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Volume 19 Issue 1
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Original Articles
Symmetry Analysis of (2+1)-Dimensional Nonlinear Klein-Gordon Equations
TANG Xiao-Yan, LOU Sen-Yue,
Chin. Phys. Lett. 2002, 19 (1): 1-3 .  
Abstract   PDF(pc) (179KB) ( 533 )
We have obtained types of two-dimensional similarity reductions for the (2+1)-dimensional Klein-Gordon system using the standard classical Lie group approach with computer algebra. The well-known one-dimensional reductions, radial and traveling reductions are equivalent to the two special cases of our general two-dimensional reductions.
Quantum Multiple Access Channel
HOU Guang, HUANG Min-Xin, ZHANG Yong-De,
Chin. Phys. Lett. 2002, 19 (1): 4-6 .  
Abstract   PDF(pc) (202KB) ( 448 )
We consider the transmission of classical information over a quantum channel by many senders, which is a generalization of the two-sender case. The channel capacity region is shown to be a convex hull bound by the Von Neumann entropy and the conditional Von Neumann entropies. The result allows a reasonable distribution of channel capacity over the senders.
Quantum Entanglement and Information Transmission Between Non-Direct-Coupled Qubits in an Array of Spatially Fixed Qubits
LUO Jun, WEI Da-Xiu, XIAO Li, ZENG Xi-Zhi
Chin. Phys. Lett. 2002, 19 (1): 7-9 .  
Abstract   PDF(pc) (321KB) ( 389 )
We propose a simple scheme to create entangled states and
realize information transmission between qubits with non-direct
interactions on the basis of quantum superdense coding and swap
operations. This may offer the possibility of applications in scalable quantum computers.
Larmor Precession and Tunneling Time of a Non-Relativistic Neutral Spin-1/2 Particle Through an Arbitrary Potential Barrier
LI Zhi-Jian, NIE Yi-Hang, LIANG Jiu-Qing, YAN Qi-Wei
Chin. Phys. Lett. 2002, 19 (1): 10-13 .  
Abstract   PDF(pc) (268KB) ( 492 )
We investigate the Larmor precession of a non-relativistic neutral spin-1/2 particle in a uniform constant magnetic field confined to the region of a one-dimensional arbitrary potential barrier. With the help of a general spin coherent state it is explicitly shown that the spin precession time is equal to the dwell time. For the special case of symmetric rectangular potential barrier, the precession time is also in agreement with the transmission time. We present a numerical estimation of the precession time showing an apparent superluminal tunneling.
Remote State Preparation via a Non-Maximally Entangled Channel
ZHENG Yi-Zhuang, GU Yong-Jian, GUO Guang-Can
Chin. Phys. Lett. 2002, 19 (1): 14-16 .  
Abstract   PDF(pc) (192KB) ( 537 )
We investigate remote state preparation (RSP) via a non-maximally entangled channel for three cases: a general qubit, a special ensemble of qubits (qubit states on the equator of the Bloch sphere) and asymptotic limit of N copies of a general state. The results show that the classical communication cost of RSP for the two latter cases can be less than that of teleportation, but for the first case, in a restricted setting, the classical communication cost is equal to that of teleportation. Whether or not this is the case for more general setting is still an open question.
Dark Lump Excitations in Bose-Einstein Condensates
HUANG Guo-Xiang, ZHU Shan-Hua
Chin. Phys. Lett. 2002, 19 (1): 17-19 .  
Abstract   PDF(pc) (211KB) ( 389 )
We investigated the dynamics of two-dimensional matter-wave pulses in a Bose-Einstein condensate with disk-shaped traps. For the case of repulsive atom-atom interactions, a Kadomtsev-Petviashvili equation with positive dispersion is derived using the method of multiple scales. The results show that it is possible to excite dark lump-like two-dimensional nonlinear excitations in the Bose-Einstein condensate.
A New Holographic Entropy Bound from Conformal Field Theory at The Killing Horizon
JING Ji-Liang
Chin. Phys. Lett. 2002, 19 (1): 20-22 .  
Abstract   PDF(pc) (202KB) ( 342 )
A new holographic entropy bound is obtained by using conformal
field theory at Killing horizon. The entropy bound is tighter than the well-known bounds, such as Bekenstein, Bekenstein-Mayo and 't Hooft bounds. The result shows that the entropy of a system decreases when quantum effects are included. Therefore, the quantum effect will increase the degree of order of the system.
Covariant Perturbation Theory of Non-Abelian Kinetic Theory
ZHENG Xiao-Ping, LI Jia-Rong
Chin. Phys. Lett. 2002, 19 (1): 23-25 .  
Abstract   PDF(pc) (201KB) ( 294 )
A “double perturbation”theory is presented in the framework of the kinetic theory of quark-gluon plasma. A solvable set of equations from the double perturbation are derived and proved to be gauge invariant. The Landau damping rate for the plasmon at zero momentum is shown to be convergent series in correlators.
Identical Superdeformed Bands in 171Ta and 173Re
LIU Zu-Hua, YANG Chun-Xiang, ZHOU Hong-Yu
Chin. Phys. Lett. 2002, 19 (1): 26-28 .  
Abstract   PDF(pc) (274KB) ( 392 )
The rotational band built on the i13/2 proton [660,1/2] Nilsson state in 173Re is proved to be identical to that in 171Ta. The close similarity of the two bands in 171Ta and 173Re suggests that the 173Re nucleus with the odd proton based on the i13/2 [660,1/2] Nilsson state may be triaxially superdeformed.
Semiclassical Calculations of Recurrence Spectra for Lithium Atoms in Parallel Electric and Magnetic Fields
LIN Sheng-Lu, ZHANG Qiu-Ju, ZHAO Ke, SONG Xiao-Hong, ZHANG Yan-Hui
Chin. Phys. Lett. 2002, 19 (1): 29-31 .  
Abstract   PDF(pc) (337KB) ( 433 )
By using region-splitting consistent and iterative method, we calculate the recurrence spectra of lithium atoms in parallel strong external electric and magnetic fields, and obtain the novel resonance structure in the photoabsorption spectrum above ionization threshold with a constant scaled electric field at F = 0.036, and a scaled energy at ε = 0.58 and ε = 0.006, respectively. The results are compared with those of hydrogen obtained by using standard closed orbit theory. It is demonstrated that the core-scattered effects exhibited in combination recurrence play a great role.
Quantum Spectra of Hydrogen Atoms in Various Magnetic Fields with the Closed Orbit Theory
PENG Liang-You, ZHANG Xian-Zhou, RAO Jian-Guo,
Chin. Phys. Lett. 2002, 19 (1): 32-35 .  
Abstract   PDF(pc) (598KB) ( 349 )
The quantum spectra of hydrogen atoms in various magnetic fields have been calculated with the closed orbit theory. The magnitude of the magnetic field decreases from 5.96 T to 0.56T with a step of 0.6T. We demonstrate schematically that the closed orbits disappear with the decrease of the magnitude of the magnetic field when the corresponding finite resolution of experiment is fixed. This may give us a good way to control the shape and the number of the closed orbits in the system, thus to control where there should exist a peak in the Fourier transformation of the quantum spectra.
Spin-Other-Orbit Effect in Two-Mode Multiphoton Ionization
LI Xiao-Feng, GAO Liang-Hui, WANG Bing-Bing, FU Pan-Ming, D. S. Guo, R. R. Freeman
Chin. Phys. Lett. 2002, 19 (1): 36-39 .  
Abstract   PDF(pc) (1030KB) ( 393 )
A previously unknown “spin-other-orbit”effect of photon modes is predicted by solving a Schrödinger-like equation for a nonrelativistic electron interacting with a two-mode intense photon field propagating in two perpendicular directions. A multiphoton ionization experiment to test this effect is suggested. Transition rates which manifest this effect to be measured in the experiment are calculated and presented graphically. A detailed comparison between this effect and the well-known spin-other-orbit effect of electrons is included.
Observation of Two Quasistatic Wings of Laser-Induced Collision Energy Transfer
ZHENG Rui-Hua, CHEN De-Ying, ZHAO Xiao-Yan, LÜ, Zhi-Wei, MA Zu-Guang
Chin. Phys. Lett. 2002, 19 (1): 40-43 .  
Abstract   PDF(pc) (384KB) ( 369 )
We investigate experimentally Laser-induced collision energy transfer for transitions both from Eu(6s6p 8P9/2 to Sr(5s10s)1S0 and from Eu(6s6p)8- P7/2 to Sr(5s8d)1D2. Two quasi-static wings are observed in their excited function spectra. By using two dipole-dipole interactions, a spectral line from numerical calculation is consistent with the experimental line in two quasi-static wings.
Infrared Spectral Hole-Burning and Spectral Diffusion of Vibrational N-D Bands in a Disordered Tutton Salt
SONG Hong-Wei, Herbert L. Strauss
Chin. Phys. Lett. 2002, 19 (1): 44-46 .  
Abstract   PDF(pc) (443KB) ( 359 )
We have studied infrared spectral hole burning of the N-D stretching bands of NH3D+ in salt [(NH4)2Co0.25Ni0.75(H2O)6(SO4)2] was at 10 K. It was observed that the spectral line broadening occurred on a logarithmic time scale, which is consistent with the theoretical prediction of standard two-level-system. The temperature of 10 K is also beyond the temperature limit in previous studies on spectral diffusion.
Distorted Wave Effects of the 1b3g Orbital in Ethylene
DENG Jing-Kang, LI Gui-Qin, HUANG Jian-Dong, WANG Fang, NING Chuan-Gang, LU Jie, HE Yao, WANG Xiao-Dong, ZHANG Yi-An, Gao Hong, WANG Yan, ZHENG Yan-You
Chin. Phys. Lett. 2002, 19 (1): 47-49 .  
Abstract   PDF(pc) (306KB) ( 354 )
We study the unexpected distorted wave effects of the 1b3g orbital in ethylene using a high resolution binary (e, 2e) electron momentum spectrometer, at an impact energy of 800eV plus the binding energy (8-22eV) with symmetric non-coplanar kinematics. The experimental momentum profile of the 1b3g orbital is obtained and compared with the data previously measured at impact energy of 1200 eV plus the binding energy. Also, the experimental momentum profiles of the 1b3g orbital are compared with the theoretical momentum distributions calculated by using Hartree-Fock and density functional theory methods. The experimental momentum profiles of the 1b3g orbital of ethylene at different impact energies show that the cross section of the orbital below the momentum p~1 a.u. is higher for lower impact energy.
Field-Correlation Effects on Rayleigh-Enhanced Nondegenerate Four-Wave Mixing
WANG Yan-Bang, JIANG Qiang, MI Xin, YU Zu-He, FU Pan-Ming
Chin. Phys. Lett. 2002, 19 (1): 50-52 .  
Abstract   PDF(pc) (303KB) ( 358 )
We study Rayleigh-enhanced nondegenerate four-wave mixing(NFWM) with time-delayed, correlated fluctuating fields. The importance of the field correlation is revealed in the Rayleigh-enhanced NFWM spectrum when the time delay is varied. The Rayleigh-enhanced NFWM is employed to study the ultrafast processes in the frequency domain. A relaxation time as short as 220 fs was deduced in the Rayleigh-enhanced NFWM experiments in carbon disulfide.
Teleportation of a Quantum State Entangled with Environment
SONG He-Shan, MI Dong, ZHOU Ling, LI Chong
Chin. Phys. Lett. 2002, 19 (1): 53-55 .  
Abstract   PDF(pc) (187KB) ( 394 )
A quantum state of a fermion entangled with thermal environment is constructed by doubling the Fock space. The teleportation of the state entangled with the thermal environment is also discussed.
Atomic Storage States
WANG Kai-Ge, ZHU Shi-Yao
Chin. Phys. Lett. 2002, 19 (1): 56-59 .  
Abstract   PDF(pc) (190KB) ( 470 )
We present a complete description of atomic storage states which may appear in the electromagnetically induced transparency (EIT). The result shows that the spatial coherence has been included in the atomic collective operators and the atomic storage states. In some limits, a set of multimode atomic storage states has been established in correspondence with the multimode Fock states of the electromagnetic field. This gives a better understanding of the fact that, in EIT, the optical coherent information can be preserved and recovered.
Storage of a Light Pulse in an Atomic Medium
PENG Fang-Lin, WANG Kai-Ge, YANG Guo-Jian, ZHU Shi-Yao
Chin. Phys. Lett. 2002, 19 (1): 60-62 .  
Abstract   PDF(pc) (359KB) ( 447 )
We perform a full numerical simulation to the electromagnetically induced transparency model in which the control beam is changed adiabatically. The numerical results show the whole process of storage and recovery for the signal pulse. This verifies a recent experiment and the approximate theoretical analysis.
Manakov Soliton Pairs in Biased Photovoltaic Photorefractive Crystals
HOU Chun-Feng, DU Chun-Guang, Abdurusul, LI Shi-Qun
Chin. Phys. Lett. 2002, 19 (1): 63-65 .  
Abstract   PDF(pc) (201KB) ( 322 )
We study, theoretically, incoherently coupled screening-photovoltaic soliton pairs in biased photovoltaic photorefractive crystals. It is shown that when the total intensity of two coupled solitons is much lower than the effective dark irradiance, the coupled soliton equations reduce to the Manakov equations. The dark-dark, bright-bright, and dark-bright soliton pair solutions of these Manakov equations are obtained under an appropriate external bias field and a photovoltaic field, and the characteristics of these Manakov soliton pairs are also discussed in detail.
Wavelength Dependence of a Two-Beam Coupling Measurement on a Fully Functional Photorefractive Polymer
ZHANG Bo, LIU Hui, GONG Qi-Huang, Jiwon Sohn, Jaehoon Hwang, Soo Young Park, Jin-Kyung Lee, Jai-Hyung Lee, Joon-Sung Chang, Geon Joon Lee
Chin. Phys. Lett. 2002, 19 (1): 66-68 .  
Abstract   PDF(pc) (328KB) ( 432 )
We have investigated the photorefractive properties of a fully functional polymer, 9-(2-Ethyl-hexyl)-3-[2-(4-methanesulfonyl-phenyl)vinyl]-9H carbazole, using a multiline He-Ne laser. We measured the wavelength-dependent two-beam coupling coefficient, which exhibited a maximal value of 105 cm-1 at 609 nm under an applied electric field of 84 V/μm at room temperature.
Large Absolute Photonic Bandgap at High Frequencies in a Two-Dimensional Photonic Crystal with a Hexagonal Structure
HE Jiang-Ping, SHEN Lin-Fang, XIAO San-Shui, HE Sai-Ling
Chin. Phys. Lett. 2002, 19 (1): 69-72 .  
Abstract   PDF(pc) (559KB) ( 508 )
A new large absolute photonic bandgap at high normalized frequencies can be obtained in a two-dimensional hexagonal structure with alumina cylinders in air by reducing the symmetry of the structure. An instructive procedure is described for finding the optimal configuration which gives the maximum absolute bandgap Δω = 0.091(2πc/a).
Band Structure of a Two-Dimensional Photonic Crystal with a Triangular Lattice of Anisotropic Elliptic Cylinders
ZHUANG Fei, WU Liang, XIAO San-Shui, HE Sai-Ling,
Chin. Phys. Lett. 2002, 19 (1): 73-75 .  
Abstract   PDF(pc) (522KB) ( 440 )
The plane-wave expansion method is used to calculate the band structure of a two-dimensional photonic crystal formed by a triangular lattice of anisotropic elliptic cylinders. After optimizing the parameters of the elliptic cylinders, we find a large bandgap (about 0.0449 ωe, ωe = 2πc/a) at high frequencies beside a coexisting large absolute gap (about 0.035 ωe) at low frequencies. Numerical results show that the optimal design is very stable under any parameter pertubation.
Temperature-Independent Stress and Displacement Bidirectional Sensing Tuned by an Applied Bilateral Cantilever Beam
ZHANG Wei-Gang, HUANG Yong-Lin, XIANG Yang, TONG Zheng-Rong, ZHAO Qi-Da, KAI Gui-Yun, YUAN Shu-Zhong, DONG Xiao-Yi
Chin. Phys. Lett. 2002, 19 (1): 76-78 .  
Abstract   PDF(pc) (354KB) ( 449 )
A novel and simple approach of temperature-independent stress and displacement bidirectional sensing tuned by an applied bilateral cantilever beam is proposed and demonstrated. The 3dB bandwidth of fiber gratings is linear with respect to the stress and displacement in the tuning range of 16nm. The sensing sensitivities of the stress and displacement are 5.76nm/N and 0.941nm/mm, respectively.
Heat Flux Boundary Conditions for a Lattice Boltzmann Equation Model
FENG Shi-De, REN Rong-Cai, JI Zhong-Zhen
Chin. Phys. Lett. 2002, 19 (1): 79-82 .  
Abstract   PDF(pc) (821KB) ( 402 )
A method simplifying the external force term for the Boltzmann equation is proposed by using the Chapman-Enskog asymptotic expansion technique, The relationship between the perturbation strength parameter and the Grashof number is presented. A heat flux boundary condition for temperature field simulation is developed according to the transforming relations between the cold and hot particles on the boundary wall. The effect of buoyant force and the heat flux boundary condition is implemented with the two-particle systems of D2Q9 and D3Q15, and the numerical results agree well with the experimental result of silicone oil.
Effects of Particle Size on Dilute Particle Dispersion in a Kármán Vortex Street Flow
WU Zuo-Bing, LING Guo-Can, XING Qi-Jiang
Chin. Phys. Lett. 2002, 19 (1): 83-86 .  
Abstract   PDF(pc) (470KB) ( 347 )
It is shown that in a Kármán vortex street flow, particle size influences the dilute particle dispersion. Together with an increase of the particle size, there is an emergence of a period-doubling bifurcation to a chaotic orbit, as well as a decrease of the corresponding basins of attraction. A crisis leads the attractor to escape from the central region of flow. In the motion of dilute particles, a drag term and gravity term dominate and result in a bifurcation phenomenon.
Quintic Nonlinearity Induced Solitary Waves in Plasma Physics
LIU Hong, , HE Xian-Tu, LOU Sen-Yue
Chin. Phys. Lett. 2002, 19 (1): 87-90 .  
Abstract   PDF(pc) (243KB) ( 442 )
The quintic nonlinearity is important in the study of the nonlinear interaction between Langmuir waves and electrons in plasma. Using the pseudoenergy approach, five types of solitary wave solutions are obtained explicitly. Only one of these is the modification of the soliton of the cubic nonlinear Schrödinger equation and can be treated perturbatively. However, other four types of solitary wave solutions are all induced by the quintic nonlinearity and cannot be treated perturbatively from the solutions of the cubic nonlinear Schrödinger equation.
Synthesis of Large Quantity Single-Walled Carbon Nanotubes by Arc-Discharge
LI Zhen-Hua, WANG Miao, WANG Xin-Qing, ZHU Hai-Bin, LU Huan-Ming, Y. Ando
Chin. Phys. Lett. 2002, 19 (1): 91-93 .  
Abstract   PDF(pc) (808KB) ( 510 )
We reported on a new method to prepare large quantity single-walled carbon nanotubes (SWCNTs) with high purity. Using a Y-Ni powder composite graphite rod as anode, at a given angle with the high purity graphite cathode rod, a cloth-like deposit can be obtained by dc arc discharge in helium at high temperature, which contained about 60% SWCNTs. In this way, we can obtain a deposit of more than one gram in ten minutes. Transmission electron microscopy and Raman spectrum have been used to observe the structure and morphology of the SWCNTs.
Relative Energy Dissipation: Sensitive to Structural Changes of Liquids
ZU Fang-Qiu, GUO Li-Jun, ZHU Zhen-Gang, FENG Yi,
Chin. Phys. Lett. 2002, 19 (1): 94-97 .  
Abstract   PDF(pc) (483KB) ( 357 )
Energy dissipation techniques, widely used in solid physics previously, are proved to be sensitive also to changes in liquid structure. It has been suggested from relative energy dissipation that changes in liquid structure can occur as a function of temperature in some ordinary binary systems such as Pb-Sn, In-Sn and In-Bi. This finding may be helpful to understand liquid structure changing patterns, therefore enriches the phenomenology of liquid state physics. This is significant for engineering practice.
Dependence of In-Tube Carbon Chain on the Radius and Helicity of Single-Wall Carbon Nanotubes
LIU Hong, DONG Jin-Ming, WAN Xian-Gang
Chin. Phys. Lett. 2002, 19 (1): 98-100 .  
Abstract   PDF(pc) (277KB) ( 356 )
Using the Lennard-Jones interaction potential, we have studied the in-tube carbon-chain structure doped into the single-wall carbon nanotubes (SWCNTs). Through minimizing the potential energy of the doped system, it is found that the optimal structure of the doping carbon chain is spiral, but not a straight line, when the radius of the SWCNT is larger than about 4.30Å.
Range and Annealing Behaviour of Pb+ Ion-Implanted into LiNbO3 Crystals at Moderate Energies
CHEN Feng, HU Hui, ZHANG Jian-Hua, LIU Xiang-Dong, XIA Hui-Hao, SHI Bo-Rong, WANG Ke-Ming
Chin. Phys. Lett. 2002, 19 (1): 101-104 .  
Abstract   PDF(pc) (438KB) ( 398 )
Pb+ ions have been implanted into LiNbO3 crystals in the energy range of 100-350keV at doses of 5 x 1015, 1 x 1016 and 2 x 1016 ions/cm2. The profile of the implanted ions was measured by Rutherford backscattering. The mean projected range and the range straggling obtained from the experiment were compared with the TRIM'98 and SRIM 2000 code. In the present case, the TRIM'98 code predicts experimental values better than those of the SRIM 2000 code. The depth distribution is also found to be independent of dose for 350-keV Pb+ implanted into LiNbO3 crystals. After 800°C annealing for 60 min in ambient air, obvious diffusion occurs to the implanted Pb+ ions at 150 keV with a dose of 5 x 1015 ions/cm2. After a low-temperature treatment at 77 K in liquid nitrogen, no obvious diffusion phenomenon occurs for the implanted Pb+ ions in LiNbO3.
Plasticity Analysis of Nano-Grain-Sized NiAl Alloy in an Atomic Scale
WANG Jing-Yang, WANG Xiao-Wei, J. Rifkin, LI Dou-Xing
Chin. Phys. Lett. 2002, 19 (1): 105-107 .  
Abstract   PDF(pc) (561KB) ( 396 )
The molecular dynamics method is used to simulate a uniaxial tensile deformation of 3.8 nm nano-NiAl alloy with curved amorphous-like interfaces at 0 K. Plastic deformation behaviour is studied by examining the strain-stress relationship and the microstructural evolution characteristic. Atomic level analysis has shown that the micro-strain is essentially heterogeneous in simulated nano-phase samples. The plastic deformation is not only attributed to the plasticity of interfaces, but also accompanied with the plastic shear strain mechanism inside lattice distortion regions and grains.
Critical Behaviour of the One-Dimensional Ferromagnetic t-J Model
YANG Fu, WANG Yu-Peng
Chin. Phys. Lett. 2002, 19 (1): 108-110 .  
Abstract   PDF(pc) (176KB) ( 371 )
The one-dimensional super-symmetric ferromagnetic t-J model is
studied via the thermal Bethe ansatz. Analytic expressions of the free energy for T → 0 are obtained. A new critical behaviour beyond the universal class of Luttinger liquids is found in this system.
D-Wave Kondo Problem in a Square Tight-Bounding Lattice
YANG Kai-Hua, SONG Bo, WANG Yu-Peng, HAN Ru-Shan
Chin. Phys. Lett. 2002, 19 (1): 111-113 .  
Abstract   PDF(pc) (319KB) ( 310 )
A Kondo model in a square tight-bonding lattice of conduction electrons is considered. The Kondo interaction takes a d-wave. Using mean-field theory and numerical simulations, it is found that there is a pseudo-gap for the impurity density of states at the Fermi level. Numerical results also show that the exponents of the low-temperature thermodynamic quantities are non-universal but dependent on the interaction.
Binding Energy of Positively and Negatively Charged Excitons in GaAs/AlxGa1-xAs Quantum Wells
LIU Jian-Jun, , ZHANG Shu-Fang, YANG Guo-Chen, LI Shu-Shen
Chin. Phys. Lett. 2002, 19 (1): 114-116 .  
Abstract   PDF(pc) (247KB) ( 367 )
Using a simple two-parameter wavefunction, we calculate variationally the binding energy of positively and negatively charged excitons in GaAs/AlxGa1-xAs quantum wells for the well widths from 10 to 300Å, We consider the effect of effective mass, dielectric constant mismatch in the two materials, and the whole correlation among the particles. The results are discussed and compared in detail with previous experimental and theoretical results, which show a fair agreement with them.
Electron States of Few-Electron Quantum Dots
DAI Zhen-Hong, , SUN Jin-Zuo, ZHANG Li-De, LI Zuo-Hong, HUANG Shi-Yong, SUI Peng-Fei,
Chin. Phys. Lett. 2002, 19 (1): 117-119 .  
Abstract   PDF(pc) (280KB) ( 409 )
We study few-electron semiconductor quantum dots using the unrestricted Hartree-Fock-Roothaan method based on the Gaussian Basis. Our emphasis is on the energy level calculation for quantum dots. The confinement potential in a quantum dot is assumed to be in a form of three-dimensional spherical finite potential well. Some valuable results, such as the rearrangement of the energy level, have been obtained.
Enhanced MgB2 Superconductivity Under High Pressure
LIU Zhen-Xing, JIN Chang-Qing, YOU Jiang-Yang, LI Shao-Chun, ZHU Jia-Lin, YU Ri-Cheng, LI Feng-Ying, WANG Ru-Ju, SU Shao-Kui
Chin. Phys. Lett. 2002, 19 (1): 120-123 .  
Abstract   PDF(pc) (256KB) ( 472 )
We report on in situ high-pressure studies up to 1.0 GPa on the MgB2 superconductor which was high-pressure synthesized. The as-prepared sample is of high quality in terms of sharp superconducting transition (Tc) at 39 K from the magnetic measurements. The in situ high-pressure measurements were carried out using a Be-Cu piston-cylinder-type instrument with the mixed oil as the pressure transmitting medium which warrants a quasi-hydrostatic pressure environment at low temperature. The superconducting transitions were measured by using the electrical conductance method. It is found that Tc increases more than 1 K with pressure in the low-pressure range, before the Tc value decreases with the further increase of the pressure.
A New Method for the Preparation of MgB2 Superconducting Tapes
XU Jia-Di, WANG Shu-Fang, ZHOU Yue-Liang, DAI Shou-Yu, CHEN Zheng-Hao, CUI Da-Fu, LÜ, Hui-Bin, ZHU Ya-Bin, HE Meng, YANG Guo-Zhen
Chin. Phys. Lett. 2002, 19 (1): 122-123 .  
Abstract   PDF(pc) (740KB) ( 415 )
Superconducting MgB2/Ta tapes with critical temperature of 38 K have been prepared successfully by a two-step method. Boron/Ta tapes were fabricated by electrophoresis followed by a post-annealing process in magnesium vapour. The critical current density is 1.7 x 104A/cm2 in zero field at 5K. Scanning electron microscopy and x-ray diffraction analysis reveal a dense flat surface with (101) orientated growth of MgB2 phase in our MgB2/Ta tapes.
Photodarkening in Amorphous As2S3 Thin Films
LIU Qi-Ming, GAN Fu-Xi
Chin. Phys. Lett. 2002, 19 (1): 124-126 .  
Abstract   PDF(pc) (301KB) ( 536 )
The photodarkening effect in amorphous As2S3 films is studied. The optical absorption edge shifts to lower energy after illumination at the bandgap light of 514.5 nm wavelength by an argon laser. The shift in well-annealed films can be recovered by annealing at 180°C for 1 h but in un-annealed films it is irreversible. In addition, it was found that the magnitude of photodarkening ΔE increased with the increase of illumination light intensity and illumination time. The reversibility of photodarkening in amorphous As2S3 films can be applied in optical memories.
Photoluminescence and Optically Pumped Ultraviolet Lasing from Nanocrystalline ZnO Thin Films Prepared by Thermal Oxidation of High Quality ZnS Thin Films
ZHANG Xi-Tian, LIU Yi-Chun, ZHANG Li-Gong, ZHANG Ji-Ying, LÜ, You-Ming, SHEN De-Zhen, XU Wu, ZHONG Guo-Zhu, FAN Xi-Wu, KONG Xiang-Gui
Chin. Phys. Lett. 2002, 19 (1): 127-130 .  
Abstract   PDF(pc) (371KB) ( 686 )
We present a simple and useful method for preparing high-quality nanocrystalline ZnO thin films, i.e. the thermal oxidation of high-quality ZnS films prepared by low-pressure metal-organic chemical vapor deposition technique. The x-ray diffraction measurements reveal that the nanocrystalline ZnO has a hexagonal wurtzite structure. Raman spectra show that the longitudinal optical phonon with the E1-mode appears at 578 cm-1. The multiple phonon scattering process is also observed, indicating the formation of a high quality nanocrystalline ZnO thin film. The photoluminescence spectrum has a single emission peak at 3.264 eV from the free-exciton mission, under the condition of low excitation power at room temperature. However, when excitation intensities exceed the threshold of 150 kW/cm2, a new and narrow peak emerges at lower energies, which are attributed to exciton-exciton collisions, and is called the P line. The intensity of this peak increases superlinearly with the pumping power over a threshold value. This supplies strong evidence of stimulated emission. The multiple longitudinal cavity modes observed in the stimulated emission spectrum indicate the successful realization of optically pumped lasing from nanocrystalline ZnO films at room temperature.
Photoluminescence of ZnSe-ZnS Single Quantum Wells Grown by Vapor Phase Epitaxy
LÜ, You-Ming, SHEN De-Zhen, LIU Yi-Chun, LI Bing-Hui, ZHANG Ji-Ying, FAN Xi-Wu, S.Iida, A. Kato
Chin. Phys. Lett. 2002, 19 (1): 131-133 .  
Abstract   PDF(pc) (418KB) ( 353 )
We study the photoluminescence (PL) of ultra thin layer ZnSe quantum wells in ZnS barriers. Samples with different well widths are grown by vapor phase epitaxy and the PL spectra of these samples are measured by the excitation of a 500 W Hg lamp. The peak positions of the bands coming from the excitonic luminescence show a larger blue shift with respect to the energy of free excitons in the ZnSe bulk material. The observed variation of the full width at half maximum and peak position of the bands in the spectra with the well width are interpreted to formation of the ZnSxSe1-x alloy layer due to the interdiffusion in the interfaces between ZnSe and ZnS. According to the behaviour of the excitons in the smaller conduction band offset, the exciton binding energy is estimated from the dependence of the PL intensity on the temperature. From this result, excitons seem to show nearly three-dimensional characteristics.
Fabrication of Nanoparticle Pattern Through Atomic Force Microscopy Tip-Induced Deposition on Modified Silicon Surfaces
LIAO Jian-Hui, HUANG Lan, GU Ning
Chin. Phys. Lett. 2002, 19 (1): 134-136 .  
Abstract   PDF(pc) (819KB) ( 570 )
With an atomic force microscopy (AFM) tip used as a “nib”and gold colloidal particles as “ink”, patterns of gold colloidal particles have been deposited successfully from AFM tip onto specific regions of silicon surfaces modified by bifunctional mercaptosilane, i.e. (3-mercaptopropyl)-triethoxysilane. This was used as an adhesion agent and can immobilize the nanoparticles delivered from AFM tip onto the substrate surface.
A Microscopic Mechanism for Muscle Motion
AI Bao-Quan, WANG Xian-Ju, LIU Liang-Gang, M. Nakano, H. Matsuura
Chin. Phys. Lett. 2002, 19 (1): 137-140 .  
Abstract   PDF(pc) (457KB) ( 417 )
We study the stochastic inclined rods model in a system with different complex potentials and discuss the effect of the spring on the system. The results of the calculation show that the spring, the effective radius of the G-actin and the intermolecular potential play a key role in the motion. The sliding speed is about 4.7 x 10-6m/s calculated from the model which well agrees with the experimental data.
Quantum Thermal Effect of Dirac Particles in a Non-uniformly Rectilinearly Accelerating Kinnersley Black Hole
WU Shuang-Qing, CAI Xu
Chin. Phys. Lett. 2002, 19 (1): 141-143 .  
Abstract   PDF(pc) (203KB) ( 366 )
We study the Hawking radiation of Dirac particles in an arbitrarily rectilinearly accelerating Kinnersley black hol, using the generalized a tortoise coordinate transformationmethod. Both the location and the temperature of the event horizon depend on the time and polar angle. The Hawking thermal radiation spectrum of Dirac particles is also derived.
Approximate Expression of Ellipse Polarization Degree for Gyrosynchrotron Radiation
ZHOU Ai-Hua
Chin. Phys. Lett. 2002, 19 (1): 144-146 .  
Abstract   PDF(pc) (378KB) ( 370 )
We study the elliptical polarization degree (EPD) of gyrosynchrotron radiation for the case of transverse propagation. The EPD decreases with increasing ellipticity R (i.e., ratio of the major and miner axial lenths) and with decreasing electron energy spectral index δ. The EPD value varies from 0.55 to 0.15 in the whole range of 3 ≤ R ≤ 10 and 2 ≤ δ ≤ 7. An approximate expression for the EPD is proposed, in which we assume that the emitting electrons have an isotropic pitch angle distribution and a power law distribution in energy. The expression is designed for the electron energy spectral index δ from 2 to 7, as well as the harmonic numbers s from 2 to 70 with a statistical error of ±6%. The expression can be applied to the polarization analysis and magnetic field strength diagnostic for solar limb events.
45 articles