (456KB) ( 382 )
We investigate the period halving of persistent currents (PCs) of non-interacting electrons in isolated mesoscopic Möbius ladders without disorder, pierced by Aharonov-Bohm flux. The mechanisms of the period halving effect depend on the parity of the number of electrons as well as on the interchain hopping. Although the data of PCs in mesoscopic systems are sample-specific, some simple rules are found in the canonical ensemble average, for example, all the odd harmonics of the PCs disappear and the signals of even harmonics are non-negative.
Features in Quasi-particle Excitations and Tunneling Spectra due to Coupling to Spin Fluctuations in High-Tc Cuprates
ZHAO Li, LI Jian-Xin, GONG Chang-De, ZHAO Bai-Ru
Chin. Phys. Lett. 2002, 19 (7): 992-995 .  
Abstract   PDF(pc) (372KB) ( 337 )
In a self-consistent mean-field treatment of the two-dimensional t-t'-J model, we theoretically examine the coupling of in-plane quasi-particles to the antiferromagnetic spin fluctuations in high-Tc superconductors, which renormalizes the fermionic self-energy. We reproduce the characteristic peak-dip-hump structure observed not only in angle-resolved photoemission spectroscopy, but also in supperconductor-insulator-normal metal junction and scan tunneling microscopy experiments. We consider the evolution of this structure with doping. It is shown that this kind of coupling can account for many anomalous properties of high-Tc superconductor in superconducting states.
Magnetic Properties and Magnetoresistance Effect of YMn6Sn6-xCrx (x = 0-0.8) Compounds
ZHANG Li-Gang, LI Yun-Bao, ZHANG Shao-Ying, YAO Jin-Lei, SHEN Bao-Gen
Chin. Phys. Lett. 2002, 19 (7): 996-999 .  
Abstract   PDF(pc) (414KB) ( 419 )
The magnetic properties and magnetoresistance effect of
YMn6Sn6-xCrx (x = 0-0.8) compounds have been experimentally studied by magnetic properties and resistivity measurements in the applied field range 0-5 T. The compound (x = 0.8) displays the ferromagnetic behaviour, while the compounds (x = 0-0.4) display the antiferromagnetic behaviour in the whole ordering temperature range. The compounds (x = 0.5, 0.6) experienced a transition from an antiferromagnetic state to ferromagnetic one with increasing temperature. The compound with x = 0.8 is rapidly saturated in the lower magnetic field with saturation magnetization of 35.92 emu/g. The compounds (x = 0-0.6) display a field induced metamagnetic transition, and the threshold fields decrease with increasing Cr content. The cell-volume V of compounds (x = 0-0.8) increases, and the ordering temperature decreases with the increasing Cr content. A large magnetoresistance effect was observed for the compounds (x = 0.4, 0.5), and the maximum absolute value at 5 K are 32% and 24% under 5 T for x = 0.4 and x = 0.5, respectively.
Giant Stress-Impedance Effect in Amorphous and High-Current-Density Electropulsing Annealed Fe73.5Cu1Nb3Si13.5B9 Ribbons
LI De-Ren, LU Zhi-Chao, ZHOU Shao-Xiong, ZHANG Jun-Feng, LIU Hui, HAN Wei
Chin. Phys. Lett. 2002, 19 (7): 1000-1001 .  
Abstract   PDF(pc) (342KB) ( 479 )
The stress-impedance (SI) effect has been observed in as-cast and high-current-density electropulsing annealed Fe73.5Cu1Nb3Si13.5B9 ribbons. Large SI ratios of -35% and 25% have been obtained in high-current-density electropulsing annealed samples but not in as-cast samples. The SI effect changes drastically with the density of annealing current and the longitudinally applied stress during the annealing process. The effective permeability has been shown to be responsible for the SI effect.
Numerical Simulation of the Two-State Decoherence Model of Nano-Spin Systems
JIANG Yong-Jin, TAO Rui-Bao
Chin. Phys. Lett. 2002, 19 (7): 1002-1003 .  
Abstract   PDF(pc) (257KB) ( 338 )
We have studied the two-state random decoherence model of the 15 system (Phys. Rev. Lett. 84 (2000)3458) with the ‘partial tracing of the environment’method. The linearity relation between the averaged decoherence time and the random dipolar interaction amplitude is verified. The distribution function of decoherence time spreads more widely as the amplitude of the random field is decreased, hence it is difficult to define a decoherence time for the system.
Extra-Large Magnetoresistance in Fe/In2O3 Granular Film
HUANG Bao-Xin, LIU Yi-Hua, WANG Jun-Hua, ZHANG Lin, ZHANG Ru-Zhen, ZHANG Lian-Sheng, MEI Liang-Mo
Chin. Phys. Lett. 2002, 19 (7): 1004-1006 .  
Abstract   PDF(pc) (321KB) ( 349 )
Nanogranular Fe0.35/(In2O3)0.65 film with complex magnetic structure were prepared by the rf sputtering method. An extra-large magnetoresistance up to 506% was obtained at 2.2 K, which is two orders of magnitude larger than that obtained at room temperature. This is related to the interaction with the impurities influencing the local magnetization, which is quite different from spin-dependent tunneling effect at room temperature. The interspacing Fe atoms dispersed in the In2O3 matrix play an important role in the transportation properties of carriers at low temperature.
Numerical Modeling of Velocity and Temperature Distribution of the Buoyancy Convection Effect in KNbO3 Melt
LIU Zhao-Hua, JIN Wei-Qing, PAN Zhi-Lei
Chin. Phys. Lett. 2002, 19 (7): 1007-1009 .  
Abstract   PDF(pc) (374KB) ( 316 )
Numerical modeling of velocity and temperature fiels in high-temperature KNbO3 melt of a loop-shaped Pt wire heater is carried out by using the commercial computational code ANSYS for the mathematical solution of the governing equations. Based on the experimental boundary conditions and the Boussinesq approximation, the numerical modeling of a steady and two-dimensional model is applied to study the process under consideration of the buoyancy-driven convection condition. The result is compared with the previous experimental and theoretical data obtained in our laboratory, and the former is in agreement with the latter. Thus a theoretical guide for reasonable growth conditions is provided by studying in depth the real fluid flow effects in the crystal growth from the melt.
Modulation Spectroscopy of GaAs Covered by InAs Quantum Dots
JIN Peng, MENG Xian-Quan, ZHANG Zi-Yang, LI Cheng-Ming, QU Sheng-Chun, XU Bo, LIU Feng-Qi, WANG Zhan-Guo, LI Yi-Gang, ZHANG Cun-Zhou, PAN Shi-Hong
Chin. Phys. Lett. 2002, 19 (7): 1010-1012 .  
Abstract   PDF(pc) (550KB) ( 441 )
Contactless electroreflectance has been employed at room temperature to study the Fermi level pinning at undoped-n+ GaAs surface covered by 1.6 and 1.8 monolayer (ML) InAs quantum dots (QDs). It is shown that the 1.8 ML InAs QDs moves the Fermi level at GaAs surface to the valence band maximum by about 70 meV compared to bare GaAs, whereas 1.6 ML InAs on GaAs does not modify the Fermi level. It is confirmed that the modification of the 1.8 ML InAs deposition on the Fermi level at GaAs surface is due to the QDs, which are surrounded by some oxidized InAs facets, rather than the wetting layer.
Efficient Visible Electroluminescence from Porous Silicon Diodes Passivated by Carbon Films
LI Hong-Jian, PENG Jing-Cui, QU Shu, YAN Yong-Hong, XU Xue-Mei, ZHAO Chu-Jun
Chin. Phys. Lett. 2002, 19 (7): 1013-1015 .  
Abstract   PDF(pc) (269KB) ( 561 )
By using n-butylamine as a carbon resource, carbon film is deposited on the p-n porous silicon (PS) surface with a radio-frequency glow discharge plasma system. Raman spectra and infrared reflection (IR) spectra of the carbon films indicate that there are amine-group and hydrogen atoms therein. The IR spectra of the passivated PS samples exhibit that the PS surfaces are mainly covered with Si-C,Si-N and Si-O bonds. Electroluminescece (EL) spectra show that EL intensity of the passivated PS diodes increases greatly and the blueshift of EL peak occurs compared with the diodes without treatment and both of them are stable while the passivated diodes are exposed to the air indoor. The I-V characteristics reveal that the passivated diodes have a smaller series resistance and a lower onset voltage. The influence of the carbon film passivation on EL properties of porous silicon has also been discussed. The results have proved that the carbon film passivation is a good way to enhance the PS luminescent intensity and stability.
Field Emission from an Array of Free-standing Metallic Nanowires
ZHANG Geng-Min, Emmanuel ROY, LIU Hong-Wen, LIU Wei-Min, HOU Shi-Min, Kui YU-ZHANG, XUE Zeng-Quan
Chin. Phys. Lett. 2002, 19 (7): 1016-1018 .  
Abstract   PDF(pc) (448KB) ( 369 )
Arrays of single crystalline gold nanowires were synthesized
electrochemically in porous polycarbonate membranes. The polycarbonate membrane was then removed to obtain freestanding nanowires for field emission measurements. The turn-on electric field strength for field emission is found to be lower than 2V/μm. The actual electric field that extracted electrons out of the gold nanowires is estimated to be about 103 times higher than the field directly expected in the model of a parallel plate condenser. The availability of the field emission is therefore attributed to the strong electric field at the tips resulting from small curvature radius of the gold nanowires.
Atomic-Scale Kinetic Monte Carlo Simulation of {100}-Oriented Diamond Film Growth in C-H and C-H-Cl Systems by Chemical Vapor Deposition
AN Xi-Zhong, ZHANG Yu, LIU Guo-Quan, QIN Xiang-Ge, WANG Fu-Zhong, LIU Sheng-Xin
Chin. Phys. Lett. 2002, 19 (7): 1019-1020 .  
Abstract   PDF(pc) (356KB) ( 460 )
We simulate the {100}-oriented diamond film growth of chemical vapor deposition (CVD) under different models in C-H and C-H-Cl systems in an atomic scale by using the revised kinetic Monte Carlo method. The simulation results show that: (1) the CVD diamond film growth in the C-H system is suitable for high substrate temperature, and the film surface roughness is very coarse; (2) the CVD diamond film can grow in the C-H-Cl system either at high temperature or at low temperature, and the film quality is outstanding; (3) atomic Cl takes an active role for the growth of diamond film, especially at low temperatures. The concentration of atomic Cl should be controlled in a proper range.
Nodular Carbon Nanotubes and Their Field Emission Characteristics
LI Qiong, XU Jing-Fang, FENG Tao, WANG Xi, LIU Xiang-Huai
Chin. Phys. Lett. 2002, 19 (7): 1021-1023 .  
Abstract   PDF(pc) (345KB) ( 342 )
A new configuration of carbon nanotubes (CNTs) has been discovered in our laboratory and their surfaces are fully covered with nano-sized node-like structures. The node structures have almost the same size of 40-50 nm. We refer to this material as the nodular carbon nanotubes (NCNTs). Field emission scanning electron microscopy shows that after a hydrogen plasma process in our homemade plasma equipment, the common carbon nanotubes were changed into NCNTs. The experimental result demontrates that this material has good field emission characteristics, low threshold field, stable and suitable emitting current, especially for the emission site density up to the order of 106cm-2.
Effect of the Quadrupole Moment of a Rotating Massive Object on the Gravitational Faraday Rotation
CHEN Yi-Han, SHAO Chang-Gui
Chin. Phys. Lett. 2002, 19 (7): 1024-1026 .  
Abstract   PDF(pc) (198KB) ( 376 )
We study the rotation of the polarization plane for a ray of
electromagnetic radiation propagating in the gravitoelectromagnetic field caused by a rotating massive object with the quadrupole moment. The effect of the quadrupole moment on the gravitational Faraday rotation is investigated. It is found that the gravitational Faraday effect of the quadrupole moment is negligible for Kerr black holes, but this effect is important for rapidly rotating neutron stars.
Heavy Ions Acceleration in Impulsive Solar Flares
Chin. Phys. Lett. 2002, 19 (7): 1027-1030 .  
Abstract   PDF(pc) (240KB) ( 329 )
The abundance enhancements of heavy ions Ne, Mg, Si and Fe in impulsive solar energetic particle (SEP) events are explained by a plasma acceleration mechanism. In consideration of the fact that the coronal plasma is mainly composed of hydrogen and helium ion, we think that the ion-ion hybrid wave and quasi-perpendicular wave can be excited by the energetic electron beam in impulsive solar flares. These waves may resonantly be absorbed by heavy ions when the frequencies of these waves are close to the second harmonic gyrofrequencies of these heavy ions. This requires the coronal plasma temperature to be located in the range of T ~ (5 - 9) x 106 K in impulsive solar flares and makes the average ionic charge state of these heavy ions in impulsive SEP events be higher than the average ionic charge state of these heavy ions in gradual SEP events. These preheated and enhanced heavy ions can successively and stochastically be accelerated by Alfvén turbulence and then form a power-law distribution in impulsive SEP events.
46 articles