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Volume 14 Issue 6
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Original Articles
On the Eigenvalue Problem in One-Dimensional Mesoscopic Rings with Electron-Phonon Coupling
WANG Xiao-guang, YU Rong-jin, XIE Cheng-jun
Chin. Phys. Lett. 1997, 14 (6): 401-404 .  
Abstract   PDF(pc) (138KB) ( 373 )
By invoking the concept of displaced number state in quantum optics, the complete eigen-states in one-dimensional mesoscopic rings with electron-phonon coupling are abtained and the eignevalues followed. It is shown that the eigenvalues and persistent current depend on both coupling strength and phonon number.
Remark on the Higher Order Perturbative Studies of Flavor Breaking in the Standard SU(3) Skyrmion Quantum Mechanics
LI Jin-ping, YAN Mu-lin
Chin. Phys. Lett. 1997, 14 (6): 405-408 .  
Abstract   PDF(pc) (234KB) ( 329 )
A quantitative criterion is proposed for testing the rationality of an effective QCD baryon theory. The higher order corrections of the standard SU(3) Skyrme model to the Gell-Mann-Okubo relations for baryons are studied according to the criterion, and some interesting results are presented. A possible prescription is recommended.
Semidecoupled Band and Shape Driving Effect of the π1/2-[541] Orbital in 170Ta
ZHANG Yu-hu, ZHAO Qing-zhong, ZHOU Xiao-hong, XU Hu-shan, GUO Ying-.iang, LEI Xiang-guo, LU Jun, ZHU Shao-fei, GOU Quan-bu, JIN Han-juan, LIU Zhong, LUO Yi-xiao, SUN Xiang-fu, ZHU Yong-tai
Chin. Phys. Lett. 1997, 14 (6): 409-412 .  
Abstract   PDF(pc) (225KB) ( 538 )
High spin states in 170Ta have been studied via 159Tb(16O, 5nγ )170Ta reaction at 105MeV beam energy. Three rotational bands have been observed among which one coupled band and an unfavored ΔI = 2 transition sequence of the semidecoupled band are identified in this work. The effects of the π1/2-[541] proton intruder orbital are qualitatively discussed.
Target Dependence of N / Z Ratio of the Fragments Produced in 30 MeV/u 40Ar Induced Reactions
XU Hu-shan, ZHU Yong-tai, WEI Zhi-yong, LU Jun, WANG Qi, LI Song-lin, ZHANG Yu-hu, XIE Yuan-xiang, WU Zhong-li, ZHAO Qing-zhong, GOU Quan-bu
Chin. Phys. Lett. 1997, 14 (6): 413-416 .  
Abstract   PDF(pc) (249KB) ( 425 )
An inclusive measurement was performed for 30 MeV/u 40Ar+58,64Ni and 115In. By employing the degree of freedom of N/Z, the production mechanism of the high energy component of the intermediate mass fragments (IMFs: 3 ≤ Z ≤ 13) has been discussed. Special attention has been paid to the target dependence of N/Z ratio of the energetic fragments. These IMFs may be produced by a projectile fragmentation process with energy dissipation.
Coherent Control of a Simple Quantum System
LIN Fu-cheng
Chin. Phys. Lett. 1997, 14 (6): 417-420 .  
Abstract   PDF(pc) (188KB) ( 493 )
The quantum dynamics of a three-level Vee-system can be controlled by using two single-mode cw lasers. The dc component of the probability for finding a specific state in laser fields can be obtained by matching the intensities, phases and detunings of the lasers to relevant eigenvalues of the quantum system. The selectivity of control does not depend strongly on the laser intensities but the absolute amount of the product does strongly. There are generally three paths to reach such a dc component control and, at some points, two of them cross each other causing a near 100% control. The stability of the process to the fluctuation of the experiment was analyzed.
A New Method for Interpreting the Effective Radius of Curvature: Two-Dimensional Case
CAO Qing, DENG Xi-ming
Chin. Phys. Lett. 1997, 14 (6): 421-423 .  
Abstract   PDF(pc) (181KB) ( 489 )
Starting from the vector field theory, the expression of the time average energy flow density < S > of a paraxial scalar light beam is deduced. In terms of this expression, the x (or y) directional weighted deviation is reasonably defined between the real-beam wavefrontand an imaginary ellipsoidal wavefront which is used to replace the real-beam wavefront. It is proved that, when Rx and Ry are just the x and y directional effective radii of curvature, respectively, the ellipsoidal wavefront Le = x2/(2Rx) + y2/(2 Ry) is the best-fit one for the real-beam wavefront L. Finally, the above results are generalized for a general polychrornatic light beams.



A Scheme for Preparing Schrödinger Cat States with Controllable Manners
GUO Guang-can, ZHENG Shi-biao
Chin. Phys. Lett. 1997, 14 (6): 424-427 .  
Abstract   PDF(pc) (197KB) ( 411 )
A scheme to generate superpositions of coherent states with variable amplitudes, phases and weighting factors is proposed. It provides experimental possibility for preparing an arbitrary Schrödinger cat state.
Radiative Cooling Instability in Large Scale Line-shaped Laser Plasma
WU Yan-qing, HAN Shen-sheng, SHEN Bai-fei, ZHANG Ling-qing, SONG Xiang-yang, XU Zhi-zhan
Chin. Phys. Lett. 1997, 14 (6): 428-431 .  
Abstract   PDF(pc) (229KB) ( 341 )
In the experiment of generating laser plasma in a line-focus system we found that the x-ray emission nonuniformity was increased rapidly after the pumping laser has been turned off. Our study indicates that radiative cooling instability is one possible reason for this x-ray emission nonuniformity.
Dust-Acoustic Soliton in a Streaming Plasma
LIU Jin-yuan, MA Jin-xiu
Chin. Phys. Lett. 1997, 14 (6): 432-435 .  
Abstract   PDF(pc) (235KB) ( 367 )
Large amplitude dust-acoustic solitons in a plasma with ion streaming are investigated on a very slow time scale of dust motion with variable grain charge. It is found that both compressional and rarefactive solitons can coexist within certain range of soliton velocities.
Electrical Activity of Frank Partial Dislocations and the influence of Metallic Impurities in Czochralski-Grown Silicon
SHEN Bo, YANG Kai, CHEN Peng, ZHANG Rong, SHI Yi, ZHENG You-dou T. Sekiguchi, K. Sumino
Chin. Phys. Lett. 1997, 14 (6): 436-439 .  
Abstract   PDF(pc) (372KB) ( 613 )
Electrical activity of Frank partial dislocations bounding stacking faults and the influence of Fe impurities in Czochralski-grown silicon are investigated by means of the electron-beam-induced-current (EBIC) technique. Frank partials free from metallic impurities exhibit EBIC contrast at low temperature but not at room temperature, indicating that they are only accompanied with shallow energy levels in the band gap. The energy level related to a Frank partial is determined to be about Ec-0.08eV in n-type Si. Frank partials decorated by Fe impurities become EBIC active at room temperature.
Raman Study of Nitrogen at High Pressure
CHEN Liang-chen, WANG Li-jun, GU Hui-cheng, XU Li-wen, CHE Rong-zheng, WANG Ji-fang
Chin. Phys. Lett. 1997, 14 (6): 440-442 .  
Abstract   PDF(pc) (150KB) ( 397 )
Raman spectra of the nitrogen loaded in a diamond anvil cell with the compressed gas have been investigated at the pressure up to 40GPa. Pressure was measured in terms of the ruby fluorescence. The curve of frequency vs pressure was obtained by micro-Raman spectrometer. According to the experimental results, the frequency of two stretching mode peaks increases steadily from 2340 and 2347cm-1 at 5.2 GPa to 2396 and 2434 cm-1 at 40 GPa, respectively. The interval between two peaks also increases gradually with pressure increasing. A new peak (2402cm-1) of the stretching mode was observed near 40 GPa, which may be associated with the distortion of the Pm3n structure or the formation of low-symmetry structure.
InAlAs/InGaAs Quantum Well Infrared Photodetectors with 3-5μm Band Grown by Gas Source Molecular Beam Epitaxy
ZHANG Yong-gang, LI Ai-zhen, CHEN Jian-xin, REN Yao-cheng
Chin. Phys. Lett. 1997, 14 (6): 443-445 .  
Abstract   PDF(pc) (181KB) ( 372 )
The relationship between well width and subband energy as well as response wavelength of the InAlAs/InGaAs multi-quantum well structures have been calculated for the design of the devices by using Kronig-Penney model. By using gas source molecular beam epitaxy grown InAlAs/InGaAs quantum well infrared photodetector (QWIP) materials have been used to fabricate QWIP devices with 3-5μm band. I-V characteristics and response spectra of the devices have been measured. Results show that the devices have peak response at 4.0μm with full width of half maximum of about 29.5meV.
Fractal Aggregation Behavior in Amorphous Silicon Nitride Films
YE Chao, NING Zhao-yuan, GUO Yu-hua, WANG Xiang-ying, XIN Yu, WANG Yuan-chang, SHEN Ming-rong, WANG Hao
Chin. Phys. Lett. 1997, 14 (6): 446-448 .  
Abstract   PDF(pc) (266KB) ( 474 )
A fractal aggregation behavior in amorphous silicon nitride (Six Ny) films deposited by microwave electron cyclotron resonance plasma chemical vapor deposition is reported. The fractal structure and dimension of 1.45 obtained by experiment and computer simulation are all in excellent agreement with the result predicted by the cluster-cluster-aggregation model. The forming of fractal structure is related to the change of discharge mode between ring plasma and bulk plasma.
Effects of Orientation on the Electron States of K3C60
LÜ, Jing, ZHANG Li-yuan
Chin. Phys. Lett. 1997, 14 (6): 449-452 .  
Abstract   PDF(pc) (265KB) ( 383 )
Effects of orientation on the electron states of K3C60 are studied by taking into account the interactions between the doped K ions and the C atoms. It is found that the density of states (DOS) curve in the disordered bidirectional structure (space group Fm 3m) is similar to that in the ordered unidirectional structure (space group Fm 3), accompanied by a slight reduction in the DOS at the Fermi level [N(EF)] due to a broadening of the DOS curve.
Magnetoresistance Behavior of La(2-x)/3Bix/3Cal/3MnO3 (x = 0.4)
TANG Wei-hua, LIANG Jing-kui, LIANG Chang-lin, SUN Ji-rong, RAO Guang-hui
Chin. Phys. Lett. 1997, 14 (6): 453-456 .  
Abstract   PDF(pc) (229KB) ( 489 )
The magnetoresistance (MR) behavior of La(2-x)/3Bix/3Cal/3MnO3 (x = 0.4) compound was investigated. The compound exhibits complex magnetic transitions, i. e., paramagnetic-canted ferromagnetic-ferromagnetic-spin glass transitions. The temperature dependence of resistivity of the compound indicates a semiconducting behavior, and no semiconductor-metal transition was associated with these magnetic transitions. The magnetoresistance ratio exhibits a critical maximum corresponding to the canted ferromagnetic transition. A MR ratio as large as 86% was observed at 85 K. The temperature dependence of MR ratio is well described by the relation of ( ρo -ρH ) / ρo = A(M/Ms)2.
Electronic Structure of SrTiO3 Nanocrystallite Thin Film at High Temperature
LIU Zhen-xiang, GUO Jun, XIE Kan
Chin. Phys. Lett. 1997, 14 (6): 457-459 .  
Abstract   PDF(pc) (220KB) ( 370 )
The electronic structure and surface composition of SrTiO3 nanocrystallite thin film at different temperature were studied by ultraviolet photoelectron spectroscopy and x-ray photoelectron spectroscopy, respectively. The electronic structure strongly depends on temperature and at high temperature is similar to that of single crystal. As the sample temperature falling down from high temperature, the valence band spectra of SrTiO3 nanocrystallite thin film shift to high binding energy and become weak rapidly; an opposite process was observed when temperature rising up. This interesting phenomenon was explained on the basis of the thermodynamic equilibrium process near grain boundaries that leads to redistribution of anions and cations and forming charged grain boundaries.
Schottky Barrier Heights of Cr Contacts on n- and p-Type 6H-SiC
ZHANG Yong-gang, LI Ai-zhen, A. G. Milnes
Chin. Phys. Lett. 1997, 14 (6): 460-463 .  
Abstract   PDF(pc) (213KB) ( 582 )
The Schottky contact characteristics of Cr on n- and p-type 6H-SiC have been investigated by using I-V and C-V methods, and the barrier heights and ideality factors have been measured. Results obtained show that Cr is also an appropriate metal to form Schottky junction on n type 6H-SiC, as the barrier height of ~ 1 eV is moderate for both low forward turn on voltage and low backward leakage current in device applications. However, the interfacial properties of Cr to p type 6H-SiC results in nonideal Schottky junctions.
Influence of Crystallization on Magnetic Properties in Co66Fe4Mo2Si16B12 Amorphous Alloy
HE Shu-li, HE Kai-yuan, WANG Zhi, CHENG Li-zhi, FU Yu-jun
Chin. Phys. Lett. 1997, 14 (6): 464-467 .  
Abstract   PDF(pc) (248KB) ( 515 )
The annealing effects on the magnetic properties and structures of Co66Fe4Mo2Si16B12 amorphous alloy were studied by means of ballistic method and x-ray diffraction technique respectively. During the isothermal annealing at Ta = 460°C, the initial permeability μi of the sample increased at first, then decreased with the annealing time ta and exhibited a maximum at about ta = 45 min. Meanwhile, it was found that magnetostriction λs changed with ta and ran through zero at about ta = 45min. The x-ray diffraction results showed that the sample was still in an amorphous state in the whole 460°C isothermal annealing process ( ta = 0-120min). After the annealing temperature increased to 480°C, α-Fe(Co,Si) phase began to precipitate, then, Co3Mo crystallites and other phases were formed subsequently at 500°C. The results of magnetic measurement indicated that the formation of any crystalline phases should lead to the deterioration of magnetic properties.

Low Temperature Phase Transition of a Crystal in the Potassium Lithium Niobate System
LI Ci-ran, HAN Jian-ru, WANG Jin-feng, ZHANG Lei, ZHAO Huan-sui
Chin. Phys. Lett. 1997, 14 (6): 468-469 .  
Abstract   PDF(pc) (120KB) ( 365 )
A potassium lithium niobate crystal with tetragonal tungsten bronze structure was prepared by the Czochralski technique. The dielectric and pyroelectric properties were investigated in the temperature range of 300 to 10 K. A broadened ferroelectric-ferroelectric transition between phases with space group 4mm and space group m was found at about 80K.

Modulation Instability of Femtosecond Optical Pulses in Long Optical Fibers with Minimum Group-Velocity Dispersion
XU Wen-cheng, WEN Shuang-chun, LIU Song-hao, GUO Qi, LIAO Ch, ulg-jun
Chin. Phys. Lett. 1997, 14 (6): 470-473 .  
Abstract   PDF(pc) (194KB) ( 376 )
A new region where modulation stability occurs in the fibers with minimum group-velocity was found due to the fourth-order dispersion effect. The spectral extent of the region is analyzed and found to be affected by initial input power and the dispersion parameter.
Electro-optic and Photorefractive Properties of Doped Poly (N-Vinylcarbazole)
WANG Shu-feng, HUANG Zhi-wen, CHEN Zhi-jian, GONG Qi-huang, ZHANG Zhi-jie, CHEN Hui-ying
Chin. Phys. Lett. 1997, 14 (6): 474-475 .  
Abstract   PDF(pc) (211KB) ( 526 )
In this work, 100μm-thick doped poly (N-vinylcarbazole) films with different contents of the electro-optic (EO) chromophore 2,5-dimethyl-4-(p-nitrophenylazo) anisole and plasticizer N-ethylcarbazole were prepared and sandwiched between two indium-tin oxide-covered glass substrates. Their EO measurements and two-beam-coupling experiments were performed by using a single mode (TEM00) He-Ne laser. Both the EO coefficient and the gain for two-beam-coupling were found to be strongly depending on the content of plasticizer.
Unit-Cell by Unit-Cell Epitaxial Growth of SrTiO3 and BaTiO3 Thin Films by Laser Molecular Beam Epitaxy
YANG Guo-zhen, , LÜ, Hui-bin, WANG Hui-sheng, , CUI Da-fu, , YANG Hai-qing, WANG Hua, ZHOU Yue-liang, , CHEN Zheng-hao,
Chin. Phys. Lett. 1997, 14 (6): 478-480 .  
Abstract   PDF(pc) (224KB) ( 420 )
Atomically regulated unit-cell by unit-cell homoepitaxial SrTiO3 and heteroepitaxial BaTiO3 films were fabricated on SrTiO3(100) substrates by laser molecular beam epitaxy. The fine streak patterns and more than 1000 cycles undamping intensity oscillation were obtained by in situ reflection high-energy electron diffraction with precisely controlled intermittence between each unit-cell layer. The surface morphology of the films was examined by atomic force microscopy. The root-mean-square surface roughness of the films is about 0.1 nm.
22 articles