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Volume 13 Issue 11
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Original Articles
Mapping the Spinless Fermion-Boson Model onto a Luttinger Liquid Model
WANG Yu-peng, PU Fu-ke,
Chin. Phys. Lett. 1996, 13 (11): 801-804 .  
Abstract   PDF(pc) (164KB) ( 397 )
The spinless fermion-boson model in one-dimension is studied via the Bethe ansatz method. The eigenstates of the model Hamiltonian are established. Some long distance correlation functions are calculated based on the prediction of the conformal field theory. It is shown that the low energy physics of the present model is equivalent to that of a Luttinger liquid model.
Evidence for Octupole Correlations in 117Xe
LIU Zhong, SUN Xiang-fu, ZHOU Xiao-hong, LEI Xiang-guo, GUO Ying-xiang, JIN Han-juan, ZHANG Yu-hu, CHEN Xin-feng, LUO Yi-xiao, WEN Shu-xian, YANG Chun-xiang, YUAN Guan-jun, LI Guang-sheng, LIU Xiang-an, Chen Yong-shou
Chin. Phys. Lett. 1996, 13 (11): 805-808 .  
Abstract   PDF(pc) (195KB) ( 530 )
High spin states in neutron-deficient 117Xe have been studied by using in-beam γ spectroscopy method. A new positive-parity rotational band has been identified. It decays into the yrast vh11/2 band via five electric dipole transitions. The magnitudes of these E1 transitions are extracted and they are much enhanced compared to the normal E1 transitions. This is taken as an evidence for octupole correlations in 117Xe.

Spectra of 230-238U by 1/N Expansion with Consistent Q Framework
ZHANG Qing-ying, FENG Mang, CHEN Xiao-lin, WANG Bao-lin
Chin. Phys. Lett. 1996, 13 (11): 809-812 .  
Abstract   PDF(pc) (185KB) ( 348 )
The energy levels and the E2 transition probabilities B(E2) of uranium isotopes 230-238U are calculated by the 1/N expansion technique with the consistent Q framework in sdIBMl. The energy spectra for the five isotopes and B(E2) of 236U can be reproduced quite well with a few number of parameters only.


Effects of Delta Degrees of Freedom on Quark Condensate in Hot and Dense Matter
LI Lei, NING Ping-zhi, LI Wen-qing
Chin. Phys. Lett. 1996, 13 (11): 813-816 .  
Abstract   PDF(pc) (214KB) ( 446 )
The relativistic mean-field theory is applied to study the quark condensate systematically in nuclear matter at zero and finite temperature in terms of the relative importance of delta degrees of freedom. Calculations have included the high-order contributions to quark condensate in nuclear medium due to the baryon-baryon interactions. Numerical results are presented for the nuclear density up to five times larger than the normal density and temperature up to 120 MeV. It is found that the delta resonance in nuclear matter can cause substantial decreases to in-medium quark condensate.
Analyzing the Photodetachment Cross Section of H- in Parallel Electric and Magnetic Fields
YANG Guang-can, DU Meng-li
Chin. Phys. Lett. 1996, 13 (11): 817-820 .  
Abstract   PDF(pc) (194KB) ( 454 )
We studied the photodetachment of H- in the presence of parallel electric and magnetic fields. This system is an important model that demonstrates the effects of closed-orbits and their bifurcations on the quantum spectra. Using Poisson's summation formula, we have obtained a reduction formula that represents the cross section a sum of oscillations. The reduction formula is valid uniformly. We compare it with the predication from the closed-orbit theory.

Magneto-Optical Trap of Cesium Atoms
GAN Jian-hua, LI Yi-min, CHEN Xu-zong, LIU Hai-feng, YANG Dong-hai, WANG Yi-qiu
Chin. Phys. Lett. 1996, 13 (11): 821-824 .  
Abstract   PDF(pc) (191KB) ( 675 )
We have trapped a cold sample of cesium atoms in a magneto-optical trap. The damped harmonic force of magneto-optical trap was used to capture and trap the cesium atoms directly from a room temperature vapor. About 1.5 x 107 cesium atoms with a density of 3 x 109 atoms/cm3 formed a 4mm3 cesium atomic cloud with temperature below 500μK.
An Improved Calculation of Nonlinear Stopping Power of an Electron Gas for Slow Hydrogen Ions
MU Yu-guang, XIA Yue-yuan, MEI Liang-mo
Chin. Phys. Lett. 1996, 13 (11): 825-828 .  
Abstract   PDF(pc) (195KB) ( 430 )
The stopping power of an electron gas for hydrogen ions is calculated based on the full self-consistent nonlinear density-functional frame. Three different configurations of hydrogen ions are considered and a criterion to test the validity of the self-consistent calculation is proposed. Comparison of calculation with available experimental data shows good agreement.
Characterization of Mass Spectra of Aluminum Anion Clusters Generated by Laser Vaporization and Pulsed Molecular Beam Techniques
NI Guo-quan, ZHOU Ru-fang, ZHAI Hua-jin, WANG Yu-zhu
Chin. Phys. Lett. 1996, 13 (11): 829-833 .  
Abstract   PDF(pc) (250KB) ( 348 )
Aluminum anion clusters are generated by laser vaporization and molecular beam techniques. Mass abundance spectra exhibit a pronounced odd-even alternation for clusters ranging from
n = 5 to n = 17, which is related to the presence of trace oxygen and water resident in He carrier gas and explained by electron pairing effects. In addition, confirmation of jellium model predictions is revealed at peaked A113-, and for the first time at Al7O-. A local maximum Al7- is also observed.
Correlation Between Additive Noises Induced First-Order Phase Transition in a Two-Mode Laser
LONG Quan, CAO Li, WU Da-jin, LI Zai-guang
Chin. Phys. Lett. 1996, 13 (11): 833-836 .  
Abstract   PDF(pc) (224KB) ( 363 )
A phenomenological theory about the correlation between additive noises, in a two-mode laser arising from scattering of photons by the medium in the laser cavity is presented. It is applied to an inhomogeneously broadened two-mode ring laser. We have obtained an approximate expression for the steady-state intensity distribution, in which a first-order phase transition is found.
A New Photorefractive Polymer with Fast Response
GAO Hong, DOU Shuo-Xing, ZHANG Jia-sen, YE Pei-xian, WANG Xue-song, ZHANG Bao-wen, HE Guang-qian, CAO Yi
Chin. Phys. Lett. 1996, 13 (11): 837-840 .  
Abstract   PDF(pc) (207KB) ( 441 )
Photorefractivity properties of a polymer are investigated by four-wave mixing (FWM) diffraction measurements. The polymer is composed of photoconducting poly (n-vinylcarbazole), photosensitizing 2,4,7-trinitro-9-fluorenone, and optically nonlinear 4-(dicyanoviny1)-N. N-diethylaniline. Its FWM diffraction efficiency and response time as a function of, respectively, electric field and writing intensity have been determined. With a 80μm-think film, a diffraction efficiency of 7.4 x10-4 has been obtained. The response time of the polymer is as short as 400ms at a writing intensity of 0.17W/cm2.
Organic Nonlinear Optical Crystal MHBA for Compact Blue-Violet Laser
YUAN Duo-rong, XU Dong, ZHANG Nan, LIU Ming-guo, JIANG Min-hua
Chin. Phys. Lett. 1996, 13 (11): 841-843 .  
Abstract   PDF(pc) (124KB) ( 579 )
By using a 3-methoxy-4-hydroxy-benzaldehyde (MHBA) crystal as frequency doubler at room temperature, an efficient blue light output for near IR automatic tunable picosecond parametric laser is obtained, and blue-violet light output by frequency doubling of GaAlAs laser diode is also realized. A 404.5nm light, with output power of 3μW is generated from the 1W input power of a 809 nm GaAlAs laser diode on a MHBA crystal device which is 3 mm thick at the phase matching angles of θ = 90°, ψ= 15°.
Mutual Quenching of Self-pumped Phase Conjugation by Incoherent ps Laser Pulses
SHE Wei-long, CHEN Ying-yu, YU Zhen-xin, LEE Wingkee
Chin. Phys. Lett. 1996, 13 (11): 844-847 .  
Abstract   PDF(pc) (300KB) ( 437 )
When two beams of incoherent cw mode-locked ps laser pulses were incident upon opposite faces perpendicular to the a-axis of a Cu-doped KNSBN crystal, no mutually pumped phase conjugation as that generated by continuous waves was observed, however, the stronger laser beam generated its self-pumped phase conjugation which was weakened by the weaker one. When the intensities of the two beams were equal, self-pumped phase conjugation was completely quenched.

Chirped Fiber Bragg Gratings for Optieal Fiber Dispersion Compensation
CHEN Gen-xiang, LI Xun, YANG Ling, JIAN Shui-sheng, GE Huang, WANG Wei
Chin. Phys. Lett. 1996, 13 (11): 848-850 .  
Abstract   PDF(pc) (138KB) ( 993 )
The use of α-power chirped fiber Bragg gratings for dispersion Cancellation in an optical fiber link is discussed. Numerical and theoretical investigation of recompressing the dispersion-broadened pulse by using α-power chirped gratings is made, which shows that, the dispersion-broadened Gaussian pulse after l00km standard fiber (with zero dispersion at λ= 1.3μm) trnasmission at λ= 1.55μm with initial width of TFWHM = 33ps (full width at half maximum) can be perfectly recompressed with the peak reflectivity of 82% by using a 30mm long α-power chirped fiber grating with proper α value and optimal grating parameters.

Ordering and Reordering of Nanophase FeAl Intermetallics Synthesized by Mechanical Alloying
TAN Qi
Chin. Phys. Lett. 1996, 13 (11): 851-854 .  
Abstract   PDF(pc) (267KB) ( 497 )
Nanophase B2-FeAl intermetallics was directly synthesized by room temperature ball milling and heat milling. The atomic ordering can be realized when compositional shift during milling is compensated and can be accelerated by heat milling. Fully ordered nanophase FeAl can be obtained by atomic reordering during annealing at temperatures below 500 °C, which results in no significant grain growth.

Nucleation and Growth Processes During Molecular-Beam Epitaxy of Ternary Compounds
MAO Hui-bing
Chin. Phys. Lett. 1996, 13 (11): 855-858 .  
Abstract   PDF(pc) (236KB) ( 553 )
In this letter the effect of the different migration rates of two kinds of cations on the nucleation and growth processes during molecular-beam epitaxy of ternary systems was studied in detail by Monte Carlo simulation. In AlGaAs ternary system, in which the migration rate of cation Ga is larger than that of Al, there are three types of nucleation: Ga-Ga, Al-Ga and Al-Al, which show different characteristics in the growth processes.
Effects of Pairing Correlations on the Korringa Relation in Doped Fullerenes
LÜ, Jing, ZHANG Li-yuan, FENG Xiao-bing
Chin. Phys. Lett. 1996, 13 (11): 859-862 .  
Abstract   PDF(pc) (190KB) ( 371 )
An effective attractive Hubbard model is applied to explain the observed non-Korringa relation in doped fullerenes, which leads to a reduced Pauli susceptibility. The results basically agree with the experiments for K3C60, Rb3C60 and RbCs2C60. It implies that the pair correlation on site possibly plays an important role in the normal state for doped fullerenes.
Effects of Off-Diagonal Electron-Electron Interactions on Exciton Energies in C60
RAO Xue-song, ZHAO Hua, FU Rou-li, SUN Xin, K. NASU
Chin. Phys. Lett. 1996, 13 (11): 863-866 .  
Abstract   PDF(pc) (233KB) ( 517 )
Since the neighboring π orbits in C60 are well overlapped, the off-diagonal part of electron interaction plays an important role. In this paper, the effects of the off-diagonal electron interactions on the exciton energies in C60 are studied by using the single configuration interaction approach. It is found that the binding energies of the low-lying singlet and triplet excitons depend sensitively upon the off-diagonal interactions which compete against the diagonal interactions and suppress the binding of the excitons. The implication of these features is discussed.
Formation Energies and Electronic Structures of Native Defects in GaN
XIE Jian-jun, ZHANG Kai-ming, XIE Xi-de
Chin. Phys. Lett. 1996, 13 (11): 867-869 .  
Abstract   PDF(pc) (207KB) ( 718 )
The electronic structures and the formation energies of native point defects in cubic GaN have been studied via the linear muffin-tin orbital method. The results show that the nitrogen vacancy is the dominant defect in the intrinsic cubic GaN. Among the antisites and interstitial defects, it is found that a tetrahedral interstitial nitrogen atom surrounded by four Ga atoms NTGa is most easily formed, and the formation energy of NGaNGa antisite is much less than that of GaN antisite. The changes of the density of states due to the introduction of defects are discussed.
Large Piezoresistance and Pressure-Induced Change in Electric Properties in Perovskite-like La0.85Sr0.15MnO3
ZHANG Ning, DING Wei-ping, GUO Zai-bing, XING Ding-yu, DU You-wei, LI Gang, ZHENG Yi-xin
Chin. Phys. Lett. 1996, 13 (11): 870-873 .  
Abstract   PDF(pc) (215KB) ( 515 )
Uniaxial pressure dependencies of the electric properties of perovskite-like Lal-xSrxMnO3(0.2 ≤x ≤0.6) system have been investigated. A large nonlinear piezoresistance effect and a remarkable pressure-induced change of metal-semiconductor (M-S) transition have been observed. For La0.7Sr0.3MnO3, the piezoresistance value can reach about 86% at 290K under a pressure of 16.8MPa, and the pressure coefficient of Tp, the onset of the M-S transition, is as high as 6.4 K/MPa, which is significantly larger than that of known similar pressure effects. These pressure effects suggest that the resistivity of the perovskite compounds is relative not only to double exchange but also to the symmetry of lattice. This phenomenon may provide another route in understanding the colossal magnetoresistance behavior in the perovskites.
Photocurrent Studies of Ultraviolet Detector Based on Gallium Nitride Epilayer
YANG Kai, QIN Lin-hong, ZHANG Rong, SHEN Bo, ZHENG You-dou, HUANG Zhen-chun, J.C. Chen
Chin. Phys. Lett. 1996, 13 (11): 874-877 .  
Abstract   PDF(pc) (199KB) ( 478 )
The properties of photoconductive blue and ultraviolet detector based on single crystal GaN epilayer grown on sapphire substrate by metalorganic chemical vapor deposition were investigated. The observed optical absorption edge of 3.39eV in optical transmission has been confirmed by the peak of 3.400eV in photoreflectance. The detectable energy span of the GaN device up to ultraviolet was obtained by photocurrent measurement. The dependence of the intensity of photocurrent on the chopper frequency in the measurement was studied, and an easy method was used to determine the response time as 0.4s.

Ion-Beam Bombarding Effects on Deposition of Carbon Nitride Films by Laser Ablation
YING Zhi-feng, REN Zhong-min, DU Yuan-cheng, LI Fu-ming, LIN Jing, REN Yun-zhu, ZONG Xiang-fu
Chin. Phys. Lett. 1996, 13 (11): 878-880 .  
Abstract   PDF(pc) (216KB) ( 545 )
In order to obtain high quality carbon nitride films, x-ray photoelectron spectroscopy and Raman spectrum were used to analyze several kinds of film: (a) laser-ablated amorphous carbon (a-C) films, (b) a-C films after a 1 keV nitrbgen ion beam bombardment. (c) carbon nitride (CNx) films synthesized by ablation assisted with ion beam bombardment, (d) CNx films after a 50eV nitrogen ion beam bombardment, and (e) CNx films after a 1 keV nitrogen ion beam bombardment. The comparison among these films showed that the concurrent deposition of CNx films by ablation and a nitrogen ion beam should be better than the post-treatment of a-C films by nitrogen ion beam bombardment. In the case of concurrent deposited CNx films, a post-treatment by a nitrogen ion beam bombardment with an appropriate energy (possibly less than 1 keV) was proposed to improve the ratio of C-N binding structures in the deposited films.
21 articles