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Volume 18 Issue 7
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Original Articles
Supercoherent State of the Orthosymplectic (2,1) Superalgebra
CHEN Yong-Qing, SONG Xing-Chang
Chin. Phys. Lett. 2001, 18 (7): 844-846 .  
Abstract   PDF(pc) (187KB) ( 416 )
The normalization supercoherent state of the orthosymplectic(OSP)(2,1) superalgebra is constructed and its properties are discussed in detail. The new inhomogeneous differential realizations of the OSP(2,1) superalgebras are given. It may be of use for determining new concrete structure of the quasi-exactly-solvable hamiltonian corresponding to the OSP(2,1) supersymmetric quantum system.

Molecular Dynamics Simulation of Diffusion Coefficients of Oxygen, Nitrogen and Sodium Chloride in Supercritical Water
XIAO Ji, LU Jiu-Fang, CHEN Jian, LI Yi-Gui
Chin. Phys. Lett. 2001, 18 (7): 847-849 .  
Abstract   PDF(pc) (310KB) ( 535 )
Molecular dynamics simulation has been performed to determine the infinite-dilution diffusion coefficients of oxygen and nitrogen, and the diffusion coefficients of NaCl in supercritical water from 703.2-763.2 K and 30-45 MPa. The results obtained show that the diffusion coefficients in supercritical water increase with temperature, while decrease with pressure. Nevertheless, the diffusion coefficients in supercritical water are much larger than those in normal water.
Two-Parameter Radon Transformation of the Wigner Operator and Its Inverse
FAN Hong-Yi, CHENG Hai-Ling
Chin. Phys. Lett. 2001, 18 (7): 850-853 .  
Abstract   PDF(pc) (211KB) ( 495 )
Using the technique of integration within an ordered product of operators, we reveal that a new quantum mechanical representation |x,μ,v > exsit, the eigenvector of operator μQ+vP (linear combination of coordinate Q and momentum P) with eigenvalue x, which is inherent to the two-parameter(μ,v) Radon transformation of the Wigner operator. It turns out that the projection operator |x,μ,v > < x,μ,v | is just the Radon transformation of the Wigner operator. The inverse of operator Radon transformation is also derived which indicates tomography in operator version.

Energy Levels of a Positronium Negative Ion
DUAN Bin, GU Xiao-Yan, MA Zhong-Qi
Chin. Phys. Lett. 2001, 18 (7): 854-856 .  
Abstract   PDF(pc) (193KB) ( 386 )
The energy levels of a positronium negative ion are calculated
directly from the Schrödinger equation. After removing the
translational and rotational degrees of freedom, only three internal variables are involved in both functions and equations.
The singularity of the solution is eliminated by choosing the right internal variables, and the series in calculation converges very fast.
“Angle” Operator Conjugate to Photon’s Intrinsic Angular Momentum
FAN Hong-Yi
Chin. Phys. Lett. 2001, 18 (7): 857-859 .  
Abstract   PDF(pc) (203KB) ( 400 )
We find the correct “angle”operator conjugate to the intrinsic angular momentum of tne photon by introducing a suitable representation which involves both left-handed and right-handed polarization photon operators.
Possibility of Quantum Teleportation and the Reduced Density Matrix
ZHU Hong-Bo, ZENG Jin-Yan
Chin. Phys. Lett. 2001, 18 (7): 860-863 .  
Abstract   PDF(pc) (211KB) ( 507 )
It is shown that only the maximally entangled two-particle (spin 1/2) states whose one-particle reduced density matrix is ρ(i) = (1/2)I2 can realize the teleportation of an arbitrary one-particle spin state. Based on this, to teleport an arbitrary k-particle spin state, one must prepare an N-particle entangled state whose k-particle (k < N) reduced density matrix has the structure 2-kI2k (I2k being the 2k x 2k identity matrix). The N-particle Greenberger-Horne-Zeilinger states cannot realize the teleportation of an arbitrary k-particle (N > k ≥ 2) state, except for special states with only two components.
Thermodynamic Properties of Sodium: A First-Principles Study
WANG Yi, SUN Yun-Feng
Chin. Phys. Lett. 2001, 18 (7): 864-867 .  
Abstract   PDF(pc) (414KB) ( 529 )
The Thermal expansion, Hugoniot state and 300 K isotherm of sodium have been calculated on the basis of: (i) the accurate calculations of 0 K total energies with the full-potential linearized augmented plane wave method within the generalized gradient approximation to exchange-correlational functional and (ii) the newly developed classical mean-field statistics where both the cold and thermal parts of the Helmholtz free-energy are entirely derived from the 0 K total energy. A quite satisfactory agreement between calculation and experiment has been observed. Our approach does not invoke any empirical parameter, which has long been a desirability on the field of material science.

Ferromagnetism in an Electron Gas Obeying Fractional Statistics
YANG Kai-Hua, HAN Ru-Shan, WANG Yu-Peng
Chin. Phys. Lett. 2001, 18 (7): 868-869 .  
Abstract   PDF(pc) (164KB) ( 374 )
We study an ideal electron gas obeying fractional statistics. The parameters for exclusion statistics are given by the strength of the repulsive interactions. In some parameter regions, it is found the system shows itinerant ferromagnetism.
Stochastic Multiresonance Induced by an Optimal Noise Pulse Interval Duo to Hopping of Energy Levels
ZHANG Ji-Qian, XIN Hou-Wen
Chin. Phys. Lett. 2001, 18 (7): 870-873 .  
Abstract   PDF(pc) (480KB) ( 725 )
An interesting phenomenon, called the Stochastic multiresonance (SMR), induced by the variation of the noise pulse interval, is described and the formative mechanism of SMR is investigated by using the concept of hopping between different energy states. Also, the SMR can be realized by choosing the optimal noise pulse interval or selecting the appropriate noise intensity.
Phase Synchronization in Coupled Oscillators: Dynamical Manifestations
ZHENG Zhi-Gang, HU Gang, Bambi Hu,
Chin. Phys. Lett. 2001, 18 (7): 874-877 .  
Abstract   PDF(pc) (599KB) ( 627 )
Phase synchronized entrainment of coupled oscillators with distributed natural frequencies is studied by exploring the dynamical manifestation. The route from partial to complete phase synchronization is identified as a cascade of transitions from high- to low-dimensional tori (quasiperiodicities) interrupted by intermittent chaos. Torus ON-OFF intermittency is found at the onset of desynchronization. Desynchronization-induced chaos originates from the mixing of intermittent ON-OFF time scales.
Controlling Strong Chaos by Adaptive Coupling Method in the Perturbed Cat Map
XU Hai-Bo, WANG Guang-Rui, CHEN Shi-Gang
Chin. Phys. Lett. 2001, 18 (7): 878-881 .  
Abstract   PDF(pc) (674KB) ( 412 )
The method for controlling Hamiltonian chaos by adaptive integrable mode coupling is extended to controlling strong chaos by adaptive integrable and near-integrable mode coupling. We illustrate this method with a highly chaotic system, the perturbed cat map. All orbits can be effectively controlled to the periodic or quasiperiodic orbits. The method is robust against the presence of weak external noise.
Critical Behaviour of the Gaussian Model on Sierpinski Carpets
LIN Zhen-Quan, KONG Xiang-Mu
Chin. Phys. Lett. 2001, 18 (7): 882-884 .  
Abstract   PDF(pc) (265KB) ( 437 )
The Gaussian model on Sierpinski carpets with two types of nearest neighbour interactions K and Kw and two corresponding types of the Gaussian. distribution constants b and bw is constructed by generalizing that on translationally invariant square lattice. The critical behaviours are studied by the renormalization-group approach and spin rescaling method. They are found to be quite different from that on translationally invariant square lattice. There are two critical points at (K* = b,K*w = 0) and (K* = 0,K*w = bw), and the correlation length critical exponents are calculated.

A Hadronic Model Calculation of the Electro-Production of d* Dibaryon
QING Di, SUN He-Ming, WANG Fan
Chin. Phys. Lett. 2001, 18 (7): 885-887 .  
Abstract   PDF(pc) (286KB) ( 424 )
The electro production cross sections of ed → ed* have been calculated based on the meson exchange current model. The cross section around 30°of 1 GeV electron in the laboratory frame is about 10 nb, which is about two orders smaller than that of the quasi-elastic and Δ resonance production. A special kinematics and detector system must be studied to pin down the weak signal of d* resonance from the strong background.
Signature Inversion of the Semi-decoupled Band in the Odd-Odd Nucleus 170Ta
DENG Fu-Guo, YANG Chun-Xiang, , SUN Hui-Bin, WU Xiao-Guang, LU Jing-Bin, ZHAO Guang-Yi, HAN Guang-Bing, PENG Zhao-Hua, YIN Li-Chang, WEN Shu-Xian, LI Guang-Sheng, YUAN Guan-Jun ZHOU Hong-Yu, LIU Yun-Zuo, ZHU Li-Hua
Chin. Phys. Lett. 2001, 18 (7): 888-890 .  
Abstract   PDF(pc) (662KB) ( 512 )
The high-spin states of the odd-odd nucleus 170Ta have been studied by the 150Gd (19F, 4n) 170Ta reaction at the beam energy of 97 MeV. The α =1 sequence of the semi-decoupled band has been pushed to higher-spin states and the signature inversion point was observed at 19.5ħ. The results are compared with those of the neighboring odd-odd nuclei.
Tensor Couplings of ω- and ρ-Mesons with Nucleons in a Derivative Scalar Coupling Model for Finite Nuclei
GUO Hua, HU Xiang
Chin. Phys. Lett. 2001, 18 (7): 891-893 .  
Abstract   PDF(pc) (358KB) ( 466 )
The ω- and ρ-meson tensor couplings to nucleons in a derivative scalar coupling model for finite nuclei are investigated. The influences of the tensor couplings on the binding energies per nucleon, the root-mean-square charge radii, spin-orbit splittings and single particle energies are discussed. The obtained results show that the spin-orbit splittings for finite nuclei are more sensitive to the ω-meson tensor coupling.
High-Spin States in the N = 50 Nucleus 88Sr
LIU Zhong, T. Ishii T. Hayakawa, M. Oshima, Y. Toh, H. Sakurai, M. Notani, M. Ishihara
Chin. Phys. Lett. 2001, 18 (7): 894-896 .  
Abstract   PDF(pc) (402KB) ( 353 )
The Excited states of 88Sr have been produced in the reaction 16O(82Se,4p6n) and studied using the in-beam γ spectroscopy techniques. Two high-spin level structures have been observed and established up to 8.5 MeV and 7.9 MeV excitation energy, respectively. Based on the measurements of the directional correlations of γ-rays de-exciting oriented states and anisotropic factors of γ-rays, spin values of the excited states have been assigned up to the highest levels observed.
Poissonian Reducibility and Thermal Scaling in Nuclear Dissociation
MA Yu-Gang, SHEN Wen-Qing, ZHU Zhi-Yuan, ZHANG Hu-Yong, YU Li-Ping, CAI Xiang-Zhou, FANG De-Qing, ZHONG Chen
Chin. Phys. Lett. 2001, 18 (7): 897-899 .  
Abstract   PDF(pc) (472KB) ( 387 )
The emission of clusters in the nuclear dissociation was investigated within the framework of isospin dependent lattice gas model. As observed in the recent experimental data, it was found that the emission probability of individual cluster is Poissonian and thermal scaling was observed in the linear Arrhenius plots made from the average multiplicity of each cluster as a function of the inverse temperature. The‘emission barriers’were extracted from the slopes of the Arrhenius plots and mainly depends on the surface energy of the cluster.
Temperature-Sensitive Broadening of Unresolved Transition Arrays in Atomic Spectra
ZHANG Ji-Yan, YANG Guo-Hong, ZHANG Bao-Han, YANG Xiang-Dong, ZHOU Yu-Qing, LI-Jun, LEI An-Le, LIU Hong-Hie, YANG Jia-Min
Chin. Phys. Lett. 2001, 18 (7): 900-902 .  
Abstract   PDF(pc) (267KB) ( 466 )
The width of an unresolved transition array, which was once regarded as insensitive to electron temperature by Audebert et al. [Phys. Rev. A 32 (1985) 409], is found to be a temperature-sensitive function to a certain extent and has the potential of being used in plasma diagnostics. In this letter, on the assumption that the plasma has achieved the local thermodynamical equilibrium and that each of the subarray has a Gaussian shape, the electron temperature of a gold plasma produced by laser irradiation of a microdot is obtained by comparing the experimental width with the theoretical width. The full widths at half maximum of the unresolved transition arrays are computed in the formalism of the spin-orbit-split arrays.

Changes of the Nuclear Charge Distribution of Nd from Optical Isotope Shifts
MA Hong-Liang, LI Mao-Sheng, YANG Fu-Jia
Chin. Phys. Lett. 2001, 18 (7): 903-905 .  
Abstract   PDF(pc) (328KB) ( 431 )
The isotope shifts and hyperfine structures of seven optical transitions for all seven stable isotopes of Nd II were measured by using collinear fast-ion-beam laser spectroscopy. The nuclear parameter λ was obtained from the measured optical isotope shifts for all seven stable isotopes with improved accuracy. The λ values were analysed by using the Fermi distribution for the nuclear charge density. The values of δ< r2 >, δ< r4 > and δ< r6 > were determined.

Novel Single-Frequency Diode Pumped Solid-State Lasers and Their Applications in Laser Ranging and Velocimetry
YANG Su-Hui, WU Ke-Ying, WEI Guang-Hui
Chin. Phys. Lett. 2001, 18 (7): 906-908 .  
Abstract   PDF(pc) (510KB) ( 493 )
Two models of laser diode pumped unidirectional single-frequency ring laser with maximum single frequency output power of 1 W and 780 mW are investigated. The Statistic linewidth of the free-run laser is measured to be 2.1 kHz within 5μs by using a single mode fiber link. We use the monolithic laser to measure the angular speed of a spinning motor and simulate a linearly frequency modulated continuous-wave ladar system in laboratory.

A New Photorefractive Polymer/Liquid Crystal System
LIU Hui, ZHANG Bo, GONG Qi-Huang, BAI Yao-Wen, CHEN Xiao-Fang, WAN Xin-Hua, ZHOU Qi-Feng
Chin. Phys. Lett. 2001, 18 (7): 909-911 .  
Abstract   PDF(pc) (271KB) ( 355 )
The Photorefractive properties of PVK-based polymeric composites
doped with three liquid crystals, 4OCB (4-pertyloxy-4'-cyanobiphenyl ), 5OCB (4-pentyloxy-4'-cyanobiphenyl ), 8OCB (4-octyloxy-4'-cyanobiphenyl ) were investigated by using the two-beam coupling experiment at 633 nm. Gain coefficient over 34 cm -1 at an applied field of 60V/μm was observed. Among the three materials, the 8OCB-doped composite demonstrated a stronger orientational effect and the influence on charge field became apparent.
Propagation of Few-Cycle Pulse Laser in Two-Level Atom Medium
XIAO Jian, WANG Zhong-Yang, XU Zhi-Zhan
Chin. Phys. Lett. 2001, 18 (7): 912-914 .  
Abstract   PDF(pc) (384KB) ( 451 )
By comparing the numerical solutions of Maxwell-Bloch equations beyond and within the slowly-varying envelope approximation and the rotating-wave approximation for the propagation of few-cycle pulse laser in a resonant two-level atom medium, we found that both the Rabi flopping and the refractive index, and subsequently the carrier and the propagation velocity of the few-cycle pulse, are closely connected with the time-derivative behaviour of the electric field. This is because of the Rabi flopping is such that soliton pulse splits during propagation and that a shorter pulse propagates faster than a broader one.
Two Photon Pumped Upconversion and Nonlinear Optical Properties of a New Lasing Dye: DEASPI
WANG Dong, WANG Xiao-Mei, ZHOU Guang-Yong, WANG Chun, SHAO Zong-Shu, JIANG Min-Hua
Chin. Phys. Lett. 2001, 18 (7): 915-917 .  
Abstract   PDF(pc) (393KB) ( 486 )
The two-ephoton pumped frequency upconversion optical properties and the two-photon absorption (TPA) induced nonlinear absorption of a new dye trans-4-[p-(N,N-diethylamino)styryl]-N-methylpyridinium iodide (abbreviated as DEASPI) have been experimentally investigated. This new dye exhibits strong superradiation properties when the pumping power is above the threshold. Furthermore, the superradiation upconversion efficiency and the nonlinear absorption at different wavelengths have been measured. The largest effective molecular TPA cross section was measured to be 3.9 x 10-47cm4.s/photon at 930 nm. At 1064 nm, it was 3.85 x 10-48cm4.s/photon, much smaller than that at 930 nm. The highest upconversion efficiency is 7.57% at 1020 nm, whereas 4.5% at 1064 nm.


A Lattice Boltzmann Method for the Chemical Clock in the Belousov-Zhabotinskii Reaction
YAN Guang-Wu, YUAN Li
Chin. Phys. Lett. 2001, 18 (7): 918-920 .  
Abstract   PDF(pc) (323KB) ( 291 )
A lattice Boltzmann method for the Belousov-Zhabotinskii reaction is proposed to simulate the chemical clock. Applying the Chapman-Enskog expansion and multiscale technique, we obtain a series of lattice Boltzmann equations in different timescales, the conservation law in time scale t0 and coefficients of macroscopic equations to find the equilibrium distribution functions. A simple numerical scheme is designed to simulate the diffusion-reaction systems. The numerical example shows that the proposed method can be used to simulate chemical systems with the chemical clock.
Opacity of Shock-Generated Argon Plasmas
WANG Fan-Hou, CHEN Jing-Ping, MENG Xu-Jun, ZHOU Xian-Ming, LI Xi-Jun, SUN Yong-Sheng, JING Fu-Qian,
Chin. Phys. Lett. 2001, 18 (7): 921-923 .  
Abstract   PDF(pc) (350KB) ( 337 )
Argon plasmas with uniform density and temperature are generated by a planar shock wave through argon gas. The opacities of argon plasma, covering the thermodynamic states at temperature of 1.4-2.2eV and in density of 0.0083-0.015g/cm3, are investigated by measuring the emitted radiance versus time at several visible wavelengths. Comparison of the measured opacities with the calculated ones demonstrates that the average atom model can be used well to describe the essential transport behaviour of photons in argon plasma under the above-mentioned thermodynamic condition. A simplified and self-consistent method to deduce the reflectivity R(λ) at the baseplate surface is applied. It demonstrates that the values of R(λ) are all around 0.4 in the experiments, which are basically in agreement with those given by Erskine previously (1994 J.Quant. Spectrosc. Radiat. Transfer 51 97.)

Detailed Spectral Line Effects on the Radiative Opacity of Laser-Produced Al Plasmas
ZENG Jiao-Long, JIN Feng-Tao, YUAN Jian-Min
Chin. Phys. Lett. 2001, 18 (7): 924-926 .  
Abstract   PDF(pc) (398KB) ( 522 )
The detailed term accounting (DTA) approximation for the line absorption and the average atom (AA) model for bound-free and free-free absorption are used to calculate the radiative opacity of high-power laser-produced plasmas in local thermodynamic equilibrium (LTE). The spectral resolved opacities of Al plasmas are calculated at the temperature and density of 40 eV and 0.0135 g/cm3 and 58 eV and 0.02 g/cm3. Rosseland and Planck mean opacities are obtained by integrating the spectral resolved opacities with Rosseland and Planck weighting functions. The results show that the Rosseland mean opacity is very sensitive to the detailed profile. Radiative opacities under the same plasma conditions are also obtained by using a completely pure AA model. The results from the DTA and pure AA models are then compared.
Suppression of Instability in Strongly Coupled Dusty Plasmas with Ion Flow
XIE Bai-Song, , LIU Ke-Fu, HE Kai-Fen,
Chin. Phys. Lett. 2001, 18 (7): 927-930 .  
Abstract   PDF(pc) (303KB) ( 345 )
The instability of low-frequency longitudinal modes in strongly coupled dusty plasmas with an ion flow is investigated. The dust charging relaxation is taken into account. It is found that when the ion flow is strong enough, the suppression, even disappearence, of instability can occur. Similar to that of the real frequency of waves, the imaginary part of waves also exhibits a transition, which arises from the sensitive dependences on the system parameters and their competition.
A New Regime for Studying the High Bootstrap Current Fraction Plasma
X. Gao, A. Isayama, Y. Kamada, K. Ushigusa, T. Fujita, T. Suzuki
Chin. Phys. Lett. 2001, 18 (7): 931-932 .  
Abstract   PDF(pc) (342KB) ( 410 )
A new experimental regime has recently been studied for achieving high fraction of the bootstrap current in the JT-60U hydrogen discharges. The high poloidal beta (βp ~ 3.61) plasma was obtained by high-power neutral beam injection heating at very high edge safety factor (Ip = 0.3 MA, Bt = 3.65 T, qeff = 25 - 35) region, and the bootstrap current fraction (fBS) was about 40% using the ACCOME code calculation. It was observed that there were no magnetohydrodynamics instabilities to retard the increase of βp and fBS parameters in the new regime.
Coherent Structures of Dust-Drift Waves in a Dusty Plasma
CHEN Yin-Hua, LU Wei, WANG Ge
Chin. Phys. Lett. 2001, 18 (7): 933-935 .  
Abstract   PDF(pc) (510KB) ( 349 )
A new type of very low-frequency electrostatic wave in a dusty plasma, called the dust-drift waves, has been investigated with the three-component fluid model. The dispersion of the waves depends strongly on the dust grain content in plasma. Due to their nonlinear interaction, the dust-drift waves can form two-dimensional dip-hump and multi-peak localized structures. The amplitudes of those structures decrease with the increasing dust content.
Collective Thomson Scattering from Laser-Produced Plasmas
BAI Bo, ZHENG Jian, YU Chang-Xuan, LIU Wan-Dong, JIANG Xiao-Hua, YUAN Xiao-Dong, ZHENG Zhi-Jian, XU Bing, XIANG Yong, ZHAO Chun-Zhuo
Chin. Phys. Lett. 2001, 18 (7): 936-938 .  
Abstract   PDF(pc) (549KB) ( 545 )
Time-resolved Thomson scattering was successfully performed to
diagnose the parameters (ZTe, Ue and Ui) of laser-produced gold plasma. The results show that the collisionless dynamic form factor is accurate enough to be used for reducing the plasma parameters from the experimental data.
Detection of NH2 Radical in Ammonia Radio-Frequency Plasmas by Laser-Induced Resonance Fluorescence
GONG Xue-Yu, X. R. Duan, H. Lange, A. A. Meyer-Plath
Chin. Phys. Lett. 2001, 18 (7): 939-941 .  
Abstract   PDF(pc) (405KB) ( 754 )
By means of one photon absorption laser-induced resonance fluorescence at 599.5 nm the relative concentrations of amidogen (NH2) radical in the ammonia (NH3) radio-frequency (rf) plasma source were measured under different discharge pressures and rf powers. The time dependence of the fluorescence which comes from the radiation 101 -211 of the P-branches of the Σ vibronic sub-bands can be described by a single-exponential decay. The decay time of NH2(A2A1) Σ (0, 9, 0) rovibronic state was determined. The spatial dependence of the NH2 density in discharge tube was measured.
Features of the Real Structure of Lanthanum Hexaboride Polycrystalline
ZHENG Shu-Qi, MIN Guang-Hui, ZOU Zeng-Da, YU Pu-Lian, HAN Jian-De, Y. B. Paderno
Chin. Phys. Lett. 2001, 18 (7): 942-943 .  
Abstract   PDF(pc) (746KB) ( 627 )
The Microstructure of lanthanum hexaboride (LaB6) polycrystalline has been studied by using transmission electron microscope. This shows that the ideal LaB6 polycrystalline can be obtained by sintering ingots at the temperature of 2273 K for holding time of 120 min in Ar pressure of 800 Torr, where the ingots are formed by pressing LaB6 powder at room temperature at a pressure of 0.4-0.5 GPa. The particles in LaB6 polycrystalline hardly bind; there are only a few of pores at the joint parts of three particles and a few of impurities exist in some pores. The sintering process for fabricating LaB6 polycrystalline is analysed and the formation of the pore and the impurities are studied from the point of surface tension.
Singlet Exciton Migration in a Conjugated Polymer by Picosecond Time-Resolved Photoluminescence
MA Guo-Hong, QIAN Shi-Xiong, LEI Hong, WANG He-Zhou, WANG Rong-Qiu, LI Yong-Fang
Chin. Phys. Lett. 2001, 18 (7): 944-946 .  
Abstract   PDF(pc) (287KB) ( 407 )
The transient photoluminescence (PL) of DO-PPV (poly-(2,5-dioctyloxy-1,4-phenylene vinylene)) solution in chloroform was
investigated by picosecond time-resolved PL spectroscopy. An ultrafast rise of PL and the following single exponential decay with a time constant about 400ps were assigned to the formation of intrachain exciton and its decay process, respectively. The redshift of the PL emission spectrum with time was caused by the subsequent exciton migration among the different conjugated segments in the DO-PPV polymer.
Second-Order Phase Transition in the Two-Dimensional Classical Lattice Coulomb Gas of Half-Integer Charges
LUO Meng-Bo, CHEN Qing-Hu, XU Zhu-An, JIAO Zheng-Kuan
Chin. Phys. Lett. 2001, 18 (7): 947-949 .  
Abstract   PDF(pc) (312KB) ( 532 )
The second-order phase transition in the two-dimensional (2D) classical Coulomb gas of half-integer charges on a square lattice is investigated by using Monte Carlo simulations. Based on the finite-size scaling analysis, we estimate the second-order phase transition temperature Tc and the static critical exponents β and v with a new numerical analysis method. More precise critical temperature Tc = 0.1311(2) and critical exponents β/v = 0.1152(12) and v = 0.857(15) are obtained. The estimated value of v indicates that the charge lattice melting transition is different from the pure 2D Ising transition.
Packing Effect of Excluded Volume on Hard-Sphere Colloids
XIAO Chang-Ming, JIN Guo-Jun, Ma Yu-Qiang
Chin. Phys. Lett. 2001, 18 (7): 950-952 .  
Abstract   PDF(pc) (250KB) ( 453 )
We apply the principle of maximum entropy to consider the excluded volume effect on the phase separation of binary mixtures consisting of hard spheres with two different diameters. We show that a critical volume fraction of hard spheres exists locating the packing of large spheres. In particular, through numerical calculation, we have found that the critical volume fraction becomes lower when the ratio α = σ12 of large-to-small sphere diameters increases, but becomes higher when the ratio of the large sphere volume fraction to the total volume fraction of large and small spheres increases.
Yang-Lee Circle Theorem for an Antiferromagnetic Heisenberg Ladder
WANG Xian-Zhi
Chin. Phys. Lett. 2001, 18 (7): 953-954 .  
Abstract   PDF(pc) (168KB) ( 358 )
The Yang-Lee zeros of an antiferromagnetic Heisenberg ladder model are determined. It is found that if J4 ≤ 0 Yang-Lee zeros are located on the unit circle and on the negative real axis in the complex activity plane. In particular, if J4 ≤ 0 and 2J2 ≥ J4, Yang-Lee zeros are located on the unit circle and Yang-Lee circle theorem is valid. If J4 > 0, Yang Lee zeros are locted on some complicated curves.
Thermal Conductivity at the Interface of CHBr3/NaCl Under Shock Compression
HU Jin-Biao, YANG Jia-Ling, LIU Ji-Ping, TAN Hua
Chin. Phys. Lett. 2001, 18 (7): 955-956 .  
Abstract   PDF(pc) (281KB) ( 398 )
A special experiment system has been proposed for studying the thermal physical property under shock compression. The optical radiation was recorded by a high time-resolution pyrometer. The ratio α of sample and window materials under shock compression was studied by using this experiment technique. The thermal conductivity of CHBr3 calculated from α under shock compression is about 103 times larger than that under normal condition.
Mechanism of Insulator-Metal Transition in La2/3 Ca1/3MnO3:Collapse of Small Polaron
LIU Ning, SUN Yang, ZHANG Yu-Heng
Chin. Phys. Lett. 2001, 18 (7): 957-959 .  
Abstract   PDF(pc) (422KB) ( 494 )
The insulator-metal (I-M) transition in colossal magnetoresistance material La2/3 Ca1/3MnO3 has been studied by electrical transport, magnetization and electron spin resonance (ESR) measurements. Around the I-M transition, the ESR signal shows a crossover from paramagnetic resonance line to ferromagnetic resonance line, which implies a coexistence of localized small polarons and itinerant carriers during the I-M transition. Based on the concept of ‘small polaron collapse’, a two-phase model is proposed to quantitatively describe the electrical transport behaviour across the insulator-metal transition. The calculations of resistivity in different applied magnetic fields have close trends with the experimental data, which strongly proves that the I-M transition results from the collapse of small polarons and two phases coexist during the transition.
An Effective Medium Approximation of Nonlinear Composites with Spherical Particle
WEI En-Bo, GU Guo-Qing
Chin. Phys. Lett. 2001, 18 (7): 960-962 .  
Abstract   PDF(pc) (184KB) ( 368 )
We have proposed a nonlinear effective medium approximation (EMA) method to estimate the bulk effective conductivities of weakly nonlinear composite media, which obey a current-field relation of the form J = σE+ X|E|2 E. As an example in three dimensions, we apply the EMA method to deal with a spherical inclusion in a host and derive the approximate analytic formulas of nonlinear effective response, which are suitable for the larger volume fraction of spherical inclusion. From our results, we can exactly obtain the generalized Landau formulas in the dilute limit.

Coexistence of Ferromagnetism and Superconductivity in EuSr2Ru1-xNbxCu2O8
FANG Ming-Bao, FANG Ming-Hu, XU Zheng, JIAO Zheng-Kuan
Chin. Phys. Lett. 2001, 18 (7): 963-966 .  
Abstract   PDF(pc) (424KB) ( 620 )
The structural, magnetic and transport properties of
EuSr2Ru1-xNbxCu2O8 (x = 0, 0.1, 0.2 and 0.5) samples have been investigated by means of x-ray diffraction, magnetization and resistance measurements. It is found that the EuSr2Ru1-xNbxCu2O8 compound exhibits a ferromagnetic order of the Ru moments below the Curie temperature 130.19 K, and becomes superconducting at a much lower critical temperature of 10 K. The experimental observation that partial substitution of Nb for Ru in this system results in the decrease of the Curie temperature further supports the idea that the ferromagnetic order involves only Ru moments in this compound. We suggest that the decrease of the superconducting critical temperature Tc due to the partial substitution of Nb for Ru originates from the decrease of the carrier concentration in the CuO2 plane because of Nb existing always in the Nb5+ valance state while Ru is in a mixted valance state between Ru4+ and Ru5+. The coexistence of ferromagnetism and superconductivity is also discussed.
Superconducting MgB2 Thin Films with Tc ≈ 39 K Grown by Pulsed Laser Deposition
WANG Shu-Fang, DAI Shou-Yu, ZHOU Yue-Liang, CHEN Zheng-Hao, CUI Da-Fu, XU Jia-Di, HE Meng, LÜ, Hui-Bin, YANG Guo-Zhen
Chin. Phys. Lett. 2001, 18 (7): 967-968 .  
Abstract   PDF(pc) (656KB) ( 558 )
Superconducting MgB2 thin films were fabricated on Al2O3(0001) substrates under an ex situ processing conditions. Boron thin films were deposited by pulsed laser deposition followed by a post-annealing process. Resistance measurements of the deposited MgB2 films show Tc of ~39 K, while scanning electron microscopy and x-ray diffraction analysis indicate that the films consist of well-crystallized grains with a highly c-axis-oriented structure.
Synthesis and Magnetic Properties of Gd3 (Fe, Co, Cr)29 Compounds
WANG Wen-Quan, WANG Jian-Li, YANG Dong, TANG Ning, YANG Fu-Ming, WU Guang-Heng, JIN Han-Min
Chin. Phys. Lett. 2001, 18 (7): 969-972 .  
Abstract   PDF(pc) (379KB) ( 886 )
Formation and magnetic properties of the Gd3Fe29-x-yCoxCry compounds have been investigated. It has been found that formation of single phase compounds Gd3Fe29-x-yCoxCry with Nd3(Fe,Ti)29-type structure depends strongly on the content of stabilizing element Cr, and the solid-solution limit of Co in Gd3Fe29-x-yCoxCry compounds increases with Cr content. Pure Co-based Gd3Co29-yCry compounds with Nd3(Fe,Ti)29-type structure have been successfully synthesized with y = 6.5 and 7.0. The Curie temperature Tc of Gd3Fe29-x-yCoxCry compounds increases with increasing Co content x at fixed y, whereas increase of the Cr content leads to an obvious decrease of Tc of the Gd3Co29-yCry compounds. Composition dependence of the saturation magnetization at 5 K reaches a maximum around x =7.5 and y = 4. It is worth noting that substitution of Co for Fe results in a significant change of magnetocrystalline anisotropy of the Gd3Fe29-x-yCoxCry compounds and changes the easy magnetization direction from basal-plane to easy-axis when x > 10 and y = 4.
Ferromagnetic Resonance in Gd/Co Multilayer
A. V. Svalov, J. M. Barandiarán, V. O.Vas’kovskiy, G. V. Kurlyandskaya, L. Lezama, N. G. Bebenin, J. Gutiérrez, D. Schmool
Chin. Phys. Lett. 2001, 18 (7): 973-975 .  
Abstract   PDF(pc) (236KB) ( 436 )
Magnetometric and ferromagnetic resonance (MFR) measurements have been performed on the polycrystalline multilayered structure, [Gd(7.5 nm)/Co(3 nm)]20. The temperature dependence of magnetization of the sample suggests a compensation temperature Tcomp in the region of 240 K, implying that the Co and Gd layers are antiferromagnetically aligned. The FMR curves are strongly temperature dependent, particularly in the vicinity of Tcomp.
Optical Absorption on Cubic β-PbF2 Crystals
REN Guo-Hao, SHEN Ding-Zhong, WANG Shao-Hua, YIN Zhi-Wen
Chin. Phys. Lett. 2001, 18 (7): 976-978 .  
Abstract   PDF(pc) (443KB) ( 424 )
The transmission spectra of cubic β-PbF2 crystals grown by non-vacuum Bridgman method were measured with a spectrophotometer. It was found that there are several optical absorption bands peaking at 300 nm, 390-400 nm, as well as 460 nm. According to composition analysis, doping and annealing experiments, It is suggested that the absorption at 300 nm originate from the electron transition of Ce ions from 4f → 5d. The absorption at 390-400 nm may result from the color centers related to oxygen impurities. In addition, the sample recrystallized from the colored β-PbF2 crystal exhibits a new absorption band at 460 nm, which might be caused by trace lead vacancies.
Coherent Phonon Detection in Ge with a Femtosecond Laser
PAN Xin-Yu, WANG Shu-Feng, HUANG Wen-Tao, YANG Hong, LI Xia, JIANG Hong-Bing, GONG Qi-Huang
Chin. Phys. Lett. 2001, 18 (7): 979-981 .  
Abstract   PDF(pc) (338KB) ( 401 )
A highly sensitive femtosecond photodeflection spectroscopy technique was first developed experimentally. Using femtosecond laser pulses we have detected ultrafast coherent phonon emission in a Ge plate. It is found that the ultrafast femtosecond laser pulses generate coherent phonons in the plate via the electronic mechanism. Supersonic expansion of photoexcited electron-hole plasma is observed.
Unusual Temperature-Dependent Optical Properties of Self-Organized InAs/GaAs Quantum Dots at High Excitation Power
WEI Yong-Qiang, LIU Hiu-Yun, CHAI Chun-Lin, XU Bo, DING Ding, WANG Zhan-Guo
Chin. Phys. Lett. 2001, 18 (7): 982-985 .  
Abstract   PDF(pc) (688KB) ( 512 )
The temperature-dependent photoluminescence (PL) properties of
InAs/GaAs self-organized quantum dots (QDs) have been investigated at high excitation power. The fast redshift of the ground-state and the first excited-state PL energy with increasing temperature was observed. The temperature-dependent linewidth of the QD ground state with high carrier density is different from that with low carrier density. Furthermore, we observed an increasing PL intensity of the first excited state of QDs with respect to that of the ground state and demonstrate a local equilibrium distribution of carriers between the ground state and the first excited state for the QD ensemble at high temperature (T > 80 K). These results provide evidence for the slowdown of carrier relaxation from the first excited state to the ground state in InAs/GaAs quantum dots.
Dependence of 1.54-μm Photoluminescence on Excess-Si Degrees of Er-Doped Si-Rich SiO2 Films Deposited by Magnetron Sputtreing
RAN Guang-Zhao, CHEN Yuan, MA Zhen-Chang, ZONG Wan-Hua, XIE Li-Qing, GUO Chun-Gang, QIN Guo-Gang,
Chin. Phys. Lett. 2001, 18 (7): 986-988 .  
Abstract   PDF(pc) (374KB) ( 499 )
Room-temperature 1.54-μm photoluminescence (PL) is observed from Er-doped Si-rich SiO2 (SiO2:Si:Er) films deposited by using the magnetron sputtering technique. To determine the optimum Si content in the SiO2: Si: Er films, the percentage area of the Si target in the composite SiO2-Si-Er target was changed from 0, to 10%, 20% and 30%. The percentage area of the Er target was fixed at 1%. It is found that the optimum annealing temperatures for Er3+ luminescence intensities are 900°C for the SiO2:Er film and 900, 800, and 700°C for the SiO2:Si:Er films containing 10%, 20% and 30% excess-Si (percentage areas of Si target), respectively. The SiO2:Si:Er film containing 20% excess-Si and annealed at 800°C has the intensest PL.
Growth and Photoluminescence of GaAs Quantum Dot on Si(100)
ZHANG Jian-Guo, LI Guang-Hai, ZHANG Yong, JIN Yun-Xia, ZHANG Li-De
Chin. Phys. Lett. 2001, 18 (7): 989-990 .  
Abstract   PDF(pc) (459KB) ( 566 )
GaAs quantum dots(QDs) with high density and remarkable uniformity in dot size and distribution grown on Si(100) surface with artificial topography by radio-frequency sputtering have been demonstrated. The photoluminescence spectrum has been recorded. The growth of GaAs QDs is initiated with the preferential nucleation of small dots along ripples controlled by the Stranski-Krastanow growth mode. This method may be useful in combining high-speed and optoelectronic GaAs devices with Si integrated-circuit technology.
Temperature Dependence of the Raman Spectra and Phase Transition of Zirconia
YOU Jing-Lin, JIANG Guo-Chang, YANG Song-Hua, MA Jin-Chang, XU Kuang-Di
Chin. Phys. Lett. 2001, 18 (7): 991-993 .  
Abstract   PDF(pc) (476KB) ( 1379 )
A newly constructed high-temperature Raman spectrometer was used to study the temperature-dependence Raman spectra (up
to 2023 K) and transformation of zirconia crystal. High-temperature Raman scattering is a useful tool in characterizing the different structures of zirconia and offers the possibility to identify the phase transformation. It shows that monoclinic zirconia transforms to tetragonal phase at about 1440 K during the process of increasing temperature, but shows a lower transformation temperature from tetragonal to monoclinic phase at about 1323 K while the temperature decreased.
A Quasar Spectrum with a Multiplet-Like Structure Caused by the Raman Effect
LIU Yong-Zhen
Chin. Phys. Lett. 2001, 18 (7): 994-996 .  
Abstract   PDF(pc) (263KB) ( 388 )
It has been shown that if a photon is scattered by a relativistic electron in a strong magnetic field, this may cause the Raman effect due to a transition between Landau levels. We study the possibility that this quantum effect occurs in some compact objects. We find that there is a multiplet-like structure in the quasi-stellar object (QSO)1303+308 spectrum, which is consistent with that expected by the Raman effect. It indicates that there might be a magnetic field strength about 5 x 106G in the environment of this QSO at redshift 1.7175.
An Exact Solution with Exit in the New Inflationary Universe Model
WANG Wen-Fu
Chin. Phys. Lett. 2001, 18 (7): 997-999 .  
Abstract   PDF(pc) (185KB) ( 423 )
Taking the cosmological expansion rate directly as a function of the inflaton field instead of as a function of time, we present a new exact solution to Einstein's equations that describe the evolution of inflationary universe model. This includes a solution which has nearly exponential inflation for , and then develops smoothly towards radiation-like evolution for . The inflation is driven by the evolution of scalar field with inflation potential, V( ) = V0 - m2/2 + λ/4. The spectral index of the scalar density, ns, is computed and ns lies well inside the limits set by the cosmic background explorer satellite.
51 articles