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Volume 23 Issue 7
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Original Articles
Reduced Properties and Applications of Y(sl(2)) Algebra for a Two-Spin System
TIAN Li-Jun, YANG Guo-Hong, ZHANG Hong-Biao, HOU Jing-Min
Chin. Phys. Lett. 2006, 23 (7): 1659-1661 .  
Abstract   PDF(pc) (215KB) ( 413 )
By taking a special constraint for a general realization of Y(sl(2)), two sets of sl(2) algebras are presented, in which a u(1) algebra is hidden. With the help of this constraint, the block-diagonal form can be written to the generator J of Yangian algebras, and especially it is a rotational transformation of a spin in the elementary quantum mechanics. This sheds new light on the physical meaning of Y(sl(2)).
Exact Solutions for a Nonisospectral and Variable-Coefficient Kadomtsev--Petviashvili Equation
DENG Shu-Fang
Chin. Phys. Lett. 2006, 23 (7): 1662-1665 .  
Abstract   PDF(pc) (203KB) ( 648 )
The bilinear form for a nonisospectral and variable-coefficient Kadomtsev--Petviashvili equation is obtained and some exact soliton solutions are derived by the Hirota method and Wronskian technique. We also derive the bilinear Bäcklund transformation from its Lax pairs and find solutions with the help of the obtained bilinear Bäcklund transformation.
Simulation of Helium Behaviour in Titanium Crystals Using Molecular Dynamics
WANG Jun, HOU Qing, SUN Tie-Ying, WU Zhong-Cheng, LONG Xing-Gui, WU Xing-Chun, LUO Shun-Zhong
Chin. Phys. Lett. 2006, 23 (7): 1666-1669 .  
Abstract   PDF(pc) (1065KB) ( 659 )
The behaviour of helium in Ti crystals at 300K has been investigated by means of the molecular dynamics. The study is focused on the influences of He--Ti interaction on the aggregation of helium atoms in the substrate. When a Born--Mayer potential is used to describe the He--Ti interaction, the He atoms are unable to cluster with each other due to the weak bridge barrier that cannot trap the helium atoms, Whereas using a He--Ti potential that is constructed by fitting the ab initio pairwise He--Ti potential, the clustering of He atoms can be observed. The results indicate that suitable He--Ti potential plays an important role in the formation of He clusters in metals. Moreover, it is noted that the shape of the formed He cluster is irregular, and the produced defect prefers to congregating on one side of the He cluster rather than spreading symmetrically around it.
Auto-Bäcklund Transformation and Soliton-Type Solutions of the Generalized Variable-Coefficient Kadomtsev--Petviashvili Equation
LIU Jian-Guo, LI Ye-Zhou, WEI Guang-Mei
Chin. Phys. Lett. 2006, 23 (7): 1670-1673 .  
Abstract   PDF(pc) (400KB) ( 649 )
Using the truncated Painlevé expansion, an auto-Bäcklund transformation and soliton-type solutions of the generalized variable-coefficient Kadomtsev--Petviashvili (GKP) equation are obtained by symbolic computation. Since the cylindrical Korteweg-de Vries (cKdV) equation, the cylindrical KP (cKP) equation and the generalized cKP (GcKP) equation are all special cases of the GKP equation, we can also obtain the corresponding results of these equations.
Separability Criteria for Quantum Mixed States in Terms of Trace Norm
Chin. Phys. Lett. 2006, 23 (7): 1674-1675 .  
Abstract   PDF(pc) (171KB) ( 545 )
A new necessary conditions for separability of mixed states in bipartite and multipartite quantum systems of arbitrary dimensions are presented. This method requires only a few local measurements. If a quantum state in a bipartite (or multipartite) system of arbitrary dimension is separable, we show that the trace norm of a constructive matrix is less than or equal to 1.
Multiparty Quantum Secret Report
DENG Fu-Guo, , LI Xi-Han, LI Chun-Yan, ZHOU Ping, LIANG Yu-Jie, ZHOU Hong-Yu,
Chin. Phys. Lett. 2006, 23 (7): 1676-1679 .  
Abstract   PDF(pc) (223KB) ( 488 )
A multiparty quantum secret report scheme is proposed with quantum encryption. The boss Alice and her M agents first share a sequence of (M+1)-particle Greenberger--Horne--Zeilinger (GHZ) states that only Alice knows which state each (M+1)-particle quantum system is in. Each agent exploits a controlled-not (CNot) gate to encrypt the travelling particle by using the particle in the GHZ state as the control qubit. The boss Alice decrypts the travelling particle with a CNot gate after performing a σx operation on her particle in the GHZ state or not. After the GHZ states (the quantum key) are used up, the parties check whether there is a vicious eavesdropper, say Eve, monitoring the quantum line, by picking out some samples from the GHZ states shared and measuring them with two measuring bases. After confirming the security of the quantum key, they use the remaining GHZ states repeatedly for the next round of quantum communication. This scheme has the advantage of high intrinsic efficiency for the qubits and total efficiency.
Controlled Bidirectional Quantum Direct Communication by Using a GHZ State
MAN Zhong-Xiao, XIA Yun-Jie
Chin. Phys. Lett. 2006, 23 (7): 1680-1682 .  
Abstract   PDF(pc) (193KB) ( 791 )
A controlled bidirectional quantum secret direct communication scheme is proposed by using a Greenberger--Horne--Zeilinger (GHZ) state. In the scheme, two users can exchange their secret messages simultaneously with a set of devices under the control of a third party. The security of the scheme is analysed and confirmed.
Remote Three-Atom Information Concentration without Bell-State Measurement
WU Zhen-Zhen, FANG Mao-Fa
Chin. Phys. Lett. 2006, 23 (7): 1683-1686 .  
Abstract   PDF(pc) (209KB) ( 451 )
We propose a scheme for information concentration of three remote two-level atoms in cavity QED. Our scheme does not involve the Bell-state measurement. During the interaction between atom and cavity, the cavity frequency is largely detuned from the atomic transition frequency, thus the scheme is insensitive to both the cavity decay and the thermal field. The idea can also be used to realize the remote information concentration of trapped ions.
Magic Wavelength for Caesium Transition Line 6S1/2-6P3/2
ZHENG Yu-Nan, ZHOU Xiao-Ji, CHEN Jing-Biao, CHEN Xu-Zong
Chin. Phys. Lett. 2006, 23 (7): 1687-1690 .  
Abstract   PDF(pc) (262KB) ( 806 )
We investigate the magic wavelengths of the trapping laser for 6S1/2-6P3/2 of the Cs atom in a region where the optical shift between two different states can be eliminated. For fine levels and linear polarized laser they are 930.4nm and 937.2nm. The magic wavelengths range from 927.7nm to 945.0nm for circle-polarized perturbing laser. Effects of nuclear spin, the hyper-fine Zeeman levels, and the polarization of the light, which generate different magic wavelengths, are further discussed.
Quantum Mechanics Helps in Learning for More Intelligent Robots
DONG Dao-Yi, CHEN Chun-Lin, CHEN Zong-Hai, ZHANG Chen-Bin
Chin. Phys. Lett. 2006, 23 (7): 1691-1694 .  
Abstract   PDF(pc) (298KB) ( 608 )
A learning algorithm based on the state superposition principle is presented. The theoretical analysis shows that the needed fundamental transformations to realize this algorithm are the same as those needed in the Grover algorithm and are within current state-of-the-art technology. The simulated experiment shows that the quantum learning algorithm can help robots to learn faster and to become more intelligent.
A Scheme for Preparation of W-Type Entangled Coherent State of Three-Cavity Fields
YUAN Chun-Hua, OU Yong-Cheng, ZHANG Zhi-Ming,
Chin. Phys. Lett. 2006, 23 (7): 1695-1697 .  
Abstract   PDF(pc) (223KB) ( 597 )
We present an experimental scheme to prepare the three-cavity W-type entangled coherent state in the context of dispersive cavity quantum electrodynamics. The discussion of our scheme indicates that it can be realized by current technology.
Controllable Magnetic Focusing of Cold Atoms on a Chip
LIU Yang, YUN Min, YIN Jian-Ping
Chin. Phys. Lett. 2006, 23 (7): 1698-1701 .  
Abstract   PDF(pc) (662KB) ( 390 )
We propose a new lens scheme to focus cold atoms by using a controllable inhomogeneous magnetic field from a square current-carrying wire fabricated on a chip. The spatial distributions of the magnetic field are calculated, and the results show that the generated magnetic field is a two-dimensional (2D) quadrupole one and can be used to focus cold atoms or a cold atomic beam. The dynamic processes of cold atoms passing through our square wire layout and its focusing properties are studied by using Monte Carlo simulations. Our study shows that the atomic clouds can be focused effectively by our magnetic lens scheme, and the focal length of the atomic lens and its radius of focused spot can be continuously changed by adjusting the current in the wires.
Bianchi Type-III String Cosmological Model With Bulk Viscosity and Magnetic Field
WANG Xing-Xiang
Chin. Phys. Lett. 2006, 23 (7): 1702-1704 .  
Abstract   PDF(pc) (201KB) ( 615 )
The Bianchi type-III cosmological model for a cloud string in the presence of bulk viscosity and magnetic field are presented. To obtain the determinate model it is assumed that there is an equation of state ρ=kλ and the scalar of expansion is proportional to the shear scalar θ α σ, which leads to a relation between metric potentials B=mCn. The physical and geometric aspects of the model are also discussed. The model describes a shearing non-rotating continuously expanding universe with a big-bang start. In the absence of magnetic field, it reduces to the string model with bulk viscosity that was previously given in the literature.
Stochastic Resonance in an Over-Damped Bias Linear System with Dichotomous Noise
GUO Feng, ZHOU Yu-Rong, JIANG Shi-Qi, GU Tian-Xiang
Chin. Phys. Lett. 2006, 23 (7): 1705-1708 .  
Abstract   PDF(pc) (228KB) ( 490 )
The stochastic resonance in an over-damped bias linear system subject to multiplicative and additive dichotomous noise (DN) is investigated. By using the linear-response theory and the properties of the DN, the exact expressions are found for the signal-to-noise ratio (SNR). It is shown that the SNR is a non-monotonic function of the correlation time of the additive DN, and it varies non-monotonically with the bias of the external field, the intensity and asymmetry of the multiplicative DN, as well as the external field frequency. Moreover, the SNR depends on the bias of the system, as well as the strength and asymmetry of the additive DN.

Phase Propagations in a Coupled Oscillator--Excitor System of FitzHugh--Nagumo Models
Chin. Phys. Lett. 2006, 23 (7): 1709-1712 .  
Abstract   PDF(pc) (469KB) ( 771 )
A one-dimensional array of 2N+1 automata with FitzHugh--Nagumo dynamics, in which one is set to be oscillatory and the others are excitable, is investigated with bi-directional interactions. We find that 1:1 rhythm propagation in the array depends on the appropriate couple strength and the excitability of the system. On the two sides of the 1:1 rhythm area in parameter space, two different kinds of dynamical behaviour of the pacemaker, i.e. phase-locking phenomena and canard-like phenomena, are shown. The latter is found in company with chaotic pattern and period doubling bifurcation. When the coupling strength is larger than a critical value, the whole system ends to a steady state.
Heat Conductivity in a Two-Dimensional Finite-Size Spin System with Dzyaloshinskii--Moriya Interactions
LIU Hui-Ping, SUN Yun-Zhou, YI Lin
Chin. Phys. Lett. 2006, 23 (7): 1713-1715 .  
Abstract   PDF(pc) (249KB) ( 777 )
Heat conductivity is studied by direct numerical simulations in a two-dimensional model with chiral Dzyaloshinskii--Moriya (DM) spin superexchange interactions for various DM strengths and finite sizes. We find that when temperature is not too low, the thermal conductivity can be well described in the semi classical spin wave picture, and connections of thermal conductivity with the specific heat and the dynamic relaxation time are verified to be suitable. In particular, the transition arising in Sr14-xCaxCu24O41 is related to a magnetic spin glass and qualitatively understood as a kind of Kosterlitz--Thouless transitions. It is shown that the critical temperature is linearly dependent on the spin--spin interactions for the relevant strong DM strength.
Annihilation of Antiprotons in Light Nuclei
M. A. Rana, E. U. Khan, M. I. Shahzad, I. E. Qureshi, F. Malik, G. Sher, S. Manzoor, H. A. Khan
Chin. Phys. Lett. 2006, 23 (7): 1716-1718 .  
Abstract   PDF(pc) (273KB) ( 639 )
CR-39 detectors have been exposed to a 5.9-MeV antiproton beam using the low energy antiproton ring (LEAR) facility at CERN. At this energy, tracks of antiprotons appear in a CR-39 detector after 135min of etching in 6M NaOH at 70°C. Fluence of the antiproton beam has been determined using track density. We have also found tracks in the etched CR-39 detector at different depths (250--500μm). These tracks have resulted from the annihilation of antiprotons with the constituents (H, C and O) of the CR-39 detector. The goal of the experiment is to develop a simple and low-cost method to study properties of antiparticles and those formed after annihilation of these particles with the target matter.
Ground-State Properties of Ca Isotopes and the Density Dependence of the Symmetry Energy
LIANG Jun, MA Zhong-Yu, CHEN Bao-Qiu
Chin. Phys. Lett. 2006, 23 (7): 1719-1722 .  
Abstract   PDF(pc) (241KB) ( 399 )
A relativistic mean field model is used to study the ground-state properties of neutron-rich nuclei in Ca isotopes. An additional isoscalar and isovector nonlinear coupling has been introduced in the relativistic mean field model, which could soften the symmetry energy, while keep the agreement with the experimental data. The sensitivity of proton and neutron density distributions and single particle states in Ca isotopes to the additional isoscalar--isovector nonlinear coupling term is investigated. We found that the binding energies, the density distributions of single particle levels are strongly correlated with the density dependence of the symmetric energy in nuclear matter.
Anomaly in the Charge Radii and Nuclear Structure
ZHANG Hong-Fei, ZUO Wei, LI Jun-Qing, Soojae Im, MA Zhong-Yu, CHEN Bao-Qiu,
Chin. Phys. Lett. 2006, 23 (7): 1723-1726 .  
Abstract   PDF(pc) (241KB) ( 652 )
The axially deformed relativistic mean field theory is applied to study the isotope shift of charge distributions of odd-Z Pr isotope chain. The nuclear structure associated with the shell and the isotope effect is investigated. The mechanism of the kink in the isotope shift at the neutron magic number N=82 is revealed to be dependent on the neutron energy level structure at the Fermi energy, demonstrating that the spin--orbit coupling interaction and p--n attraction are well described by the relativistic mean field theory.
Properties of the πh9/2 otimes νi13/2 Oblate Band in 188Tl
MA Long, ZHOU Xiao-Hong, XING Ye-Bing, ZHANG Yu-Hu, GUO Ying-Xing, LEI Xiang-Guo, XIE Chen-Ying, Oshima M., Toh Y., Koizumi M., Osa A., Hatsukawa Y., Sugawara M.
Chin. Phys. Lett. 2006, 23 (7): 1727-1730 .  
Abstract   PDF(pc) (262KB) ( 491 )
High spin states in 188Tl have been investigated via the 157Gd(35Cl,4n) reaction at beam energy of 170MeV. A rotational band built on the πh9/2 otimes νi13/2 configuration with oblate deformation has been established. Considering the similarity between the band structure observed in odd--odd Tl nuclei, spin values have been tentatively proposed for the new band in 188Tl. The πh9/2 otimes νi13/2 oblate band in 188Tl shows low-spin signature inversion, and it can be interpreted qualitatively by the two quasiparticle plus rotor model including a J-dependent p--n residual interaction.

Exotic Behaviour of Angular Dispersion of Weakly Bound Nucleus 17F at Small Angles
WANG Qi, HAN Jian-Long, XIAO Zhi-Gang, XU Hu-Shan, SUN Zhi-Yu, HU Zheng-Guo, ZHANG Xue-Ying, WANG Hong-Wei, MAO Rui-Shi, YUAN Xiao-Hua, XU Zhi-Guo, ZHAO Tie-Cheng, ZHANG Hong-Bin, XU Hua-Gen, QI Hui-Rong, WANG Yue, JIA Fei, WU Li-Jie, DING Xian-Li, GAO Qi, GAO Hui, LI Song-Lin, BAI Zhen, XIAO Guo-Qing, JIN Gen-Ming, REN Zhong-Zhou, ZHOU Shan-Gui, SERGEY Yu-Kun,
Chin. Phys. Lett. 2006, 23 (7): 1731-1733 .  
Abstract   PDF(pc) (250KB) ( 581 )
The differential cross sections of 17F and 17O elastic scattering products on 208Pb have been measured at the Radioactive Ion Beam Line at Lanzhou (RIBLL). Two angular dispersion plots of ln(dσ/dθ) versus θ2 are obtained from the angular distribution of the elastic scattering differential cross sections. The angular dispersion plot exhibits a clear turning point for 17F in the range of small scattering angles 6--20° due to its exotic structure, but for 17O, the turning point is not observed in the same angular range. The experimental results have been compared with previous data of other groups. Systematical analysis on the available data supports the above conclusion that there is an exotic behaviour of the angular dispersion plot of weakly bound nuclei with halo or skin structure as compared with that of the ordinary nuclei near stable line. Therefore the turning point of the angular dispersion plot appears at small angle for weakly bound nuclei with halo or skin structure, and can be used as a new probe to investigate the halo and skin phenomena of weakly bound nuclei.
Alpha Decay Half-Lives of New Superheavy Elements through Quasimolecular Shapes
ZHANG Hong-Fei, LI JUN-Qing, ZUO Wei, CHEN Bao-Qiu, MA Zhong-Yu, Soojae Im, Royer Guy
Chin. Phys. Lett. 2006, 23 (7): 1734-1737 .  
Abstract   PDF(pc) (247KB) ( 937 )
The lifetimes of α decays of the recently produced isotopes of the elements 112, 114, 116 and the element 294118 and of some decay products have been calculated theoretically within the Wentzel--Kramers--Brillouin approximation. The α decay barriers have been determined in the quasimolecular shape path within a generalized liquid drop model including the proximity effects between nuclei in a neck, the mass and charge asymmetry and the precise nuclear radius. These calculations provide reasonable estimates for the observed α decay lifetimes. The calculated results have been compared with the results of the density-dependent M3Y effective interaction and the experimental data. It is indicated that the theoretical foundation of the generalized liquid drop model is as good as that of the microscopic DDM3Y model, at least in the sense of predicting the T1/2 values as long as one uses a correct α decay energy. The half lives of these new nuclei are well tested from the consistence of the macroscopic, the microscopic and the experimental data.

Analysis of Time-Dependent Density Functional Theory of Transition Wavelengths of Thioaldehydes and Thioketones
HE Xiang, WANG Fan
Chin. Phys. Lett. 2006, 23 (7): 1738-1741 .  
Abstract   PDF(pc) (243KB) ( 617 )
Thioaldehydes and thioketones are candidates of new photoluminescence materials. The time-dependent density functional theory is applied to calculate the absorption and emission wavelengths of ten thiocarbonyl compounds using both B3LYP and PBE0 functionals. The theoretical results are in agreement with the measurable ones. Furthermore, it is found that the maximum absorption and emission wavelengths are linearly correlated to the C-S bond lengths.
Calculation of Energies of the Ground and Low Excited States of a Confined Helium Atom in a Spherical Parabolic Well
XIE Wen-Fang
Chin. Phys. Lett. 2006, 23 (7): 1742-1744 .  
Abstract   PDF(pc) (200KB) ( 489 )
Making use of the adiabatic hyperspherical approach, we report a calculation for the energy spectrum of the ground and low-excited states of the confined helium atom in a spherical parabolic well. We find that the energies of a spherical parabolic well are in good agreement with those of an impenetrable spherical box for the larger confined potential radius. However, the energy values of a spherical parabolic well are much lower than those of an impenetrable spherical box for small values of rc. We also find that the confinement may cause accidental degeneracies between levels with different low-excited states and the inversion of the energy values.
Temperature Dependence of Dark Lines in Coherent Population Trapping
DENG Jian-Liao, HU Zheng-Feng, HE Hui-Juan, WANG Yu-Zhu
Chin. Phys. Lett. 2006, 23 (7): 1745-1748 .  
Abstract   PDF(pc) (249KB) ( 795 )
We measure the signal amplitude and linewidth of a dark line in coherent population trapping in the Rb vapour cell filled with mixed buffer gas N2 and Ar as a function of cell temperature. We find that the dark line signal amplitude increases with temperature up to a maximum at 49°C and then drops at higher temperatures due to quenching effects of N2. The linewidth of the dark line remains basically constant, at 1080Hz. We also measure the linewidth of the dark line as a function of laser intensity. The linewidth increases linearly with laser intensity. An intrinsic linewidth (FWHM=896Hz at 3.4GHz) of the Rb cell is obtained.
Pondermotive Shift of Photoelectron Spectra in Intense Laser Field
BAI Li-Hua, ZHANG Jing-Tao, WANG Yi, XU Zhi-Zhan
Chin. Phys. Lett. 2006, 23 (7): 1749-4752 .  
Abstract   PDF(pc) (327KB) ( 640 )
In a recent experimental work on the excess photon detachment (EPD) of H- ions [Phys. Rev. Lett. 87(2001)243001], it has been found that the ponderomotive shift of each EPD peak increases with the order of the EPD channel. By using a nonperturbative quantum scattering theory, we obtain the kinetic energy spectra for the differential detachment rate along the laser polarization for several laser intensities. It is demonstrated that higher order EPD peaks are produced mainly at relatively higher laser intensities. By calculating the overall EPD spectra with varying laser intensities, it is found that the ponderomotive shift of each EPD peak increases with the order of the EPD channel. Our calculations are in good agreement with the experimental observation. It is found that different EPD channels occur mainly when the laser field reaches some values, thus the intensity distribution of the laser field is responsible for the varying ponderomotive shifts.
Positron--Lithium Atom and Electron--Lithium Atom Scattering Systems at Intermediate and High Energies
K. Ratnavelu, S. Y. Ng
Chin. Phys. Lett. 2006, 23 (7): 1753-1756 .  
Abstract   PDF(pc) (289KB) ( 455 )
The coupled-channel optical method is used to study positron scattering by atomic lithium at energies ranging from the ionization threshold to 60eV. The present method simultaneously treats the target channels and the positronium (Ps) channels in the coupled-channel method together with the continuum effects via an ab-initio optical potential. Ionization, elastic and inelastic cross sections in target channels, and the total cross section are also reported and compared with other theoretical and experimental data. A comparative study with the corresponding electron--lithium data is also reported.
A Theoretical Study of Clusters: Realizing Differences between the Second-Row and the Third-Row Elements
XU Ya-Ge, JI Dong, SHEN Xu-Yang, WANG Xiao-Lu, LI Jia-Ming,
Chin. Phys. Lett. 2006, 23 (7): 1757-1760 .  
Abstract   PDF(pc) (228KB) ( 377 )
Based on the characteristics of valence bonds and the first-principle molecular dynamics simulation we present an optimum valence bond scheme to study properties of important critical clusters with limited computational effort. The differences between the second-row and the third-row elements belonging to the same families can be understood by examining electronic structures and geometric structures even for small size clusters.
Assignment of Photoelectron Spectra of MC2 (M= V, Cr, Fe, and Co)
YUAN Yong-Bo, DENG Kai-Ming, LIU Yu-Zhen, TANG Chun-Mei
Chin. Phys. Lett. 2006, 23 (7): 1761-1764 .  
Abstract   PDF(pc) (236KB) ( 437 )
Hybrid density functional theory (DFT) calculations are performed to study MC2 (M= V, Cr, Fe and Co) clusters in the neutral and anionic charge states. We find that the equilibrium geometries of MC2 and their anions are all cyclic structures with C2v symmetry, which agrees well with the previous theoretical studies. The Mulliken charge and spin populations of MC2 clusters and their anions are also calculated, and it is found that the electron charge transformations from anions to neutral molecules mainly take place on the M atoms. Time-dependent DFT is used to calculate the excited states, and a theoretical assignment for the features in the experimental photoelectron spectrum is given, which are in good agreement with the available experimental data.
Coherent Control of Absorption Resonances via Antirotating Coupling
ZHANG Xiu, CHENG Guang-Ling, HU Xiang-Ming
Chin. Phys. Lett. 2006, 23 (7): 1765-1768 .  
Abstract   PDF(pc) (272KB) ( 368 )
Effects of the antirotating coupling on the absorption resonances are presented for a microwave driven three-level system. It is shown that nonlinear sideband generation, selective suppression and switching between peaks and dips in the absorption spectrum are obtained as the microwave Rabi frequency is varied. A physical explanation is given in terms of the coherent superposition of an infinite set of transitions that are associated with an infinite set of dressed states, which are created by the rotating and nonrotating couplings as the equivalent bichromatic excitation.
Negative Refractive Index in a Four-Level Atomic System
ZHANG Hong-Jun, , GONG Shang-Qing, NIU Yue-Ping, LI Ru Xin, XU Zhi-Zhan
Chin. Phys. Lett. 2006, 23 (7): 1769-1772 .  
Abstract   PDF(pc) (250KB) ( 505 )
We propose a scheme for realizing negative refractive index in a four-level atomic system. It is shown that such a system can simultaneously exhibit negative permittivity and negative permeability in an optical frequency range. Furthermore, by analysing the dispersion property of the left-handed material, we find that the probe beam can be controlled from superluminal to subluminal or vice versa via choosing appropriate parameters.
Bistable Behaviour of N Two-Level Atoms Interacting with the Field inside a High-Q Cavity Containing a Nonlinear Kerr-Like Medium
LUO Jin-Ming, LI Jia-Hua, XIE Xiao-Tao
Chin. Phys. Lett. 2006, 23 (7): 1773-1776 .  
Abstract   PDF(pc) (242KB) ( 479 )
Taking the intensity-dependent coupling between atoms and cavity mode into account, we investigate a system consisting of N homogeneously broadened two-level atoms interacting with the field inside a single-mode Fabry--Perot cavity containing a nonlinear Kerr-like medium. We derive the steady-state bistable behaviour of the system, and further analyse in details the influence of several critical parameters on the bistable behaviour.
Reduce of the Linewidth of a Diode Laser by Locking to a High-Finesse Fabry--Perot Cavity
HUANG Kai-Kai, ZHANG Jian-Wei, CHEN Jing-Biao, YANG Dong-Hai
Chin. Phys. Lett. 2006, 23 (7): 1777-1779 .  
Abstract   PDF(pc) (253KB) ( 801 )
We report frequency locking of a commercial 657nm diode laser to a high finesse Fabry--Perot cavity by the Pound--Drever--Hall method. The laser linewidth relative to the cavity is estimated to be about 6kHz.
Pulse Wavelength Scan of Room-Temperature Mid-Infrared Distributed Feedback Quantum Cascade Lasers for N2O Gas Detection
ZHANG Yong-Gang, XU Gang-Yi, LI Ai-Zhen, LI Yao-Yao, GU Yi, LIU Sheng, WEI Lin
Chin. Phys. Lett. 2006, 23 (7): 1780-1783 .  
Abstract   PDF(pc) (252KB) ( 666 )
The tunable diode laser absorption spectroscopy under a pulse wavelength scan scheme is adapted to home-made room-temperature mid-infrared distributed feedback quantum cascade lasers; and identification of N2O spectral fingerprint is demonstrated experimentally. By driving the laser at 800ns pulse duration, a wave number tuning of about 1.6cm-1 is produced, which make both 1289.04cm-1 and 1289.86cm-1 absorption fingerprints of N2O gas to be definitely assigned. The measured relative absorption intensity is consistent with the HITRAN data precisely.
High-Power and Low-Threshold-Current-Density GaAs/AlGaAs Quantum Cascade Lasers
LIU Jun-Qi, LIU Feng-Qi, LI Lu, SHAO Ye, GUO Yu, WANG Zhan-Guo
Chin. Phys. Lett. 2006, 23 (7): 1784-1786 .  
Abstract   PDF(pc) (401KB) ( 607 )
We report on the realization of GaAs/AlGaAs quantum cascade lasers with an emission wavelength of 9.1μm above the liquid nitrogen temperature. With optimal current injection window and ridge width of 24 and 60μm respectively, a peak output power more than 500mW is achieved in pulsed mode operation. A low threshold current density Jth=2.6kA/cm2 gives the devices good lasing characteristics. In a drive frequency of 1kHz, the laser operates up to 20% duty cycle.
Multi-Wavelength Erbium-Doped Fibre Lasers on Assistance of High-Nonlinear Photonic-Crystal Fibres
LIU Xue-Ming, ZHAO Wei, ZHANG Tong-Yi, LU Ke-Qing, SUN Chuan-Dong, WANG Yi-Shan, OUYANG Xian, HOU Xun, CHEN Guo-Fu
Chin. Phys. Lett. 2006, 23 (7): 1787-1789 .  
Abstract   PDF(pc) (214KB) ( 695 )
On the basis of self-stability effect of four-wave mixings (FWMs) in high-nonlinear photonic-crystal fibres, a novel multi-wavelength erbium-doped fibre (EDF) laser is proposed and demonstrated experimentally at room temperature. The proposed lasers have the capacity of switching and tuning with excellent uniformity and stability. By means of adjusting the attenuators, the triple-, four-, or five-wavelength EDF lasers can be lasing simultaneously. With the assistance of the FWM self-stability function, the multi-wavelength spectrum is excellently stabilized with uniformity less than 0.9dB.
Experimental Study of a Pulsed Ytterbium-Doped Fibre Laser with Fast and Slow Saturable Absorbers in a Linear Cavity
GAN Yu, XIANG Wang-Hua, ZHOU Xiao-Fang, ZHANG Gui-Zhong, ZHANG Bing, WANG Yong-Gang, MA Xiao-Yu,
Chin. Phys. Lett. 2006, 23 (7): 1790-1792 .  
Abstract   PDF(pc) (400KB) ( 410 )
We present a linear-cavity stretched-pulse fibre laser with mode locking by a nonlinear polarization rotation and by semiconductor saturable-absorber mirrors. A Q-switched mode-locking cw train and a mode-locking pulse train are obtained in the experiment. We investigate the effects of the equivalent fast saturable absorber and the slow saturable absorbers in experiment. It is found that neither the nonlinear polarization evolution effect nor a semiconductor saturable absorber mirror is enough to produce the stable cw mode-locking pulses in this experiment. A nonlinear polarization evolution effect controls the cavity loss to literally carve the pulses; semiconductor saturable absorber mirrors provide the self-restarting and maintain the stability of the mode-locking operation.
A Dual-Wavelength Cladding-Pumped Er3+/Yb3+ Codoped Fibre Laser System with More Than 2W Output and Tunable Wavelength Spacing
LIU Yan-Ge, ZHANG Chun-Shu, SUN Ting-Ting, LU Yun-Fei, YUAN Shu-Zhong, KAI Gui-Yun, DONG Xiao-Yi
Chin. Phys. Lett. 2006, 23 (7): 1793-1796 .  
Abstract   PDF(pc) (242KB) ( 493 )
A dual-wavelength laser system with wideband tunable wavelength spacing and more than 2W output power is proposed and demonstrated. The operation principle of the laser system is based on the saturation gain characteristic of a cladding-pumped Er3+/Yb3+ co-doped fibre amplifier combining with a wideband tunable fibre laser with flat power spectrum. The tuning range of the wavelength spacing is continuous within a 35nm spectral range, and the power difference between both lasing wavelengths can be easily adjusted and controlled by a variable optical attenuator. The total output power can approximately keep unchangeable when the wavelength spacing and the power difference between both lasing wavelengths are continuously tuned and changed. The maximum total output power of the laser system is about 2.22W.

Kilohertz Electro-Optic Q-Switched Nd:YAG Ceramic Laser
WANG Chun-Yu, JI Jiang-Hua, QI Yun-Feng, LOU Qi-Hong, ZHU Xiao-Lei, LU Yu-Tian
Chin. Phys. Lett. 2006, 23 (7): 1797-1802 .  
Abstract   PDF(pc) (350KB) ( 767 )
We investigate the lasing characteristics of a laser-diode-array side-pumped electro-optic Q-switched Nd:Y3Al5O12 ceramic laser operating at 1000Hz pulse repetition rate. Using a YAG polycrystalline rod with Nd3+ concentration of 1at.% as the gain medium, pumping with 808nm laser-diode-arrays, the Q-switched laser output at 1064nm wavelength with 23mJ pulse energy and less than 12ns FWHM pulse width are obtained at a pumping power of about 400W, the slope efficiency is around 15%, the output beam divergence angle is about 1.2mrad.
Timing Jitter and Pulse Width Reduction in a Hybrid Q-Switched Cr,Nd:YAG Laser
WANG Xue-Jun, XU Zu-Yan
Chin. Phys. Lett. 2006, 23 (7): 1800-1802 .  
Abstract   PDF(pc) (273KB) ( 737 )

We present a detailed study of a combined actively and passively Q-switched (CAPQ) laser with an acousto-optic modulator (AOM) and a codoped Cr4+, Nd3+:YAG crystal. The hybrid Q-switch approach is used to produce a short laser pulse with stable and tunable repetition rates. The timing jitter, average pulse width, and average pulse amplitude vary periodically with the AOM modulation frequency under a fixed pump power. The repetition rate of the CAPQ laser can be turned approximately from 4kHz to 16kHz with the jitter less than 400ns.

A Scaling Law of Photoionization in Ultrashort Pulses
ZHANG Xiao-Ming, ZHANG Jing-Tao, BAI Li-Hua, GONG Qi-Huang, XU Zhi-Zhan
Chin. Phys. Lett. 2006, 23 (7): 1803-1805 .  
Abstract   PDF(pc) (236KB) ( 420 )
By means of the numerical solution of time-dependent Schrödinger equation, we verify a scaling law of photoionization in ultrashort pulses. We find that for a given carrier-envelope phase and duration of the pulse, identical photoionizations are obtained provided that when the central frequency of the pulse is enlarged by k times, the atomic binding potential is enlarged by k times, and the laser intensity is enlarged by k3 times. The scaling law allows us to reach a significant control over direction of photoemission and offers exciting prospects of reaching similar physical processes in different interacting systems which constitutes a novel kind of coherent control.
Single-to-Multiple Channel Wavelength Conversions and Tuning of Picosecond Pulses in Quasi-Phase-Matched Waveguides
WANG Jian, SUN Jun-Qiang, LUO Chuan-Hong, SUN Qi-Zhen, ZHANG Xin-Liang, HUANG De-Xiu
Chin. Phys. Lett. 2006, 23 (7): 1806-1809 .  
Abstract   PDF(pc) (264KB) ( 430 )
We report the single-to-multiple channel wavelength conversions of 1.57-ps pulses based on cascaded second-harmonic generation and difference frequency generation in quasi-phase-matched periodically poled lithium niobate waveguides. For single-to-single channel wavelength conversion, no external cavity laser is required with use of a fibre ring laser. The conversion efficiency is about -21.44dB. The converted idler wavelength can be tuned from 1526.4nm to 1537.5nm as the lasing pump wavelength is varied from 1566.1nm to 1555.0nm. By employing several input pumps, tunable single-to-dual and single-to-triple channel wavelength conversions are experimentally demonstrated.
High Efficiency Infrared-to-Visible Upconversion Emission in Er3+,Yb3+, and Ho3+ Codoped Tellurite Glasses
DAI Shi-Xun, ZHANG Xiang-Hua, XU Tie-Feng, SHEN Xiang, WANG Xun-Shi, NIE Qiu-Hua
Chin. Phys. Lett. 2006, 23 (7): 1810-1812 .  
Abstract   PDF(pc) (228KB) ( 688 )
A novel method of codoping the Er3+, Yb3+, and Ho3+ ions in tellurite glasses is demonstrated to obtain a high efficiency of infrared-to-visible upconversion. Three intense emission bands observed in Er3+, Yb3+, and Ho3+ codoped tellurite glasses centred at 525, 547, and 657nm correspond to Er3+: 2H11/24I15/2, Er3+: 4S3/24I15/2+Ho3+: 5S2(5F4) → 5 I8, and Er3+: 4 S3/20 → 4I15/2+Ho3+: 5F55I8 transitions, respectively. No visible upconversion quenching phenomenon is observed when three rare-earth ions are codoped together in tellurite glasses. In contrast, the upconversion intensity of red and green emissions in Er3+, Yb3+, and Ho3+ codoped glasses is enhanced largely when compared with Er3+/Yb3+-codoped glasses. The dependence of upconversion intensities on excitation power and the possible upconversion mechanisms are evaluated. The three emissions are based on two-photon absorption processes.

Fabrication of Two-Dimensional Organic Photonic Crystal Microcavity
JIANG Ping, HU Xiao-Yong, YANG Hong, GONG Qi-Huang
Chin. Phys. Lett. 2006, 23 (7): 1813-1815 .  
Abstract   PDF(pc) (639KB) ( 536 )
A two-dimensional polystyrene photonic crystal microcavity is fabricated by the method of focused ion beam etching. The scanning electron microscopy and the transmittance spectrum are used to characterize the properties of the photonic crystal microcavity. The quality factor and the transmittance of the photonic crystal microcavity is more than 530 and 90%, respectively. The measured results are in agreement with the theoretical predictions.
Transient Emission of Three-Level Atoms in a Photonic Crystal with a Pseudogap
XU Xing-Sheng, CHEN Hong-Da
Chin. Phys. Lett. 2006, 23 (7): 1816-1819 .  
Abstract   PDF(pc) (242KB) ( 644 )
We study the transient behaviour of an external field induced transient emission of three-level atomic systems embedded in a photonic crystal with a pseudogap. The expressions for fluorescence spectra and emission dynamics for luminescent materials in the pseudogap are obtained. The properties of the transient gain in the pseudogap are discussed. It shows that the transient emission in the pseudogap can be effectively controlled.

A Novel Nano-Grating Structure of Polarizing Beam Splitters
ZHANG Liang, LI Jing, LI Cheng-Fang, ZHANG Fei, SHI Li-Na
Chin. Phys. Lett. 2006, 23 (7): 1820-1822 .  
Abstract   PDF(pc) (550KB) ( 519 )
A metal wire nanograting is fabricated and used as a polarizing beam splitter that reflects TE polarization and transmits TM polarization. The metal wire nanograting is based on a fully optimized design structure that consists of not only the core nanowire metal grid but also the substrate nanograting. The substrate nanograting is designed to provide better performance for both TM and TE polarizations. We fabricate metal-stripe gratings on a glass substrate using nanoimprint lithography and reactive ion etching process. A detailed investigation of the polarization effect at 1550nm wavelength is carried out with the theoretical analysis and experimental results. The polarizing beam splitter has uniform performance with wide variations in the incident angle (±25) and has high efficiency for both the reflected and the transmitted beams.
SOI-Based 16×16 Thermo-Optic Waveguide Switch Matrix
CHEN Yuan-Yuan, LI Yan-Ping, SUN Fei, YANG Di, CHEN Shao-Wu, YU Jin-Zhong
Chin. Phys. Lett. 2006, 23 (7): 1823-1825 .  
Abstract   PDF(pc) (517KB) ( 509 )
A 16×16 thermo-optic waveguide switch matrix has been designed and fabricated on silicon-on-insulator wafer. For reducing device length, blocking switch matrix configuration is chosen. The building block of the matrix is a 2×2 switch cell with a Mach--Zehnder interferometer configuration, where a multi-mode interferometer serves as splitter/combiners. Spot size converters and isolating grooves are integrated on the same chip to reduce loss and power consumption. Average power consumption of the switch cell is 220mW. The switching time of a switch cell is less than 3μs.
Transmission Loss due to Modes Conversion Caused by Random Surface Imperfections in Left-Handed-Material Slab Waveguides
ZHANG Gao-Ming, PENG Jing-Cui, JIAN Zhi-Jian, HUANG Xiao-Yi
Chin. Phys. Lett. 2006, 23 (7): 1826-1829 .  
Abstract   PDF(pc) (271KB) ( 515 )
Based on the orthogonality relations among the modes in left-handed-material (LHM) slab waveguides (SWGs), we derive the coupled equations among the modes caused by imperfect surfaces, and compute the transmission loss due to mode conversion. The computation shows that the transmission loss is very large, which is due to three facts: (1) there exist slow waves in the LHM SWG, whose electric field is mainly distributed in the surface; (2) the absence of fundamental node-less modes, so the fundamental modes have a node, whose electric field is also mainly distributed in the surface; and (3) the different focusing effects of the random RHM and LHM imperfections cause the electric field to suffer from severe deformations aggravated by the electric field distribution of the guided wave and the slow wave, which of course dissipates the power carried by the guided wave more severely. Therefore, we can safely conclude that the LHM SWG is unsuitable for transmitting the fundamental modes with a node.
Band Gap and Waveguide States in Two-Dimensional Disorder Phononic Crystals
LI Xiao-Chun, LIU Zheng-You, LIANG Hong-Yu, XIAO Qing-Wu
Chin. Phys. Lett. 2006, 23 (7): 1830-1833 .  
Abstract   PDF(pc) (239KB) ( 410 )
The influences of the configurational disorders on phononic band gaps and on waveguide modes are investigated for the two-dimensional phononic crystals consisting of water cylinders periodically arrayed in mercury. Two types of configurational disorders, relevant to the cylinder position and cylinder size respectively, are taken into account. It is found that the phononic band gap and the guide band are sensitive to the disorders, and generally become narrower with the increasing disorders. It is also found that the waveguide side walls without disorder can significantly prevent the guide modes in the waveguide from influence by the disorders in the crystals to a large amount.
Focusing of Surface Acoustic Wave on a Piezoelectric Crystal
QIAO Dong-Hai, WANG Cheng-Hao, WANG Zuo-Qing
Chin. Phys. Lett. 2006, 23 (7): 1834-1837 .  
Abstract   PDF(pc) (822KB) ( 910 )
We investigate the focusing phenomena of a surface acoustic wave (SAW) field generated by a circular-arc inter-digital transducer (IDT) on a piezoelectric crystal. A rigorous vector field theory of surface excitation on the crystal we developed previously is used to evaluate the convergent SAW field instead of the prevalent scalar angular spectrum used in optics. The theoretical results show that the anisotropy of a medium has great impact on the focusing properties of the acoustic beams, such as focal length and symmetrical distributions near the focus. A dark field method is used in experiment to observe the focusing of the SAW field optically. Although the convergent phenomena of SAW field on the anisotropic media or piezoelectric crystals are very complicated, the experimental data are in agreement with those from the rigorous theory.
Improvement of Low-Frequency Acoustic Spatial Correlation by Frequency-Shift Compensation
ZHANG Ren-He, SU Xiao-Xing, LI Feng-Hua
Chin. Phys. Lett. 2006, 23 (7): 1838-1841 .  
Abstract   PDF(pc) (239KB) ( 995 )
Interference of normal modes can lead to longitudinal decorrelation of an ocean acoustical field, so it can decrease the gain of a wide-aperture array. Based on waveguide invariance, we propose a frequency-shift compensation method that can be used to improve the signal correlation received at different locations with certain longitudinal separations. The method is verified by experimental data.
Lattice Bhatnagar--Gross--Krook Simulations of Hydromagnetic Double-Diffusive Convection in a Rectangular Enclosure with Opposing Temperature and Concentration Gradients
MA Chang-Feng, , SHI Bao-Chang
Chin. Phys. Lett. 2006, 23 (7): 1842-1845 .  
Abstract   PDF(pc) (488KB) ( 533 )
The temperature-concentration lattice Bhatnagar--Gross--Krook (TCLBGK) model with a robust boundary scheme is developed for two-dimensional hydromagnetic double-diffusive convective flow of a binary gas mixture in a rectangular enclosure, in which the upper and lower walls are insulated, while the left and right walls are constant temperature and constant concentration, and a uniform magnetic field is applied in the x-direction. In the model the velocity, temperature and concentration fields are solved by three independent LBGK equations, which are combined into a coupled equation for the whole system. In our simulations, we take the Prandtl number Pr=1.0, the Lewis number Le=2.0, the thermal Rayleigh number RaT=105, and the aspect ratio A=2 for the enclosure. The numerical results are found to be in good agreement with those of previous studies.
Higher-Order Bragg Resonance in Gravity Surface Waves over Periodic Bottoms
XIAO Yu-Meng, TAO Zhi-Yong, WANG Xin-Long
Chin. Phys. Lett. 2006, 23 (7): 1846-1849 .  
Abstract   PDF(pc) (418KB) ( 689 )
A calculation method based on the Bloch theorem is developed for the gravity surface waves over the periodic bottoms of large undulations. The study shows the existence of comparable high-order bandgaps, which are demonstrated to result from the higher-order Bragg resonances, i.e. the resonant interactions between surface waves and the harmonic components of the fluctuating bottom. It is also shown that the band widths of the high-order gaps are quite sensitive to the amplitudes of high-order harmonics of the bottom.
Simulations of the Instability Experiments in Stratified Cylindrical Shells
BAI Jing-Song, LI Ping, TAN Duo-Wang
Chin. Phys. Lett. 2006, 23 (7): 1850-1852 .  
Abstract   PDF(pc) (433KB) ( 549 )
A high-resolution multi-fluid parabolic piecewise method (MFPPM) is presented to simulate the Richtmyer--Meshkov (RM) instability in stratified cylindrical shells. However, the algorithm captures do not track the interfaces between distinct large deformation materials. To reach verification and validation of our MFPPM code, we select two experimental models for simulations, one is from the Lawrence Livermore National Laboratory, and the other is from our Laboratory for Shock Wave and Detonation Physics. The former result is in excellent agreement with the experiment and the Couple Arbitrary Lagrange--Euler (CALE) code, the latter is in general consistent with our experiment. It is found that the MFPPM code is reasonably successful in simulating many aspects of the gelatin-ring RM experiments.
Influence of Defect Particles on Configuration of a Two-Dimensionally Confined Dusty Plasma
HUANG Feng, LIU Yan-Hong, YE Mao-Fu, WANG Long
Chin. Phys. Lett. 2006, 23 (7): 1853-1856 .  
Abstract   PDF(pc) (421KB) ( 388 )
The behaviour of defect particles in a two-dimensional (2D) confined dusty plasma system is investigated by molecular dynamics (MD) simulations. The mean square displacement (MSD) and the pair correlation function g(r) are used to characterize the structural and dynamical properties of the system. The influences of the number and the charge (mass) of the defect particles on the system configurations are simulated. All the defect particles with charges (masses) larger than the normal particles have the trend to move towards the system centre. The moving speed of the defect particles towards the centre increases with the increasing number and charge (mass) of defect particles and with the system temperature.
Simulation of Z-Pinch Processes of Nested Tungsten Wire-Array on Angara-5-1 Facility
NING Cheng, DING Ning, LIU Quan, YANG Zhen-Hua, FAN Wen-Bin, ZHANG Yang
Chin. Phys. Lett. 2006, 23 (7): 1857-1860 .  
Abstract   PDF(pc) (236KB) ( 682 )
Based on the hydrodynamic shell-on-shell collision model, the Z-pinch processes of nested tungsten wire-array in Sino-Russian joint experiments on Angara-5-1 facility are simulated by means of our one-dimensional three-temperature radiation magneto-hydrodynamic code. The results show the evolutions of x-ray radiation burst, implosion trajectories of interfaces, current transfer in inner and outer wire-array plasmas, and the temporal and spatial changes of magnetic field and current density in the process. About 20% of the total driven current is transferred into the inner wire-array plasma by convection and diffusion of magnetic field when the two shells are pinched closest. Compared to the measured x-ray power, the simulated full width at half maximum and time at the strongest radiation agree approximately with the measured values. It is also demonstrated in our simulation that the radiation of nested wire-array Z-pinch is enhanced. The effects of fluctuations of driven current on yields of x-ray are also investigated.
Synchrotron Small-Angle X-Ray Scattering Investigation on Integral Membrane Protein Light-Harvesting Complex LH2 from Photosynthetic Bacterium Rhodopseudomonas Acidophila
DU Lu-Chao, WENG Yu-Xiang, HONG Xin-Guo, XIAN Ding-Chang, Kobayashi Katsumi
Chin. Phys. Lett. 2006, 23 (7): 1861-1863 .  
Abstract   PDF(pc) (443KB) ( 628 )
Structures of membrane protein in solution are different from that in crystal phase. We present the primary results of small angle x-ray scattering (SAXS) resolved topological structures of a light harvesting antenna membrane protein complex LH2 from photosynthetic bacteria Rhodopseudomonas acidophila in detergent solution for the first time. Our results show that the elliptical shape of the LH2 complex in solution clearly deviates from its circular structure in crystal phase determined by x-ray diffraction. This result provides an insight into the structure and function interplay in LH2.
Medium-Range Order Structure and Fragility of Superheated Melts of Amorphous CuHf Alloys
BIAN Xiu-Fang, SUN Bao-An, HU Li-Na
Chin. Phys. Lett. 2006, 23 (7): 1864-1867 .  
Abstract   PDF(pc) (259KB) ( 490 )
The structural factors of amorphous CuHf alloys at different temperatures are determined by using a high temperature x-ray diffractometer. It is found that not only the short-range order structure but also the medium-range order structure exists in amorphous CuHf alloys. The dynamic viscosities of CuHf alloy melts are measured by a torsional oscillation viscometer. The fragility of superheated melts of CuHf alloys is calculated based on the viscosity data. The experimental results show that the glass-forming ability of the CuHf alloys is closely related to the fragility of their superheated melt. The relationship between the medium-range order structures and the fragility of superheated melts has also been established in amorphous CuHf alloys. In contrast to the fragility of supercooled liquids, the fragility of superheated liquids promises a better approach to reflecting the dynamics of glass forming liquids.

Effect of Structural Relaxation on Deformation Behaviour of Zr-Based
LIU Yuan, ZHANG Tai-Hua, WEI Bing-Chen, XING Dong-Mei, LI Wei-Huo, ZHANG Ling-Chen
Chin. Phys. Lett. 2006, 23 (7): 1868-1871 .  
Abstract   PDF(pc) (566KB) ( 525 )
Structural relaxation through isothermal annealing at temperature below glass transition is conducted on Zr46.75Ti8.25Cu7.5Ni10Be27.5 (Vitreloy-4) bulk metallic glass. Defect concentration is correlated with the annealing time t according to differential scanning calorimetry thermalgrams. The effects of structural relaxation on mechanical properties and deformation behaviour are investigated by using instrumented nanoindentation. It is found that the as-cast alloy exhibits pronounced serration flow during the loading process of nanoindentation, and the size and number of the serrations decrease with the annealing time. The change of the deformation behaviour with structural relaxation is explained using a free volume model.
Phonon Dispersion in Ca70Mg30 Metallic Glass
Aditya M. Vora
Chin. Phys. Lett. 2006, 23 (7): 1872-1875 .  
Abstract   PDF(pc) (254KB) ( 481 )
The phonon dispersion curves (PDC) of Ca70Mg30 metallic glass has been studied at room temperature in terms of phonon eigen frequencies of longitudinal and transverse modes employing three different approaches proposed by Hubbard and Beeby (J. Phys. C: Solid State Phys. 13 (1969) 556), Takeno and Goda (Prog. Theor. Phys. 45 (1971) 331; 47 (1972) 790) and Bhatia and Singh (Phys. Rev. B 31 (1985) 4751). The well recognized model potential of Gajjar et al. is employed successfully to explain electron-ion interaction in the metallic glass. The effective pair potential is used to generate the pair correlation function g(r). The local field correction function (Int. J. Mod. Phys. B 17 (2003) 6001) is used for the first time to introduce the exchange and correlation effects on the aforesaid properties. The present findings of PDCs are found to be in agreement with the available theoretical as well as experimental data. The thermodynamic and elastic properties, i.e. longitudinal and transverse sound velocities, isothermal bulk modulus, modulus of rigidity, Poisson's ratio, Young's modulus and Debye temperature, are also investigated successfully.
First-Principles Calculation of Static Equation of State and Elastic Constants for GaSe
ZHANG Dong-Wen, JIN Feng-Tao, YUAN Jian-Min
Chin. Phys. Lett. 2006, 23 (7): 1876-1879 .  
Abstract   PDF(pc) (260KB) ( 617 )
The all-electron full potential augmented plane-wave plus local orbital (APW+lo) method with the local-density approximation (LDA) is used to calculate the static equation of state (EOS) and elastic constants of crystalline GaSe. After the full relaxation of atomic positions, the calculated band structure at ambient pressure is consistent with the experimental data to the extent expected to give the known limits of LDA one-electron energies. The equilibrium lattice parameters found here exhibit the usual LDA-induced contraction. However, constrained with the experimental cell volume, the interlayer separation exhibits an expansion due to the LDA underestimate of the weak interlayer bonding. The calculated values of elastic constants are in good agreement with acoustic measurements. The pressure derivatives of the lattice constants derived from the theoretical elastic constants are in very good agreement with x-ray spectra measurements. Two analytical EOSs have been determined at pressures up to 4.5GPa. The pressure evolution of the structure indicates that the layer thickness decreases slightly under pressure.
Spontaneous Hillock Growth on Indium Film Surface
WEI He-Lin, ZHANG Xi-Xiang, HUANG Han-Chen
Chin. Phys. Lett. 2006, 23 (7): 1880-1883 .  
Abstract   PDF(pc) (1451KB) ( 743 )

Uniformly distributed indium hillocks are grown on silicon substrates by dc magnetron sputtering. The morphologies and the microstructures have been investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and x-ray diffraction (XRD). From the TEM and SEM images, we find that, at the earlier stage, the grain coalescent process dominates. This coalescent process induces a larger compressive stress. We believe that the drive force for hillock growth comes from this compressive stress. Under this compressive stress, the grain locating in the middle of several grains are extruded from these grains, and then a hillock forms with the increasing deposition time. For low melting point and high diffusion coefficient metal, such as bismuth and indium, this spontaneous-hillock growth mechanism can be used to fabricate well aligned nanostructures.

Beam Focusing by a Non-Uniformly-Spaced Nanoslit Array in a Metallic Film
JIAO Xiao-Jin, WANG Pei, ZHANG Dou-Guo, LU Yong-Hua, XIE Jian-Ping, MING Hai
Chin. Phys. Lett. 2006, 23 (7): 1884-1887 .  
Abstract   PDF(pc) (629KB) ( 550 )
A finite difference time domain simulation has been performed to analyse the optical transmission through a non-uniformly-spaced nanoslit array in silver film. The phase change of surface plasmons propagating on the silver film is used to modulate the initial phase of the output beam. The beam deflection and focusing function are designed, and the focal depth of the focusing metallic structure are mainly considered. It is found that the focal depth can be controlled by altering the effective width of this structure, i.e. the number of slits, when the relative spacing is fixed.
Spin-Flip Process through Double Quantum Dots Coupled to Ferromagnetic Leads
YAN Cong-Hua, WU Shao-Quan, HUANG Rui, SUN Wei-Li
Chin. Phys. Lett. 2006, 23 (7): 1888-1891 .  
Abstract   PDF(pc) (319KB) ( 546 )
We investigate the spin-flip process through double quantum dots coupled to two ferromagnetic leads in series. By means of the slave-boson mean-field approximation, we calculate the density of states in the Kondo regime for two different configurations of the leads. It is found that transport shows some remarkable properties depending on the spin-flip strength. These effects may be useful in exploiting the role of electronic correlation in spintronics.
Kondo Effect in a Quantum Dot Coupled to Ferromagnetic Leads and a Mesoscopic Ring
HUANG Rui, WU Shao-Quan, YAN Cong-Hua, SUN Wei-Li, YU Wan-Lun
Chin. Phys. Lett. 2006, 23 (7): 1892-1896 .  
Abstract   PDF(pc) (283KB) ( 547 )
Using an equation of motion technique, we investigate the Kondo effect in a quantum dot coupled to ferromagnetic leads and a mesoscopic ring. It is shown that the Kondo resonance at the Fermi level of the dot presents the periodic change along with the aggrandizement of the magnetic flux and the number of lattice sites NR in the mesoscopic ring, and for the antiparallel spin alignment the Kondo resonances for spin-up and spin-down configurations appear at the same position. However, for the parallel spin alignment, the Kondo resonance splits for the spin-up and spin-down configurations.

Application of Plane Wave Method to the Calculation of Electronic States of Nano-Structures
LI Shu-Shen, XIA Jian-Bai
Chin. Phys. Lett. 2006, 23 (7): 1896-1899 .  
Abstract   PDF(pc) (267KB) ( 597 )
The electronic states of nano-structures are studied in the framework of effective-mass envelope-function theory using the plane wave basis. The barrier width and the number of plane waves are proposed to be 2.5 times the effective Bohr radius and 15n, respectively, for n-dimensional nano-structures (n = 1, 2, 3). Our proposals can be widely applied in the design of various nano-structure devices.
Thermal Stability of Strained AlGaN/GaN Heterostructures
ZHANG Min, XIAO Hong-Di, LIN Zhao-Jun
Chin. Phys. Lett. 2006, 23 (7): 1902-1902 .  
Abstract   PDF(pc) (223KB) ( 464 )
The thermal stability of strained AlGaN/GaN heterostructures is characterized by comparing unannealed and 700°C 30-min annealed Ni Schottky contacts prepared on strained AlGaN/GaN heterostructures. Using photoemission, capacitance--voltage measurements, and the self-consistent solution of Schrodinger's and Poisson's equations, it is found that after 700°C 30-min thermal annealing the Schottky barrier height of Ni Schottky contacts on strained AlGaN/GaN heterostructures is increased, and the sheet density of polarization charges and the sheet density of two-dimensional electron gas (2DEG) electrons for the strained AlGaN/GaN heterostructures are reduced. These results are closely related to the performance of AlGaN/GaN HFETs at high temperature.

Photoinduced Charge-Ordering Fluctuation in Wide-Bandwidth La0.7Sr0.3MnO3 Films
WU Da-Jian, WU Xue-Wei, LIU Xiao-Jun
Chin. Phys. Lett. 2006, 23 (7): 1903-1906 .  
Abstract   PDF(pc) (249KB) ( 509 )
Photoinduced effects on the transmission and resistivity in wide-bandwidth manganite La0.7Sr0.3MnO3 films (TC= 350K) have been investigated at various temperatures in the range of 5--470K by means of the time-resolved pump--probe method. Below TC, we have observed a negative transmission change ΔTM/TM at 2.54eV and a positive resistivity change Delta R/R under photo-irradiation at excited energy Eexc = 3.20eV. With temperature approaching to TC, the values of ΔTM/TM and ΔR/R show a significant reduction. We have ascribed the photoinduced changes on the transmission and resistivity of the La0.7Sr0.3MnO3 film to the charge-ordering fluctuation in the ferromagnetic phase, which is similar to that observed in the narrow-bandwidth La0.7Ca0.3MnO3 films.
A Chemical Synthesis of Ferromagnetic Zn0.99Co0.01O Nano-Needles
BI Hong, , CHEN Qian-Wang, YOU Feng-Yong, ZHOU Xiao-Li
Chin. Phys. Lett. 2006, 23 (7): 1907-1910 .  
Abstract   PDF(pc) (221KB) ( 523 )
Zn0.99Co0.01O nano-needles are synthesized by using pure ZnO powder as the starting material via chemical reactions in ammonia aqueous solution. The nano-needles show the room-temperature ferromagnetism (RTFM) characterized by using a superconducting quantum interference device. Non-reductive chemical synthesis steps ensure to prevent forming Co-metal nanoclusters within the doped sample. All the results of thermal gravimetric analysis, Fourier transform infrared spectroscopy, x-ray diffraction and ultraviolet spectroscopy demonstrate that Co ions have doped into ZnO lattices and occupied some Zn sites without changing the wurtzite structure of ZnO lattices, and no potential second phase except for the doped Co ions substituting the Zn sites in ZnO lattice can account for the observed RTFM behaviour. Moreover, the synthesis process is of high reproducibility over 80% which is higher than that of commonly-used sol-gel method.
Constitutive Relations of Ferroelectric Ceramics with Electric Fatigue Effects
YU Li, YU Shou-Wen, FENG Xi-Qiao
Chin. Phys. Lett. 2006, 23 (7): 1911-1914 .  
Abstract   PDF(pc) (236KB) ( 519 )
Recent experiments have demonstrated that cyclic electric loading may cause polarization switching fatigue of ferroelectric ceramics. We formulate a novel constitutive model for ferroelectric ceramics with electric fatigue induced by the two most important physical mechanisms, i.e. accumulation of point defects (or microcracking damage) and domain wall pinning. The local domain pinning effect is considered to be associated with the nonhomogeneous spatial distribution of positive and negative space charges. The proposed model can elucidate various experimental phenomena reported in the literature. It is found that the electric property of space charges has an essential effect on the asymmetry of strain hysteresis loops while point defects influence the change of remanent polarization and coercive field.
Optical Properties of Pr3+-Doped Y2SiO5 Crystals
SUN Cheng-Lin, LI Jian-Fu, HU Chang-Hong, JIANG Zhan-Kui,
Chin. Phys. Lett. 2006, 23 (7): 1915-1918 .  
Abstract   PDF(pc) (273KB) ( 649 )
Optical properties of Pr3+ doped in Y2SiO5, including absorption spectra, emission spectra, and fluorescence decay, have been investigated with a special attention in the UV region. Broad band (270--350nm) UV fluorescence assigned to the transitions 4f5d → 4f2 3HJ, 3FJ is found. The spontaneous transition probabilities in the 4f2 intraconfiguration are calculated by utilizing the Judd--Ofelt theory, by which three phenomenological parameters (Ω2, Ω4, Ω6,) are obtained by fitting the absorption spectra. For the evaluation of transition probability of the interconfiguration 4f5d → 4f2, a formula for electric dipole transition is employed. In comparison of the measured fluorescence lifetime with the calculated spontaneous radiative lifetime, the fluorescence quantum efficiency is deduced.
Photoluminescence from Electron-Beam Deposited CeO2 Thin Film after High Temperature Thermal Annealing
FANG Ying-Cui, ZHANG Zhuang-Jian, SHEN Jie, LU Ming
Chin. Phys. Lett. 2006, 23 (7): 1919-1922 .  
Abstract   PDF(pc) (231KB) ( 846 )
CeOx films are deposited onto the surface of a SiO2 matrix embedded with Si nanocrystals (nc-Si/SiO2) by electron-beam evaporation of CeO2 powder in high vacuum. By tuning the thickness of the CeOx film, photoluminescence (PL) spectra centred at 330, 358, 378, 388, 400, and 450nm, respectively, are observed. It has been identified that the PL centred at 358, 388 and 400nm are from cerium silicide compounds, and those centred at 330nm, 378nm are due to Ce3 ions, while the 450nm PL is from the defects in the SiO2 matrix.

Concentration Quenching in Erbium Doped Bismuth Silicate Glasses
DAI Shi-Xun, XU Tie-Feng, NIE Qiu-Hua, SHEN Xiang, WANG Xun-Si
Chin. Phys. Lett. 2006, 23 (7): 1923-1925 .  
Abstract   PDF(pc) (227KB) ( 435 )
Er2O3-doped bismuth silicate glasses are prepared by the conventional melt-quenching method, and the Er3+:4+I13/24I15/2 fluorescence properties are studied for different Er3+ concentrations. Infrared spectra are measured to estimate the exact content of OH- groups in the samples. Based on the electric dipole--dipole interaction theory, the interaction parameter CEr,Er for the migration rate of Er3+:4I13/24I13/2 in proposed glasses is calculated.
Microstructure Modification of Silicon Nanograins Embedded in Silicon Nitride Thin Films
FU Guang-Sheng, DING Wen-Ge, SONG Wei-Cai, ZHANG Jiang-Yong, YU Wei
Chin. Phys. Lett. 2006, 23 (7): 1926-1928 .  
Abstract   PDF(pc) (212KB) ( 417 )
Microstructure modification of silicon nanograins embedded in silicon nitride films by introducing hydrogen reactant in the plasma enhanced chemical vapour deposition process and their optical properties are analysed using Raman scattering, optical absorption and photoluminescence (PL) measurements. It is found that the silicon nanograins embedded in the silicon nitride (SiNx) matrix are transformed into silicon nanocrystals and the optical properties of the films change dramatically when introducing H2 into Ar-sustained plasma. The optical absorption coefficient of the films within the band gap decreases by about one order of magnitude and the PL intensity increases significantly, compared with that without hydrogen introduction. These results suggest that atomic hydrogen in the plasma has the function of crystallizing silicon nanograins and passivating defects at the silicon nanograins/SiNx interface.
Characterization of Al2O3 Thin Films on GaAs Substrate Grown by Atomic Layer Deposition
LU Hong-Liang, LI Yan-Bo, XU Min, DING Shi-Jin, SUN Liang, ZHANG Wei, WANG Li-Kang
Chin. Phys. Lett. 2006, 23 (7): 1929-1931 .  
Abstract   PDF(pc) (393KB) ( 1053 )
Al2O3 thin films are grown by atomic layer deposition on GaAs substrates at 300°C. The structural properties of the Al2O3 thin film and the Al2O3/GaAs interface are characterized using x-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and x-ray photoelectron spectroscopy (XPS). The XRD results show that the as-deposited Al2O3 film is amorphous. For 30 atomic layer deposition growth cycles, the thicknesses of the Al2O3 thin film and the interface layer from the HRTEM are 3.3nm and 0.5nm, respectively. XPS analyses reveal that the Al2O3/GaAs interface is almost free from As2O3.
A Micromachined SiO2/Silicon Probe for Neural Signal Recordings
SUI Xiao-Hong, PEI Wei-Hua, ZHANG Ruo-Xin, LU Lin, CHEN Hong-Da
Chin. Phys. Lett. 2006, 23 (7): 1932-1934 .  
Abstract   PDF(pc) (509KB) ( 561 )
The development of an implantable five channel microelectrode array is presented for neural signal recordings. The detailed fabrication process is outlined with four masks used. The SEM images show that the probe shank is 1.2mm long, 100μm wide and 30μm thick with the recording sites spaced 200μm apart for good signal isolation. The plot of the single recording site impedance versus frequency is shown by test in vitro and the impedance declines with the increasing frequency. Experiment in vivo using this probe is under way.

Organic Thin Film Field Effect Transistors with PMMA-GMA Gate Dielectric
JIANG Wen-Hai, DU Guo-Tong, YU Shu-Kun, WANG Wei, CHANG Yu-Chun, WANG Xu
Chin. Phys. Lett. 2006, 23 (7): 1939-1942 .  
Abstract   PDF(pc) (1000KB) ( 494 )
We fabricate organic thin films using the copolymer of methyl methacrylate and glycidyl methacrylate (PMMA-GMA) as a gate dielectric with a simple top-contact structure. Copper phthalocyanine (CuPc) TFTs are fabricated and the influences of annealing on the performance are studied. The mobilities increase from 2.5× 103cm2/Vs to 4.2×103cm2/Vs and threshold voltages decrease from -18V to -10V after annealing. The good performances of the devices approach those obtained with inorganic gate dielectric materials such as silicon dioxide under the same technical conditions. It is fully proven that PMMA-GMA is a competitive candidate as an excellent gate insulation layer.
Inductance of Long Intrinsic Josephson Junction Arrays Composed of Misaligned Tl2Ba2CaCu2O8 Thin Films
ZHOU Tie-Ge, YAN Shao-Lin, FANG Lan, ZUO Xu, LI Song, JI Lu, ZHAO Xin-Jie
Chin. Phys. Lett. 2006, 23 (7): 1939-1938 .  
Abstract   PDF(pc) (449KB) ( 1052 )
We observe and measure the inductance of long intrinsic Josephson junction arrays composed of misaligned Tl2Ba2CaCu2O8 thin films grown on LaAlO3 substrates. The array consists of about 9.1×103 intrinsic Josephson junctions, where 90° phase shift between ac voltage across the array and ac current flowing through has been measured. Furthermore, the voltage is proportional to the frequency of the current. The measured inductance values of the intrinsic Josephson junction arrays are basically consistent with the theoretically calculated results, confirming that the inductance is mainly due to the Josephson effect. The dependence of the array inductance on its critical current is also discussed.
Fabrication Process of Sol-Gel Spin Coating for SrBi2Ta2O9 Films Applied to FeRAM
JIA Ze, REN Tian-Ling, ZHANG Zhi-Gang, LIU Tian-Zhi, WEN Xin-Yi, XIE Dan, LIU Li-Tian
Chin. Phys. Lett. 2006, 23 (7): 1943-1946 .  
Abstract   PDF(pc) (451KB) ( 535 )
We investigate SrBi2Ta2O9 (SBT) films prepared by the sol-gel spin method with different spin rates or different anneal conditions for the first layer of SBT, as promising ferroelectric layer materials applied to ferroelectric random access memory (FeRAM). All the specimens in this experiment have similar SBT crystal orientations of (115), (020), (220), and (135). The Pt/SBT/Pt capacitor with coating of 3000rpm spin rate has a perfect rectangle shape of hysteresis loops, remanent polarization of 7.57μC/cm2 and coercive voltage of 0.816V at 5V voltage amplitude. These characteristics are better than those with coating of 3500rpm spin rate, which is attributed to the influence for thickness and grain size of the film from depressed spin rate. Slow-rate anneal in the furnace for the first layer of SBT can improve the crystallization processes and properties for SBT layers slightly, compared with rapid thermal annealing. The ion damage from etching for the top electrode can influence leakage current characteristics of the Pt/SBT/Pt capacitor at positive voltage bias.
Certain Properties of a Quantum Information Network Driven by External Fields
BI Qiao, FANG Jin-Qing, ZOU Qin
Chin. Phys. Lett. 2006, 23 (7): 1947-1950 .  
Abstract   PDF(pc) (326KB) ( 630 )
A quantum information network with the structure of the Gaussian channel is proposed. The network topological property and information characteristic is studied. Under the catastrophic and exponential external field driving, the degree distribution has the spatial and temporal characteristics, and the positive or negative power index appears, which can influence the assortativity coefficient. This is possibly helpful to open a way to using the different type of driving to introduce the expected properties for the network.
Wavelet Space Partitioning for Symbolic Time Series Analysis
Venkatesh Rajagopalan, Asok Ray
Chin. Phys. Lett. 2006, 23 (7): 1951-1954 .  
Abstract   PDF(pc) (238KB) ( 586 )
A crucial step in symbolic time series analysis (STSA) of observed data is symbol sequence generation that relies on partitioning the phase-space of the underlying dynamical system. We present a novel partitioning method, called wavelet-space (WS) partitioning, as an alternative to symbolic false nearest neighbour (SFNN) partitioning. While the WS and SFNN partitioning methods have been demonstrated to yield comparable performance for anomaly detection on laboratory apparatuses, computation of WS partitioning is several orders of magnitude faster than that of the SFNN partitioning.
Responses of the Ionosphere to the Great Sumatra Earthquake and Volcanic Eruption of Pinatubo
HAO Yong-Qiang, XIAO Zuo, ZHANG Dong-He,
Chin. Phys. Lett. 2006, 23 (7): 1955-1957 .  
Abstract   PDF(pc) (414KB) ( 671 )
A sudden ionospheric disturbance was detected by the Doppler shift sounding equipment at Beijing, about 25min later after the outbreak of the Sumatra earthquake on 26 December 2004. This ionospheric disturbance appeared less than 10min after the earthquake was first recorded at Beijing seismological station by the arrival of the seismic Rayleigh wave. The analysis shows that about 18min is the time necessary for the seismic Rayleigh wave to propagate from the epicentre to Beijing and then about 5--10min for acoustic waves to propagate from the surface of the Beijing area to the altitude of the ionosphere. Also, a report was made as another example to show the ionospheric response of Doppler shift observation at Beijing area during the Mount Pinatubo eruption of 1991. These two examples show clear evidence of the lithosphere--atmosphere--ionosphere coupling. The former case is in the frequency domain of infrasonic waves of the Earth surface
oscillation due to the Rayleigh waves caused by the earthquake, while the latter is in the acoustic--gravity wave category directly excited in the atmosphere by the mass and energy eruptions of Mount Pinatubo.
The Massive Bipolar Outflow in IRAS 20110+3321
Li Jing-Jing, XU Ye, MIYAZAKI Atsushi, SHEN Zhi-Qiang, CHEN Xi,
Chin. Phys. Lett. 2006, 23 (7): 1958-1960 .  
Abstract   PDF(pc) (353KB) ( 572 )
Mapping observations were made towards IRAS 20110+3321 using the Nobeyama 45m and the Delingha 13.7m radio telescopes. The high angular resolution (~ 21'') image with the 45m telescope shows that there is a high-velocity bipolar molecular outflow in this region, which is in the NW--SE direction with a collimation factor of ~2.2. The outflow has significantly higher mass loss rate and mechanical luminosity than those from low mass YSOs, indicating that the outflow is driven by the IRAS source. A dense massive core was detected by mapping C18O (J=1-0) line in the area with the 13.7m telescope. The IRAS source lies within the core but slightly offsets from its emission peak.
83 articles