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Volume 13 Issue 3
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Original Articles
Parametrization of Spin Rotation and the Two-Level Problem
ZHOU Jin-yuan, LI Li-yun, YE Chao-hui
Chin. Phys. Lett. 1996, 13 (3): 161-164 .  
Abstract   PDF(pc) (160KB) ( 535 )
The evolution behavior of a spin system subject to a time-varying magnetic field and the relevant two-level problem essentially exhibit like a rotation in a three-dimensional space. It is shown that the parametrization of this rotation is shifted into solving the time-dependent Schrödinger equation of a spin-1/2 system and the rotation parameters can thus be obtained by a straightforward method.
Mixed Rescaling Model and Direct Photon Production
LIN Zhong-jin
Chin. Phys. Lett. 1996, 13 (3): 165-167 .  
Abstract   PDF(pc) (125KB) ( 413 )
Using the mixed rescaling model, the main features of the European Muon Collaboration effect can be explained. Then the ratio of cross sections, free proton(p)-bound nucleon of Iron(Fe) to free proton-free proton, for large-PT direct photon production is calculated.
Evolution from Sequential Decay to Simultaneous Multifragmentation with Increasing Beam Energy
HE Zhi-yong, JIN Gen-ming, LI Zu-yu, DUAN Li-min, DAI Guang-xi, ZHANG Bao-guo, WU He-yu, WEN Wan-xin, LUO Qing-zheng, QI Yu-jin
Chin. Phys. Lett. 1996, 13 (3): 168-171 .  
Abstract   PDF(pc) (187KB) ( 367 )
Two-fragment correlation functions have been measured for 40Ar+197Au collisions at E/A = 25MeV. Based on the three-body trajectory calculation, a mean emission time of τ ~ 450 fm/c for light fragments was extracted from the measured correlation functions. This result suggests that the sequential decay occurs at this energy.
Measured Stopping Powers of 7Li Ions in Silicon Single Crystal at 1-5 MeV
LI Zhong*, ZHAO Guo-qing, ZHOU Zhu-ying, TANG Jia-yong, YANG Fu-jia
Chin. Phys. Lett. 1996, 13 (3): 172-174 .  
Abstract   PDF(pc) (119KB) ( 559 )
Stopping powers of 7Li ions in silicon single crystal at I-5 MeV in random and < 111 > channeling directions were determined in transmission geometry, with the uncertainties less than 6%. The measured results were compared with the available literature results and the values of TRIM-91 and TRIM-95.
K-Shell Ionization of Molybdenum and Iron by Electron Bombardment
HE Fu-qing, LONG Xian-guan, PENG Xiu-feng, LUO Zheng-ming, AN Zhu
Chin. Phys. Lett. 1996, 13 (3): 175-177 .  
Abstract   PDF(pc) (168KB) ( 671 )
K-ionization cross sections of Mo and Fe by electron impact were measured by detecting characteristic x-ray emitted by thin solid film targets of known mass thickness with a Si (Li) detector. Reflection correction of a substrate was done by bipartition model of electron transport. The experimental results are compared with theoretical calculation and empirical formula calculation.
Experimental Study of Nd3+:KGd(WO4)2 Laser Pumped by Laser Diode
ZHAO Ting-jie, TU Chao-yang, LUO Zun-du
Chin. Phys. Lett. 1996, 13 (3): 178-181 .  
Abstract   PDF(pc) (150KB) ( 513 )
This paper presents the cw output characteristics of Nd3+:KGd(WO4)2 (KGW) laser crystal with different Nd3+ concentration grown in our laboratory. The laser output at 1.067μm of KGW crystal (3x3x6mm) was obtained to be 68.9mW and the slope efficiency reached 28.8% when pumped by laser diode of power 305mW at 807nm.
Large Non-resonant Nonlinear Optical Susceptibility of Cu2O Microcrystallites
WANG You-gui, SI Jin-hai, ZHAO Jiang, ZOU Bing-suo, YE Pei-xian
Chin. Phys. Lett. 1996, 13 (3): 182-184 .  
Abstract   PDF(pc) (192KB) ( 395 )
We report the measured results of non-resonant nonlinearity by degenerate four-wave mixing for Cu2O nanoparticles having central diameter of 9nm. The value of (3) obtained in a 10ns pulse experiment is 8.48 x 10-10 esu, and the nonlinear response time of the sample is estimated to be in the order of nanosecond.
A Chaotic Neural Network Model
SHUAI Jian-wei, CHEN Zhen-xiang, LIU Rui-tang, WU Bo-xi
Chin. Phys. Lett. 1996, 13 (3): 185-188 .  
Abstract   PDF(pc) (175KB) ( 416 )
A chaotic neural network model is introduced in this letter. With the variation of a controlling parameter, the model can process the input by a content-addressable means or fall into a chaotic state. Hence the features of brain such as the clear active state and the chaotic rest state can be simply simulated.
SiGe Optical Waveguide Modulators Based on the Plasma Dispersion Effect
GAO Yong, LI Guo-zheng, LIU Xi-ding, LIU En-ke, ZHANG Xiang-jiu*, LU Xue-kun*, WANG Xun*
Chin. Phys. Lett. 1996, 13 (3): 189-191 .  
Abstract   PDF(pc) (166KB) ( 448 )
Based on plasma dispersion of Si1-xGex, the single mode waveguide modulators consisting of Si1-xGex/Si and Si/ Si1-xGex/Si which were grown by molecular beam epitaxy have been fabricated. For Si1-xGex/Si structure, the switch current and insertion loss at wavelength 1.3 μm are 36 mA and 2.8 dB, respectively. The switching response time is 40 ns.

Emission Spectroscopy for Hot Filament Diamond Growth Process with Positive Substrate Biasing
CUI Jing-biao, FANG Rong-chuan
Chin. Phys. Lett. 1996, 13 (3): 192-195 .  
Abstract   PDF(pc) (189KB) ( 507 )
Optical emission spectrum has been successfully measured on a hot filament diamond growth process with substrate biasing. The emission lines of atomic hydrogen, H2, CH and CH+ were observed. Effects of methane concentration on the emission intensity of observed lines were systematically studied. The experimental results suggest that atomic hydrogen and CH+ radicals play an important role in diamond growth, while CH radical facilitates the formation of amorphous carbon.
Study on the Relation Between Magnetic Moment and Charge Transfer of Metallic Glasses By LCAO-Xα Method
LIU Hong-lin*, CHEN Nian-yi*, NI Min, HE Li-ming, JIN Qian-yuan
Chin. Phys. Lett. 1996, 13 (3): 196-198 .  
Abstract   PDF(pc) (140KB) ( 472 )
The calculations of the clusters, T27 and T27B7 (T=Fe, Go and Ni), modelling metallic glasses have been performed using the quantum chemical linear combination of atomic orbitals (LCAO)-Xα method. The argument about the relation between magnetic moment and charge transfer has been clarified based on the calculated results.
Relationship Between Octagonal Quasicrystal and β-Mn Type Crystal in Cut Description
LI Fang-hua, CHENG Yi-fan
Chin. Phys. Lett. 1996, 13 (3): 199-202 .  
Abstract   PDF(pc) (176KB) ( 491 )
The transformation from the octagonal lattice to a square lattice is demonstrated straightforward under the cut description by introducing a peculiar linear phason strain. The calculated lattice parameter of the β-Mn structure from the edge length of squares and rhombi forming the octagonal quasilattice is in agreement with experimental results.
Growth, Defects and Non-critical Phase Matching of Nb Doped KTP Crystals
WEI Jing-qian, WANG Ji-yang, LIU Yao-gang, WANG Chang-qing, SHAO Zong-shu, GUAN Qing-cai, JIANG Min-hua
Chin. Phys. Lett. 1996, 13 (3): 203-206 .  
Abstract   PDF(pc) (258KB) ( 504 )
A series of Nb doped KTP crystals are grown with seed flux method and flux pulling method. The results of our investigation on growth, morphology defects of the crystals are reported in this paper. We obtained the relationship between Nb contents and second-harmonic generation angles of the crystals. Noncritical phase matching has been realized by 4% Nb doped KTP crystal for Nd:YAG laser 1.06μm output.
Exactly Solved Anderson Lattice Model
LIU Wu-ming, , ZHAO Hong-wei, PU Fu-ke,
Chin. Phys. Lett. 1996, 13 (3): 207-210 .  
Abstract   PDF(pc) (167KB) ( 330 )
A solvable Anderson lattice model is formulated. The exact eigenstates of model Hamiltonian are constructed by using the Bethe ansatz. The Bethe ansatz equations are obtained from the periodic boundary conditions.
Width of Soliton and the Electron Correlation in Polymer
MA Yun-sheng, WU Chang-qin, FU Rou-li, SUN Xin
Chin. Phys. Lett. 1996, 13 (3): 211-214 .  
Abstract   PDF(pc) (167KB) ( 367 )
The effect of electron correlation on the width of the soliton in polymer is studied. Our theory shows that the screening plays a key role in the effect of electron correlation on the width of soliton: In weak screening, the width of soliton is reduced by the electron-electron interaction; whereas, in strong screening, it will be increased. The physical reason is given at the end.
Some New Transition Classes in the Fractional Quantum Hall Effect and Their Critical Filling Factors
CHEN Ying-jian
Chin. Phys. Lett. 1996, 13 (3): 215-218 .  
Abstract   PDF(pc) (209KB) ( 427 )
The transitions between fractional quantum Hall states are classified into three equivalence classes by virtue of the matrix theory. It is pointed out that there probably exist two new transition classes and the critical filling factors for these transitions have been calculated by exploiting the law of corresponding states.
A Coherent Updating Algorithm for the XYZ Model
YING He-ping, JI Da-ren
Chin. Phys. Lett. 1996, 13 (3): 219-222 .  
Abstract   PDF(pc) (206KB) ( 464 )
A scheme of loop-cluster algorithm is developed for simulating an anisotropic Heisenberg antiferromagnet-the XYZ model. Results of numerical simulations are presented, suggesting that this quantum system may also be studied by using the cluster updating techniques.

Direct-Current Magnetization of Y-Type Zeolites Containing Fe Ions
TONG Li-tai, WU Feng, LI Guo-hong, YAN Shou-sheng, JI Tian-hao*, LIN Bing-xiong*
Chin. Phys. Lett. 1996, 13 (3): 223-226 .  
Abstract   PDF(pc) (208KB) ( 391 )
The dc magnetization of Y-type zeolite containing Fe ions and that after reduction treatment were measured in the temperature range of 1.5-300K. The samples show paramagnetic behavior. The obtained value for the magnetic moment of the paramagnetic units strongly implies the existence of ferromagnetic coupling between the Fe ion at site I in hexagonal prism and the one at the nearest site I' in β cage.

Influence of Cr Addition on Magnetic Properties of Amorphous Nd4Fe77.5B18.5 Alloy
GU Ben-xi, SHEN Bao-gen, WANG Hao, ZHU Xiao-bin, ZHAI Hong-ru
Chin. Phys. Lett. 1996, 13 (3): 227-230 .  
Abstract   PDF(pc) (207KB) ( 525 )
The influence of Cr addition on the magnetic moment, Curie temperature and crystallization temperature of amorphous Nd4Fe77.5B18.5 alloy was investigated. With increasing Cr content, the magnetization and Curie temperature decrease, but the crystallization temperature increases. It is found that the substitution of Cr for Fe can enhance greatly the coercivity of crystallized sample.
Structure and Magnetostriction of Dy0.9-xTbxPr0.1Fe1.85 and Dy0.9-xTbxPr0.1(Fe0.95Al0.05)1.8 Alloys
WANG Bo-wen, WU Chang-heng, TANG Shao-long, JIN Xi-mei, ZHUANG Yu-zhi, ZHONG Xia-ping, LI Ru-qi, LI Jing-yuan
Chin. Phys. Lett. 1996, 13 (3): 231-233 .  
Abstract   PDF(pc) (157KB) ( 383 )
The structure and magnetostriction of Dy0.9-xTbxPr0.1Fe1.85 and Dy0.9-xTbxPr0.1(Fe0.95Al0.05)1.8 alloys were investigated. These alloys are substantially single phase with MgCu2-type cubic structure. The lattice parameter and Curie temperature of Dy0.9-xTbxPr0.1(Fe0.95Al0.05)1.8 alloys increase steadily with increasing Tb content. Tb dependence of magnetostriction in various applied fields for polycrystalline Dy0.9-xTbxPr0.1Fel.85 alloys exhibits a peak at x = 0.25. The magnetostriction of polycrystalline Dy0.9-xTbxPr0.1(Fe0.95Al0.05)1.8 alloys in high applied fields (H > 160 kA/m) and in low applied fields (H≤ 160 kA/m) exhibits a peak at x = 0.3 and x = 0.25, respectively.
Optical Absorption of the Nanostructured SiO2 in Ultraviolet-Near Infrared Light Range
ZHANG Biao, ZHANG Li-de, MO Chi-mei *
Chin. Phys. Lett. 1996, 13 (3): 234-236 .  
Abstract   PDF(pc) (176KB) ( 544 )
The electronic structure of nanostructured SiO2 was studied by means of ultravioletnear infrared absorption spectra. A strong and broad absorption band was observed in the wavelength range of ultraviolet-near infrared light. This band is caused by the electronic transition from the valence band to the defect energy level in the bandgap which was theoretically calculated by using molecular orbital approach. With increasing the annealing temperature, the red shift of this band was observed. The mechanism of this band is discussed.
Femtosecond Reflections of Bulk GaAs and GaAs/AlGaAs Multiple Quantum Wells
LI Wei-liang, QIU Zhi-ren, PENG Wen-ji, HUANG Xu-guang, ZHOU Jian-ying, YU Zhen-xin
Chin. Phys. Lett. 1996, 13 (3): 237-240 .  
Abstract   PDF(pc) (231KB) ( 379 )
We present room temperature femtosecond reflection studies on the photocarrier dynamics of GaAs and GaAs/AlGaAs multiple quantum wells (MQW). A rising wing with a time constant of about 5ps and an increased amplitude per carrier is observed for the MQW sample at carrier densities lower than 5 x 1011cm-2. This phenomenon is explained as the saturation of the excitonic transitions.

22 articles