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Volume 21 Issue 5
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Original Articles
A Realization and Truncation of Yangian Algebra in the Generalized Hydrogen Atom with a U(1) Monopole
TIAN Li-Jun, JIN Shuo, ZHANG Hong-Biao, XUE Kang
Chin. Phys. Lett. 2004, 21 (5): 767-769 .  
Abstract   PDF(pc) (213KB) ( 478 )
We establish an extended hydrogen atom associated with a U(1) monopole in which a realization of Yangian Y(sl(2)) is proposed and the energy spectrum is also given. By solving the RTT relation R(u-v)[T(u) T(v)]=[T(v) T(u)] R(u-v) for the truncation T(3) = 0, the obtained model is shown to be related to the truncated Yangian.

Is ‘Superluminal’Light Propagation Possible in Dispersive Media?
CHEN Kai, WU Ling-An, SHIH Yan-Hua
Chin. Phys. Lett. 2004, 21 (5): 770-773 .  
Abstract   PDF(pc) (295KB) ( 702 )
In a dispersive medium, different monochromatic modes of light have different phase velocities. Under special circumstances, a superposition of these modes results in an interesting effect wherein the group velocity (the velocity at which the peak of the wavepacket propagates) could be greater than c or even negative although the phase velocities of the modes are all less than c. Can this superluminal group velocity be used for information transfer? We show here that the‘superluminal’effect is due to a coherent optical wave superposition effect. Whatever the velocity of the‘peak’, the whole pulse cannot travel with a speed greater than the fastest phase velocity of its component modes. Thus the maximum speed for information transfer, which involves the sending of a finite pulse, cannot be greater than the maximum phase velocity in the medium.
Influence of Multi-Photon Process on Entanglement of Interacting System of the Qubit and Thermal Field
LI Wei-Jun, LI Shang-Bin, XU Jing-Bo
Chin. Phys. Lett. 2004, 21 (5): 774-777 .  
Abstract   PDF(pc) (371KB) ( 475 )
We study the system of a single qubit couples to a single mode thermal field according to a multi-photon Jaynes-Cummings-type interaction with phase decoherence. Both the time evolving entanglement and the stationary state entanglement are calculated by adopting the log-negativity as a measure. It is found that the multi-photon process can enhance the stationary state entanglement of this system and can enlarge the range of the parameter Δ/g and the mean photon number of initial thermal field in which the stationary state is distillable.
Spin Switch and Qubit Register from a Spin Particle Controlled by a Time-Dependent Magnetic Field
WANG Shun-Jin, JIA Cheng-Long, AN Jun-Hong, LUO Hong-Gang,
Chin. Phys. Lett. 2004, 21 (5): 778-781 .  
Abstract   PDF(pc) (210KB) ( 463 )
A spin particle subjected to any time-dependent magnetic field is investigated in detail at different magnetic field configurations. Spin flip probability, spin alignment, cyclic and noncyclic nonadiabatic geometric phases are calculated exactly and their analytical expressions are presented. Our theoretical study shows that a spin particle controlled by a resonant time-dependent magnetic field can be used as efficient controllable devices of spin switch or qubit register.
Bright Solitons in an Atomic Tunnel Array with Either Attractive or Repulsive Atom-Atom Interactions
YANG Xiao-Xue, YOU Jun, WU Ying,
Chin. Phys. Lett. 2004, 21 (5): 782-785 .  
Abstract   PDF(pc) (356KB) ( 379 )
Taking a coherent state representation, we derive the nonlinear Schrödinger-type differential-difference equations from the quantized model of an array of traps containing Bose—Einstein condensates and linked by the tunnelling process among the adjacent traps. It is shown that no matter whether two-body interactions among atoms are repulsive or attractive, a nearly uniform atom distribution can evolve into a bright soliton-type localized ensemble of atoms and a lump of atom distribution can also be smeared out by redistributing atoms among traps under appropriate initial phase differences of atoms in adjacent traps. These two important features originate from the tailoring effect of the initial phase conditions in coherent tunnelling processes, which differs crucially from the previous tailoring effect coming mainly from the periodicity of optical lattices.
A Novel Frequency Measurement Method Suitable for a Large Frequency Ratio Condition
ZHOU Wei, XUAN Zong-Qiang, YU Jian-Guo, WANG Hai, ZHOU Hui, LI Zhi-Qi
Chin. Phys. Lett. 2004, 21 (5): 786-788 .  
Abstract   PDF(pc) (261KB) ( 891 )
As for the obstacles to direct comparison between superhigh and lower frequencies, we accomplish the accurate comparison between low and microwave frequencies with the 105 ratios of the operating frequencies on the basis of phase comparison between the signals whose frequencies are related by an arbitrary integer. This method is simple and accurate, and will be widely used as a special frequency comparison approach.
Searching for Electrical Dipole and Chromodipole Moments of a Charm Quark in J/ψ → γФФ Decay
PING Rong-Gang,
Chin. Phys. Lett. 2004, 21 (5): 789-791 .  
Abstract   PDF(pc) (263KB) ( 355 )
We propose a scheme to search for the electrical dipole moments (EDMs) and chromodipole moments (CDMs) of a charm quark in the decay J/ψ → γФФ based on J/ψ data samples accumulated on the Beijing Electron Positron Collider (BEPC). The EDM and CDM interactions are introduced in this decay and then we relate them to some CP asymmetrical observables, which are predicted in the valence quark model. We propose a method to hunt for these values by measuring associated CP asymmetrical observables, and we also discuss the prospect of such measurement on the BEPC.
Trace Anomalies and Chiral Ward Identities
YANG Ji-Feng
Chin. Phys. Lett. 2004, 21 (5): 792-794 .  
Abstract   PDF(pc) (174KB) ( 462 )
In a simple Abelian spinor field theory, the canonical trace identities for certain axial-vector and axial scalar operators are re-examined in dimensional regularization, some disagreements with previous results are found and an interesting new phenomenon is observed and briefly discussed.
Strangeness Production in a Chemically Equilibrating Quark-Gluon Plasma
HE Ze-Jun, , LONG Jia-Li, MA Yu-Gang, MA Guo-Liang
Chin. Phys. Lett. 2004, 21 (5): 795-798 .  
Abstract   PDF(pc) (321KB) ( 369 )
We study the strangeness of a chemically equilibrating quark-gluon plasma at finite baryon density based on the Jüttner distribution of partons. We find that the strangeness production depends obviously on the initial values, and will accelerate with the change of the initial system from a chemically non-equilibrated to an equilibrated system. We also find that the calculated strangeness is very different from the one in the thermodynamic equilibrium system. This study may be helpful to understand the formation of quark-gluon plasma via a chemically non-equilibrated evolution framework.
Identification of Oblate Band in Odd-Odd 184Au
ZHANG Yu-Hu, WANG Hua-Lei, G. de Angelis, N. Marginean, A. Gadea, D. R. Napoli, M. Axiotis, C. Rusu, T. Martinez, ZHOU Xiao-Hong, GUO Wen-Tao, LIU Min-Liang, LEI Xiang-Guo, GUO Ying-Xiang, XU Fu-Rong
Chin. Phys. Lett. 2004, 21 (5): 799-801 .  
Abstract   PDF(pc) (528KB) ( 499 )
High-spin states in 184Au have been populated via the 149Sm(29Si, 4nγ) 184Au reaction at a beam energy of 140 MeV. Three- or higher-fold γ-ray coincidences have been measured using the multidetector array of GASP. A rotational band built on the 11- oblate πh-111/2 vi-113/2 structure has been newly observed, similar to those reported in 186-194Au. This result extends the knowledge of shape coexistence to the currently lightest odd-odd Au isotope.

Theoretical Simulation for Identical Bands
CHEN Yong-Jing, CHEN Yong-Shou, GAO Zao-Chun
Chin. Phys. Lett. 2004, 21 (5): 802-805 .  
Abstract   PDF(pc) (346KB) ( 336 )
The frequency of occurrence of identical bands is studied by analysing a large number of rotational bands calculated with the reflection asymmetric shell model, and the statistical properties of identical bands indicated in all the experimental observations are reproduced within the mean field approximation and beyond mean field treatment, such as angular momentum projection. The distributions of the calculated J(2), Eγ and the fractional change of J(2) are discussed.

Rotational Band Structures of Non-Axial Octupole Deformed Shapes
GAO Zao-Chun, CHEN Yong-Shou, MENG Jie,
Chin. Phys. Lett. 2004, 21 (5): 806-809 .  
Abstract   PDF(pc) (354KB) ( 436 )
The rotational band structures associated with the intrinsic non-axial octupole deformed states, especially for the intrinsic ground state of the even--even nuclei, are analysed by using the reflection asymmetric shell model. These band structures are expected to be useful in identifying such exotic shapes from experiment. As an example, a possible triangular shape of 148Sm is suggested.
Isoscalar Giant Resonances of 120Sn in the Quasiparticle Relativistic Random Phase Approximation
CAO Li-Gang, MA Zhong-Yu,
Chin. Phys. Lett. 2004, 21 (5): 810-812 .  
Abstract   PDF(pc) (240KB) ( 413 )
The quasiparticle relativistic random phase approximation (QRRPA) is formulated based on the relativistic mean field ground state in the response function formalism. The pairing correlations are taken into account in the Bardeen-Cooper-Schrieffer approximation with a constant pairing gap. The numerical calculations are performed in the case of various isoscalar giant resonances of nucleus 120Sn with parameter set NL3. The calculated results show that the QRRPA approach could satisfactorily reproduce the experimental data of the energies of low-lying states.

Identical Bands and Alignment in 193,194Tl
HE Xiao-Tao, YU Shao-Ying, LIU Shu-Xin, LIU Yan-Xin, ZHAO En-Guang,
Chin. Phys. Lett. 2004, 21 (5): 813-816 .  
Abstract   PDF(pc) (554KB) ( 367 )
The microscopic mechanism of the identical bands in odd-odd nucleus 194Tl and its neighbour odd-A nucleus 193Tl are investigated using the particle-number conserving method with monopole and quadrupole pairing interaction. It is found that the blocking effect plays an important role in the variation of moments of inertia (J(1) and J(2)) with rotational frequency for the superdeformed bands and identical bands. The alignment of 194Tl bands with respect to the 193Tl(1) band used as a reference is also discussed.

In-Medium K+ and K- Production and K- Condensation in Supernova Matter
GUO Hua, ZHOU Ran, LIU Yu-Xin, , LIU Bo, LI Xi-Guo
Chin. Phys. Lett. 2004, 21 (5): 817-820 .  
Abstract   PDF(pc) (412KB) ( 391 )
In-medium effects and neutrino trapping on K+ and K- production and K- condensation in supernova matter are investigated in a chiral hadronic model. Our results show that neutrino trapping shifts the critical density for K- condensation to higher density, the Q values for K+ and K- production are not sensitive to neutrino trapping, in-medium effects decrease the Q values for NN → NNK+K- and ΛN → NNK- and increase those for NN → NΛK+, K-p → Λπ0 and K-n → Λπ- as the density of supernova matter increases. Moreover, it is shown that neutrino trapping decreases the maximum masses of protoneutron stars compared with the neutrino-free case.
Quantitative Single-Ion Irradiation by ASIPP Microbeam
WANG Xu-Fei, CHEN Lian-Yun, HU Zhi-Wen, WANG Xiao-Hua, ZHANG Jun, LI Jun, CHEN Bin, HU Su-Hua, SHI Zhong-Tao, WU Yu, XU Ming-Liang, WU Li-Jun, WANG Shao-Hu, YU Zeng-Liang
Chin. Phys. Lett. 2004, 21 (5): 821-824 .  
Abstract   PDF(pc) (512KB) ( 624 )
A single-ion microbeam facility has been constructed by the microbeam research group in ASIPP (Institute of Plasma Physics, Chinese Academy of Science). The system was designed to deliver defined numbers of hydrogen ions produced by a van de Graaff accelerator, covering an energy range from 200 keV to 3 MeV, into living cells (5 μm-20 μm diameter) growing in culture on thin plastic films. The beam is collimated by a 1-μm inner diameter HPLC (high performance liquid chromatography) capillary, which forms the micron dimensional beam-line exit. A microbeam collimator, a scintillation ion counting system and a fast beam shutter, which constitute a precise dosage measuring and controlling system, jointly perform quantitative single-ion irradiation. With this facility, we can presently acquire ion-hitting efficiency close to 95%.
Ab Initio Calculations for the BaTiO3 (001) Surface Structure
XUE Xu-Yan, WANG Chun-Lei, ZHONG Wei-Lie
Chin. Phys. Lett. 2004, 21 (5): 825-828 .  
Abstract   PDF(pc) (479KB) ( 834 )
The ab initio method within the local density approximation is applied to calculate cubic BaTiO3 (001) surface relaxation and rumpling for two different terminations (BaO and TiO2). Our calculations demonstrate that cubic perovskite BaTiO3 crystals possess surface polarization, accompanied by the presence of the relevant electric field. We analyse their electronic structures (band structure, density of states and the electronic density redistribution withm emphasis on the covalency effects). The results are also compared with that of the previous ab initio calculations. Considerable increases of Ti-O chemical bond covalency nearby the surface have been observed. The band gap reduces especially for the TiO2 termination.

Relativistic Energy of Highly Triply Excited 3l3lnl2 Po(m) (m = 1-5) States of Lithium
WANG Fei, GOU Bing-Cong, YU Kai-Zhi, ZHANG Meng
Chin. Phys. Lett. 2004, 21 (5): 829-831 .  
Abstract   PDF(pc) (196KB) ( 374 )
The high-lying triply excited 3l3lnl2 Po (n ≥ 3) states of the double hollow lithium atom are studied by using the saddle-point variational method. Relativistic corrections are evaluated with the first-order perturbation theory, and the mass polarization effect is also included. The dominant configuration mixtures of these triply excited states are given. The results are compared with other theoretical and experimental data in the literature.

Time-Dependent Quantum Dynamics of T+CH4 → CH3+HT Reaction
BAI Li-Hua, ZHANG Jing-Tao, ZHANG Qing-Gang, XU Zhi-Zhan
Chin. Phys. Lett. 2004, 21 (5): 832-835 .  
Abstract   PDF(pc) (382KB) ( 421 )
Reaction probability, cross section and rate constant are studied for polyatomic reaction T+CH4 → CH3+HT using the semirigid vibrating rotor target (SVRT) model. The numerical calculation for the reaction system is carried out using the time-dependent wavepacket method, and the wavepacket is propagated by the split-operator method. The calculation exhibits a variety of features that can be used for comparison with future experimental investigations. The reaction probability as a function of the translational energy shows slight oscillatory structures, similar to those observed in H abstraction reactions H+H2 and H+CH4. The comparisons with the H+CH4 reaction are described.
Extracting Closed Classical Orbits from Quantum Recurrence Spectra of a Non-Hydrogenic Atom in Parallel Electric and Magnetic Fields
WANG De-Hua, LIN Sheng-Lu
Chin. Phys. Lett. 2004, 21 (5): 836-839 .  
Abstract   PDF(pc) (534KB) ( 491 )
We show how to extract the closed orbits from the quantum spectra data. According to the closed orbit theory, each closed orbit produces a sharp peak in the recurrence spectra of a non-hydrogenic atom in parallel electric and magnetic fields. For a given initial state, closed-orbit theory gives the dependence of this recurrence amplitude on the initial angle of an orbit. By comparing the recurrence amplitude for different initial states, we can determine the initial angles of the closed classical orbits from the quantum recurrence spectra. Therefore, by integrating the Hamiltonian motion equations, we can obtain the closed orbits directly. This method can also be used to extract the closed orbits from the experimental data.

Evaluation of Light Frequency Shift in a Caesium Beam Frequency Standard with Sharp Angle Incident Detecting Laser
ZHANG Jun-Hai, WANG Feng-Zhi, WANG Yi-Qiu, YANG Dong-Hai
Chin. Phys. Lett. 2004, 21 (5): 840-842 .  
Abstract   PDF(pc) (290KB) ( 336 )
Light frequency shift measured in a small optically pumped caesium beam frequency standard is reported and analysed. Two light sources, the diffused laser light scattered from the caesium beam tube parts and the fluores-cence light from the beam atoms excited by the laser light, for the light frequency shift are discussed.
A New Method for Determining Dipole Moment Orientation of Single Molecules
WANG Chen, LIU Li, WANG Gui-Ying, XU Zhi-Zhan
Chin. Phys. Lett. 2004, 21 (5): 843-845 .  
Abstract   PDF(pc) (295KB) ( 668 )
A new imaging method is proposed to determine the three-dimensional dipole moment orientation of single fluorophore. Far-field microscopy can provide orientational information projected in the sample plane, while total internal reflection fluorescence microscopy (TIRFM) can offer the knowledge perpendicular to the surface because longitudinal electric-field components can be generated in total internal reflection geometry. By comparing fluorescence intensities measured with far-field epi-fluorescence microscopy and TIRFM, the exact information of single-fluorescent-molecule orientation is extracted. Detailed analysis of the method is given with a numerical example.

Generation of an Entangled State of Two Multilevel Atoms in Cavity QED
ZHAN Zhi-Ming, YANG Wen-Xing, LI Jia-Hua
Chin. Phys. Lett. 2004, 21 (5): 846-848 .  
Abstract   PDF(pc) (226KB) ( 492 )
We present a simple scheme to generate a maximally entangled state of two four-level Rydberg atoms with a nonresonant cavity by cavity-assisted collisions. By using this scheme, the maximally entangled state of two N-level (N > 4) Rydberg atoms can also be obtained. During the passage of the atoms through the cavity field, they are only virtually excited. There is no quantum information that will be transferred from the atoms to the cavity in this case.

Tunnelling-Induced Transient Gain in an Asymmetric Double Quantum Well
XU Wei-Hua, WU Jin-Hui, GAO Jin-Yue
Chin. Phys. Lett. 2004, 21 (5): 849-852 .  
Abstract   PDF(pc) (433KB) ( 457 )
We investigate the transient behaviour of a weak probe in asymmetric double quantum well structures, where two excited states are coupled by resonant tunnelling through a thin barrier in a three-level system of electronic subbands. There is no external coherent coupling field applied, and we find that probe gain can be achieved during the transient process, which is induced by the coherent coupling of the upper states via the resonant tunnelling. We show that the transient behaviour of the probe depends on the coupling strength and the dephasing rate and can be tuned by changing the width of the tunnelling barrier.

Observation of Electromagnetically Induced Transparency by a Train of Short Pulses
YE Cun-Yun
Chin. Phys. Lett. 2004, 21 (5): 853-855 .  
Abstract   PDF(pc) (310KB) ( 448 )
We report the experimental demonstration of electromagnetically induced transparency in hot rubidium (85Rb) atomic vapour by using an actively mode-locked external cavity diode laser in Littman-Metcalf configuration. We can make opaque resonant transitions transparent to any two optical comb components in the pulse trains which excite atomic coherence in the ground states of 85Rb.

Slow Light by Modified Reservoir Induced Transparency with a Non-Singular Density of Modes
ZHOU Bo, DU Chun-Guang, LI Shi-Qun
Chin. Phys. Lett. 2004, 21 (5): 856-859 .  
Abstract   PDF(pc) (514KB) ( 443 )
We investigate the dispersive property of a Λ-type atomic system embedded in photonic band gap structures. The atomic coherence is established by the structured reservoir which consists of a double-band photonic band gap (PBG) and defect modes. With an atomic density of 7 x 1015 atoms/cm3, the group velocity of a probe laser being detuned far away from the gap is shown to be reduced to 3 x 102m/s near the transparency window associated with the PBG edges and 6 x 103m/s at the transparency window associated with the defect modes, without using any deriving field. The influence of the smoothness of the density of modes and the decay rate of the second ground state of atoms are analysed.

Photoelectric Hybrid Optical Bistable Device Using Fibre Bragg Gratings with Two Feed Signals
YE Hong-An, ZHANG Xin-Ming, ZHU Yong
Chin. Phys. Lett. 2004, 21 (5): 860-862 .  
Abstract   PDF(pc) (342KB) ( 539 )
A photoelectric hybrid optical bistable device (OBD) is investigated by using fibre Bragg gratings as a light-intensity modulator. A new operation with two feed signals is proposed, and with this method the output characteristic of the OBD is remarkably improved. The potential application of such a device in optic stabilizer for fibre laser is also briefly discussed.

Tolerance of Photonic Crystal Impurity Bands to Disorder of Defects in Coupled Cavity Waveguides
LIN Xu-Sheng, HUANG Chong, OUYANG Yan-Dong, LAN Sheng
Chin. Phys. Lett. 2004, 21 (5): 863-866 .  
Abstract   PDF(pc) (420KB) ( 407 )
We investigate the tolerance of photonic crystal impurity bands to the disorder of defects in one-dimensional coupled cavity waveguides. Although impurity bands formed by defect modes close to the air band are quasiflat in the absence of disorder, they are easily deteriorated when disorders are introduced into defects. In contrast, impurity bands created by defect modes near the dielectric band are less sensitive to disorder in the defect size. It is found that the sensitivity of defect mode frequency to defect size and the quality factor of defect modes are two crucial factors in determining the tolerance of impurity bands to the disorder of defects.

Barrier Optical Waveguide Formation in La3Ga5SiO14 Crystals by High Energy Carbon Ion Implantation
WANG Xue-Lin, CHEN Feng, LU Fei, FU Gang, LI Shi-Ling, WANG Ke-Ming, ZHANG Huai-Jin, SHEN Ding-Yu, MA Hong-Ji, NIE Rui
Chin. Phys. Lett. 2004, 21 (5): 867-869 .  
Abstract   PDF(pc) (302KB) ( 490 )
The barrier planar waveguides are fabricated for the first time in z-cut LGS (La3Ga5SiO14) crystals by 3.0 MeV and 6.0 MeV carbon ion implantations with dose of 2 x 1015ions/cm2 at room temperature. Four and six dark modes were observed by the prism-coupling method, respectively. The refractive index profiles were reconstructed by using the reflectivity calculation method. There are about 1.6% and 0.9% decreases at the optical barriers in the 3.0 MeV and 6.0 MeV cases, and the positions of the optical barriers are close to that of the damage peaks calculated by the TRIM'98 (Transport of Ions in Matter) code. It is found that the refractive index change may partly be due to the damage induced by the nuclear collision.

Thickness Measurement of a Film on a Substrate by Low-Frequency Ultrasound
LI Ming-Xuan, WANG Xiao-Min, MAO Jie
Chin. Phys. Lett. 2004, 21 (5): 870-873 .  
Abstract   PDF(pc) (465KB) ( 894 )
We describe a new simple technique for the low-frequency ultrasonic thickness measurement of an air-backed soft thin layer attached on a hard substrate of finite thickness through the frequency-shifts of the substrate resonances by the substrate-side insonification. A plane compressive wave impinging normally on the substrate surface from a liquid is studied. Low frequency here means an interrogating acoustical wave frequency of less than half of the ‘half-wavelength resonance frequency’of the thin layer depending on the acoustical impedance ratio of the coating to the substrate. Equations for the frequency-shifts are derived and solved by the Newton iterative method and the Taylor expansion method, respectively, indicating satisfactory agreement within the range of interest of thickness ratio of the thin layer to the substrate for a polymer-aluminium structure. An experimental setup is constructed to verify the validity of the technique.

Characterization of Density Profile of Cylindrical Pulsed Gas Jets
YU Quan-Zhi, LI Yu-Tong, ZhANG Jie, ZHENG Jun, LI Han-Ming, PENG Xiao-Yu, LI Kun
Chin. Phys. Lett. 2004, 21 (5): 874-876 .  
Abstract   PDF(pc) (427KB) ( 811 )
We investigated the characteristics of argon and helium gas jets produced by a cylindrical nozzle under pressures from 1 to 6 MPa using a femtosecond laser interferometry. A radial parabolic distribution and an axial exponential distribution of the gas jet density profiles are identified. The results show that the density increases linearly with the backing pressure.
Ionization Balance in Non-Local-Thermodynamic-Equilibrium Plasmas
WU Ze-Qing, PANG Jin-Qiao, HAN Guo-Xing, YAN Jun
Chin. Phys. Lett. 2004, 21 (5): 877-880 .  
Abstract   PDF(pc) (211KB) ( 1058 )
A collisional-radiative model is developed for population calculations of plasmas in non-local thermodynamic equilibrium. The rate equations in detailed configuration accounting are solved to obtain ion populations. The configuration averaged rate coefficients are used in the rate equations. The cross sections are calculated based on the first perturbation theory. Wavefunctions required in cross section calculations are obtained by the Hartree-Fock-Slater self-consistent-field model. This kinetic model is applied to low- and medium-Z as well as high-Z plasmas. The results are compared with those of other theoretical models and experiments. The comparisons show that the present results of the mean charge state for low- and medium-Z elements agree well with other theoretical ones, while for high-Z elements, the present mean ionization stages are about two stages lower than the experimental ones.
A New Kinetic Mode Driven by Electron Temperature Gradient
Chin. Phys. Lett. 2004, 21 (5): 881-883 .  
Abstract   PDF(pc) (356KB) ( 405 )
A new unstable short wavelength mode is identified in sheared slab plasmas using a fully kinetic integral equation code. This mode is driven by the electron temperature gradient and propagates in the ion diamagnetic direction. The instability occurs due to the electron inverse Landau damping effect at short cross-field wavelength regions.

Large Amplitude Low Frequency Waves in a Magnetized Nonuniform Electron-Positron-Ion Plasma
Q. Haque, H. Saleem
Chin. Phys. Lett. 2004, 21 (5): 884-887 .  
Abstract   PDF(pc) (205KB) ( 784 )
It is shown that the large amplitude low-frequency electromagnetic drift waves in electron-positron-ion plasmas might give rise to dipolar vortices. A linear dispersion relation of several coupled electrostatic and electromagnetic low-frequency modes is obtained. The relevance of this work to both laboratory and astrophysical situations is pointed out.
Nonlinear Inertial Alfvén Waves in Plasmas with Sheared Magnetic Field and Flow
CHEN Yin-Hua, WANG Ge, TAN Li-Wei
Chin. Phys. Lett. 2004, 21 (5): 888-890 .  
Abstract   PDF(pc) (192KB) ( 455 )
Nonlinear equations describing inertial Alfvén waves in plasmas with sheared magnetic field and flow are derived. For some specific parameters chosen, we have found a new type of electromagnetic coherent structures in the tripolar vortex-like form.
Stimulated Raman Scattering in Bi-temperature Vlasov Plasma
CAI Hong-Bo, ZHU Shao-Ping
Chin. Phys. Lett. 2004, 21 (5): 891-894 .  
Abstract   PDF(pc) (359KB) ( 418 )
We obtain the nonlinear coupling equations for describing stimulating Raman scattering (SRS) of ultra-intense laser beam starting from the relativistic Vlasov-Maxwell equations. It is found that the relativistic electrons play an important role in the inhibition of the SRS instability and the growth rate of backward SRS strongly decreases with the increasing number of relativistic electrons.

Nuclear Fusion Induced by Coulomb-Hydrodynamic Explosion of Deuterium Clusters in Intense Laser Pulses
AN Wei-Ke, QIU Xi-Jun, ZHU Zhi-Yuan
Chin. Phys. Lett. 2004, 21 (5): 895-897 .  
Abstract   PDF(pc) (207KB) ( 560 )
Considering the Coulomb-hydrodynamic explosion induced by the interaction of a deuterium cluster target with an ultra-intensity femtosecond laser, we analyse the mechanism of generating energetic deuterium nuclei for the fusion. We propose formulae for expansions of deuterium ion cluster which are driven by Coulomb-hydrodynamic explosion. Hence the kinetic energies of deuterium nuclei, the expansion time and exploding efficiency of deuterium ion cluster have been estimated.
Compression Behaviour and Equation of State of Zr44.4Nb7Cu13.5Ni10.8Be24.3 Bulk Metallic Glass up to 39 GPa
LI Gong, ZHAN Zai-Ji, WANG Li-Min, SUN Li-Ling, LIU Jing, WANG Wen-Kui,
Chin. Phys. Lett. 2004, 21 (5): 898-900 .  
Abstract   PDF(pc) (403KB) ( 652 )
The compression of Zr44.4Nb7Cu13.5Ni10.8Be24.3 bulk metallic glass (BMG) is investigated at room temperature up to 39 GPa using in situ high-pressure energy dispersive x-ray diffraction with a synchrotron radiation source. The equation of state of the BMG is obtained by the calculation of the radial distribution function. Pressure-induced structural relaxation is exhibited. It is found that below about 6 GPa, the existence of excess free volume contributes to the rapid structural relaxation, which gives rise to rapid volumetric change, and the structural relaxation results in structural stiffness under higher pressure.

Binary Cu--Zr Bulk Metallic Glasses
TANG Mei-Bo, ZHAO De-Qian, PAN Ming-Xiang, WANG Wei-Hua
Chin. Phys. Lett. 2004, 21 (5): 901-903 .  
Abstract   PDF(pc) (336KB) ( 1947 )
We report that bulk metallic glasses (BMGs) can be produced up to 2 mm by a copper mould casting in CuxZr1-x binary alloy with a wide glass forming composition range (45 < x < 60 at.%). We find that the formation mechanism for the binary Cu-Zr binary BMG-forming alloy is obviously different from that of the intensively studied multicomponent BMGs. Our results demonstrate that the criteria for the multicomponent alloys with composition near deep eutectic and strong liquid behaviour are no longer the major concern for designing BMGs.
Preparation of Nano-Graphite Films and Field Emission Properties
ZHAO Yong-Mei, ZHANG Bing-Lin, YAO Ning, LU Zhan-Ling, ZHANG Xin-Yue
Chin. Phys. Lett. 2004, 21 (5): 904-906 .  
Abstract   PDF(pc) (425KB) ( 797 )
Nano-graphite films have been deposited on n-Si substrates by microwave plasma chemical vapour deposition. The surface morphology and microstructure of the films were tested by scanning electron microscopy, x-ray diffraction and Raman spectroscopy. In the field emission measurement, a turn-on field of 0.5 V/μm and a high emission-site density of 105/cm2 on a tested emission area of (34 x 35 mm2) have been obtained.

Direct Measurement of Evanescent Wave Interference with a Scanning Near-field Optical Microscope
HONG Tao, WANG Jia, XU Tie-Jun, SUN Li-Qun
Chin. Phys. Lett. 2004, 21 (5): 907-910 .  
Abstract   PDF(pc) (402KB) ( 495 )
Evanescent wave interference is studied theoretically and experimentally. The interference patterns were directly measured with a scanning near-field optical microscope. The acquired image of the interference pattern is clear and has better contrast than that previously acquired with a photon-scanning tunnelling microscope or laser-trapped particles. The spatial period of the interference fringes is 180 nm, which agrees with the theoretical value. The results indicate that the probe of the scanning near-field optical microscope has a resolution beyond 100 nm. The relation between the evanescent field intensity and the distance is also measured. When the separation between the probe and the interface is up to 180 nm, the intensity can decrease to 1/e of the maximum.

Giant Persistent Current in a Mesoscopic Ring with Parallel-Coupled Double Quantum Dots
CHEN Xiong-Wen, WU Shao-Quan, WANG Peng, SUN Wei-Li
Chin. Phys. Lett. 2004, 21 (5): 911-914 .  
Abstract   PDF(pc) (473KB) ( 494 )
We theoretically study the properties of the ground state of the parallel-coupled double quantum dots embedded in a mesoscopic ring in the Kondo regime by means of the two-impurity Anderson Hamiltonian. The Hamiltonian is solved by means of the slave-boson mean-field theory. Our results show that in this system, the persistent current depends sensitively on both the parity of this system and the size of the ring. Two dots can be coupled coherently, which is reflected in the giant current peak in the strong coupling regime. This system might be a candidate for future device applications.

Magnetointersubband Oscillations of the Two-Dimensional Electron Gas in AlxGa1-xN/GaN Heterostructures
JIANG Chun-Ping, YANG Fu-Hua, ZHENG Hou-Zhi, QIU Zhi-Jun, GUI Yong-Sheng, GUO Shao-Ling, CHU Jun-Hao, SHEN Bo, ZHENG You-Dou
Chin. Phys. Lett. 2004, 21 (5): 915-918 .  
Abstract   PDF(pc) (432KB) ( 485 )
Shubnikov-de Haas (SdH) measurements are performed over a temperature range of 1.5-20 K in Al0.22Ga0.78N/GaN heterostructures with two subbands occupied. In addition to an intermodulation between two sets of SdH oscillations from the first and second subbands, a beating in oscillatory magnetoresistance at 12 K is observed, due to the mixing of the first subband SdH oscillations and `magnetointersubband' (MIS) oscillations. A phase shift of π between the SdH and MIS oscillations is also clearly identified. Our experimental results, i.e. that the SdH oscillations dominate at low temperature and MIS oscillations dominate at high temperature, fully comply with the expected behaviour of MIS oscillations.

Variational Calculations of Neutral Bound Excitons in GaAs Quantum-Well Wires
LIU Jian-Jun, , DI Bing, YANG Guo-Chen, LI Shu-Shen
Chin. Phys. Lett. 2004, 21 (5): 919-922 .  
Abstract   PDF(pc) (400KB) ( 519 )
The binding energy of an exciton bound to a neutral donor (D0,X) in GaAs quantum-well wires is calculated variationally as a function of the wire width for different positions of the impurity inside the wire by using a two-parameter wavefunction. There is no artificial parameter added in our calculation. The results we have obtained show that the binding energies are closely correlated to the sizes of the wire, the impurity position, and also that their magnitudes are greater than those in the two-dimensional quantum wells compared. In addition, we also calculate the average interparticle distance as a function of the wire width. The results are discussed in detail.
Dynamical Localization in an Asymmetric Two-Electron Quantum Dot Molecule by an Alternating-Current Electric Field
LIU Yu-Shen, CHEN Hao
Chin. Phys. Lett. 2004, 21 (5): 923-926 .  
Abstract   PDF(pc) (338KB) ( 379 )
We investigate the dynamics of two interacting electrons in an asymmetric double coupled quantum dot under an ac electric field. The numerical results demonstrate that dynamical localization and Rabi oscillation still exist in such a system under the stronger electron correlation. The two electrons can be regarded as a quasiparticle, which move together between two dots similarly to a boson. The dynamics of two electrons in such a quantum system are mainly confined in a Q subspace, which is constructed by two double-occupied states.
Blue Upconversion Luminescence in Tm3+/Yb3+-Codoped Lead Chloride Tellurite Glass
XU Shi-Qing, ZHANG Jun-Jie, WANG Guo-Nian, DAI Shi-Xun, HU Li-Li, JIANG Zhong-Hong
Chin. Phys. Lett. 2004, 21 (5): 927-929 .  
Abstract   PDF(pc) (323KB) ( 844 )
The upconversion properties of Tm3+/Yb3+-codoped lead chloride tellurite glass under 980 nm excitation were investigated. The intense blue (476 nm) emission and weak red (649 nm) emission corresponding to the 1G43H6 and 1G43H4 transitions of Tm3+ ions, respectively, were simultaneously observed at room temperature. The dependence of upconversion intensities on excitation power and the possible upconversion mechanisms are evaluated. The intense blue upconversion luminescence of Tm3+/Yb3+-codoped lead chloride tellurite glass can be used as potential host material for the development of blue upconversion optical devices.

Intersubband Transitions of Si δ-Doped GaAs Layer for Different Donor Distribution Models
Chin. Phys. Lett. 2004, 21 (5): 930-933 .  
Abstract   PDF(pc) (445KB) ( 695 )
For different donor distribution types we theoretically investigate the intersubband transitions of single Si δ-doped GaAs structure as dependent on the applied electric field. The diffusion of donor impurities is taken into account in two different models: a triangular distribution and a non-uniform distribution. The electronic properties such as the effective δ-potential, the subband energies and the eigen-envelope wavefunctions have been calculated by solving the Schrödinger and Poisson equations self-consistently. Abrupt changes of the subband energy difference and the absorption peak are realized whenever the applied electric field reaches a certain value. These critical electric field values change dependent on the donor distribution model. The intersubband absorption spectrum shows that redshifts appear up to the critical electric field value for the (1-2) and (1-3) intersubband transitions. This spectrum also shows that blueshifts can occur when the electric fields are higher than certain values. These changing intersubband absorption peaks can be used in various infrared optical device applications.
Effects of Induced Flux on Andreev Levels in a Quantum Point Contact Embedded in Superconducting Ring
QIN Zhi-Jie, HU Dong-Sheng, XIONG Shi-Jie
Chin. Phys. Lett. 2004, 21 (5): 934-936 .  
Abstract   PDF(pc) (459KB) ( 398 )
We investigate the effects of flux induced by persistent current on the states of Andreev levels in a quantum point contact (QPC) embedded in a superconducting ring. The Andreev levels correspond to the bound states in the QPC created by multiple reflection at the boundaries. We self-consistently calculate the eigenstates and persistent current of such a system with different external fluxes threaded through the ring by using a tight-binding model with Bogoliubov-de Gennes potential. We show that the induced flux can significantly change the dependence of the Andreev levels and the persistent current on the external flux if the inductance of the system is large. By solving the time-dependent Schrödinger equation we obtain the dynamical behaviour of Andreev states in the presence of flux oscillations in the equivalent LC circuit.

Antiferromagnetic Phase Transition in the Quasi-Two-Dimensional Hubbard Model at Half Filling
LIU Qin-Yong, TIAN Guang-Shan, YAN Xin-Zhong
Chin. Phys. Lett. 2004, 21 (5): 937-940 .  
Abstract   PDF(pc) (264KB) ( 412 )
We study the antiferromagnetic phase transition in the quasi-two-dimensional Hubbard model at half filling for a wide range of the Coulomb interaction U. By using the fluctuation-exchange approximation, we calculate the Néel transition temperature of the system as a function of the Coulomb interaction U. For weak-to-intermediate Coulomb interactions, the present calculation provides a reasonable result for the Néel temperature.
Pseudo-Spin-Valve Trilayer Using Amorphous CoNbZr Layer: Giant Magnetoresistance, Domain Structures and Potentials for Spin-Electronic Devices
WEN Qi-Ye, ZHANG Huai-Wu, JIANG Xiang-Dong, SHI Yu, TANG Xiao-Li, ZHANG Wan-Li
Chin. Phys. Lett. 2004, 21 (5): 941-944 .  
Abstract   PDF(pc) (482KB) ( 470 )
We propose a pseudo-spin-valve (PSV) trilayer using amorphous CoNbZr alloy for soft magnetic layers. The giant magnetoresistance (GMR), domain structures and their variation upon thermal annealing are investigated. The GMR effect is not only stable up to 300°C but also enhanced due to the improvement of the interfaces between Cu and magnetic layers. With high annealing temperature, the magnetoresistance (MR) ratio decreases rapidly as a result of serious layer interdiffusion. Dense stripe domains, which disappear after annealing at 300°C for 1 h, are observed in the sandwiched films. It is found that after patterning to elliptic stripe with aspect ratio of 6:1, the trilayers have a single domain and their MR ratio increases. The dynamic MR behaviour under an ac magnetic field indicates that the patterned stripes have good linear MR responses. Therefore, it is believed that the CoNbZr/Cu/Co PSV trilayers have strong potentials for spin-electronic devices including magnetic random access memory.

Remanence Properties and Magnetization Reversal Mechanism of Fe Nanowire Arrays
WANG Jian-Bo, LIU Qing-Fang, XUE De-Sheng, LI Fa-Shen
Chin. Phys. Lett. 2004, 21 (5): 945-948 .  
Abstract   PDF(pc) (467KB) ( 566 )
Remanence properties and magnetization reversal mechanism of Fe nanowire arrays with diameters 16 nm and 13 nm are studied. Isothermal remanent magnetization curves show that the contribution of irreversible magnetization decreases when the diameter changes from 16 nm to 130 nm. The remanence coercivities of these nanowires obtained in dc-demagnetization curve are about 2400 Oe and 800 Oe, respectively. The magnetization reversal mechanism is different in these two samples. For the nanowire array with diameter 16 nm, both the nucleation and the pinning have effects on magnetization reversal mechanism, and the pinning field (about 2500 Oe) is larger than the nucleation field (about 2200 Oe). However, for the nanowire array with diameter 130 nm, the magnetization reversal mechanism is dominated by the pinning effect of domain walls.

Structural and Magnetic Properties of FePt-C Nanocomposite Films
WANG Hao, YANG Fu-Jun, CHEN Kan-Song, ZHOU Bin, ZHANG Yuan-Wei, GU Hao-Shuang, CHIAH M. F., CHEUNG W. Y., WONG S. P
Chin. Phys. Lett. 2004, 21 (5): 949-951 .  
Abstract   PDF(pc) (424KB) ( 552 )
Nanocomposite FePt-C thin films were prepared by a pulsed filtered vacuum arc deposition technique. The films were characterized by non-Rutherford backscattering spectrometry, x-ray diffraction, and magnetic force microscopy. The dependence of magnetic properties against annealing temperature was studied by using a vibrating sample magnetometer. Both x-ray diffraction and magnetic force microscopy analyses confirmed the formation of nano-crystallites of face-centred-tetragonal phase of FePt in the carbon matrix after annealing at a sufficiently high temperature. For the film with a composition of (Fe0.55Pt0.45)0.78C0.22, the coercivity and the grain size were observed to increase with increasing annealing temperature, up to a value of 3.5 kOe at an annealing temperature of 650°C, and with a grain size about 10.5 nm.
Polarization of Hemicyanine Langmuir-Blodgett Films
LI Shu-Hong, MU Jian, WANG Wen-Jun, MA Shi-Hong, SUN Jing-Lan, CHU Jun-Hao, WANG Wen-Cheng
Chin. Phys. Lett. 2004, 21 (5): 952-954 .  
Abstract   PDF(pc) (381KB) ( 608 )
The polarization dependence of electric field for hemicyanine layers deposited by the Langmuir-Blodgett (LB) technique has been measured. The experimental results show that ferroelectricity exists not only in thick films (200 nm) but also in thinner films (30 nm), and the remnant polarization is related to film thickness. In order to interpret the measured results, a planar rotor model was introduced, and a relation between polarization and film thickness was obtained by perturbation theory. The theory fitting agrees with experimental results well. It is confirmed that ferroelectricity in organic molecular LB films mainly arose from altering of molecular orientation.
Preparation and Properties of GaN Films on GaAs Substrates
YANG Ying-Ge, MA Hong-Lei, MA Jin, ZHANG Ya-Fei
Chin. Phys. Lett. 2004, 21 (5): 955-957 .  
Abstract   PDF(pc) (421KB) ( 526 )
Polycrystalline gallium nitride films with hexagonal structure were prepared by a post-nitridation technique. A strong blue photoluminescence located at 458 nm and a UV photoluminescence located at 368 nm were observed at room temperature. The 368 nm peak is PL from band-edge emission. The blue luminescence is attributed to the transition from deep donor level to the valence band.

Blue Luminescence of CdS Nanowires Synthesized by Sulfurization
GAO Tao, MENG Guo-Wen, WANG Tai-Hong
Chin. Phys. Lett. 2004, 21 (5): 959-962 .  
Abstract   PDF(pc) (328KB) ( 552 )
Polycrystalline CdS nanowires have been synthesized by sulfurizing metal Cd nanowires deposited electrochemically within the nanochannels of porous anodic alumina (PAA) templates. Photoluminescence (PL) investigation shows that the CdS nanowires have an intensive and broad PL emission band peaked around 435 nm. The investigation results suggest that localized defects and excess S atoms existing in the CdS nanowires are responsible for this blue luminescence.
Enhancement of the Spectral Width of High-Power 1.5 μm Integrated Superluminescent Light Source by Quantum Well Intermixing Process
XU Cheng-Dong, DU Guo-Tong, SONG Jun-Feng, HUANG Yong-Zhen
Chin. Phys. Lett. 2004, 21 (5): 963-965 .  
Abstract   PDF(pc) (464KB) ( 504 )
A novel type of integrated InGaAsP superluminescent light source was fabricated based on the tilted ridge-waveguide structure with selective-area quantum well (QW) intermixing. The bandgap structure along the length of the device was modified by impurity free vacancy diffusion QW intermixing. The spectral width was broadened from the 16 nm of the normal devices to 37 nm of the QW intermixing enhanced devices at the same output power level. High superluminescent power (210 mW) was obtained under pulsed conditions with a spectral width of 37 nm.

Formation of Co3O4 Nanotubes and the Magnetic Behaviour at Low Temperature
LI Tao, YANG Shao-Guang, HUANG Li-Sheng, GU Ben-Xi, DU You-Wei
Chin. Phys. Lett. 2004, 21 (5): 966-969 .  
Abstract   PDF(pc) (479KB) ( 689 )
Tubular Co3O4 nanostructures were prepared from cobalt nanowires embedded in an anodic alumina template. The morphologies of nanowires/nanotubes were studied by transmission electron microscopy, and x-ray diffraction was used in the analysis of the nanostructures and phases. A possible formation mechanism of the process from nanowires to nanotubes is discussed. The vibrating sample magnetometer measurements show anomalous magnetic behaviour of the cobalt oxide nanotubes at low temperature.

Growth of a-Plane GaN Films on r-Plane Sapphire Substrates by Metalorganic Chemical Vapour Deposition
LI Dong-Sheng, CHEN Hong, YU Hong-Bo, ZHENG Xin-He, HUANG Qi, ZHOU Jun-Ming
Chin. Phys. Lett. 2004, 21 (5): 970-971 .  
Abstract   PDF(pc) (237KB) ( 659 )
Nonpolar a-plane GaN films were grown on r-plane sapphire substrates by metalorganic chemical vapour deposition (MOCVD) under various conditions. The surface morphologies of epitaxial films are studied by atomic force microscopy. The pit density and size both decrease with the increasing growth temperature, decreasing growth pressure or V/III ratio, while the roughness of the surface increases. Formation mechanisms of the pits in the films are discussed.
Dynamics of Aggregate Growth Through Monomer Birth and Death
KE Jian-Hong, LIN Zhen-Quan
Chin. Phys. Lett. 2004, 21 (5): 972-975 .  
Abstract   PDF(pc) (218KB) ( 748 )
We investigate the kinetic behaviour of the growth of aggregates through monomer birth and death and propose a simple model with the rate kernels K(k) ∝ ku and K'(k) ∝ kv at which the aggregate Ak of size k respectively yields and loses a monomer. For the symmetrical system with K(k) = K'(k), the aggregate size distribution approaches the conventional scaling form in the case of u < 2, while the system may undergo a gelation-like transition in the u > 2 case. Moreover, the typical aggregate size S(t) grows as t1/(2-u) in the u < 2 case and increases exponentially with time in the u = 2 case. We also investigate several solvable systems with asymmetrical rate kernels and find that the scaling of the aggregate size distribution may break down in most cases.
Single-Mode Behaviour Judgment of Optical Waveguides by Imaginary-Distance Beam Propagation Method Under Perfectly Matched Layer Boundary Condition
LI Yan-Ping, YU Jin-Zhong, XIA Jin-Song, Chen Shao-Wu
Chin. Phys. Lett. 2004, 21 (5): 976-979 .  
Abstract   PDF(pc) (409KB) ( 405 )
Imaginary-distance beam propagation method under the perfectly matched layer boundary condition is applied to judge single-mode behaviour of optical waveguides, for the first time to our knowledge. A new kind of silicon-on-insulator-based rib structures with half-circle cross-section is presented. The single-mode behaviour of this kind of waveguide with radius 2 μm is investigated by this method. It is single-mode when the slab height is not smaller than the radius.
Effect of a New Eliassen-Palm Flux on Barotropic Basic Flow
RAN Ling-Kun, GAO Shou-Ting, LEI Ting
Chin. Phys. Lett. 2004, 21 (5): 980-982 .  
Abstract   PDF(pc) (190KB) ( 421 )
We investigate the interaction of eddy and barotropic basic flow in virtue of a new Eliassen-Palm (EP) flux, without introducing residual meridional circulation, by using a multi-scale method. The results show that the evolution of the zonally symmetric barotropic basic flow is completely dominated by the new zonal-averaged EP flux divergence.
61 articles