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Volume 19 Issue 4
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Original Articles
Form Invariance and Lie Symmetries of the Rotational Relativistic Birkhoff System
LUO Shao-Kai
Chin. Phys. Lett. 2002, 19 (4): 449-451 .  
Abstract   PDF(pc) (174KB) ( 462 )
For a rotational relativistic Birkhoff system, the relation between the form invariance and the Lie symmetries are given under infinitesimal transformations of groups. If the infinitesimal transformation generators ξ0 and ξμ satisfy the conditions of the form invariance, and the determining equation of Lie symmetries holds, the form invariance leads to a Lie symmetry of the system. Furthermore, if the infinitesimal transformations generators ξ0 and ξμ satisfy the conditions of the form invariance and the determining equation of Lie symmetry holds, and if there exists a gauge function G satisfying the structure equation of Lie symmetry, then the form invariance will lead to the Lie symmetrical conserved quantity of the system. An example is given to illustrate the application of the results.
Stability of Dust Acoustic Waves in Weakly Two-Dimensional Dust Plasma with Vortex-Like Ion Distribution
DUAN Wen-Shan
Chin. Phys. Lett. 2002, 19 (4): 452-455 .  
Abstract   PDF(pc) (197KB) ( 580 )
By considering the vortex-like ion distribution, we know that the nonlinear dust acoustic wave can be described by the modified Korteweg-de Vries equation. If there are high-order transverse perturbations in this system, the governing equation for this system is the modified Kadomtsev-Petviashvili equation. We also find that for this system under the transverse perturbation the one-dimensional solitary wave solution is stable.

Quantum Teleportation of a Three-Particle Entangled State
LIU Jin-Ming, GUO Guang-Can
Chin. Phys. Lett. 2002, 19 (4): 456-459 .  
Abstract   PDF(pc) (196KB) ( 1011 )
We present a scheme for teleporting a three-particle entangled state to three remote particles. In this scheme, three pairs of pure nonmaximally entangled states are considered as quantum channels. It is found that by means of optimal discrimination between two nonorthogonal quantum states, probabilistic teleportation of the three-particle entangled state can be achieved.
A New Searching Problem Solved by Quantum Computers
YAN Hai-Yang
Chin. Phys. Lett. 2002, 19 (4): 460-462 .  
Abstract   PDF(pc) (159KB) ( 380 )
It is well known that a quantum computer can search more quickly than a classical computer in solving the so-called Grover-searching problem. We present a new searching problem which cannot be classified into Grover's problem and can be solved by using the modified searching iterations with the same efficiency of Grover's problem.
An Exact Solution and the Pancharatnam Phase for the Generalized Two-Mode Optical System
HOU Bang-Pin, WANG Shun-Jin, YU Wan-Lun
Chin. Phys. Lett. 2002, 19 (4): 463-465 .  
Abstract   PDF(pc) (210KB) ( 369 )
Using the algebraic dynamical method, we obtain the exact solution for the generalized two-mode optical system. From the solution, the Pancharatnam phase and the mean values of the number operators of the system are calculated. It is emphasized that the system can be used as a quantum memory.
Significance of the Formal Quantum Number in the Highly Excited Vibration of the DCN molecule
ZHENG Dun-Sheng, WU Guo-Zhen
Chin. Phys. Lett. 2002, 19 (4): 466-469 .  
Abstract   PDF(pc) (325KB) ( 420 )
For the eigenstates of the highly excited vibration of the simple molecule DCN with two stretching modes, a classical approach in a multi-dimensional coset phase space is employed to show that the formal quantum numbers are related to regular or least“irregular”trajectories, with zero or least Lyapunov exponents, and are always located in the inner regions of the phase space. This property reflects that they are the approximate constants of motion. It is also demonstrated that formal quantum numbers correspond to the significant phase space density.
Demonstration of the Symmetry Properties of Gravitational Metric Fields
SHAO Liang, H. NODA, SHAO Dan, SHAO Chang-gui
Chin. Phys. Lett. 2002, 19 (4): 470-473 .  
Abstract   PDF(pc) (201KB) ( 424 )
We calculate some Wilson loop functionals in a static sphere-symmetrical diagonal metric field and a gravitational metric field established by a cosmic string. Using the direction change of vector when it is parallelly transported in the metric field of cosmic string, the cone symmetry of the metric field is shown.
First Quantum Correction to Dirac Entropy for Rotating U(1) U(1) Dilaton Black Hole
GAO Chang-Jun, SHEN You-Gen,
Chin. Phys. Lett. 2002, 19 (4): 474-476 .  
Abstract   PDF(pc) (223KB) ( 365 )
The first quantum correction to rotating U(1) U(1) dilaton black hole entropy is calculated by using the improved brick wall model. We propose not to consider superradiant mode for the reason that fermion fields do not display supperradiance. We found that the nonsuperradiant mode does contribute exactly the first quantum correction to the non-extreme black hole entropy. Moreover, our cut-off Newman-Penrose ε which does not require an angular cut-off is independent of angle. As for the extreme black hole, we found that its entropy is zero.
De Broglie-Bohm Quantization of the Reissner-Nordstrom Black Hole with a Global Monopole in the Background of de Sitter Space-Time
GAO Chang-Jun, SHEN You-Gen,
Chin. Phys. Lett. 2002, 19 (4): 477-480 .  
Abstract   PDF(pc) (218KB) ( 505 )
We present the classical solution of Lagrange equations for the
Reissner-Nordstrom black hole with a global monopole in the
background of de Sitter space-time. Then we obtain the wavefunction of the space-time by solving Wheeler-De Witt equation. De Broglie-Bohm interpretation applied to the wavefunction gives the quantum solution of the space-time. Finally, the quantum effect on Hawking radiation is studied.
Charged Particle Motion in Temporal Chaotic and Spatiotemporal Chaotic Fields
ZHANG Hai-Yun, HE Kai-Fen
Chin. Phys. Lett. 2002, 19 (4): 481-484 .  
Abstract   PDF(pc) (649KB) ( 423 )
We investigated charged particle motion in temporal chaotic and spatiotemporal chaotic field. In its steady wave frame a few key modes of the solution of the driven/damped nonlinear wave equation are used as the field. It is found that in the spatiotemporal chaotic field the particle drifts relative to the steady wave, in contrast to that in the temporal chaotic field where the particle motion is localized in a trough of the wave field. The result is of significance for understanding stochastic acceleration of particles.
High-Energy Proton-Induced Dimuon Production from Nuclei
DUAN Chun-Gui, WANG Hong-Min, LI Guang-Lie,
Chin. Phys. Lett. 2002, 19 (4): 485-487 .  
Abstract   PDF(pc) (266KB) ( 366 )
In the framework of the Glauber model, taking into account the energy loss of the beam proton through nucleus, We analyse the measured Drell-Yan production cross sections for 800 GeV proton beam incident on Be, Fe and W nuclear targets. We have found that the nuclear Drell-Yan cross section ratios are suppressed due to the energy loss in the initial state, the calculated results of energy loss are in very good agreement with the Fermilab experiment 866.
Nuclear Shadowing Effect on K Factor in Au-Au Collision
HOU Zhao-Yu, ZHENG Qiao, ZHANG Ben-Ai
Chin. Phys. Lett. 2002, 19 (4): 488-491 .  
Abstract   PDF(pc) (305KB) ( 382 )
We investigate the nuclear shadowing effect on K factor in the Drell-Yan process by introducing a shadowing factor into the corresponding quantum chromodynamical αs order corrections. K factors for Au-Au collision are calculated at the center-of-mass system energies √s = 60, 130 and 200 GeV while the nuclear shadowing factor is taken into account. The numerical results indicate that the nuclear shadowing factor obviously raises the K value in the small x region, and for the same nucleon the K value becomes smaller as the energy increases. Nuclear shadowing effect would be one reason of creating the non-constancy of the K factor.
Process of Energetic Carbon Atom Deposition on Si (001) Substrate by Molecular Dynamics Simulation
YU Wei, TENG Xiao-Yun, LI Xiao-Wei, FU Guang-Sheng
Chin. Phys. Lett. 2002, 19 (4): 492-494 .  
Abstract   PDF(pc) (376KB) ( 606 )
The process of energetic C atom deposition on Si (001)-(2x1) is studied by the molecular dynamics method using the semi-empirical many-bond Tersoff potential. It is found that the incident energy of the carbon atom has an important effect on the collision process and its diffusion process on the substrate. Most of the incident energy of the carbon atom is transferred to the substrate atoms within the initial two vibration periods of substrate atoms and its value increases with the incident energy. The spreading distance and penetration depth of incident atom increasing with the incident energy are identified as well. The simulated results imply that an important effect of energy of incident carbon on the film growth at low substrate temperature provides activation energy for silicon carbide formation through the vibration enhancement of local substrate atoms, in addition, suppressing carbon atoms inhomogeneous collection and dispensing with the silicon diffusion process may be effectively promoted by the spreading and penetration of the energetic carbon atom in the silicon substrate.
Photoabsorption Spectrum and Optically Forbidden Transitions of Krypton by Electron Impact
YUAN Zhen-Sheng, ZHU Lin-Fan, LIU Xiao-Jing, LI Wen-Bin, CHENG Hua-Dong, XU Ke-Zun
Chin. Phys. Lett. 2002, 19 (4): 495-496 .  
Abstract   PDF(pc) (322KB) ( 805 )
A high resolution fast electron energy loss spectrometer with
multi-channel energy analyse was employed. The maxima just above the threshold 4-1(2P1/2), which is regarded as a shape resonance, was obtained at 16.3 eV. The optically forbidden excitations of 4s electron were measured for the first time, and the energy positions are 23.75 eV(4s-15s), 25.66 eV(4-16s/4d) and 26.60 eV(4-17s/5d), respectively.
Correlative Collapses and Revivals in Two Trapped Ions
ZENG Hao-Sheng, KUANG Le-Man, GAO Ke-Lin
Chin. Phys. Lett. 2002, 19 (4): 497-499 .  
Abstract   PDF(pc) (350KB) ( 364 )
An analytic solution is presented for two trapped ions resonantly interacting with laser beams to the first red side-band of center-of-mass mode, in Lamb-Dicke regime and under rotation wave approximation. This shows the existence of correlative quantum collapses and revivals for the occupation of two atoms.
Reduction of Lasing Threshold by Deforming a Circular Resonator
PU Xiao-Yun, XIA Yun-Jie, LEE Wing-Kee
Chin. Phys. Lett. 2002, 19 (4): 500-503 .  
Abstract   PDF(pc) (261KB) ( 439 )
We have reduced the lasing threshold of a circular resonator formed by a dye-doped pendant drop, by changing its shape from a circle to an oval. This phenomenon can be explained by the decrease of the number (p) of modes that support lasing in the resonator. A theory that connects wave and ray pictures in dealing with the cavity resonance is used to estimate p and its dependence on the eccentricity of an oval-shaped resonator. The measured lasing threshold and the calculated p have a linear relationship in agreement with our prediction.
Intracavity-Doubled Self-Q-Switched Nd,Cr:YAG 946/473 nm Microchip Laser
LI De-Hua, WANG Ling, GAO Chun-Qing, ZHANG Zhi-Guo, FENG Bao-Hua, Volker Gaebler, LIU Bai-Ning, H. J. Eichler, ZHANG Shi-Wen, LIU An-Han, SHEN De-Zhong
Chin. Phys. Lett. 2002, 19 (4): 504-506 .  
Abstract   PDF(pc) (328KB) ( 867 )
We carried out the operation of an intracavity frequency-doubled self-Q-switched Nd,Cr:YAG/KNbO3 946/473nm microchip laser pumped by a Ti:sapphire laser. The overall cavity length was about 4 mm. The maximum average blue power of 12 mW was achieved with a repetition rate of 13 kHz at an absorbed pump power of 545 mW. The pulses of 473 nm laser had duration of 7ns and peak power of 132 W at this pump level. The conversion efficiency was 2.2 % with respect to absorbed pump power of 808 nm laser.

A Pseudospectral Time-Domain Algorithm for Calculating the Band Structure of a Two-Dimensional Photonic Crystal
HE Jiang-Ping, SHEN Lin-Fang, ZHANG Quan, HE Sai-Ling
Chin. Phys. Lett. 2002, 19 (4): 507-510 .  
Abstract   PDF(pc) (539KB) ( 525 )
A pseudospectral time-domain (PSTD) method is developed for
calculating the band structure of a two-dimensional photonic crystal. Maxwell's equations are rewritten in terms of period fields by using the Bloch theorem. Instead of spatial finite differences, the fast Fourier transform is used to calculate the spatial derivatives. To reach a similar accuracy, fewer sample points are required in the present PSTD method as compared to the conventional finite-difference-time-domain methods. Our numerical simulation shows that the present PSTD method is an efficient and accurate method for calculating the band structure of a photonic crystal.
Formation Process of TiO2 Inverse Opal
NI Pei-Gen, CHENG Bing-Ying, ZHANG Dao-Zhong
Chin. Phys. Lett. 2002, 19 (4): 511-514 .  
Abstract   PDF(pc) (1204KB) ( 741 )
Inverse opals of TiO2 with different filling fractions were fabricated by using opal of polystyrene spheres as a template. Scanning electron micrograph showed the accumulative process of TiO2. The transmission spectra of inverse opal with different filling fraction were measured and the shifts of transmission dip with the filling fraction were observed. Our investigation made the infiltration process clear, and it might be helpful for further improvement of the fabrication of TiO2 inverse opal.
Lattice Bhatnagar-Gross-Krook Simulations of Turbulent Natural Convection in a Cavity
SHI Bao-Chang, GUO Zhao-Li, WANG Neng-Chao
Chin. Phys. Lett. 2002, 19 (4): 515-517 .  
Abstract   PDF(pc) (362KB) ( 1760 )
A thermal lattice Bhatnagar-Gross-Krook (LBGK) model with a robust boundary scheme is developed for the Boussinesq incompressible fluids. In the model the velocity and temperature fields are solved by two independent LBGK equations which are combined into a coupled one for the whole system. The two-dimensional natural convection flow of air in a differentially heated cavity of aspect ratio 4 is simulated for the Rayleigh number up to 1010. The numerical results are found to be in good agreement with those of previous studies.
Opacity Calculations for Non-local Thermodynamic Equilibrium Mixtures
WU Ze-Qing, HAN Guo-Xing, PANG Jin-Qiao
Chin. Phys. Lett. 2002, 19 (4): 518-520 .  
Abstract   PDF(pc) (326KB) ( 840 )
Based on the average atom model, a non-local thermodynamic equilibrium (non-LTE) model is developed to calculate opacity for mixtures. This model could be applied to high-Z problems. The mean ionization degrees of SiO2 of present calculation are slightly higher compared with another model for mixtures. As an example, opacity of Au and Nd mixture is calculated. The results show concrete non-LTE effects and the increase in opacity of the mixture is shown clearly.
Self-Consistent Description of Nitrogen dc Glow Discharge
FU Guang-Sheng, WANG Jiu-Li, YU Wei, HAN Li
Chin. Phys. Lett. 2002, 19 (4): 521-523 .  
Abstract   PDF(pc) (302KB) ( 550 )
A self-consistent hybrid Monte Carlo fluid model is presented to describe the nitrogen dc glow discharge. The movement of fast electrons is simulated by the Monte Carlo method while the dynamics of slow electrons and ions is by fluid equations. The spatial features of charged species and the corresponding electric field throughout the discharge have been calculated, which include the creation rates of ions and slow electrons, densities of the charged species, the electric field and the potential distribution. These closely related results can give a self-consistent explanation of the discharge characteristics throughout the space of nitrogen dc glow discharge. The calculated ion density is also compared with the corresponding experimental result.
Structural Properties of Water by a Flexible Water Model
LIANG Yun-Feng, ZHU Zhen-Gang, LIU Chang-Song
Chin. Phys. Lett. 2002, 19 (4): 524-527 .  
Abstract   PDF(pc) (429KB) ( 395 )
The structural properties of water at different temperatures have been investigated using a flexible water model in the isothermal-isobaric ensemble. With decreasing temperature, the tetrahedrality of the distribution of the water molecules around the central water molecule is enhanced, and the hydrogen bonds become more linear. By means of a conjugate gradient energy minimization, dynamical configurations at various temperatures have been mapped onto nearby potential-energy minima, the 50°-60°peak (P1) in the distribution function of the O-O-O angle of a trimer becomes far smaller. However there appears to be a small but observable temperature dependence of P1, i.e., the higher the temperature, the higher the P1 intensity.

Behaviour of Grüneisen Parameter at High Pressure and Temperature Inferred from Shock Compression Data
WU Qiang, JING Fu-Qian, LI Xin-Zhu
Chin. Phys. Lett. 2002, 19 (4): 528-530 .  
Abstract   PDF(pc) (280KB) ( 452 )
A new method is proposed to calculate the Grüneisen parameter directly from the experimental Hugoniot data, without any assumption on the lattice vibrational mode of the material being studied. Compared with the results calculated by the methods proposed previously, the values of the Grüneisen parameter calculated have three distinguishable features that support the rationality of the method. A new phenomenon that the lattice vibrational mode changes with thermodynamic state of the solid has been first observed from the calculated results, which implies that the material parameter g, characterizing the lattice vibrational mode, is material dependent rather than a material constant.

A New Hugoniot Equation of State for Shocked Porous Materials
GENG Hua-Yun, TAN Hua, WU Qiang
Chin. Phys. Lett. 2002, 19 (4): 531-533 .  
Abstract   PDF(pc) (373KB) ( 724 )
A thermodynamic equation of state (EOS) is derived to be appropriate for investigating the thermodynamic variations along isobaric paths to predict the compression behaviour of porous materials. This EOS model is tested on porous iron, copper, lead and tungsten with different initial densities. The calculated temperature and Hugoniot are in good agreement with the corresponding experimental and theoretical data published previously. It is interesting that this model can satisfactorily predict the shock behaviour of porous materials over a wide scope of porosity and pressure.

Effect of the Coadsorption of CO and O2 on the Phase Diagram of the Ziff-Gulari-Barshad Model
HUA Da-Yin, MA Yu-Qiang
Chin. Phys. Lett. 2002, 19 (4): 534-536 .  
Abstract   PDF(pc) (297KB) ( 485 )
The effect of the coadsorption of CO and O2 on the Ziff-Gulari-Barshad surface catalytic reaction system is studied by Monte Carlo simulation. The coadsorption of both species adds an extra reaction step to the classical Ziff-Gulari-Barshad model. It is shown that the second-order phase transition from the reactive state to the O-passivated state in the Ziff-Gulari-Barshad model is eliminated, and the production rate of CO2 increases linearly along the fraction yco of CO in gas phase when it is low, in agreement with experimental results. We also find that the increase of the probability of the coadsorption leads to the decrease of the critical value of yco of the discontinuous phase transition to the CO-passivated state.
Modified Transition State Theory for Evaporation and Condensation
WANG Zun-Jing, CHEN Min, GUO Zeng-Yuan
Chin. Phys. Lett. 2002, 19 (4): 537-539 .  
Abstract   PDF(pc) (327KB) ( 330 )
A modification of transition state theory for evaporation and
condensation is presented by analysing the kinetic characteristics of liquid-vapor interphase transport. In the modified transition state theory, the moving orientation of molecules is introduced into the calculation of the free volume of the activated complex. The condensation coefficients of argon at different temperatures are calculated with the modified transition state theory. The results agree well with those from molecular dynamics simulations.
Pressure Fluctuation of 1/ fα in the Film Boiling of He II
ZHANG Peng, MURAKAMI Masahide, WANG Ru-Zhu
Chin. Phys. Lett. 2002, 19 (4): 540-542 .  
Abstract   PDF(pc) (598KB) ( 538 )
A detailed study of the pressure oscillation induced by the film boiling of He II is presented. The film boiling state and the stability of the vapor film are determined by the governing parameter (i.e. the immersion depth). It is found that the power density spectrum of the pressure oscillation induced by the film boiling displays the 1/ fα-behaviour, The exponent α was found to be within the range from one to two, which indicates the existence of self-organized criticality in the film boiling of He II.

Interfacial Properties of AlN/Si(111) Grown by Metal-Organic Chemical Vapor Deposition
XI Dong-Juan, ZHENG You-Dou, CHEN Peng, ZHAO Zuo-Ming, CHEN Ping, XIE Shi-Yong, JIANG Ruo-Lian, SHEN Bo, GU Shu-Lin, ZHANG Rong
Chin. Phys. Lett. 2002, 19 (4): 543-545 .  
Abstract   PDF(pc) (394KB) ( 923 )
We have studied the interfacial structures of AlN/Si(111) grown by metal-organic 0chemical vapor deposition. X-ray photoelectron spectrum and Auger electron spectrum were employed to analyse the components and chemical structures of AlN/Si(111). The results indicated that a mix-crystal transition region, approximately 12nm, was present between AlN film and Si substrate and it was composed of AlN and Si3N4. After analysis we found the existence of Si3N4 could not be avoided in AlN/Si(111) interface because of strong diffusion at 1070°C. Even in AlN layer Si-N bonds, Si-Si bonds can be found.
Effects of Magnetic Field on the Valence Bond Property of the Double-Quantum-Dot Molecule
WANG Li-Min, LUO Ying, MA Ben-Kun
Chin. Phys. Lett. 2002, 19 (4): 546-549 .  
Abstract   PDF(pc) (615KB) ( 402 )
Effects of magnetic field on the valence bond property of the double-quantum-dot molecule are numerically studied by the finite element method and perturbation approach because of the absence of cylindrical symmetry in the horizontally coupled dots. The calculation results show that the energy value of the ground state changes differently from that of the first excited state with increasing magnetic field strength, and they cross under certain magnetic field. The increasing magnetic field makes the covalent bond state change into an ionic bond state, which agrees qualitatively with experimental result and makes ionic bond states remain. The oscillator strength of transition between covalent bond states decreases distinctly with the increasing magnetic field strength, when the molecule is irradiated by polarized light. Such a phenomenon is possibly useful for actual applications.
Improved Coupled Reservoir Model for Inelastic Scattering in One-Dimensional Mesoscopic Metal Rings
DING Hong-Sheng, CHEN Geng-Hua, ZHAO Shi-Ping, YANG Qian-Sheng
Chin. Phys. Lett. 2002, 19 (4): 550-552 .  
Abstract   PDF(pc) (261KB) ( 352 )
In order to strictly solve the problem of persistent current in one-dimensional mesoscopic metal rings, a model with a perfect ring coupled to an external reservoir by a four-lead junction is introduced to independently describe inelastic scattering. The junction is expressed by a 4 x 4 S-matrix, which is very similar to that used by Büttiker in sequential tunneling. Since the S-matrix is unitary, the current conservation keeps automatically. Since the quadruplet of the matrix problem can be reduced into two topologically separate doublets, it gives a simple and elegant method compared with the former description with 3 x 3 matrix.
Schottky Barrier Height Inhomogeneity of Ti/n-GaAs Contact Studied by the I-V-T Technique
JIANG Yu-Long, RU Guo-Ping, LU Fang, QU Xin-Ping, LI Bing-Zong, LI Wei, LI Ai-Zhen
Chin. Phys. Lett. 2002, 19 (4): 553-556 .  
Abstract   PDF(pc) (377KB) ( 707 )
The current-voltage characteristics of Ti/n-GaAs Schottky diodes measured over a temperature range of 78 to 299 K have been interpreted on the basis of thermionic emission across an inhomogeneous Schottky contact. The experiment shows that the apparent barrier height (Фap) increases from 0.437 eV at 78 K to 0.698 eV at room temperature. The plot of Фap versus 1/T does not exhibit a simple linear relationship over the whole temperature range, indicating that the barrier height distribution is more complicated than the frequently observed single Gaussian distribution. A new multi-Gaussian distribution model is developed. Our experimental results can be explained by a double Gaussian distribution of the barrier heights. The weight, the mean barrier height, and the standard deviation of the two Gaussian functions are 0.00001 and 0.99999, 0.721 and 0.696, 0.069 and 0.012eV, respectively.
Characterization of Femtosecond Low-Temperature-Grown GaAs Photoconductive Switch
LIN Wei-Zhu, LIU Zhi-Gang, LIAO Rui, ZHANG Hai-Chao, GUO Bing, WEN Jin-Hui, LAI Tian-Shu
Chin. Phys. Lett. 2002, 19 (4): 557-559 .  
Abstract   PDF(pc) (309KB) ( 333 )
A photoconductive response time, As short as 350 fs, of a
low-temperature-grown GaAs (LT-GaAs) micro-coplanar photoconductive switch has been measured and modeled to the ultrafast trapping of the photoexcited carriers in LT-GaAs. The coherent interference of the pump and probe pulses results in a narrow spike photocurrent autocorrelation signal which maps the femtosecond optical pulses.
Temperature Dependence of Energy Gaps in Spin-1/2 Dimerized Heisenberg Chain
JIANG Xue-Fan, XING Ding-Yu, CHEN Hong
Chin. Phys. Lett. 2002, 19 (4): 560-562 .  
Abstract   PDF(pc) (240KB) ( 337 )
We present a method which combines a thermal coherent state approach with a self-consistent quantum theory to investigate the spin-1/2 dimerized antiferromagnetic Heisenberg chain. It is found that both excitation gaps between the ground state and two lowest excited modes, the triplet one-magnon excitation and the singlet two-magnon bound state decrease monotonically with increasing temperature. Our results are consistent with those obtained from the other approximations.
Dielectric Enhancement and Maxwell-Wagner Effect in Polycrystalline BaTiO3/Ba0.2Sr0.8TiO3 Multilayered Thin Films
GE Shui-Bing, SHEN Ming-Rong, NING Zhao-Yuan
Chin. Phys. Lett. 2002, 19 (4): 563-565 .  
Abstract   PDF(pc) (580KB) ( 589 )
Polycrystalline BaTiO3/Ba0.2Sr0.8TiO3 multilayer thin films were fabricated by pulsed-laser deposition onto Pt/Ti/SiO2/Si substrates with various stacking periodicities. The dielectric constant of the films was obviously enhanced with decrease of the individual layer thickness, while the dielectric loss was kept at a low level comparable to that of the pure Ba0.6Sr0.4TiO3 thin films. The Maxwell-Wagner model is used to explain the experimental data.
Polarization Fatigue in Ferroelectric Thin Films
WANG Yi, K. H. WONG, WU Wen-Bin
Chin. Phys. Lett. 2002, 19 (4): 566-568 .  
Abstract   PDF(pc) (352KB) ( 616 )
The fatigue problem in ferroelectric thin films is investigated based on the switched charge per unit area versus switching cycles. The temperature, dielectric permittivity, voltage bias, frequency and defect valence dependent switching polarization properties are calculated quantitatively with an extended Dawber-Scott model. The results are in agreement with the recent experiments.
Thermal Diffusivity Measurements of Li2B4O7 and KNbO3 Solution by Laser Flash Method
JIN Wei-Qing, NAGASHIMA Toshio, YODA Shinichi, LIANG Xin-An, PAN Zhi-Lei
Chin. Phys. Lett. 2002, 19 (4): 569-571 .  
Abstract   PDF(pc) (414KB) ( 378 )
The thermal diffusivities of Li2B4O7 +KNbO3(20wt.%) solution have been determined at temperature between 900°C and 990°C using a three layered laser flash method on the differential scheme. The thermal diffusivity of this Li2B4O7 and KNbO3 solution ranges from 3.6.x 10-3cm2/s to 4.1 x 10-3cm2/s. A positive temperature dependence of thermal diffusivity of solution is obtained.

Improved Carrier Transfer in Red Organic Light Emitting Diodes Doped with Rubrene
LIU Hong-Yu, GAO Wen-Bao, YANG Kai-Xia, LIU Shi-Yong
Chin. Phys. Lett. 2002, 19 (4): 572-574 .  
Abstract   PDF(pc) (385KB) ( 426 )
A red organic light emitting diode doped with rubrene is constructed with the configuration of ITO/NPB/Alq3: rubrene: DCM/Alq3/LiF/Al. In the device, N,N'-bis-(1-naphthl)-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine (NPB) is used as the hole-transporting layer, tris(8-quinolinolato) aluminum (Alq3) as the electron-transporting layer and Alq3 doped with 5,6,11,12-tetraphenylnaphthacene (rubrene) and 4-dicyanomethylene-2-methyl-6- p-dimethyla- minostyryl)-4H-pyran (DCM) as the emitting layer. When the doping concentration of rubrene is 6% and that of DCM is 4%, red purity of the device is improved effectively. The experimental phenomena are explained as the result of the improved carrier transfer from rubrene to DCM.
Ultrafast Optical Kerr Effect in Amorphous As2Se3 Film Induced by Ultrashort Laser Pulses
LIU Qi-Ming, MI Jun, QIAN Shi-Xiong, GAN Fu-Xi,
Chin. Phys. Lett. 2002, 19 (4): 575-577 .  
Abstract   PDF(pc) (308KB) ( 369 )
Nonresonant third-order nonlinear optical properties of amorphous As2Se3 film were investigated experimentally by the method of the femtosecond optical heterodyne detection of optical Kerr effect at 805 nm with the 80 fs ultrafast pulses. The results showed that the values of real and imaginary components of third-order susceptibility of amorphous As2Se3 film were 5.6 x 10-12 esu and -2.0 x 10-13 esu, respectively. Amorphous As2Se3 film demonstrated a very fast response time within 200 fs. The ultrafast response and large third-order nonlinearity are attributed to the ultrafast distortion of the electron cloud of As2Se3 film.

Exciton-Phonon Scattering in CdSe/ZnSe Quantum Dots
ZHANG Li-Gong, SHEN De-Zhen, FAN Xi-Wu, LU Shao-Zhe
Chin. Phys. Lett. 2002, 19 (4): 578-580 .  
Abstract   PDF(pc) (306KB) ( 483 )
A temperature-dependent photoluminescence measurement is performed in the CdSe/ZnSe quantum dots with a ZnCdSe quantum well. We deduce the temperature dependence of the exciton line-width and peak energy of the zero-dimensional exciton in the quantum dots and two-dimensional exciton in the CdSe wetting layer. The experimental data reveals a reduction of homogeneous broadening of exciton line in the quantum dots in comparison with that in the two-dimensional wetting layer, which indicates the decrease of exciton and optical phonon coupling in the CdSe quantum dots.
Influences of Annealing on the Opto-electronic Properties of ZnO Films Grown by Plasma-Enhanced MOCVD
WANG Jin-Zhong, DU Guo-Tong, WANG Xin-Qiang, CHANG Yu-Chun, YAN Wei, YANG Shu-Ren, MA Yan, WANG Hai-Song, GAO Ding-San, LIU Xiang, CAO Hui, XU Jun-Ying, R. P. H. Chang
Chin. Phys. Lett. 2002, 19 (4): 581-583 .  
Abstract   PDF(pc) (322KB) ( 510 )
ZnO thin films have been grown on C-plane sapphire substrates by plasma-enhanced metal-organic chemical vapor deposition. The samples are then annealed at a higher temperature. The resistivity, concentration of electron, mobility and optically pumped threshold of both as-grown and annealed films are investigated. Furthermore, their structural and optical properties are also examined with x-ray diffraction, emission spectra and optical transmission spectra. The results indicate that the quality of ZnO thin films can be improved by annealing.

Rapid Hypoeutectic Growth Within a Highly Undercooled Liquid Under Containerless Condition
HAN Xiu-Jun, YAO Wen-Jing, WEI Bing-Bo
Chin. Phys. Lett. 2002, 19 (4): 584-587 .  
Abstract   PDF(pc) (1032KB) ( 519 )
Rapid hypoeutectic growth from a highly undercooled liquid was
accomplished by containerlessly processing Ni-32%Sb hypoeutectic alloy in a 3m drop tube. The containerless state during free fall of droplet produces substantial undercooling up to 350K (0.24TL). The growth mechanism is found to transform from primary α-Ni dendrite plus lamellar eutectic to lamellar eutectic and finally to anomalous eutectic if droplet undercooling exceeds the two thresholds of 112K and 242K, respectively. Based on the current eutectic and dendritic growth models, the eutectic coupled zone is calculated and used to explain the growth mechanism transition. Calculations also indicate that the growth of α-Ni primary dendrite was mainly controlled by solute diffusion.
A Novel GaAs/InGaAs/AlGaAs Structure of Modulation-Doped Field-Effect Transistors with High Transconductances
CHANG Yu-Chun, Hailin Luo, Y. Wang, WANG Hai-Song, WANG Jian-Gang, DU Guo-Tong
Chin. Phys. Lett. 2002, 19 (4): 588-590 .  
Abstract   PDF(pc) (400KB) ( 533 )
Novel structure GaAs/InGaAs/AlGaAs pseudomorphic modulation-doped field-effect transistors (MODFETs) with a buried p-i-n dipole layer and a 200 nm buffer layer have been fabricated. According to the calculation, the dipole buried layer not only results in the very thin buffer layer required, but also enhances the density of two-dimensional electron gas. The measured transconductances of these MODFETs, with a gate length of 2 μm and a drain-source spacing of 5 μm, are as high as 320 mS/mm and the measured maximum drain currents of the typical devices are higher than 500 mA/mm.
Magnetocrystalline Anisotropy and Magnetoelasticity of Preferentially Oriented Martensitic Variants in Ni52Mn24Ga24 Single Crystals
QU Jing-Ping, WANG Wen-Hong, MENG Fan-Bin, LIU Bao-Dan, LIU Zhu-Hong, CHEN Jing-Lan, LI Yang-Xian, WU Guang-Heng
Chin. Phys. Lett. 2002, 19 (4): 591-594 .  
Abstract   PDF(pc) (444KB) ( 663 )
The magnetocrystalline anisotropy and magnetoelasticity of preferentially oriented martensitic variants in an off-stoichiometric Ni52Mn24Ga24 single crystal were investigated. We found that the easy magnetization direction of the martensite phase is the [110] direction, and the hard magnetization exhibited in [001], the growth direction of single crystals. The temperature dependence of the anisotropy fields and constants of Ni52Mn24Ga24 have been determined. It was found that at martensite phase, the anisotropy field increases monotonically with decreasing temperature, but the anisotropy constant first increases rapidly and then the increasing rate become smaller and smaller. Based on a previous model, present results suggest that the competition between the Zeeman energy and the magnetocrystalline anisotropy energy is mainly responsible for the magnitude of magnetic-field-induced strain in this material.
Mössbauer Evidence for Ferromagnetic Ordering in Copper-Iron Cyanometallates
XIA Yuan-Fu, YU Zhi, SONG Yong, HUANG Hong-Bo, YOU Xiao-Zeng, X. Z. Zhou, Z. W. Li, H. P. Kunkel, Gwyn Williams
Chin. Phys. Lett. 2002, 19 (4): 595-598 .  
Abstract   PDF(pc) (442KB) ( 613 )
A novel member of the Prussian blue family, CuII3 [FeIII (CN)6]2.3NH3.6H2O, was synthesized, in which NH3 ligands are in stochastic distribution. X-ray diffraction data, zero-field-cooled magnetization and field-cooled magnetization curves, Mössbauer spectra with/without an external field of 5 T and a structural model are presented. This Prussian blue analog displays considerable magnetic hardness below the magnetic transition temperature Tc, which is about 19.8 K. The coercive field determined from the magnetization hysteresis loop at 5 K was 2.76 kOe. The copper-iron cyanometallates have potential applications in the design of novel magnetic systems.
Lattice Strain Induced by Ion Implantation in AlGaAs/AlGaInAs Quantum Well Samples
LIU Pi-Jun, XIA Yue-Yuan, LIU Xiang-Dong, YUAN Feng-Po, PAN Jiao-Qing, XUE Cheng-Shan, LI Yu-Guo, ZHAO Ming-Wen, MA Yu-Chen
Chin. Phys. Lett. 2002, 19 (4): 599-601 .  
Abstract   PDF(pc) (290KB) ( 662 )
Si+ ions of 350 keV have been implanted into AlGaAs/AlGaInAs quantum well samples in the dose range from 5 x 1013cm-2 to 5 x 1014cm-2. The Raman spectra and high resolution x-ray diffraction (HRXRD) were measured from these implanted samples as well as the un-implanted one. In the implanted layers the average strain which was evaluated by HRXRD increases with the implantation doses and varies from 0.0011 to 0.0029. The quantum well interface intermixing effect and compositional modification also observed from HRXRD. At the higher doses, an abnormal annealing procedure takes place and it partly removes damage, but the strain is kept almost unchanged in the epilayers.
Contribution of the Atmospheric Dynamics to the Sporadic Sodium Layer Formation
YANG Guo-Tao, WANG Jia-Min, LIU Bing-Mo, CHENG Xue-Wu, WAN Wei-Xing, GONG Shun-Sheng
Chin. Phys. Lett. 2002, 19 (4): 602-604 .  
Abstract   PDF(pc) (366KB) ( 500 )
We report on a sporadic sodium layer (SSL) event observed by our Na fluorescence lidar at Wuhan, China (31°N, 114°E) on March 16, 1999, and we reveal some special behaviour. From careful analysis of various sodium content variations of the layer during the development of this SSL event, it is found that besides the sodium injection mechanism as expected, another mechanism we called the atmospheric dynamics also made a noticeable contribution to this SSL formation. Computer simulations conformed that under the combined action of a suitable sodium injection and a bi-direction vertical wind field, an SSL profile can be reproduced with a pronounced SSL
peak on normal sodium layer as we observed in this event. From these results, it is emphasized that atmospheric dynamics is important for the SSL formation.
A Unified Model of Magnetic Extraction of Spin Energy from a Black Hole
WANG Ding-Xiong, XIAO Kan, LEI Wei-Hua
Chin. Phys. Lett. 2002, 19 (4): 605-608 .  
Abstract   PDF(pc) (322KB) ( 328 )
A unified model of magnetic extraction of spin energy from a black hole is discussed based on the theory of black hole magnetosphere. The magnetic extracting power is expressed by a unified formular, which is applicable to both the Blandford-Znajek (BZ) process and the magnetic coupling (MC) process. Strength and characteristics of the BZ power and the MC power are compared detailedly. In addition, the impedance matching condition for the BZ power is extended to the more general case.
48 articles