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Volume 16 Issue 10
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Original Articles
Geometric Phase Approach to Dielectricity Based on the Born-Oppenheimer Approximation
WANG Zheng-chuan, LI Bo-zang
Chin. Phys. Lett. 1999, 16 (10): 703-705 .  
Abstract   PDF(pc) (229KB) ( 959 )
Macroscopic polarization differences in crystal dielectrics have been accurately treated by certain authors using the geometric phase approach. However, in their treatments the explicit meaning of the slowly varying parameters was not explored. In this paper we restudy the problem under the Born-Oppenheimer approximation. It turns out that the coordinates of nuclei in the system can be taken as the slowly varying parameters. In addition, our treatment is no longer restricted to the case of null electric field.
Angular Momentum Conserved Coherent State for an Electron in a Uniform Magnetic Field
FAN Hong-yi, ZOU Hui, FAN Yue,
Chin. Phys. Lett. 1999, 16 (10): 706-708 .  
Abstract   PDF(pc) (195KB) ( 439 )
For an electron in the uniform magnetic field, we construct the angular momentum conserved coherent state || r2, l 〉, based on which we establish a new complete and orthonormal << l, r | representation, where l represents the angular momentum and r the electron's orbit radius. Squeezing of the state | l , r >> is examined.

Pressure and Spectral Density of Fermions at Finite Temperature
HOU De-fu, U. Heinz, LI Jia-rong
Chin. Phys. Lett. 1999, 16 (10): 709-711 .  
Abstract   PDF(pc) (253KB) ( 327 )
The pressure of a fermion system is expressed as a mass integral over the full two-point spectral densities within the real time formalism by use of the Keldysh representation for the propagators. This simplifies the calculation significantly and allows a Dyson resummation. The expression is used to demonstrate that potential infrared divergences are rendered harmless. We apply it to check the pressures of an ideal fermion gas and of a chemically non-equilibrated quantum chromodynamics plasma.
K →πvv: New Contributions from Unit-Charged Scalars in Topcolor-Assisted Technicolor Models
XIAO Zhen-jun
Chin. Phys. Lett. 1999, 16 (10): 712-714 .  
Abstract   PDF(pc) (260KB) ( 351 )
We calculate the new contributions to the rare K-decays K+→π+vv and KL →π0 vv from the unit-charged scalars appearing in the topcolor-assisted technicolor models. By using the square-root ansatz for the mixing matrices DL and DR, we find that: (a) the new contributions from top-pions π± and b-pions H± dominate over that from ordinary technipions π1 and π8; (b) for ats*RatdR = -1/4, the enhancements to the ratios B(K+→π±vv ) and B(KL →π0 vv ) from new scalars can be as large as a factor 7 and 11, respectively; (c) the theoretical predictions are still consistent with the data after including the new contributions.
Octupole Deformation and Signature Inversion in 145Ba
ZHU Sheng-jiang, M. Sakhaee, J. H. Hamilton, A. V. Ramayya, GAN Cui-yun, ZHU Ling-yan, YANG Li-ming, LONG Gui-lu, PAN San-li, B. R. S. Babu, J. K. Hwang, W. C. Ma, J. Komicki, X. Q. Zhang, E. F. Jones, J .D. Cole, R. Aryaeinejad, M.W. Drigert, J. O. Rasmussen M. A. Stoyer, S. Y.Chu, K. E. Gregorich, M.F.Mohar, S. G. Prussin, I. Y. Lee, Yu. Ts. Oganessian, G. M. Ter-Akopian, A. V. Daniel
Chin. Phys. Lett. 1999, 16 (10): 715-717 .  
Abstract   PDF(pc) (209KB) ( 356 )
High spin states in Neutron-rich odd-N 145Ba nucleus have been investigated from study of prompt γ -rays in spontaneous fission of 252Cf. The alternating party bands are identified indicating octupole deformation with simplex quantum number s = - i. The groud state band shows signature splitting and inversion at low spin. These collective band structures exhibit the competition and co-existence between symmetric and asymmetric shapes.
Competition of Stimulated Raman Scattering in H2-CH4 Mixed Gases
XU Jian-qiu, LOU Qi-hong, DONG Jing-Xing
Chin. Phys. Lett. 1999, 16 (10): 718-720 .  
Abstract   PDF(pc) (320KB) ( 317 )
Competition of stimulated Raman scattering was observed in hydrogen-methane mixed gases pumped by a KrF laser. The Stokes pulse of methane gas oscillated, shortened and was destroyed with the addition of various ratios of hydrogen gas. A model including the feedback of the cell windows as well as competition between hydrogen and methane gas agree well with the experimental observations.
Analysis of Distributed Phase Shift in Distributed Feedback Semiconductor Lasers
SHEN Dan-xun, GU Wan-yi, XU Da-xiong
Chin. Phys. Lett. 1999, 16 (10): 721-722 .  
Abstract   PDF(pc) (177KB) ( 397 )
A new algorithm based on a transfer matrix method is given to analyze a new distributed feedback (DFB) structure-distributed phase shift in DFB laser. In the small signal analysis, a new model is presented with this algorithm. Compared with λ/4 phase-shifted DFB and three phase shifted DFB lasers, this structure shows superior characteristics in both static and dynamic behavior.
Effect of a Static Electric Field on High-Harmonic Generation in a Polarized Laser Field
WANG Bing-bing, LI Xiao-feng, FU Pan-ming
Chin. Phys. Lett. 1999, 16 (10): 723-725 .  
Abstract   PDF(pc) (239KB) ( 389 )
We study the ellipticity dependence of high-order harmonic generation (HOHG) when a static electric field is present. Through investigating the corresponding classical trajectories of the electron for the harmonic generation, it is found that there exists two different mechanisms. For the elliptical incidence HOHG, we also find that the application of a static electric field can generate harmonics far beyond the usual cutoff.
Investigation of Effective Nonlinear Coefficient of Nd3+-Doped GdCOB and YCOB
LÜ, Jun-hua, LI Guang-ming, ZHANG Shu-jun, CHEN Huan-chu, GONG Bo, WANG Ji-yang, LIU Yao-gang, JIANG Min-hua, SHAO Zong-shu
Chin. Phys. Lett. 1999, 16 (10): 726-727 .  
Abstract   PDF(pc) (189KB) ( 363 )
Second harmonic generation conversion efficiencies of Nd:YCOB and Nd:GdCOB were measured, the effective nonlinear coefficient (deff) for both crystals at different phase-matching angles were estimated by comparison with a KTP crystal. The self-frequency doubling laser performance of these crystals were theoretically calculated by using these deff values and slope efficiency of the fundamental wave and lasing threshold. The results coincide very well.
Femtosecond Time-Resolved Exciton Recombination Dynamics in ZnO Microcrystallite Thin Films at Room Temperature
ZHANG Wei-li, CHAI Lu, XING Qi-rong, WANG Qing-yue, K. S . Wong, Ping Yu, H. Wang, Z. K. Tang, G. K. L, Wong
Chin. Phys. Lett. 1999, 16 (10): 728-730 .  
Abstract   PDF(pc) (276KB) ( 490 )
We report the femtosecond time-resolved studies of room temperature exciton recombination and ultrafast stimulated emission dynamics in ZnO microcrystallite thin films. A free exciton photoluminescence lifetime of few tens of picoseconds and a decay time of a few picoseconds for the stimulated emission were observed. The relatively slow rise time (3ps) for the P band as the result of exciton-exciton scattering compared with the 0.8 ps rise time for the N band attributed to electron-hole plasma recombination clearly distinguished the two stimulated emission processes.
Planar Optical Waveguides in KNbO3 Formed by MeV B and He Ion Implantation
LI Yan, XIA Zong-huang, SHEN Ding-yu, WANG Xue-mei, ZHAO Qiang, MA Xiao-yan, SHEN De-zhong, WANG Kui-ru
Chin. Phys. Lett. 1999, 16 (10): 731-733 .  
Abstract   PDF(pc) (647KB) ( 355 )
Planar optical waveguides in single crystals of KNbO3 were fabricated by MeV B and He ion implantation. The depth profiles of radiation damage in these waveguides were compared and analyzed by high resolution transmission electron microscope. Non leaky waveguiding modes (TE0 and TM0), which are due to implantation induced increase of nb and nc, were observed in 6.0 MeV B ion implantated waveguides with a dose of 1 x 1015cm-2.
An Active Optical Multi-channel Switch
GU Guo-chang, ZHU Shi-yao, WU Xiang, CHEN Hong
Chin. Phys. Lett. 1999, 16 (10): 734-736 .  
Abstract   PDF(pc) (276KB) ( 426 )
We present the theoretical results on using the spontaneous emission which is induced from a two-level atom embedded in a photonic crystal with two bands and one forbidden gap. It is shown that the emission field from the atom is composed of two parts, one is a localized field, which always exists, and the other is one or two propagating modes. The emission of the propagating mode depends on the gap size and the relative position of the upper-level of the atom with respect to the edges of the two bands. The propagating modes have a sudden jump from zero to a certain value when the gap or the related position of the upper level changes. This jump can be used to design an active optical two-channel or four-channel switch. Due to the localized field being within a few dozen atoms, the switch can be designed in a few micrometers.
High Acoustic Nonlinearity of a Liquid Containing Microbubbles
LIU Jie-hui, ZHANG Dong, GONG Xiu-fen, SHAO Li-zheng, LI Xiao-rong, CHEN Xi, ZHANG Qin-lan
Chin. Phys. Lett. 1999, 16 (10): 737-739 .  
Abstract   PDF(pc) (259KB) ( 375 )
The acoustic nonlinearity parameter B/A of a liquid containing microbubbles, sonicated dextrose albumin, has been measured by using second harmonic insert-substitution method. Results show that the value of nonlinearity parameter B/A for a bubbly liquid is significant and it obviously increases with increase of bubble number density. The high nonlinearity of the bubbly liquid is mainly dependent on the microbubble nonlinear oscillation.
High Velocity Acoustical Head Wave on Surface of ST Quartz
WANG Cheng-hao, LIU Yuan, HE Shi-tang, HUANG Xin
Chin. Phys. Lett. 1999, 16 (10): 740-741 .  
Abstract   PDF(pc) (185KB) ( 637 )
According to surface transient excitation theory of elastic wave for piezoelectric crystal, in the surface of a piezoelectric crystal can exist acoustical high velocity head wave except the general surface acoustic wave (SAW). Such a mode is to propagate with the group velocity of the longitudinal bulk wave along the crystal surface. For ST quartz its value is 5.744xl03m/s, which agrees with our experiments. The fact that the longitudinal head wave mode has a high propagation velocity offers potential applications for high frequency SAW devices.
Characterizing the Chaos in a Steady-State Plasma Discharge
MA Lian-xi, WANG Long
Chin. Phys. Lett. 1999, 16 (10): 742-744 .  
Abstract   PDF(pc) (252KB) ( 314 )
Chaos transited from period doubling in plasmas is characterized with several methods. Waveform and fast Fourier transform confirm that the signal is nonperiodic. One dimensional unimodal like structures of the return maps of next amplitude with peak and valley values are obtained to illustrate the deterministic feature. Numerical experiments on one-dimensional logistic map are carried out to simulate the experimental results. Positive Lyapunov exponent 1.33 ± 0.10, directly calculated from the experimental data, provides the evidence that the signal is chaotic. Correlation dimension 2.75 ± 0.05 demonstrates that this signal is decreased to a low dimensional attractor in the plasma.

Loss of Light Yield of Doped Lead Tungstate Crystals After Irradiation
HE Jing-tang, LÜ, Yu-sheng, CHEN Duan-bao, LI Zu-hao, BIAN Jian-guo, ZHU Guo-yi, TANG Xiao-wei, CHEN Gang, ZHENG Lian-rong, CHEN Xiao-hong, REN Shao-xia
Chin. Phys. Lett. 1999, 16 (10): 745-746 .  
Abstract   PDF(pc) (162KB) ( 274 )
Loss of light yield of doped lead tungstate crystals after irradiation with a low dose rate has been observed. The La, Pr, and Y doping may improve radiation hardness, whereas Bi or Mo doping is harmful.
Experimental Study of InP-Based InAlAs/InGaAs Quantum Well Infrared Photodetectors Operating at the 3-5 μm Wavelength Region
ZHANG Yong-gang, LI Ai-zhen, CHEN Jian-xin, YANG Quan-kui, REN Yao-cheng
Chin. Phys. Lett. 1999, 16 (10): 747-749 .  
Abstract   PDF(pc) (277KB) ( 375 )
Gas source molecular beam epitaxy grown InP-based InAlAs/InGaAs quantum well infrared photodetectors operating at 3-5μm atmosphere window have been fabricated; their structural, electrical and optical characteristics have been investigated. The detectors show peak response wavelength λp at 3.85μm, with spectral width Δλ/λp of 4.6% and 7.2% at 1 and 5V bias voltages, respectively. Very low dark current of the detectors has been observed. At 2V bias the dark current is below 1nA at 77K and remains low value of 10nA at 150K. The background limited infrared performance temperature TBLIP as high as 165 K has been measured.

Growth and Characterization of High Quality Sil-x-yGexCy Alloy Grown by Ultra-High Vacuum Chemical Vapor Deposition
QI Zhen, HUANG Jing-yun, YE Zhi-zhen, LU Huan-ming, CHEN Wei-hua, ZHAO Bing-hui, WANG Lei
Chin. Phys. Lett. 1999, 16 (10): 750-752 .  
Abstract   PDF(pc) (342KB) ( 408 )
High quality Sil-x-yGexCy alloy with 2.2% C is grown at a relatively high temperature (760°C) on Si(100) using ultra-high vacuum/chemical vapor deposition (UHV/CVD) system. The samples are investigated with high resolution cross-sectional transmission electron microscope and x-ray diffraction. Compared with Sil-x-yGex alloys, Sil-x-yGexCy alloys with small amounts of C have much less strain and larger critical layer thickness. The quality of interface is also improved. Relatively flat growing profiles of the film are confirmed by secondary ion mass spectroscopy. Fourier transform infrared spectroscopy is also used to testify that the carbon atoms are on the substitutional sites. It is proved that the UHV/CVD system is an efficient method of growing Sil-x-yGexCy alloys.
Photovoltaic Effect of ZnO/Si Heterostructure
FU Zhu-xi, LIN Bi-xia, LIAO Gui-hong
Chin. Phys. Lett. 1999, 16 (10): 753-755 .  
Abstract   PDF(pc) (246KB) ( 443 )
A type of semiconductor heterostructure fabricated by zinc-oxide films deposited on silicon substrates is investigated. The current-voltage characteristics under dark or illumination were determined. It is indicated that the sample is likely a semiconductor junction, and this structure generates an obvious photovoltaic effect. Spectral responses of photovoltage, cathodotoluminescence and excitation spectra at room temperature were employed to study the structural properties and the mechanism generating photovoltaic effect of the samples. The energy level and the process of electron transition in the ZnO film have also been deduced.
Longitudinal Magnetoresistance Effect at Low Temperature in Silver Telluride Thin Films
LIANG Bing-qing, WANG Yin-jun
Chin. Phys. Lett. 1999, 16 (10): 756-757 .  
Abstract   PDF(pc) (3474KB) ( 504 )
Large longitudinal magnetoresistance (LMR) was observed in nonmagnetic silver telluride films. The magnitude of the LMR is not simply dependent on T and H, for example, multi-peaks of ρ at low field and low temperature appear in the Ag-Te film. Because both of -Δρ/ρ and a transition from -Δρ/ρ to +Δρ/ρ exist in Ag-Te films, the magnetoresistance (MR) behavior of the Ag-Te film does not like the bulk Ag-Te, but likes the doped semiconductors. About -27% of LMR was observed at low field in the Ag-Te films, while it could be negligible in the doped semiconductors. The MR behavior in Ag-Te films is discussed by means of a formation of impurity bands in the films.

Ultrafast Heavy Hole-Phonon Scattering in Highly n-Doped GaAs
LIN Wei-zhu, HUANG Chun, ZHANG Hai-chao, WEN Jin-hui, GUO Bing, LAI Tian-shu
Chin. Phys. Lett. 1999, 16 (10): 758-760 .  
Abstract   PDF(pc) (249KB) ( 320 )
Ultrafast heavy hole-phonon interactions in highly n-doped GaAs have been selectively studied with femtosecond absorption saturation measurements by tuning the pump-probe photon energy just above the doped electron Fermi edge. A heavy hole-phonon scattering time of ~ 300fs has been measured, which is consistent with that calculated by a numerical model. Accordingly, an optical deformation potential of about 31 eV has been estimated for this highly n-doped sample.
Influence of Sb on the Scintillation Properties of Lead Tungstate Crystal
LIU Xian-cai, HU Guan-qin, FENG Xi-qi, LI Pei-jun, ZHANG Ming-rong, XU Li, YIN Zhi-wen
Chin. Phys. Lett. 1999, 16 (10): 761-763 .  
Abstract   PDF(pc) (246KB) ( 422 )
Sb-doped lead tungstate (PWO) crystals were grown and investigated. The measurements of Sb content in crystals indicated that the segregation coefficient of Sb in PWO is about 0.63. Even with a little Sb3+ introduced into PWO crystal, the transmission, especially the light yield was enhanced significantly. Furthermore, after the Sb-doped PWO crystals were annealed, not only the fast component still remained a high percentage but also the radiation hardness was improved evidently. The main reason may be that Sb-doping can compensate the composition deficiency and then reduce the density of hole centers such as Pb3+and O-.
Field-Induced Luminescence Quenching in Electroluminescent Conjugated Polymers
FU Rou-li, CHU Jun-hao, JIANG Hao, SUN Xin
Chin. Phys. Lett. 1999, 16 (10): 764-766 .  
Abstract   PDF(pc) (281KB) ( 438 )
The basic physical processes of field-induced luminescence quenching in electroluminescent conjugated polymers is studied by a theoretical model of electron-lattice tight binding with an applied electric field, plus the extended Hubbard interactions, in an unrestricted Hartree-Fock approximation. It is found that there exists a critical field Ec, beyond which the self-trapping singlet- and triplet-excitons (the emitting species) in conjugated polymers will be split directly into hole-polarons and electron-polarons, leading to luminescence quenching. Why the luminescence intensity decreases with increase of the applied field and why the luminescence intensity will not be quenched completely in stronger fields are elucidated. The critical field increases with the electron interactions and the binding energy of self-trapping excitons. Possible approaches to decrease field-induced luminescence quenching are increasing the binding energy of the exciton and reducing the conjugation length.
Dynamic Casimir Effect in Single Bubble Sonoluminescence
CHEN Wei-zhong, WEI Rong-jue
Chin. Phys. Lett. 1999, 16 (10): 767-769 .  
Abstract   PDF(pc) (182KB) ( 339 )
The bubble dynamics for the single bubble sonoluminescence (SBSL) has been coupled with the dynamic Casimir effect due to the quantum vacuum fluctuation. The numerical results show that the power radiated by the Casimir effect is on the order of 10-38 W and too weak to fit the experimental observation of SBSL although the spectrum of the radiation can be fitted well. It is impossible to take the quantum Casimir effect as a candidate for the origin of SBSL.
In Situ Rutherford Backscattering Spectrometry Analysis of Films by Combination with Sputter Etching
JIANG Lei, LIU Bo, ZHOU Zhu-ying, HE Mian-hong, ZHAO Guo-qing, ZONG Xiang-fu
Chin. Phys. Lett. 1999, 16 (10): 770-772 .  
Abstract   PDF(pc) (225KB) ( 461 )
We have set up an experimental system consisting of an ion gun and a Rutherford backscattering spectrometry(RBS) analysis chamber. Using this system, in situ 2MeV 4He+ RBS analysis of films is carried out by combination with sputter etching of low energy Ar+ ions. As an example of the sputtering/RBS method, the analysis of three samples, i.e., Si/(GexSi1-x/Si)/Si(100), WSix/SiO2/Si and CoSix/Si, is presented in this paper. After an appropriate fraction of the thick layer is removed by sputtering, the back edge of the Ge peak is separated from Si RBS spectrum on the interface and the O peak of the buried SiO2 layer can be identified. The change of the doped Ti and W concentrations related to Co on the top surface is observed. The advantages of this analytical method and its possible applications in film are discussed.

Field Emission from Acid Treated Diamond Films
YUAN Guang, JI Hong, HAN Li, WANG Xiu-feng, GU Chang-zhi, ZHANG Bao-lin, JIANG Hong, WANG Yong-zhen, ZHAO Hai-feng, TIAN Yuan, JIN Chang-chun, JIN Yi-xin
Chin. Phys. Lett. 1999, 16 (10): 773-774 .  
Abstract   PDF(pc) (176KB) ( 346 )
A stable electron emission was obtained at as low as about 2.5V/μm from acid treated diamond films. The emission data were fitted with Folwer-Nordheim theory. It is found that the non-electrons are emitted from some protrusions on surface of diamond films, and that after acid treatment, the effective work function is lowered, and the emission area is increased to two folds of those of as-grown films. These results were discussed.
Overall Evolution of Realistic Gamma-Ray Burst Remnant and Its Afterglow
HUANG Yong-feng, DAI Zi-gao, LU Tan,
Chin. Phys. Lett. 1999, 16 (10): 775-777 .  
Abstract   PDF(pc) (249KB) ( 523 )
Conventional dynamic model of gamma-ray burst remnants is found to be incorrect for adiabatic blastwaves during the non-relativistic phase. A new model is derived, which is shown to be correct for both radiative and adiabatic blastwaves during both ultra-relativistic and non-relativistic phases. Our model also takes the evolution of the radiative efficiency into account. The importance of the transition from the ultra-relativistic phase to the non-relativistic phase is stressed.
Electric Character of Strange Stars
XU Ren-xin, QIAO Guo-jun
Chin. Phys. Lett. 1999, 16 (10): 778-780 .  
Abstract   PDF(pc) (235KB) ( 374 )
Using the Thomas-Fermi model, we investigated the electric characteristics of a static non-magnetized strange star without crust. The exact solutions of electron number density and electric field above the quark surface are obtained. These results are useful if we are concerned about physical processes near the quark matter surfaces of strange stars.
28 articles