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Volume 12 Issue 10
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Original Articles
Quantum Signature of Classical Chaos in the Temporal Mean of Expectation Values of Observables
JIE Quanlin, XU Gongou,
Chin. Phys. Lett. 1995, 12 (10): 577-580 .  
Abstract   PDF(pc) (0KB) ( 259 )
In an integrable quantum system, the time averages of expectation values of a complete set of commuting observables (CSCO) form a regular pattern when every common eigenstate of the CSCO is chosen as the initial state. As the system transits to chaotic, the regular pattern is destroyed and these points cluster.
Electron Impact Excitation Cross Section and Rate: Revised Bethe Formula
QU Yizhi, WANG Jianguo, TONG Xiaomin, LI Jiaming
Chin. Phys. Lett. 1995, 12 (10): 581-584 .  
Abstract   PDF(pc) (190KB) ( 545 )
Based on Born approximation, we introduce a revised Bethe formula to calculate the excitation cross sections and rates conveniently for multi-electron atoms, whose generalized oscillator strength may have nodes and/or peaks. With the quasi-universal correction function, it can also be extended to low energy region.
Deflection and Re-focusing of Relativistic Electrons in a Cylindrical Condenser
TIAN Renhe, GU Yongti, LU Wuxing, ZHANG Huixing
Chin. Phys. Lett. 1995, 12 (10): 585-588 .  
Abstract   PDF(pc) (182KB) ( 406 )
The relativistic equation of motion for electrons in a Cylindrical condenser is presented precisely. The analytical expression for the trajectory of electrons in the vicinity of the circular trajectory is given approximately, which has an error of about 1% in comparison with numerical calculations. The properties of the focuses are discussed with the theoretical results of this paper.
Evolution of the Density Operator in a Dissipative System --A Non-master-Equation Approach
DUAN Luming, GUO Guangcan
Chin. Phys. Lett. 1995, 12 (10): 589-592 .  
Abstract   PDF(pc) (177KB) ( 526 )
For a typical dissipative system, a driven harmonic oscillator put in a heat bath, we obtain a simple and exact solution for the reduced density operator of the system, which gives the result obtained by the master equation approach under the small damping approximation. This method gives a simple way to get exact solutions of many problems about dissipative systems in quantum optics.

Nonclassical Bose-Einstein Condensate
ZENG Heping, LIN Fucheng
Chin. Phys. Lett. 1995, 12 (10): 593-596 .  
Abstract   PDF(pc) (216KB) ( 417 )
A scheme for the generation of a nonclassical Bose-Einstein condensate is proposed in a Jg = 1 →Je = 0 system where ultracold atoms are populated in one ground-state sublevel |g_〉 and form a Bose-Einstein condensate. By coupling the condensate to copropagating classical (σ-) and quantum (σ+) non-resonant travelling-wave laser fields, effective two-photon excitations between two ground-state sublevels |g_〉and |g+〉create a new condensate in |g+〉. For an appropriate selection of the interaction time and atom-field coupling strengths, the quantum features of the quantized laser field, which may be prepared in a certain nonclassical state, can be exchanged with those of the quantum density field of the generated condensate.

Two Mechanisms in a Relativistic Electron Cyclotron Maser with a Special Quasioptical Cavity
LIU Pukun, YANG Zhonghai, LIU Shenggang, QIAN Shangjie*
Chin. Phys. Lett. 1995, 12 (10): 597-600 .  
Abstract   PDF(pc) (205KB) ( 354 )
In a relativistic electron cyclotron maser with an axisymmetrical quasioptical cavity of oblique rotation at arbitrary angle, the rotating angle has a great influence on beam-wave interaction. Two different physical mechanisms are found with the rotating angle ranging from 0° to 90°. One is cyclotron auto-resonance maser regime for small angle, with small optimized external magnetic field; the other is electron cyclotron resonance maser regime for large angle, with comparatively large optimized magnetic field.

Time-Evolution of X-Ray Emission Nonuniformity in Line-Shaped Laser Plasmas
ZHANG Lingqing, HAN Shensheng, XU Zhizhan, ZHANG Zhengquan, WANG Xiaofang, FAN Pinzhong, SONG Xiangyang, QIAN Aidi
Chin. Phys. Lett. 1995, 12 (10): 601-604 .  
Abstract   PDF(pc) (193KB) ( 388 )
The spatially and time resolved 2D images of x-ray emission of line-shaped Ti laser plasmas have been obtained with a pinhole transmission grating spectrometer coupled with a x-ray streak camera. The x-ray emission nonuniformity of the plasma is quantitatively analyzed using a perturbation spectrum analysis method. The results show that the nonuniformity has a minimum value at a time corresponding to the peak time of the pumping laser pulse, and increases after that. A brief discussion on the nonuniformity mechanism has also been presented.

Experimental Study on Copper Vapor Laser-Induced B-Doping in Si-Substrate
QIAN Yujun, PAN Bailiang, YAO Zhixin
Chin. Phys. Lett. 1995, 12 (10): 605-608 .  
Abstract   PDF(pc) (219KB) ( 469 )
In this paper we report the experimental results of copper vapor laser-induced B-doping in Si-substrate. The laser doped p-n junctions have depths less than 0.2μm and surface B concentrations more than 1021cm-3. The highest photoelectric efficiency of solar cell reaches 9.2%. It shows that copper vapor laser has the distinguished advantage in laser-induced doping.
Reflectionless Acoustic Waves in One-Dimensional Elastic Structure with Correlated Disorder
ZHANG Zhiyong, XIONG Shijie
Chin. Phys. Lett. 1995, 12 (10): 609-612 .  
Abstract   PDF(pc) (192KB) ( 439 )
We study, via Dean's method and scattering transfer-matrix approach, the acoustic waves of one-dimensional structure with correlated disorder, which is realized by randomly inserting impurity segments into a pure host chain. There exist completely reflectionless acoustic modes, whose number is less than the number of atoms in a segment by 1. The frequencies of these modes are situated in the smooth parts of the phonon spectrum. We present the curves of transmission of incident waves versus frequencies, which show sharp resonant peaks at the reflectionless modes. The possible applications of this property are discussed.
Reactive Deposition Epitaxial Growth of β-FeSi2 Film on Si(001): in situ Observation by Reflective High Energy Electron Diffraction
WANG Lianwei, LIN Chenglu, SHEN Qinwo, NI Rushan, ZOU Shichang
Chin. Phys. Lett. 1995, 12 (10): 613-616 .  
Abstract   PDF(pc) (209KB) ( 397 )
Reactive deposition epitaxial growth of β-FeSi2 film on Si(001) has been studied by in situ observation of reflective high energy electron diffraction. Metastable strained phase was observed at initial stages. Surface roughness due to the islanding was observed during the deposition. The existed great tendency to transform the alignment of the orientation of crystallites into random as the thickness of deposited iron increased.
Influence of Photovoltaic Effect on Photorefractive Phase Gratings
ZHANG Guoquan, GUO Ru
Chin. Phys. Lett. 1995, 12 (10): 617-620 .  
Abstract   PDF(pc) (225KB) ( 400 )
We solve the Kukhtarev’s nonlinear equations of the photorefractive effect with the participation of diffusion, drift and the photovoltaic effect without the approximation of linear generation and linear recombination, and especially discuss in detail the effects of photovoltaic field on the photorefractive grating and its equivalence to an applied electric field in the photovoltaic photorefractive materials.
Dependence of Weak Localization Magnetoconductivity on Flux Line Structure
LI Guohong, WANG Min, LIU Guoliang, LIU Sangtian, WANG Shiguang, YAN Shousheng
Chin. Phys. Lett. 1995, 12 (10): 621-624 .  
Abstract   PDF(pc) (222KB) ( 478 )
A numerical simulation in real space was developed to investigate weak localization corrections to the conductivity in inhomogeneous magnetic fields created by flux lines. Both cylinder model and exponential one of flux lines were studied. It was shown that the corrections are sensitive to the flux line structure. Comparing to the experiments of Bending et al., the results show that the flux line in Pb film can be approximately described by the cylinder model.
Microstructure and Superconductivity of Ultrathin YBa2Cu3O7-δ Films
ZHENG Lizhen, SUN Jijun, ZHAO Bairu, XU Bo, LI Jinwei, YIN Bo, WU Fei, JIA Shunlian, LI Lin, ZHAO Zhongxian, ZHU Chuanfeng, BAI Chunli
Chin. Phys. Lett. 1995, 12 (10): 625-628 .  
Abstract   PDF(pc) (335KB) ( 453 )
Two unit cells to 200Å thick ultrathin YBa2Cu3O7-δ films have been synthesized and their growth mechanism and physical properties have been studied. Atomic force microscopy showed that the films grow with both spiral and layer by layer modes and the screw dislocations appeared even in the 6 unit cells thick films. In the initial growth stages of the films, the strong dependence of Tc on the film thickness is discussed.
Magnetic Properties of lT-TaS2
DAI Shouyu, YU Chengtao, LI Donghong, FAN Shiyong, JIN Jiucheng, CAI Fengxin
Chin. Phys. Lett. 1995, 12 (10): 629-632 .  
Abstract   PDF(pc) (237KB) ( 390 )
The magnetic properties of 1T-TaS2 and 1T-Fe0.07Ta0.93S2 have been studied. Experimental results show that the phase transition temperature of IT-TaS2 is a function of the magnetic field. At low temperatures, both compounds are in a mixed state of charge density wave -spin density wave due to the coherent superposition of antifer-romagnetic coupling.

Universality of Non-exponential Relaxation
WEN Chao, JIN Kejian
Chin. Phys. Lett. 1995, 12 (10): 633-636 .  
Abstract   PDF(pc) (203KB) ( 405 )
A two-state model for polarization relaxation in condensed matter is studied. It is found that if the low-frequency effective spectrum follows a power-law the model gives the fractional exponential and power-law relaxation forms exactly. The origin and universality of the scaling behavior are also discussed.
Theoretical Studies on Vibrationally Assisted Adsorption of H2 on Cu(100) Surface
XIE Jianjun, JIANG Ping, ZHANG Kaiming
Chin. Phys. Lett. 1995, 12 (10): 637-640 .  
Abstract   PDF(pc) (212KB) ( 407 )
Trajectory simulations are carried out for vibrationally assisted adsorption of H2 on Cu(100) surface. The potential-energy surfaces for H2 approaching the copper surface in any molecular orientation are obtained by using the embedded-atom method. It is clearly shown that the vibrational energy of incident H2 greatly promotes the dissociation by assisting H2 to surmount the activation barrier at the reaction zone. The dependence of initial sticking coefficient S0 for H2 activated adsorption on Cu(100) surface on the normal incident translational energy EN has been calculated. The different contributions from H2 (v = 0) and H2 (v = 1) to the sticking probability of H2 molecular beam adsorption on Cu(100) are investigated. The results are in well agreement with the experimental observations and other theoretical calculations.
16 articles