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Volume 15 Issue 8
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Original Articles
Phase Operator and Lattice Green’s Function for Ring-Lattice Model in p-th Nearest Neighbour Interact ion Approximation
FAN Hong-yi, PAN Xiao-yin
Chin. Phys. Lett. 1998, 15 (8): 547-549 .  
Abstract   PDF(pc) (150KB) ( 398 )
In dealing with the one-dimensional lattice model, we replace the traditionally needed Born-Von-Karmann periodic boundary condition with two additional Hamiltonian terms to make up a ring-lattice. In so doing, a unitary phase operator and the corresponding Hermite phase angle operator can be introduced as those in quantum optics theory. The new Hamiltonian is invariant under the phase shift transformation. Moreover, the lattice Green’s function in the p-th nearest interaction approximation can also be easily derived from the new Hamiltonian. which becomes the well-known lattice Green’s function when the ring is infinite.
Bogoliubov Quasiparticles Carried by Dark Solitonic Excitations in Nonuniform Bose-Einstein Condensates
HONG Tao, WANG Yu-zhu, HUO Yun-sheng
Chin. Phys. Lett. 1998, 15 (8): 550-552 .  
Abstract   PDF(pc) (233KB) ( 349 )
We consider the noncondensate part of the Bose gas in presence of dark solitons. We get a stationary equation of Bogoliubov quasiparticles and find that these Bogoliubov quasiparticles are confined by a dark soliton and carried to propagate with it. This model of the compound structure of the soliton and Bogoliubov quasiparticles provides more precise description of localized sound excitations in Bose-Einstein condensates.
Vaidya-de Sitter Black Hole with Spin Fields
LI Zhong-heng
Chin. Phys. Lett. 1998, 15 (8): 553-554 .  
Abstract   PDF(pc) (106KB) ( 320 )
The generalized Teukolsky-type master equation in Vaidya-de Sitter space-time is given. It is found that the massive Dirac field of spin state p = 1/2 differs greatly from the massive Dirac field of spin state p =-1/2 in radiative mechanism. This effect originates from the variance of Dirac vacuum near the event horizon in the nonstatic space-time caused by spin state.
Static Three-Body Potential in Baryons
LIU Jue-ping, WANG Ping
Chin. Phys. Lett. 1998, 15 (8): 555-557 .  
Abstract   PDF(pc) (224KB) ( 339 )
The first principle of quantum chromodynamics is used to calculate the static perturbative three-body potential between three valence quarks in baryons, which is gauge invariant and flavor-dependent, and of magnitude of the same order as the next non-leading static q-q potential. Its effect on an S-state baryon composed of three valence quarks of equal mass may be viewed as a slight increase of the constituent quark masses with respect to those in mesons.
Decay Widths of Excited Heavy Mesons from Quantum Chromodynamics Sum Rules in the Infinite Mass Limit
DAI Yuan-ben, HUANG Chao-shang, HUANG Ming-qiu, JIN Hong-ying, LIU Chun
Chin. Phys. Lett. 1998, 15 (8): 558-560 .  
Abstract   PDF(pc) (218KB) ( 382 )
The widths for pionic decays of the lowest two excited doublets (0+, 1+) and (1+, 2+) of heavy mesons are studied with quantum Chromodynamics sum rules in the heavy quark effective theory. The interpolating currents used allow us to distinguish the two 1+ states without contamination in the infinite mass limit. The soft pion approximation is not used in the calculations.
Superdeformed Bands of 150Gd in the Interacting Boson Model
LIU Yu-xin
Chin. Phys. Lett. 1998, 15 (8): 561-563 .  
Abstract   PDF(pc) (275KB) ( 411 )
The electric quadrupole transition γ-ray energies and the dynamical moments of inertia of the five superdeformed (SD) bands of 150Gd have been investigated with a four parameter approach inspired of the interacting boson model. The calculated results agree with experimental data well. It indicates that the four parameter approach is powerful in describing both the yrast SD band and the excited SD bands of even-even nucleus no matter whether the bands are built upon some extra single particle excitations.
Quadrupole Moment of the h11/2 Quasineutron Band in 129Ce
LI Guang-sheng, DAI Zheng-yu, LIU Xiang-an, ZHANG Lan-kuan, WEN Shu-xian, WU Xiao-guang, YUAN Guan-jun, WENG Pei-kun, LI Sheng-gang, YANG Chun-xiang
Chin. Phys. Lett. 1998, 15 (8): 564-565 .  
Abstract   PDF(pc) (154KB) ( 295 )
Mean lifetimes of the h11/2 quasineutron band in 129Ce were measured by using the Doppler shift attenuation method in connection with the reaction 116Sn (l6O, 3n)129Ce at a bombarding energy of 73MeV. The data indicate that transition quadrupole moment of 129Ce is smaller than that of 128Ce. This reduction in collectivity caused by the addition of an h11/2 neutron can be interpreted as due to triaxiality induced by γ driving effect.
A Rigidity Measurement of Pseudo-Rapidity Spectrum of Produced Particles in High Energy Nucleus-Nucleus Collisions
ZHOU Dai-cui, CAI XU, LI Yun-de, LIU Lian-shou, QIAN Wan-yan, WANG Xiao-rong, YANG Chun-bin, YAN Wen-biao
Chin. Phys. Lett. 1998, 15 (8): 566-567 .  
Abstract   PDF(pc) (169KB) ( 379 )
A new concept, rigidity of pseudo-rapidity spectrum, is extended into the study of the multiplicity fluctuations in high energy nucleus-nucleus interactions. In using the novel method to analyze the data of l6O-Em at 14.6, 60, and 200A GeV, and 32S-Em at 200A GeV, it is found that the rigidity of pseudo-rapidity spectrum in the central domain of pseudo-rapidity might be a mixture of Poisson type and Wigner one.
Eigensolution of Schrödinger Equation for Harmonically Bound Two-Body Coulomb System
DUAN Yi-wu, SHI Lei, FENG Mang, YAN Min, ZHU Xi-wen
Chin. Phys. Lett. 1998, 15 (8): 568-570 .  
Abstract   PDF(pc) (201KB) ( 503 )
Taking two identical ions in a Paul trap, we solved the SchrÖdinger equation for one-, two-, and three-dimensional harmonically bound two-body Coulomb models, in which the eigenfunctions are written in a series form and the eigenenergies are obtained from a continued fraction. Numerical calculations are made for specific discussion of two- and three-dimensional case. The comparison with a former one-dimensional approximate work shows that our result is more general and accurate.

Effects of Pump Phase Noise on the Linewidth of a Λ-Laser Without Inversion: Linewidth Reduction
HU Xiang-ming, PENG Jin-sheng
Chin. Phys. Lett. 1998, 15 (8): 571-573 .  
Abstract   PDF(pc) (250KB) ( 485 )
The effects of the pump phase fluctuation on a Λ-laser with and without inversion are investigated. It is shown that the pump phase fluctuation can reduce the linewidth of the laser without inversion. It is also shown that, when the system exhibits a transition from lasing without inversion to lasing with inversion, the laser linewidth can still be reduced.
Light-Induced Absorption in Photorefractive Barium Titanate Doped with Rhodium
YANG Chang-xi, ZHU Yong, ZHANG Dao-fan, NIU Xiao-juan, ZHOU Tang, WU Xing, LIU Hong-bin
Chin. Phys. Lett. 1998, 15 (8): 574-576 .  
Abstract   PDF(pc) (230KB) ( 438 )
The light-induced absorption of barium titanate doped with rhodium (BaTiO3:Rh) is characterized in near-infrared spectral region. It decreases with the wavelength of the probe beam from 700 to 840 nm, and is significantly dependent on the polarization of the probe beam and insensitive to the polarization of the pump beam. The light-induced absorption as high as 0.32 cm-1 is obtained for ordinary-polarized probe beam at λ =730 nm. The observations are interpreted by the photorefractive two-center or one center with three valence states model.
Computer Simulation of Radial Viscous Fingering in Two-Dimension Porous Media
TIAN Ju-ping, YAO Kai-lun,
Chin. Phys. Lett. 1998, 15 (8): 577-578 .  
Abstract   PDF(pc) (177KB) ( 385 )
A computer model of capillary and viscous fingering in a porous medium is presented which treats the medium as a square lattice connected with randomly chosen radius. The fractal properties of the model are studied for circular shell-shell aggregation by a Monte Carlo simulation. The simulation results show that the dimension D increases with decrease of the viscous ratio M and increase of the throat radius. It is found that the displacement process is stable when M=1, and viscous fingering pattern of porous media in the limit M → ∞ is similar to the diffusion-limited aggregation pattern in a uniform system. For larger viscous ratio M and smaller positive integer k, the fluid is situated in the co-existence region of viscous and capillary fingering.
Observation of Low Frequency Ion Mode Turbulence in Tokamak Plasma
WANG Gui-ding, LIU Wan-dong, YU Chang-xuan, WEN Yi-zhi, WANG Chao, PAN Ge-sheng, ZHUANG Ge, ZHAI Kan, XU Yu-hong, WANG Cheng, WAN Shu-de
Chin. Phys. Lett. 1998, 15 (8): 579-581 .  
Abstract   PDF(pc) (259KB) ( 467 )
Features of a low frequency ion mode were observed together with the electron drift wave type fluctuations by a Langmuir probe array in the bulk plasma inside the velocity shear layer in the KT-5C tokamak. The measured ion mode wavenumber, scaling of the ion mode with chord-averaged density, and the estimated ηi value suggest that the observed ion mode may be the theoretically predicted ηi mode driven by ion temperature gradient.

Steady-State Reversed Shear Mode Sustained by Lower Hybrid Current Drive
LI Duo-chuan, LI You-yi
Chin. Phys. Lett. 1998, 15 (8): 582-584 .  
Abstract   PDF(pc) (195KB) ( 546 )
A simple model is presented for analysis of radial diffusion of current during lower hybrid current drive (LHCD). Considering the effect of radial diffusion of LH driven current and the bootstrap current, a steady-state reversed shear magnetic configuration can be sustained simply by LHCD and a such case on HT-7U tokamak was calculated as an example.
Path Integral Approach for Multi-dimensional Polarons in a Symmetric Quantum Dot
CHEN Qing-hu, REN Yu-hang, CAO Yi-gang, JIAO Zheng-kuan
Chin. Phys. Lett. 1998, 15 (8): 585-587 .  
Abstract   PDF(pc) (208KB) ( 398 )
Within the framework of Feynman-Haken path-integral theory, the general expression of the ground-state energy for multi-dimensional polarons in symmetric quantum dots for arbitrary electron-phonon coupling constants are derived. Moreover, in the weak-coupling limit, the previous results by the second-order Rayleigh-Schrodinger perturbative theory are completely recovered. More interestingly, the extended- and localized-state solutions to the ground-state energy are obtained analytically.
Binding Energy of Biexcitons in Two-Dimensional Semiconductors
LIU Jian-jun, KONG Xiao-jun, WEI Cheng-wen, LI Shu-shen
Chin. Phys. Lett. 1998, 15 (8): 588-560 .  
Abstract   PDF(pc) (215KB) ( 532 )
The binding energies of a two-dimensional (2D) biexciton have been calculated variationally for all values of the effective electron-to-hole mass ratio u by using a three-parameter wave function. The ratio of the binding energy of a 2D biexciton to that of a 2D exciton is found to be from 0.582 to 0.220. The results agree fairly well with previous experimental results. The results of this approach are compared with those of earlier theories.
First-Principles Electronic Structure of Cu+ Luminescence Centers in Cu-Doped ZnS
ZHANG Zhi-peng, SHEN Yao-wen, HUANG Mei-chun
Chin. Phys. Lett. 1998, 15 (8): 591-593 .  
Abstract   PDF(pc) (205KB) ( 481 )
The electronic structures of various Cu+ luminescence centers in wurtzite ZnS are studied by using first-principles linear muffin-tin-orbital method combining atomic sphere approximation. The results for ZnS:Cu:Cl and ZnS:Cu:Al show that Cu acceptor states are anomalously deep (beyond 2.7eV above the top of valence band) and located near the bottom of conduction band in these two cases. On the other hand, the results for ZnS:Cu with sulfur vacancies manifest that the Cu+ center is an associated center, whose Cu d-like states are situated above the top of valence band.
Electronic Structure of InAsxP1-x/InP Strained Quantum Wires
HE Guo-min, LI Kai-hang, WANG Ren-zhi, ZHENG Yong-mei
Chin. Phys. Lett. 1998, 15 (8): 594-596 .  
Abstract   PDF(pc) (248KB) ( 724 )
The electronic structure of InAs0.25P0.75/InP strained quantum wires grown on InP(001) oriented substrates is studied within the framework of effective-mass envelope-function theory. At the Γ point, the electron and valence subband energy levels with and without spin-split-off band, and the absorption spectra are calculated. The effects of strain and spin-split-off band on valence energy levels are presented. The results show that the uppermost valence subband is almost unaffected by the strain induced coupling between the heavy- and light-hole bands and the spin-split-off bands while the other subbands are more markedly affected in the InAs0.25P0.75/InP strained quantum wires.
Effect of the Transition Sublayers at the Interfaces on Giant Magnetoresistance
XU Hui-ying, YU Wen-xue, MAI Zhen-hong
Chin. Phys. Lett. 1998, 15 (8): 597-599 .  
Abstract   PDF(pc) (255KB) ( 287 )
A thin transition sublayer between the ferromagnetic and the nonmagnetic sublayers is introduced for describing the interface roughness and/or the interface alloying. Based on the Kubo formalism in the real spaces, the giant magnetoresistance effects for both the cases of the structures with and without the transition sublayers at the interfaces are discussed. The numerical results show that the transition sublayers induce a phase shift on the curves of magnetoresistance (MR) vs the thicknesses of the ferromagnetic and the nonmagnetic sublayers, and there exists a critical thickness dc of the ferromagnetic sublayer, the ratio of the MR values for the structures with and without the transition sublayers at the interfaces changes at the critical thickness.
Spectroellipsometric Study of Lead Lanthanum Zirconate Titanate Amorphous Ferroelectric-Like Thin Films
LI Qiu-jun, ZHU De-rui, MO Dang, XU Yu-huan, J. D. Mackenzie
Chin. Phys. Lett. 1998, 15 (8): 600-602 .  
Abstract   PDF(pc) (203KB) ( 463 )
Lead lanthanum zirconate titanate (PLZT) amorphous thin films whose composition is stoichiometric 9/65/35 have been grown and they show some wonderful ferroelectric-like properties. The ellipsometric spectra of the PLZT ferroelectric-like amorphous films have been obtained by a homemade automatic ellipsometer in the wave-length range of 200-700nm, and their optical constant (refractive index n and extinction coefficient k) spectra have been determined. As the photon energy changes from 1.9 to 5.8eV, the refractive index n of the PLZT amorphous films increases from 2.13 to 2.46, then decreases to 1.45. The absorption edge of the PLZT amorphous films is about 300nm, while that of the transparent ceramics with the same composition is about 377nm.
Energy Transfer in Er:CeF3 Crystals
LEI Ning, FENG Xi-qi, HU Guan-qin, YIN Zhi-wen, YUAN Shuai, XUE Shan-hua, HOU Xiao-yuan
Chin. Phys. Lett. 1998, 15 (8): 603-604 .  
Abstract   PDF(pc) (123KB) ( 394 )
Two Er:CeF3 crystals doped with 1.0 and 1.2 wt.% Er2O3 and one pure CeF3 crystal were grown, their absorption and fluorescence spectra at room temperature were measured. Compared with pure crystal, the emission intensity of Ce3+ in Er : CeF3 decreased obviously, it is the sign of energy transfer from 5d state of lattice Ce3+ to 4f state of Er3+ ions which improves the stimulation emission efficiency of Er3+ ions.
Ultraviolet Photoelectron Spectroscopy Study of Oxygen Adsorption on Rb-Covered InSb (111) Surfaces
WU Jian-xin, MA Mao-sheng, LIU Xian-ming
Chin. Phys. Lett. 1998, 15 (8): 605-607 .  
Abstract   PDF(pc) (264KB) ( 319 )
Oxygen adsorption on Rb-covered InSb(111) surface has been studied at room temperature as a function of Rb coverage using ultraviolet photoelectron spectroscopy. At low O2 exposures, the intensity ratio of O2-2 to O2- increases with Rb coverage. The surfaces with low Rb coverages are mainly covered by Sb oxides, causing an increase of work function. For high Rb coverages, the Sb atoms are oxidized below a thin layer of Rb peroxide, which is related to an initial decrease of the work function. At high O2 exposures, the intensity of O-2 ion increases with Rb coverage.
An Electrothermodynamic Analysis of the Field Evaporation in the Configuration of Scanning Tunneling Microscope
LI Zhi-yang, LIU Wu, LI Xing-jiao
Chin. Phys. Lett. 1998, 15 (8): 608-610 .  
Abstract   PDF(pc) (283KB) ( 387 )
This paper presents an electrothermodynamic(Born-Haber-type) analysis of field evaporation in the configuration of scanning tunneling microscope, in which the adatom is only partially ionized and evaporated to counter electrode. As a result a formula was derived, which employed a so-called effective binding energy Aeff. The calculated evaporation field for Au-1, at a tip-sample distance of d = 7.23Å and an evaporation rate of 1011s-1, is 0.6 V/Å, which agrees well with Chang's experiment [Phys. Rev.Lett.72(1994) 574].
High Average Emission Sites Density of Electron Field Emission from Broad Area Diamond-Amorphous Carbon Thin Films
WANG Xiao-ping, YAO Ning, LI Yun-jun, ZHANG Bing-lin
Chin. Phys. Lett. 1998, 15 (8): 611-612 .  
Abstract   PDF(pc) (242KB) ( 307 )
Diamond-amorphous carbon films were deposited on metal Mo substrates by using microwave chemical vapor deposition technique and masked technique (the Mo substrates were pretreated by special techniques). Round area of diamond-amorphous carbon films is 0.78±0.001cm2. The films were characterized by x-ray diffraction, Raman spectrum, optical microscopy, and scanning electron microscopy. The result of experiment indicates that diamond-amorphous carbon films with graphite particulates surface morphologies and diamond submicro-sized crystalline grains located in it were obtained. Based on this, a novel electron field emission device was made. The lowest turn-on field of 1V/μm, high average emission current density of 8.0± 0.1mA/cm2, and high average emission sites density of (2.00±0.03) x 103 sites/cm2 from a broad well-proportioned emission area of 0.780±0.001 cm2 were obtained, and the smaller the graphite particulate, the better the emission character. Field enhancement due to a ‘projection on a projection’ geometry could be a partial explanation of the result.


Effect of Microgravity on Interface Structural Features in Space Crystal Growth
CHEN Wan-chun, MAI Zhen-hong, K.Kato
Chin. Phys. Lett. 1998, 15 (8): 613-614 .  
Abstract   PDF(pc) (167KB) ( 282 )
The distribution of Ca2+ at boundary layer of α-LiIO3 crystal grown both in space and on earth was studied by the synchrotron x-ray fluorescence microanalysis. It was found that: (1) the Ca2+ concentration in the space-crystal is higher than that in the earth-crystal, (2) a sharp discontinuity of Ca2+ concentration is found at boundary layers of space-crystals alone. This finding provides an evidence of microgravity effect on interface structural features in space crystal growth.
Effect of the Compressive Stress for the Growth of Cubic-BN Film
ZHAO Yong-nian, ZOU Guang-tian, HE Zhi, ZHAO Bing, WANG Bo
Chin. Phys. Lett. 1998, 15 (8): 615-616 .  
Abstract   PDF(pc) (169KB) ( 340 )
In this work, it is found that the compressive stress on the surface of cubic-BN (c-BN) film is all smaller than that inside c-BN film and after a longer period, the depositing matter mainly is of hexagonal-BN phase rather than c-BN phase, those just are the reason why a pure thicker c-BN film cannot, as yet, be obtained. Up to now the lowest IR peak position of 1004.7cm-1 detected from a broken and part delaminated c-BN film may be one close to the stressless c-BN.
A New Estimate for the Dispersion Velocity of Galactic Dark Matter Particles
ZHU Zong-hong, WU Jiang-hua, ZHANG Yuan-zhong
Chin. Phys. Lett. 1998, 15 (8): 617-619 .  
Abstract   PDF(pc) (289KB) ( 379 )
An independent method is proposed to estimate the dispersion velocity of galactic dark matter particles. This method is based on the observed quasar-galaxy association samples that are caused by gravitational lensing. All resulting dispersion velocities are much higher than ~220km.s-1, a value expected from the virial theorem, which shows that the conventional assumption of virialization may be invalid in the halo regions of galaxies.
Search for TeV Gamma Ray Bursts from Evaporating Primordial Black Holes
XU Chun-xian, HE Hui-lin, CHEN Yong-zhong, HE Hui-hai, LI Hui-dong, ZHANG Yong, JIANG Yin-lin
Chin. Phys. Lett. 1998, 15 (8): 620-621 .  
Abstract   PDF(pc) (157KB) ( 313 )
Data taken with ACT2 and ACT3 between 1995 and 1997 are used to search for 0.1 s bursts of TeV gamma ray from evaporating primordial black holes (PBHs). There is no evidence for such bursts in the dataset. Using the result, the upper limit of 3x l08 pc-3yr-1on the rate-density of evaporating PBHs is set in the vicinity of the solar system at a 99% confidence level.
Strong Energy Condition of Simple Gauge Field System
ZHANG Yang
Chin. Phys. Lett. 1998, 15 (8): 622-624 .  
Abstract   PDF(pc) (259KB) ( 437 )
An investigation is carried out for the violation of the strong energy condition by a generic field system consisting of charged scalar boson condensate, fermions, and U(1) gauge field. The Bose-Einstein condensation of the system is also studied by the Hamiltonian formulation. It is found that the strong energy condition can be violated by this quantum field system at high densities.
29 articles