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Volume 18 Issue 4
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Original Articles
New Applications of the <λ| Representation in Studying the Angular Momentum of Laughlin State Vector
FAN Hong-Yi, LIN Jing-Xian
Chin. Phys. Lett. 2001, 18 (4): 469-472 .  
Abstract   PDF(pc) (226KB) ( 462 )
We use the complete and orthonormal <λ| representation (Phys. Lett. A126 (1987) 150) constructed in terms of guiding centers K± = MΩ/2(x0 iy0) and kinetic momenta II± describing an electron in a uniform magnetic field, to identify that the Laughlin state vector is N i < j(K+i - K+j)m ||0 >, where ||0 > is annihilated by ( II-,K-). Following this, we further employ the <λ| representation to derive the angular momentum of the Laughlin ground state and excited state in a direct and convenient way. This approach for studying some properties of the Laughlin state seems to be new.

Integer and Half-Integer Quantization Conditions in Quantum Mechanics
Integer and Half-Integer Quantization Conditions in Quantum Mechanics
Chin. Phys. Lett. 2001, 18 (4): 473-475 .  
Abstract   PDF(pc) (196KB) ( 434 )
The integer and half-integer quantization conditions are found in quantum mechanics based on the topological structure of symmetry group of the singlet and spinor wavefunction. The internal symmetry of physical system is shown to be sufficient to determine the topological structure in quantum mechanics without taking into account the dynamical details about the interaction.
New Method for Universal Models Composed of Arbitrary Boson Modes with Arbitrary Two-Body Interactions
YANG Xiao-Xue, WU Ying
Chin. Phys. Lett. 2001, 18 (4): 476-478 .  
Abstract   PDF(pc) (205KB) ( 454 )
We propose a new method for the energy eigenvalue problem for boson systems with either weak or strong two-body interactions. It is also shown that this method is particularly simple and effective to obtain the explicit analytical expressions of energy eigenvalues and eigen-states for interacting harmonic oscillators especially when the number of the oscillators is huge.
An Empirical Formula for the Measurement of Spatial Coherence of Trapped Bose Gases
ZHOU Xiao-Ji, CHEN Shuai, WANG Yi-Qiu, CHEN Xu-Zong, ZHANG Jian-Wei,
Chin. Phys. Lett. 2001, 18 (4): 479-481 .  
Abstract   PDF(pc) (306KB) ( 486 )
An empirical formula, which demonstrates the interference fringe visibility as a function of the slit separation and the temperature of thermal atoms, is obtained by analysing a recent experiment [Bloch et al. Nature 403 (2000) 166] that refers to the spatial correlation function of a trapped Bose gas below the critical temperature. We find that the decay rate of the coherence function for the non-condensed component is of about two orders larger than that of the pure condensed component. The changes of the interference fringe visibility versus the falling time for different temperatures and slit separations are also discussed.
Quasi-Normal Oscillations of a Black Hole with Deficit Angle for Electromagnetic Perturbations
LI Xin-Zhou, ZHOU Bing-Lu, ZHU Jiong-Ming
Chin. Phys. Lett. 2001, 18 (4): 482-484 .  
Abstract   PDF(pc) (210KB) ( 427 )
We consider an electromagnetic perturbation in the external space-time of a black hole with deficit angle, and describe the perturbation equation. Approximate analytic formulas for the quasi-normal frequencies have been provided, which may play a significant role in the continuing search for gravitational radiation and black hole. These frequencies can be distinguished from the ordinary quasi-normal frequencies of Schwarzschild black hole.
Hawking Radiation of Dirac Particles in a Variable-Mass Kerr Black Hole
WU Shuang-Qing, CAI Xu
Chin. Phys. Lett. 2001, 18 (4): 485-487 .  
Abstract   PDF(pc) (205KB) ( 400 )
Hawking effect of Dirac particles in a variable-mass Kerr space-time is investigated by using method of the generalized tortoise coordinate transformation. The location and the temperature of event horizon of the non-stationary Kerr black hole are derived. It is shown that the temperature and the shape of event horizon depend not only on the time but also on the polar angle. However, our results demonstrate that the Fermi-Dirac spectrum displays a residual term which is absent from that of Bose-Einstein distribution.
Effects of Asymmetry of Potential on Stochastic Stokes’ Drift
LI Yu-Xiao, CAO Tian-Guang, WU Xi-Zhen, ZHUO Yi-Zhong,
Chin. Phys. Lett. 2001, 18 (4): 488-490 .  
Abstract   PDF(pc) (301KB) ( 394 )
The directed motion of Brownian particles is generated by a travelling asymmetric potential. The asymptotic behaviour of probability density of the particles at long time is a solitary wave. The Brownian particles can do work against an external opposing force with high efficiency. The analytical expressions of the solitary wave and the efficiency of the Brownian particles are obtained. The average velocity and the efficiency of the particles depends strongly on the travelling speed and the asymmetry of the potential.
Phase Diagram of the 2-Dimensional Ising Model with Dipolar Interaction
SUN Gang, CHU Qian-Jin
Chin. Phys. Lett. 2001, 18 (4): 491-494 .  
Abstract   PDF(pc) (383KB) ( 600 )
We treat the 2-dimensional Ising model with the dipolar interaction by the numerical calculation under the restriction that the spin configurations are distributed with a 4 x 4 period. The phase diagram with respect to temperature and dipolar interaction strength is constructed. Most characters of the phase diagram are consistent with those obtained in the references by the Monte Carlo simulation, except that we find a new rectangle phase, which is ordered in the spin structure with the 1 x 2 rectangle.
Structures of Liquid Aluminum under High Pressure
LI Hui, WANG Guang-Hou, BIAN Xiu-Fang, ZHANG Lin
Chin. Phys. Lett. 2001, 18 (4): 495-497 .  
Abstract   PDF(pc) (446KB) ( 388 )
Molecular dynamics simulation has been carried out for melt Al under the constant-temperature and constant-pressure. The interaction between atoms is described by tight-binding many body potentials based on the second-moment approximation to the electronic density of states. The pair correlation function and the pair analysis technique are used to reveal the structural features of liquid Al under the normal and high pressure. The high pressure is favorable to the existence of bcc-cluster 1661 and 1441, but has no effect on the fcc-cluster 1421. The bond pair 1551 and 1541 with fivefold symmetry exists at high pressure. The microstructure of liquid is more similar to the structure of non-crystalline than to crystalline. The simulation results are supported by the x-ray experimental results.
Perturbative Quantum Chromodynamics Effects in Bc →PP Decays
GUO Li-Bo, DU Dong-Sheng
Chin. Phys. Lett. 2001, 18 (4): 498-500 .  
Abstract   PDF(pc) (248KB) ( 462 )
Using the leading order low energy effective Hamiltonian, we calculate Bc →PP (where P stands for pseudoscalar meson) decays induced by pure W-emission mechanisms. In order to estimate the hadronic matrix elements, we apply the perturbative quantum chromodynamics (PQCD) method proposed by Szczepaniak et al. [Phys. Lett. B 243 (1990) 287] and developed by Simma et al. [Phys. Lett. B 272 (1991) 395]. Comparing with predictions of other models, we find that the PQCD method is suitable for these decays and therefore the spectator ansatz seems questionable.
Influence of the Unique-Parity States on Collectivity of Low-Lying States
LUO Yan-An, CHEN Jin-Quan, GAO Ya-Chen, NING Ping-Zhi, J. P. Draayer
Chin. Phys. Lett. 2001, 18 (4): 501-504 .  
Abstract   PDF(pc) (305KB) ( 710 )
The importance of the unique-parity single particle level in the description of nuclear collectivity is stressed in the framework of the nucleon-pair shell model truncated to the SD subspace. It is found that with the shell model Hamiltonian which includes the single particle energy term, the unique-parity single particle level has to be included for describing the low-lying collective states reasonably.

Enhancement of M1 Transition Rates at High Spin in 90Mo
WU Xiao-Guang, LI Guang-Sheng, PENG Zhao-Hua, WEN Shu-Xian, HAN Guang-Bing, LI Cheng-Po, LU Shao-Jun, WU Shao-Yong, YUAN Guan-Jun, YANG Chun-Xiang
Chin. Phys. Lett. 2001, 18 (4): 505-507 .  
Abstract   PDF(pc) (311KB) ( 411 )
High spin states in 90Mo have been populated through the 59Co (35Cl,2p2n) 90Mo reaction at beam energy of 116 MeV. Level lifetimes of the positive-parity decay sequence are measured by using the Doppler shift attenuation method. It is observed that the M1 transition strengths show a substantial enhancement at high spin. This behaviour may be related to occupation of high Ω orbitals by a pair of g9/2 protons. A deformed shape with oblate is suggested above the 13+ state.

Proton Spin from General Colour Symmetry Model
LÜ, Xiao-Fu, LI Ying-Chuan, SUN Ming-Shan, WEN Xin-Min
Chin. Phys. Lett. 2001, 18 (4): 508-510 .  
Abstract   PDF(pc) (237KB) ( 389 )
The quark wave function in a proton has been calculated by using the global colour symmetry model. We find that the property of this wave function is closely related to the nonperturbative vacuum configuration. Using the wave function we make the calculation of the matrix element of the axial vector current of the quarks in the proton ground state. Its value is found to be 0.17, which is perfectly consistent with 0.23(+6).

Optical Transition Radiation Measurement of Electron Beam for Beijing Free Electron Laser
ZHAO Qiang, XIE Jia-Lin, LI Yong-Gui, ZHUANG Jie-Jia
Chin. Phys. Lett. 2001, 18 (4): 511-512 .  
Abstract   PDF(pc) (382KB) ( 472 )
We used transition radiation techniques instead of the original phosphor targets to improve the electronic beam diagnostic system at Beijing Free Electron Laser. The beam profile, size (3.3×2.4mm), position and divergence angle (σrms=2.5mrad) in transverse have been obtained from optical transition radiation. We also present the experimental set-up and some preliminary results.

Scintillation Characteristics of Doped PbWO4 Crystals
SHAO Ming, CHEN Hong-Fang, LI Cheng, XU Tong, SHI Chao-Shu, WU Jian, CHEN Hui, XU Zi-Zong, WANG Zhao-Min, WANG Xiao-Lian, DENG Qun, YIN Zhi-Wen
Chin. Phys. Lett. 2001, 18 (4): 513-515 .  
Abstract   PDF(pc) (445KB) ( 803 )
Emission spectra, longitudinal transmission and light output for the Sb-doped and Y-doped PbWO4 crystals are presented. Scintillation decay kinetics has been measured by using gate integration and single photon counting method with blue and green filters. Radiation hardness has also been measured by using 60Co γ-ray irradiation under different dose rates and different dose rate profiles. The light yield and radiation hardness of the Sb-doped and Y-doped PbWO4 crystals are improved as compared to the undoped crystals and are suitable for the requirements of compact muon solenoid.

Electron Branching Ratios Following Autoionization of the Ba 6pns States
LÜ, Jun, DAI Chang-Jian, XU Yun-Fei, LI Shi-Ben
Chin. Phys. Lett. 2001, 18 (4): 516-518 .  
Abstract   PDF(pc) (331KB) ( 404 )
The excitation spectra and branching ratios of ejected electrons of the Ba 6pns (J = 1) autoionizing states are measured using multistep laser excitation scheme and time-of-flight electron spectroscopy. The energy dependence of branching ratios of Ba+ 6s state on energy is determined for the low-lying 6p1/2,3/2ns states, and compared with a previous R-matrix calculation.
Optimization of Scatterer Concentration in High-Gain Scattering Media
ZHU Jiu-Gao, ZHU He-Yuan, SUN Die-Chi, DU Ge-Guo, LI Fu-Ming
Chin. Phys. Lett. 2001, 18 (4): 519-521 .  
Abstract   PDF(pc) (382KB) ( 702 )
We report the scatterer concentration-dependent behaviour of laser action in high-gain scattering media. A modified model of random laser is proposed to explain the experimental results in good agreement. We may use this modified model to design and optimize random laser system. A further detailed model is needed to quantitatively analyse the far-field distribution of random laser action.
Energy Transfer Pathways in Reaction Center upon Femtosecond Excitation of Accessory Bacteriochlorophylls
GUO Li-Jun, MA Guo-Hong, ZOU Yong-Long, XU Chun-He, LIU Ye, MI Jun, QIAN Shi-Xiong, LIU Jian-Hua
Chin. Phys. Lett. 2001, 18 (4): 522-524 .  
Abstract   PDF(pc) (317KB) ( 391 )
The energy transfer pathways from the excited accessory
bacteriochlorophylls (B*) within native and modified (pheophytin-exchanged) reaction center isolated from Rhodobacter
sphaeroides (RS601) have been investigated by using the femtosecond pump-probe technique. For native RS601, B* decays with time constant of 240 fs, followed by a partial recovery of the ground state bleaching with time scale of about 2 ps. In modified RS601(Phe), however, B* decays with time constant of 800 fs for magic angle (54.7°) polarization configuration. In addition to the general assumption of energy transfer pathway from B* to the special pair P, an alternative pathway for energy transfer probably operates as well.

Enhancement in Energy Loss of MeV Silicon Clusters in C Films
SHEN Yi-Xiong, JIANG Dong-Xing, LU Xi-Ting, SHEN Ding-Yu
Chin. Phys. Lett. 2001, 18 (4): 525-527 .  
Abstract   PDF(pc) (352KB) ( 561 )
Energy losses of 0.63-1.03MeV/atom Sin (n ≤ 3) clusters in thin carbon films (2-12μg/cm2) have been measured by using a special experimental setup with Rutherford backscattering (RBS) technique. The experimental results show that for a given energy per atom, the energy loss of Si+2 ions, as well as Si+3 ions, is significantly larger than that of Si+ ions. This is the first observation of energy loss enhancement in the measurements with RBS technique. The enhancement in energy loss (i.e. the cluster effect) is evident when the effective thickness of the carbon target is thin enough, but not evident when it is thick. The effect will not be obvious until the energy of the projectile is over a certain limit for a special target. This suggests that the cluster effect only occurs in the first layers of the target film, and that the energy of the projectile must be large enough for the effect to be seen.

Charge Transfer for Reactions of Sc3+ with N2 and H2 at Electron-volt Energy
JIANG Yu-Rong, NIE Zong-Xiu, LI Jiao-Mei, GAO Ke-Lin
Chin. Phys. Lett. 2001, 18 (4): 528-530 .  
Abstract   PDF(pc) (335KB) ( 466 )
The charge transfer rate coefficients for reactions of Sc3+ with N2 and H2 have been measured at the mean collision energy of 4.2eV. The rate coefficients are derived from the decay rate of ion signals by using ion storage in a radio-frequency ion trap. The rate coefficients are 8.18(0.18)×10-10cm3.s-1 at Tequiv ≈1.26×104K for Sc3+ with N2 and 1.44(0.39)×10-9cm3.s-1 at Tequiv> ≈ 1.67×103 K for Sc3+ with H2, respectively. Both results are comparable with the Langevin rate coefficients.

Measurement and Multiple Scattering Correction of K-Shell Ionization Cross Sections of Silver by Electron Impact
ZHOU Chang-Geng, FU Yu-Chuan, AN Zhu, TANG Chang-Huan, LUO Zheng-Ming
Chin. Phys. Lett. 2001, 18 (4): 531-532 .  
Abstract   PDF(pc) (241KB) ( 397 )
The K-Shell ionization cross sections of silver have been measured by electron impact. In order to overcome the difficulties in preparing a self-supporting thin target, a thin target with a thick substrate was used in our experiments. The influence of electrons reflected from the substrate was corrected by means of a detailed calculation of electron transport. The path of the electrons passing through silver target of 31.2μg/cm2 was calculated by the EGS4 Monte Carlo program. This method of correction for the measurement is reported for the first time.

Zeeman-Birefringence He-Ne Dual Frequency Lasers
JIN Yu-Ye, ZHANG Shu-Lian**, LI Yan, GUO Ji-Hua, LI Jia Qiang
Chin. Phys. Lett. 2001, 18 (4): 533-536 .  
Abstract   PDF(pc) (305KB) ( 1302 )
We demonstrate an approach to obtain the frequency differences from 1 MHz to hundreds of MHz including 3-40 MHz, which was a blank range of the frequency difference in the traditional dual frequency lasers. We employ an intra-cavity stress-birefringence element in an He-Ne laser, and at the same time apply a transverse magnetic field to the laser. The intra-cavity stress birefringence element, which is the window plate or the mirror substrate applied by a force, is used to split a frequency into two; i.e. to make a single-frequency laser outputting two frequencies. Moreover, the transverse magnetic field is used to decrease greatly the mode competition between the two frequencies so that they are able to oscillate simultaneously. The minimum value of magnetic field for efficiently eliminating the mode competition to ensure the two frequencies working together is studied experimentally. The power tuning performance of the two frequencies (o-light and e-light) is investigated.

All-Solid-State Multi-Wavelength Laser System from 208 to 830 nm
ZHAO Shang-Hong, CHEN Guo-Fu, ZHAO Wei, WANG Yi-Shan, YU Lian-Jun
Chin. Phys. Lett. 2001, 18 (4): 537-538 .  
Abstract   PDF(pc) (272KB) ( 446 )
Four-wavelength lasers from near-infrared to deep-ultraviolet range, 532, 830, 415 and 208 nm, have been developed in one all-solid-state laser system. The laser system is pumped by a diode-Q-YLF laser at 532 nm, a Ti:sapphire laser and the nonlinear second-harmonic-generation crystals LBO and BBO are used to generate different wavelengths. Maximum average powers (repetition rate 1 kHz) of 1.1 W at 830 nm, 380 mW at 415 nm, and 39 mW at 208 nm are obtained when the pumping power is 3.6 W. The main characteristics of this system are presented.
Red and Blue Light Generation in an LiTaO3 Crystal with a Double Grating Domain Structure
LIU Zhao-Wei, ZHU Shi-Ning, ZHU Yong-Yuan, WANG Hui-Tian, LUO Guo-Zhen, LIU Hui, MIN Nai-Ben, LIANG Xiao-Yan, XU Zu-Yan
Chin. Phys. Lett. 2001, 18 (4): 539-540 .  
Abstract   PDF(pc) (251KB) ( 455 )
Simultaneous red and blue light generation in an LiTaO3 crystal with a double grating structure is first reported. The double grating consists of two separate domain reversal sequences (superlattices) in series and is fabricated by field poling technique at room temperature. Using a picosecond 532 nm laser as a pump source, the red light at 631 nm and blue light at 460 nm are generated at the same time. A possible application of the superlattice crystal is presented.
Feasibility of Femtosecond Laser Writing Multi-Layered Bit Planes in Fused Silica for Three-Dimensional Optical Data Storage
LI Cheng-De, WANG Dan-Ling, LUO Le, YANG Hong, XIA Zong-Ju, GONG Qi-Huang
Chin. Phys. Lett. 2001, 18 (4): 541-543 .  
Abstract   PDF(pc) (767KB) ( 508 )
The ultrashort pulse laser writing multi-layered data bits in fused silica for three-dimensional optical data storage through the mechanism of optical damage induced by multi-photon absorption is demonstrated. The 800 nm, 120 fs Ti:Sapphire laser beam is focused into cubic samples with a 0.65 NA commercial microscope objective. The size of the recorded bits can be smaller than 0.5 x 0.5 x 2.5μm as the laser pulse energy is lower than 300 nJ and the corresponding bit data storage density is 0.2 x 1012 Tbits/cm3. Due to the aberration produced by the mismatch of the refractive indices between the recording material and its immersion medium, the longitudinal size of the recorded bit increases and the contrast of the bit to surrounding uninfected zone decreases as the bit plane gets deeper. Hence a relatively lower storage density of 0.05 x 1012 Tbits/cm3 is realized.
Viscous Fingering in Correlated Site-Bond Square Lattice
TIAN Ju-Ping, YAO Kai-Lun,
Chin. Phys. Lett. 2001, 18 (4): 544-546 .  
Abstract   PDF(pc) (387KB) ( 482 )
A new porous media model with correlated sites-bonds has been
constructed. Taking into account both the pore and throat geometries, the viscous fingering (VF) in porous media has been investigated by using the standard over-relaxed Gauss-Seidel scheme. The simulation results show that the VF's structure varies with the correlation parameter ε and the viscous ratio M. The sweep efficiency E decreases along with the increase of the correlation parameter ε and the lattice size Rls. The surface fractal Ds gradually increases as the correlation parameter ε increases, whatever the viscous ratio M is. Also, Ds gradually increases as M increases whatever ε is. These mean that not only the viscosity ratio but also the topology and the geometry of the porous media have a strong effect on the displacement process, the VF's structure, the sweep efficiency and the surface pattern.
Diffusion in Two-Temperature Partially Ionized Gases
LI He-Ping, CHEN Xi
Chin. Phys. Lett. 2001, 18 (4): 547-549 .  
Abstract   PDF(pc) (195KB) ( 455 )
to date, some confusion exists in the literature concerning the employment of the diffusion driving force and the calculation of the diffusion velocity for the gas species in a two-temperature (2-T) plasma. In this letter, a derivation is presented concerning the species diffusion driving force and diffusion velocity under 2-T plasma conditions. Expressions for the ambipolar diffusion coefficients and the electric conductivity of the 2-T plasma are also given.

Absorption Measurement of Radiatively-Heated Low-z Mixture
YANG Jia-Min, DING Yao-Nan, ZHANG Bao-Han, YANG Guo-Hong, ZHENG Zhi-Jian, ZHANG Wen-Hai, WANG Yao-Mei, YAN Jun, LI Jia-Ming
Chin. Phys. Lett. 2001, 18 (4): 550-552 .  
Abstract   PDF(pc) (620KB) ( 405 )
High-resolution transmission spectra of radiatively-heated low-z C10H16O6 plasma have been measured on‘Xingguang II’ laser facility by using flat field grating spectrometer. Absorption lines of oxygen and carbon ions in the region of 1.6 to 5.0 nm have been observed clearly and identified. Using the unresolved transition array model, we also calculated the transmission spectra of C10H16O6 plasma. The measured transmission spectrum has been compared with the calculated ones.

Envelope Soliton in Multi-ion Plasma and Ion-Ion Hybrid Wave Excited by Energetic Electron Beam
WANG De-Yu, HUANG Guang-Li,
Chin. Phys. Lett. 2001, 18 (4): 553-555 .  
Abstract   PDF(pc) (372KB) ( 527 )
Another envelope soliton event below the H+ gyrofrequency and localized density depletion was discovered in low auroral region ( ~1760 km ) by Freja satellite. This envelope soliton has a characteristic frequency at ~190 Hz, which is also closed to the resonance frequency of hydrogen ion-oxygen ion hybrid wave. This event is correlated in time with the observations of the sharp increase of the ratio of oxygen ion density to hydrogen and with the electrons energization along the magnetic field. A theoretical model on the ion-ion hybrid wave excited by energetic electron beam has also been presented. It is found that the ion-ion hybrid wave is mainly excited by the Cherenkov instability in auroral region.

Reduced Magnetohydrodynamic Equations in Toroidal Geometry
REN Shen-Ming, YU Guo-Yang
Chin. Phys. Lett. 2001, 18 (4): 556-558 .  
Abstract   PDF(pc) (188KB) ( 643 )
By applying a new assumption of density, i.e. R2ρ = const, the continuity equation is satisfied to the order of ε2 with ε being the inverse aspect ratio. In the case of large aspect ratio, a set of reduced magnetohydrodynamic equations in toroidal geometry are obtained. The new assumption about the density is supported by the experimental observation in some extent.
Preliminary Analysis of Hysteresis Phenomenon in Electron Cyclotron Resonance Plasma
LIU Ming-Hai, HU Xi-Wei, YU Guo-Yang, WU Qin-Chong, PAN Yuan
Chin. Phys. Lett. 2001, 18 (4): 559-561 .  
Abstract   PDF(pc) (312KB) ( 398 )
The hysteresis phenomenon in electron cyclotron resonance plasma has been investigated theoretically by solving the equations of the density and energy balance of electron and by taking the effects of several collisions such as ionization and recombination into account. The results show that multiple-steady states in experimental measurements can be characterized by considering a fact that the energy balance function has three different real roots in certain region of parameters. One root represents a saddle point and other roots represent stable points, that is, the system is bistable. The effects of ionization and the energy transformation due to the collisions between the electron and neutral gas are discussed also.

Energy Resolution Effects on Plasma Electron Temperature Measurements by Soft X-Ray Pulse-Height-Analysis
SHI Yue-Jiang, WAN Bao-Nian
Chin. Phys. Lett. 2001, 18 (4): 562-563 .  
Abstract   PDF(pc) (257KB) ( 467 )
The soft x-ray pulse-height-analysis technique is a conventional tool to measure electron temperature on tokamak. The soft x-ray spectra distortion due to energy resolution of detector will affect the temperature and impurity concentration determination. To evaluate these effects, distorted spectra as functions of energy resolution are derived by numerical modeling. The results show that the low energy resolution detector can fit for the large-sized tokamak soft x-ray spectra.
Amorphous Hydrogenated Carbon-Nitrogen Alloy Thin Films for Solar Cell Application
ZHOU Zhi-Bin, DING Zheng-Ming, PANG Qian-Jun, CUI Rong-Qiang
Chin. Phys. Lett. 2001, 18 (4): 564-566 .  
Abstract   PDF(pc) (380KB) ( 595 )
Amorphous hydrogenated carbon-nitrogen alloy (a-CNx:H) thin films have been deposited on silicon substrates by an improved dc magnetron sputtering from a graphite target in nitrogen and hydrogen gas discharging. The films are investigated by using the Raman spectroscopy, x-ray photoelectron spectroscopy, spectral ellipsometer and electron spin resonance techniques. The optimized process condition for solar cells application is discussed. The photovoltaic property of a-CNx:H/silicon heterojunction can be improved by adjustment of pressure ratio of hydrogen to nitrogen and unbalanced magnetic field intensity. Open circuit voltage and short circuit current reach 300 mV and 5.52 mA/cm2, respectively.
Structural Relaxation of Pd39Ni10Cu30P21 Bulk Metallic Glass Under High Pressure
WANG Li-Min, ZHAN Zai-Ji, SUN Li-Ling, LI Gong, WANG Wen-Kui,
Chin. Phys. Lett. 2001, 18 (4): 567-569 .  
Abstract   PDF(pc) (309KB) ( 494 )
The Pd39Ni10Cu30P21 bulk metallic glass is isothermally relaxed under various pressures. The degree of the structural relaxation is evaluated in terms of the enthalpy recovery behaviours involved in the irreversible glass transition processes by using a temperature-modulated differential scanning calarimetry technique. A roughly linear increase of the recovery enthalpy is observed within the experimental pressure range from 2.67 to 4.45 GPa, which reflects the release of the frozen-in enthalpy in the as-quenched glass with increasing relaxation pressure. The pressure dependence of the time scale of the enthalpy recovery processes is also exhibited.

Phason-Strain Influence on Low-Temperature Specific Heat of the Decagonal Al-Ni-Co Quasicrystal
LI Cui-Lian, LIU You-Yan
Chin. Phys. Lett. 2001, 18 (4): 570-573 .  
Abstract   PDF(pc) (269KB) ( 450 )
According to the quasicrystal continuum model and linear elasticity theory, based on the equivalence assumption of phonons and phasons in quasicrystals we have deduced five phase-velocities of elastic wave propagating in the decagonal quasicrystals. By inserting these velocities into the specific heat expression, we have successed in explaining the experiment of specific heat performed on the single-grained decagonal Al-Ni-Co quasicrystals at low temperature. Our results show that the contribution of the phason-strain to the specific heat cannot be neglected at low-temperature. Moveover, the phason-strain may be a main reason that the decagonal quasicrystals possess anisotropic thermal conductivity.
Identification of Defects in Undoped Semi-insulating InP by Positron Lifetime
MAO Wei-Dong, WANG Shao-Jie, WANG Zhu, SUN Nie-Feng, SUN Tong-Nian, ZHAO You-Wen
Chin. Phys. Lett. 2001, 18 (4): 574-576 .  
Abstract   PDF(pc) (288KB) ( 444 )
Positron lifetime measurements, carried out over the temperature range of 10-300 K, have been used to investigate defects in two undoped semi-insulating InP samples. The positron lifetime spectra were analysed by both PATFIT and MELT techniques. The results at room temperature reveal a positron lifetime around 273 ps, which is associated with indium vacancies VIn or VIn-hydrogen complexes. The positron average lifetime is temperature dependent and decreases with increasing temperature at the beginning (≤ 80 K and ≤ 120 K), and then keeps unchanged, which is attributed to the influence of negative vacancies and detrapping of the positron from those negative ions of Mg, Zn, Ag, and Ca with ionization level (1-).

X-Ray Diffraction Study of Carbon Nanotubes Under High Pressure
CHEN Liang-Chen, WANG Li-Jun, TANG Dong-Sheng, XIE Si-Shen, JIN Chang-Qing
Chin. Phys. Lett. 2001, 18 (4): 577-578 .  
Abstract   PDF(pc) (354KB) ( 1343 )
The structure and physical properties of carbon nanotubes have been investigated by using in situ high pressure energy dispersive x-ray diffraction with synchrotron radiation at pressures up to 50.7 GPa. At atmospheric pressure, the structure of carbon nanotubes is similar to the hexagonal close-packed lattice of graphite with the interplanar spacing of the diffraction line (002) d002 = 0.3404 nm and that of the line (100) d100 = 0.2116 nm. According to the high pressure x-ray diffraction results, the diffraction line (002) is broadened and weakened above 8 GPa, and carbon nanotubes become partly amorphous. When the pressures of 10 and 20 GPa are decreased down to zero, the diffraction line (002) is partly recovered. While at the maximum pressure of 50.7 GPa, they entirely become amorphous and this amorphous transition is irreversible. We used the equation of state of Birch-Murnaghan to fit the P-V data of carbon nanotubes and obtained the bulk modulus K0 = 54.3±3.2 GPa (at K'0 = 4.0).

Effects of GaAs on Photoluminescence Properties of Self-Assembled InAs Quantum Dots
WANG Xin-Qiang, ZHANG Ye-Jin, DU Guo-Tong, LI Xian-Jie, YIN Jing-Zhi, CHEN Wei-You, YANG Shu-Ren
Chin. Phys. Lett. 2001, 18 (4): 579-581 .  
Abstract   PDF(pc) (394KB) ( 332 )
Room temperature photoluminescence(PL) spectra of InAs self-assembled quantum dots (QDs) deposited on a GaAs/InP and InP substrate are investigated. From the PL spectra, we find that the peak position of InAs QDs appears red-shift from 0.795 to 0.785 eV after we insert a thin tensile GaAs layer between InAs QD layer and InP buffer layer. In order to explain this phenomenon in theory, we examine the strain tensor in InAs quantum dots by using a valence force field model and use a five-band k . p formalism to obtain the electronic structure. The calculated results show that the ground transition energy decreases from 0.789 to 0.780 eV when the thin GaAs layer is inserted. Therefore, the PL peak position should appear red-shift as shown in the experiment.
Time-Reversal Symmetry Breaking: an Evidence for Spin Pairing in High-Tc Superconductors
GUO Wei, HAN Ru-Shan
Chin. Phys. Lett. 2001, 18 (4): 582-583 .  
Abstract   PDF(pc) (210KB) ( 496 )
Effective spin coupling leads to local triplet pairing in the antiferromagnetically ordered CuO2 plane as shown by the K-J model [Guo et al. Chin. Phys. Lett. 18 (2001) 103]. The precession of the spin triplet(S=1, Sz = 0) in the CuO2 plane does not hold time-reversal invariance due to the dimpled CuO structure, which not only modifies the gap function but also contributes to the asymmetry of the high-Tc tunneling conductance. In principle, the effect of time-reversal symmetry breaking can be manifested by the variation of the conductance asymmetry by applying a magnetic field at superconductor-insulator-normal metal junction, which should provide a direct evidence for triplet pairing in the high-Tc superconductors.

Dynamic Approach to the Ground State of Vortex System with Random Pinning
LUO Meng-Bo, CHEN Qing-Hu, XU Zhu-An, JIAO Zheng-Kuan
Chin. Phys. Lett. 2001, 18 (4): 584-586 .  
Abstract   PDF(pc) (304KB) ( 387 )
We study the ground state of a two-dimensional vortex system with random pinnings by cooling the vortex system to zero temperature. The peak of structure factor S(k) of vortices increases with vortex density B but decreases with pin density BФ, indicating that the vortex lattice becomes better and better ordered with increasing B. When B > BФ, the triangular vortex lattice is observed away from the pins. Repulsive vortex interactions destroy the Mott insulator phase which is predicted to occur at B = BФ. The crossover line between the strong Bose glass and the weak Bose glass is nearly independent of BФ for small BФ.
Preparation and Characterization of the New Superconductor MgB2
SUN Yu-Ping, SONG Wen-Hai, DAI Jian-Ming, WU Xing-Cai, WANG Kai-You, ZHAO Bing, XIAO Hong, DU Jia-Ju, WEN Hai-Hu, ZHAO Zhong-Xian
Chin. Phys. Lett. 2001, 18 (4): 587-588 .  
Abstract   PDF(pc) (356KB) ( 470 )
Polycrystalline samples of the new superconductor MgB2 are prepared by solid state reaction using Mg and B powders. The resistance measurement shows that the onset transition temperature and zero resistance transition temperature are Tonsetc = 43.8 K and Tc0 = 37 K, respectively. The Tc0 depends on measuring current strongly. The diamagnetic transition temperature of ~38 K is obtained by the ac susceptibility measurement. X-ray powder diffraction spectra of MgB2 can be indexed using hexagonal structure with space group P6/mmm and lattice parameters a=0.30864 and c=0.35212 nm. A second phase, probably MgO, is also found.
Superconducting Properties of MgB2 Prepared by High Pressure and Ambient Pressure
REN Zhi-An, CHE Guang-Can, ZHAO Zhong-Xian, CHEN Hong, DONG Cheng, NI Yong-Ming, JIA Shun-Lian, WEN Hai-Hu
Chin. Phys. Lett. 2001, 18 (4): 589-591 .  
Abstract   PDF(pc) (460KB) ( 528 )
The new superconductor MgB2 has been prepared by two ways: high pressure and ambient pressure synthesis. Their superconducting properties were measured and compared. It is found that the sample prepared by high pressure is much denser than that prepared under ambient pressure. Accordingly the high pressure sample has a very narrow transition width and a much higher bulk critical current density.
Statistic Ensemble Theory of Small Superconducting Grains
CHEN Zhi-Qian, ZHENG Ren-Rong,
Chin. Phys. Lett. 2001, 18 (4): 592-594 .  
Abstract   PDF(pc) (424KB) ( 500 )
We apply random matrix theory to small metallic grains in different spin-states of S=0, 1/2, 1, 3/2, 2, 5/2, ..., and find that there exist theoretical critical level spacings dc at which the superconductivity would break down. We also find that the higher the spin-state, the smaller the critical level spacing, and for the state of S = 0 there actually exists the superconducting enhancement.

Properties of Quantum XY Spin Glass in Longitudinal Field
SHANG Yu-Min, YAO Kai-Lun
Chin. Phys. Lett. 2001, 18 (4): 595-597 .  
Abstract   PDF(pc) (333KB) ( 362 )
By using the generalized static replica symmetry approximation, the quantum XY spin-glass model in a longitudinal field is investigated. The thermodynamic quantities, spin-glass and self-interaction order parameters are calculated numerically. The local susceptibility depending on temperature has the typical spin-glass plateau characteristic; the specific heat against temperature display a crossover feature which was discovered experimentally in the CuMn sample by Brodale et al. (J. Magn. Magn. Mater. 31-34 (1983) 1331) and cusps sharper than that in the model with the Dzyaloshinskii-Moriya interaction.
Magnetic Properties and Low-Field Magnetoresistance of Pr0.7Pb0.3MnO3 Single Crystals
GU Ben-Xi, ZHANG Shi-Yuan, DU You-Wei
Chin. Phys. Lett. 2001, 18 (4): 598-600 .  
Abstract   PDF(pc) (302KB) ( 391 )
The magnetic properties and magnetoresistance of Pr0.7Pb0.3MnO3 single crystals have been studied. At low temperature, the temperature dependence of magnetization can be represented as M(T) =M(0)(1-BT3/2). A large B value was observed. The spontaneous magnetic moment is slightly larger than the spin-only value for Mn3+ and Mn4+ ions. Above the Curie temperature, the susceptibility obeys the Curie-Weiss Law and the resistivity R can fit well with R0 exp(T0/T)1/4. It is found that the effective paramagnetic moment obtained from the Curie constant is larger than the theoretical value. The large effective paramagnetic moment may originate from the magnetic clusters. A large low-field magnetoresistance of Δ R/R(0) = -50% is observed at 230 K in 1T.

Effects of Manganese Substitution in the Nd2Co17-xMnx Compounds on Structural and Magnetic Properties
HAO Yan-Ming, LI Yang-Xian, SUN He-Xu, QU Jing-Ping, GAO Yan, WANG Bo-Wen
Chin. Phys. Lett. 2001, 18 (4): 601-603 .  
Abstract   PDF(pc) (302KB) ( 580 )
The structural and magnetic properties of the Nd2Co17-xMnx (x ≤ 14) compounds have been investigated by means of x-ray diffraction and magnetization measurements. The Nd2Co17-xMnx (x ≤ 14) compounds have a rhombohedral Th2Zn17-type structure. The unit-cell volume increases with increasing x. The Curie temperature and the saturation magnetization of these compounds show a marvelous drop with increasing x. The spin reorientation is observed at about 190 K in the Nd2Co15Mn2 compound.

Delocalizing Effect of Polarons in Colossal Magnetoresistance Material FeCr2S4
YANG Zhao-Rong, TAN Shun, CHEN Zhi-Wen, ZHANG Yu-Heng
Chin. Phys. Lett. 2001, 18 (4): 604-607 .  
Abstract   PDF(pc) (466KB) ( 372 )
The electrical transport and magnetic properties of colossal
magnetoresistance material FeCr2S4 are studied. The temperature dependence of resistivity ρ and thermoelectric power S are investigated from 5 to 300 K and from 77 to 300 K, respectively. The activation energy Eρ obtained from ρ-T is larger than the activation energy ES, obtained from S-T. This indicates that magnetic polarons dominate the conduction behaviour at temperatures above Tc. The M-T curve and electron spin resonance spectra show that the paramagnetic-ferromagnetic transition is incomplete, and that a paramagnetic phase coexists with a ferromagnetic phase in a certain temperature range below Tc. It is proposed that the insulator-metal transition near Tc could be attributed to the gradual delocalizing effect from magnetic polarons to naked carriers. The resistivity in the presented temperature range can be described by considering the coexistence of magnetic polarons and naked carriers.

A Narrow Photoluminescence Linewidth of 19.2 meV at 1.35μm from In0.5Ga0.5As/GaAs Quantum Island Structure Grown by Molecular Beam Epitaxy
WANG Xiao-Dong, NIU Zhi-Chuan, FENG Song-Lin, MIAO Zhen-Hua
Chin. Phys. Lett. 2001, 18 (4): 608-610 .  
Abstract   PDF(pc) (673KB) ( 471 )
Self-organized In0.5Ga0.5As/GaAs quantum island structure emitting at 1.35μm at room temperature has been successfully fabricated by molecular beam epitaxy via cycled (InAs)1/(GaAs)1 monolayer deposition method. Photoluminescence measurement shows that a very narrow linewidth of 19.2 meV at 300 K has been reached for the first time, indicating effective suppression of inhomogeneous broadening of optical emission from the In0.5Ga0.5As island structure due to indium segregation reduction by introducing an AlAs layer and the strain reduction by inserting an In0.2Ga0.8As layer overgrown on the top of islands. The mounds-like morphology of the islands elongated along the [1ī0] azimuth are observed by the atomic force microscopy measurement, which reveals the fact that strain in the islands is partially relaxed along the [1ī0] direction. Our results present important information for the fabrication of 1.3μm wavelength quantum dot devices.
Influence of Residual Phases on the Behaviour of Gradual Spin Transition Complexes
SHI Hai-Rong, YU Zhi, HUANG Hong-Bo, XIA Yuan-Fu, YOU Xiao-Zeng
Chin. Phys. Lett. 2001, 18 (4): 611-613 .  
Abstract   PDF(pc) (342KB) ( 403 )
In order to interpret the large shift between the observed high spin fraction and the so-called molar high spin fraction in the Mössbauer study on gradual spin transition complexes, numerically we reveal that the effects from residual phases in the substance should be considered in the correction by Debye-Waller factors. This result shows that similar Debye-Waller factors in high and low spin states agree well with the conclusion of experimental investigations for such gradual spin transition complexes.
Surface Instability of a Vertically Oscillating Granular Layer
SUI Lei, MIAO Guo-Qing, WEI Rong-Jue
Chin. Phys. Lett. 2001, 18 (4): 614-615 .  
Abstract   PDF(pc) (468KB) ( 361 )
In the study of the surface instability of a vertically oscillating granular layer, we obtained experimentally the phase diagram for the surface states of the layer in the driving frequency-acceleration plane, and measured the dispersion relation for the surface waves in a granular layer in comparison to that in viscous fluids. Our experiments show that the onset dimensionless acceleration increases with the driving frequency, and the wavelength of the surface waves increases with the depth of granular layer. These experimental results are in agreement with our theoretical model qualitatively.
Enhancement of Band Edge Emission from ZnS/Zn(OH)2 Quantum Dots
Hatim Mohamed El-Khair, XU Ling, HUANG Xin-Fan, LI Ming-Hai, CHEN Kun-Ji
Chin. Phys. Lett. 2001, 18 (4): 616-618 .  
Abstract   PDF(pc) (587KB) ( 969 )
ZnS and Zn(OH)2 capped ZnS semiconductor quantum dots (QDs) have been synthesized by the colloidal chemical method using inorganic reagents. Transmission electron microscopy and electron diffraction results showed that the monodispersed ZnS QDs have 1 to 5 nm in diameter and the wurtzite structure. The polarities of the precursors and surfactant solvents have shown strong effects on the properties of the photoluminescence for ZnS QDs. For ZnS QDs capped with a wider band gap Zn(OH)2 shell, the surface trap states were passivated and hence the band-edge emissions have been enhanced.
On the Stability of a Magnetized Disk with a Massive Corotating Halo
CHOU Chih-Kang, PENG Qiu-He,
Chin. Phys. Lett. 2001, 18 (4): 619-621 .  
Abstract   PDF(pc) (207KB) ( 332 )
Effects of magnetic fields on the stability of a differentially rotating disk are considered in the shearing sheet approximation. An explicit stability criterion is derived in terms of Toomre's Q value and the field strength. The combined effects of both magnetic fields and a corotating dark matter halo are briefly discussed.

Robustness of the Sunyaev-Zel’dovich Effect as a Measure of the Hubble Constant
CAO Li, ZHANG Yuan-Zhong, ZHU Zong-Hong,
Chin. Phys. Lett. 2001, 18 (4): 622-624 .  
Abstract   PDF(pc) (286KB) ( 428 )
After inversing the x-ray surface brightness of the cooling flow cluster Abell 1689 through the isothermal β model, the isothermal double β model and the x-ray surface brightness distribution model derived from the universal dark matter density profile, we calculate the electron distribution and the Sunyaev-Zel'dovich (SZ) effect of the cluster. The resulting temperature decrements, which are inversely proportional to the square root of H0, are very different for the three models, with uncertainty of 15%. Thus, the SZ/x-ray route can not be taken as a precise measurement of H0 until further observations (e.g. from the satellite AXAF) constrain well the amount and distribution of cluster gas.
53 articles