#### Current Issue

Volume 22 Issue 8
Online Date:
Original Articles
 Select Darboux Transformations to (2+1)-Dimensional Lattice Systems CHEN Jin-Bing, ZHU Jun-Yi, GENG Xian-Guo Chin. Phys. Lett. 2005, 22 (8): 1825-1828 .   Abstract   PDF(pc) (203KB) ( 557 ) Two (2+1)-dimensional (3D) lattice systems are proposed in view of the compatibility of 2D lattice systems in the same hierarchy. Furthermore, the Darboux transformation (DT) method is generalized to the case of 3D lattice equations. As a consequence, some exact solutions for the resulting discrete systems are presented.
 Select Ground-State Entanglement and Mixture in an XXZ Spin Chain WANG Cheng-Zhi, LI Chun-Xian, GUO Guang-Can Chin. Phys. Lett. 2005, 22 (8): 1829-1832 .   Abstract   PDF(pc) (236KB) ( 514 ) We study the pairwise entanglement and mixture of a three-qubit XXZ spin chain in the ground state in the presence of an external magnetic field B. The effects of the magnetic field, the anisotropy and the temperature on the entanglement and mixture are considered, and entanglement versus the mixture of all the two-spin states is investigated. We find that the maximal entangled mixed state can be obtained in the considered system by controlling the magnetic field. Our results provide another way to generate maximally entangled mixed states.
 Select Quantum Decoherence for Multi-Photon Entangled States SUN Yan-Hua, ZHU Xia, KUANG Le-Man Chin. Phys. Lett. 2005, 22 (8): 1833-1837 .   Abstract   PDF(pc) (714KB) ( 657 ) We investigate quantum decoherence of the multi-photon entangled state |ψN m> =Nm[cosγ|N-m>1|m>2 +eiθmsinγ|m>1|N-m>2]. When the entangled channel |ψN m> is embedded in an environment, the channel decoheres and becomes a mixed state governed by a master equation. We calculate the linear entropy and the relative entropy of entanglement, which describe the mixedness and the amount of entanglement for the mixed state, respectively. We show that quantum decoherence weakens the amount of entanglement and enhances the mixedness with the time evolution. It is indicated that the relative entropy of entanglement depends on not only the initial entanglement angle and the decohering parameter, but also the number of photons in each mode. In particular, we find that the decohering speed depends on the number-difference of photons in the two modes. The larger the number-difference of photons is, the higher the decohering speed.
 Select Dynamical Behaviour of a Modulated Torsion Pendulum in Test of Weak Equivalence Principle YUE Ying, FAN Shu-Hua, LIU Lin-Xia, LUO Jun Chin. Phys. Lett. 2005, 22 (8): 1837-1840 .   Abstract   PDF(pc) (215KB) ( 475 ) The dynamic behaviour of a modulated torsion pendulum used to test the weak equivalence principle (WEP) is studied in detail. Theoretical analysis shows that the pendulum will be driven by a force with double-frequency of the rotating turntable no matter whether the WEP is valid or not. This double-frequency effect should be considered for improving the sensitivity of the modulated pendulum in test of the WEP.
 Select Microscopic Phase-Field Simulation of Atom Substitution Behaviour in Ni--Cr--Al Alloy CHU Zhong, CHEN Zheng, WANG Yong-Xin, LU Yan-Li, ZHANG Jian-Jun Chin. Phys. Lett. 2005, 22 (8): 1841-1844 .   Abstract   PDF(pc) (352KB) ( 515 ) Simulations are performed on atom substitution behaviour in Ni75Al25-xCrx alloys based on a microscopic phase-field model at 873K. The ordering of both the Al and Cr atoms takes place simultaneously, Cr occupies both the Al and Ni sites with a preference for the Al sites, and Cr and Al atoms together occupy the β -sites, and the complex γ’ Ni3(Al1-xCrx) (L12 structure) phases are formed during the precipitation. At the ordering boundary of L12 phases, Cr atoms occupy the Al sites, then Ni3Cr phases are formed.
 Select Ballistic Diffusion of a Charged Particle in a Blackbody Radiation Field BAO Jing-Dong, BAI Zhan-Wu Chin. Phys. Lett. 2005, 22 (8): 1845-1847 .   Abstract   PDF(pc) (216KB) ( 603 ) The generalized Langevin equation is used to describe the motion of a charged particle interacting with a blackbody radiation field via dipole coupling. The exact expressions for the mean-square displacement and velocity of such a particle are obtained, which show a ballistic diffusion and a modified Kubo fluctuation--dissipation relation. In particular, a velocity-dependent coupling or force can induce this novel phenomenon.
 Select Universal Form of Renormalizable Knots in Symbolic Dynamics GAO Wen, PENG Shou-Li Chin. Phys. Lett. 2005, 22 (8): 1848-1851 .   Abstract   PDF(pc) (234KB) ( 660 ) The knot structure of three-dimensional flow has been constructed based on minimal braid assumption [Chin. Phys. Lett. 20(2003)1444]. Here we provide a new universal form of renormalizable knots. From this universal form an arbitrary renormalizable knot can be decomposed into a unique set of elementary templates.
 Select A Noise Cleaning Method for Chaotic Time Series and Its Application in Communication FENG Jiu-Chao Chin. Phys. Lett. 2005, 22 (8): 1851-1854 .   Abstract   PDF(pc) (305KB) ( 670 ) A new algorithm for filtering highly noisy contaminated chaotic time series is proposed and realized. It is indicated by computer simulation that this algorithm can effectively reduce noise on chaotic signal no mater how parameter of chaos generator varies with time. In comparison with the extended-Kalman-filter-based method, this algorithm has a better filtering performance in the case of low signal-to-noise (SNR) ratios, and has the similar performance in the case of high SNR. In addition, a chaotic modulation communication system is also used to evaluate the performance of the algorithm, the result shows the effectiveness of the method.
 Select Soliton Solutions in Bose--Einstein Condensates with Time-Dependent Atomic Scattering Length in an Expulsive Parabolic Potential ZHANG Jie-Fang, YANG Qin Chin. Phys. Lett. 2005, 22 (8): 1855-1857 .   Abstract   PDF(pc) (293KB) ( 674 ) We present both the bright and dark solitons of Bose--Einstein condensates with a time-dependent atomic scattering length in an expulsive parabolic potential. As a discussed example, we select the experimental parameter, i.e. the Feshbach-managed nonlinear coefficient reading a(t)=g0exp(λt), and obtain the results which can be recovered in the literature [Phys. Rev. Lett. 94(2005)050402].
 Select Euler--Lagrange Forms and Cohomology Groups on Jet Bundles CHEN Jing-Bo Chin. Phys. Lett. 2005, 22 (8): 1858-1861 .   Abstract   PDF(pc) (195KB) ( 402 ) Using the language of jet bundles, we generalize the definitions of Euler--Lagrange one-form and the associated cohomology which were introduced by Guo et al. [Commun. Theor. Phys. 37(2002)1]. Continuous and discrete Lagrange mechanics and field theory are presented. Higher order Euler--Lagrange cohomology groups are also introduced.
 Select Energy Density and Production Ratios of Baryon from QGP with Diquarks MA Zhong-Biao, GAO Chong-Shou, Chin. Phys. Lett. 2005, 22 (8): 1862-1865 .   Abstract   PDF(pc) (239KB) ( 480 ) At a very high temperature, the quark matter is a hot and dense matter under the colour deconfinement condition, and quarks can coalescent diquarks. Energy density of this system is figured out. A way to calculate baryon ratios produced from quark gluon plasma with diquarks in relativistic heavy ion collisions is presented.
 Select Improved Quark Mass Density-Dependent Model with Non-Linear Scalar Interaction WU Chen, QIAN Wei-Liang, SU Ru-Keng, Chin. Phys. Lett. 2005, 22 (8): 1866-1869 .   Abstract   PDF(pc) (233KB) ( 582 ) We present an improved quark mass density-dependent model which includes the quark and non-linear scalar field coupling. The wavefunction of quark is given. The rms charge radius, the magnetic moment, and the ratio between the axial-vector and the vector β-decay coupling constants of the nucleon are calculated. We find that the results given the present model are in agreement with experiments.
 Select Radius of 9C from the Asymptotic Normalization Coefficient LI Zhi-Hong, GUO Bing, LIU Wei-Ping, BAI Xi-Xiang, LIAN Gang, SU Jun, YAN Sheng-Quan, WANG Bao-Xiang, ZENG Sheng Chin. Phys. Lett. 2005, 22 (8): 1870-1872 .   Abstract   PDF(pc) (229KB) ( 487 ) The asymptotic normalization coefficient (ANC) of 9C = 8B+p deduced from 8Li(d,p)9Li reaction is used to obtain the root-mean-square (rms) radius of the loosely bound proton in the 9C ground state. We obtain (r2)1/2 = 3.61fm for the valence proton, which is significantly larger than the matter radius of 9C. The probability of the valence proton outside the matter radius of 9C is greater than 60%. The present work supports the conclusion that 9C has a proton halo structure.
 Select High-Spin States in Odd--Odd 140Pr Nucleus YU Hai-Ping, GOU Ying-Xiang, ZHOU Xiao-Hong, ZHANG Yu-Hu, LEI Xiang-Guo, LUO Peng, LIU Min-Liang, SONG Li-Tao, WANG Hua-Lei, XIE Cheng-Ying, ZHENG Yong, GUO Wen-Tao, ZHU Li-Hua, WU Xiao-Guang Chin. Phys. Lett. 2005, 22 (8): 1873-1876 .   Abstract   PDF(pc) (270KB) ( 404 ) High-spin level structure of doubly odd nucleus 140Pr has been investigated via the 130Te(14N,4n)140Pr reaction at beam energies from 55 to 65MeV. Measurements of γ-ray excitation functions, γ-ray singles and γ-γ-t coincidences were performed with twelve BGO(AC)HPGe detectors. The level scheme of 140Pr, including 27 new levels and 42 new γ rays, has been established for the first time. The level structure is compared with those in the neighbouring odd--odd nuclei, and interpreted qualitatively.
 Select Dynamical Structure of Nuclear Excitation in Continuum ZHANG Chun-Lei, ZHANG Huan-Qiao, ZHANG Xi-Zhen Chin. Phys. Lett. 2005, 22 (8): 1877-1879 .   Abstract   PDF(pc) (265KB) ( 480 ) Dynamical structures of collective excitation in continuum are studied by calculating the isoscalar and isovector strength as well as transition density of nuclei near the drip-line such as 28O and 34Ca. It is found that for some excited states in continuum the proton and neutron transition density calculated from isoscalar and isovector excitation at some given energies may be different, which will affect the calculation of the polarization for nuclei with N≠Z.
 Select Oscillation of Hot Fissioning Nuclei around a Saddle Point BAO Jing-Dong, Lü Kun, LIU Ling, JIA Ying Chin. Phys. Lett. 2005, 22 (8): 1880-1883 .   Abstract   PDF(pc) (245KB) ( 390 ) Three time scales of a fissioning nucleus starting from the ground state to the scission point are defined and calculated by the Monte Carlo method. The result shows that the time of oscillating around the saddle point is longer than both the mean first passage time from the ground state to the saddle point and the time of descent from the saddle to scission points. Thus it is suggested that more neutrons could be emitted from a hot heavy fissioning nucleus during the period of the stretching and contracting of the deformation process.
 Select Relativistic Multichannel Treatment of Krypton Spectra across the First Ionization Threshold QU Yi-Zhi, PENG Yong-Lun Chin. Phys. Lett. 2005, 22 (8): 1884-1886 .   Abstract   PDF(pc) (205KB) ( 620 ) The relativistic multichannel theory has been extended to calculate both the eigen quantum defects μα, transformation matrix Uiα, and the eigen dipole matrix elements Dα of krypton. The Rydberg and autoionization spectra of krypton across the first ionization threshold are calculated within the framework of multichannel quantum defect theory. Our calculated spectra are in agreement with the absolute measurement data.
 Select A Novel Electrostatic Guiding Scheme for Cold Polar Molecules in Weak-Field-Seeking States DENG Lian-Zhong, XIA Yong, YIN Jian-Ping Chin. Phys. Lett. 2005, 22 (8): 1887-1890 .   Abstract   PDF(pc) (278KB) ( 846 ) We propose a novel electrostatic guiding scheme for cold polar molecules in weak-field-seeking states using a single charged wire half embanked in a ceramic substrate (i.e., a chip) and a homogeneous bias electric field, which is produced by a capacitor composed of two large parallel metal plates. We calculate the spatial distribution of the electrostatic fields generated by the combination of the charged wire and the plate capacitor and the corresponding trapping potentials for CO molecules, and analyse the relationships between the electric field and the parameters of the charged-wire layout. Our study shows that the proposed scheme with a single charged-wire can be used to guide cold polar molecules in the weak-field-seeking states, and has some potential applications in construction of various molecule-optical elements.
 Select Charge State Evolution of Uranium in Electron Beam Ion Trap LIU Ya-Feng, YAO Ke, Roger Hutton, ZOU Ya-Ming, Chin. Phys. Lett. 2005, 22 (8): 1891-1894 .   Abstract   PDF(pc) (313KB) ( 445 ) We present a calculation scheme with significant modifications and improvements for determining the ionization balance and the ion temperature evolution in an electron beam ion trap (EBIT). The scheme is applied to uranium and nitrogen ions using a specific set of EBIT operating parameters. The calculation results are compared to the experimental data. Rates for the individual atomic processes in EBIT, especially single and multiple charge exchange processes, are discussed. The time evolution of the ion temperatures for uranium and its coolant nitrogen are also given.
 Select Optical Potential Calculations of Positron--H2 Elastic Collision LIU Ling, CHI Bao-Qian, ZHOU Ya-Jun Chin. Phys. Lett. 2005, 22 (8): 1895-1897 .   Abstract   PDF(pc) (209KB) ( 375 ) We report the calculations of the elastic scattering differential cross section for positron--H2 collisions with the impact energy below the positronium formation threshold. Our calculation is based on the static-exchange-optical model which has obtained great success in the case of electron scattering. The effective potential used here includes the static and optical potentials. The optical method can completely include the second-order effect arising from real and virtual excitation of target states, which is important for the scattering. A comparison is made with the available theoretical calculations.
 Select Nonresonant Saturation Absorption in Electrostatic Self-Assembly Films Containing Methanofullerene ZHANG Xue-Ru, OUYANG Qiu-Yun, WANG Yu-Xiao, JIANG Li, SONG Ying-Lin, LI Yu-Liang, WEI Tai-Huei Chin. Phys. Lett. 2005, 22 (8): 1898-1901 .   Abstract   PDF(pc) (239KB) ( 499 ) Ultrathin films containing methaofullerene are prepared by electrostatic layer-by-layer self-assembly of a positively charged trifluoroacetic acid salt of monoamino-substituted methanofullerene (TMAF) derivative and a negatively charged poly (sodium 4-styrenesulfonate) (PSS). Absorptive optical nonlinearities of 30 bilayer TMAF/PSS films and TMAF in water solution are measured using the Z-scan technique at 532nm. Nonresonant saturation absorption is observed in the film sample, whereas reverse saturation absorption was for TMAF in water. The saturation-absorption behaviour is interpreted by a special formula. The saturation intensity is extracted to be 15.2±0.8MW/cm2. The mechanism of saturation absorption in the TMAF/PSS film is discussed.
 Select Intensity Tuning Characters of Frequency Split Lasers ZONG Xiao-Bin, LIU Wei-Xin, ZHANG Shu-Lian Chin. Phys. Lett. 2005, 22 (8): 1906-1908 .   Abstract   PDF(pc) (213KB) ( 689 ) Laser frequency splitting generated by intracavity birefringence elements has been applied widely, but tuning characters of such lasers have not been successfully studied quantitatively. Based on the vectorial extension of Lamb's semi-classical theory, we study the intensity tuning of frequency splitting of He--Ne lasers. It is found that the intensity tuning curve is affected obviously by the compositive ratio of isotopes in the gain medium and the frequency difference of splitting modes. The threshold of locking is also quantitatively obtained. All the calculations are consistent with the experimental results.
 Select Multiple Scattering Effects of Ag Particles in Random Ag--SiN film ZHU Ruo-Jian, WANG Jia, OU Ding-Rong, ZHU Jing, JIN Guo-Fan Chin. Phys. Lett. 2005, 22 (8): 1906-1905 .   Abstract   PDF(pc) (663KB) ( 861 ) A layer of 40nm-thick Ag--SiN film with Ag nano-particles embedded and distributed randomly in the SiN thin film were deposited by the method of radiant-frequency magnetron sputtering. Specimens orderly comprising a random Ag--SiN film and an optical phase change recording layer were exposed to a focused laser beam with wavelength of 690nm. It is shown that, with a random Ag--SiN layer deposited above the recording layer. Calculation by the finite difference time domain method of a 40nm-thick SiN film under a Gaussian beam irradiation has been carried out to simulate the near-field distribution in the film, which showed a huge local near-field intensity enhancement of about 200 times if small Ag particles with diameter of 6nm were modelled in the SiN film in the central region of the incident laser spot.
 Select Spectral Optical Coherence Tomography Using Two-Phase Shifting Method MA Zhen-He, Ruikang K. Wang, ZHANG Fan, YAO Jian-Quan Chin. Phys. Lett. 2005, 22 (8): 1909-1912 .   Abstract   PDF(pc) (394KB) ( 398 ) A two-phase shifting method is introduced to eliminate the strong autocorrelation noise inherent in spectral optical coherence tomography and to mitigate the unwanted auto- and cross-coherent terms introduced by the reflections from various optical interfaces present in the system. Furthermore, this method is also able to amplify the desired signal by a factor of 2. The feasibility of such a method is demonstrated using a mirror-like object. An intact porcine cornea tissue in vitro is also used to show the potential of this method for biological imaging.
 Select High-Order Harmonic Generation by Two Non-Collinear Femtosecond Laser Pulses in CO WANG Run-Hai, JIANG Hong-Bing, YANG Hong, WU Cheng-Yin, GONG Qi-Huang Chin. Phys. Lett. 2005, 22 (8): 1913-1915 .   Abstract   PDF(pc) (185KB) ( 1011 ) We have experimentally studied the high order harmonic generation (HHG) in CO molecules by two femtosecond laser pulses using a pump--probe technique. The delay time between two pulses is longer than the pulse duration, and the pump intensity is about 6.2×1014 W/cm2. It is found that the HHG signal is independent of the time delay in the picosecond region, but it is dependent on the distance between the centres of focuses of the two beams. The phase modulation induced by the pump pulse is regarded to be responsible for this.
 Select Phase Determination Method to Directly Measure Intensity and Frequency of Temporal Profiles of Attosecond EUV Pulses GE Yu-Cheng Chin. Phys. Lett. 2005, 22 (8): 1916-1919 .   Abstract   PDF(pc) (276KB) ( 450 ) A new method of phase determination is presented to directly measure the intensity and frequency temporal profiles of attosecond EUV pulses. The profiles can be reconstructed from the photoelectron energy spectra measured with two different laser intensities at 0°and 180° with respect to the linear laser polarization using a cross correlation between the femtosecond laser and the attosecond EUV. The method has a temporal measurement range from a quarter to about half of a laser oscillation period. The time resolution depends on the jitter and control precision of laser and EUV pulses. This method improves the time resolution in measuring attosecond EUV pulses.
 Select Continuous and Widely Wavelength-Tunable Optical Short Pulse Generation by Use of a Self-Seeded Fabry-Pérot Laser Diode FANG Xiao-Hui, CHEN Jin-Hua, WANG Dong-Ning, JIN Wei, TONG Fu-Wua Chin. Phys. Lett. 2005, 22 (8): 1920-1922 .   Abstract   PDF(pc) (209KB) ( 597 ) We present a system to produce continuous and widely wavelength-tunable optical short pulses by use of a self-seeded Fabry-Pérot laser diode. The system exhibits a good sidemode suppression ratio of greater than 37dB over a large wavelength tuning range of 48nm. The system is also easy to operate and is convenient for continuous wavelength tuning.
 Select Flat Supercontinuum Generated in a Single-Mode Optical Fibre with a New Chromatic Dispersion Profile XU Yong-Zhao, REN Xiao-Min, ZHANG Xia, HUANG Yong-Qing, XU Wen-Cheng Chin. Phys. Lett. 2005, 22 (8): 1923-1926 .   Abstract   PDF(pc) (248KB) ( 647 ) A new chromatic dispersion profile of a single-mode optical fibre is proposed for generating a supercontinuum with a flatly broadened spectrum. The chromatic dispersion D(λ,z) is a convex function of wavelengths and has no zero-dispersion wavelengths over the whole part of the fibre as D(λ,z) is negative. It is shown that the flat supercontinuum spectrum is obtained when the pump wavelength is set in the vicinity of the wavelength at which the peak chromatic dispersion is near zero and the strong residual pump component is eliminated.
 Select Optimal Design of Dual-Pump Fibre-Optical Parametric Amplifiers with Dispersion Fluctuations Based on Hybrid Genetic Algorithm LIU Xue-Ming, LI Yan-He Chin. Phys. Lett. 2005, 22 (8): 1927-1929 .   Abstract   PDF(pc) (245KB) ( 437 ) Solutions of dual-pump fibre-optical parametric amplifiers (DP-FOPAs) with dispersion fluctuations are derived by using a matrix operator. Based on these solutions and a hybrid genetic algorithm, we have optimized three-section DP-FOPAs to increase the signal band and improve the gain uniformity. The optimizations demonstrate that when dispersion fluctuations are taken into account, the 44-nm signal band with the 0.37-dB ripple and over 14.8-dB gain can be obtained from the three-section DP-FOPA, instead of the lowest gain of ～13dB with the ripple of more than 15dB from the single-section DP-FOPA.
 Select Abnormal Modulation of Dielectric Band Transmittance of Polystyrene Opal HU Xiao-Yong, GONG Qi-Huang, CHENG Bing-Ying, ZHANG Dao-Zhong Chin. Phys. Lett. 2005, 22 (8): 1930-1933 .   Abstract   PDF(pc) (283KB) ( 453 ) The abnormal transmittance in the dielectric band edge of a polystyrene opal is observed and analysed. The transmittance is periodically modulated and the period of modulation varies with the wavelength, which destroys the perfect structure of the photonic band gap. The transmittance modulation originates from the propagation of the low order whispering-gallery mode excited in polystyrene spheres. These results indicate that the whispering-gallery mode has a great influence on practical applications of polystyrene opal.
 Select A Y-Branch Photonic Crystal Slab Waveguide with an Ultrashort Interport Interval HAN Shou-Zhen, TIAN Jie, REN Cheng, XU Xing-Sheng, LI Zhi-Yuan, CHENG Bing-Ying, ZHANG Dao-Zhong Chin. Phys. Lett. 2005, 22 (8): 1934-1936 .   Abstract   PDF(pc) (451KB) ( 816 ) We fabricated two-dimensional photonic crystal slab Y-branch waveguides with different intervals between the two output ports and measured their light guiding characteristics. The field intensity distributions of the TE polarized wave modes are also calculated by means of a transfer matrix method. Both the theoretical and experimental results show that the minimum interval between the two output ports is about 1.4 times the transport wavelength of 1.55μm. If the interval becomes smaller, light waves in the two branches will couple each other seriously. The result will be helpful for designs of ultracompact wave demultiplexers and all-optical integrated circuits.
 Select Bessel-Modal Method for Finite-Height Two-Dimensional Photonic Crystal SHI Jun-Feng, HUANG Sheng-Ye, WANG Dong-Sheng Chin. Phys. Lett. 2005, 22 (8): 1937-1940 .   Abstract   PDF(pc) (253KB) ( 824 ) By applying the dyadic Green function, the dispersion relation of two-dimensional photonic crystal can be expressed as the cylindrical wave expansions of eigenmodes. With the aid of Green’s theorem, the plane-wave coefficients of eigenmodes are reconstructed and employed to formulate the scattering matrix of finite-height two-dimensional photonic crystal. These operations make the convergence rate very rapid, and reduce the dimension of the scattering matrix. As a demonstration, we present the transmission and electromagnetic field distributions for an InGaAsIn photonic crystal, and investigate their convergence.
 Select Complete Band-Gap in Two-Dimensional Quasiperiod Photonic Crystals with Hollow Cylinders FENG Zhi-Fang, FENG Shuai, REN Kun, LI Zhi-Yuan, CHENG Bing-Ying, ZHANG Dao-Zhong Chin. Phys. Lett. 2005, 22 (8): 1941-1943 .   Abstract   PDF(pc) (395KB) ( 675 ) The transmission properties of quasiperiodic photonic crystals (QPCs) based on the random square-triangle tiling system are investigated by the multiple scattering method. The hollow cylinders are introduced in our calculation. It is found that QPCs with hollow cylinders also possess a complete band gap common to s- and p-polarized waves when the inner radius of hollow cylinders is larger than a certain value. The QPCs possessing the complete band gap can be applied to the fields of light emitting, wave-guides, optical filters, high-Q resonators and antennas.
 Select Performance of a 10-Gbit/s Transmission System over 1500km G.652 Fibre Compensated by Cascaded Narrow-Band Chirped Fibre Bragg Gratings LIU Yan, CHEN Yong, TAN Zhong-Wei, CAO Ji-Hong, ZHENG Kai, NING Ti-Gang, CHEN Ting, DONG Xiao-Wei, JIAN Shui-Sheng Chin. Phys. Lett. 2005, 22 (8): 1944-1947 .   Abstract   PDF(pc) (415KB) ( 652 ) We obtain the error-free transmission of an 8×10Gb/s signal over a 1500km G.652 fibre by means of significantly improving the quality of narrow-band chirped fibre Bragg gratings (FBGs). Asymmetric apodization is one of the powerful measures to improve the quality of gratings. Wavelength-dependent transmission performance is also observed. The experimental results indicate that the total in-band local dispersion deviation of the cascaded gratings in each channel could be a good indicator of the performance degradation tendency at different operating wavelengths, which further reveals the potential of local dispersion deviation as a performance evaluating indicator of chirped FBGs.
 Select Improvement of Amplitude-Shift-Keying Signal Quality by Employing an Effective Spectrum Equalization Method in a Combined FSK/ASK Modulation Scheme XIN Xiang-Jun, P. S. André, A. L. J. Teixeira, YU Chong-Xiu, Ana Ferreira, Tiago Silveira, P. M. Monteiro, F. da Rocha, J. L. Pinto, Chin. Phys. Lett. 2005, 22 (8): 1948-1950 .   Abstract   PDF(pc) (644KB) ( 836 ) A simple, economical and applicable spectrum equalization method is implemented by employing a reshaping filter in the combined frequency-shift-keying/amplitude-shift-keying modulation scheme to improve the quality of amplitude-shift-keying optical signal. The 3-dB improvement for eye diagram height is experimentally demonstrated.
 Select Spectral Characteristics of Mechanically Induced Long-Period Fibre Gratings by New Double-Layer Grating Templates WANG Xin-Wei, ZHANG Zhen-Yu, ZHUANG Huai-Xuan, SHENG Qiu-Qin Chin. Phys. Lett. 2005, 22 (8): 1951-1954 .   Abstract   PDF(pc) (409KB) ( 598 ) We design a new double-layer grating template, which has the advantages of period uniformity, period number adjustability and continuous period regulation. By studying the transmission spectrum under the new template, we also find some new characteristics different from traditional fibre gratings: the resonant wavelength is mainly determined by the grating period; the intensity of transmission peak loss lies in the external pressures; the bandwidth of transmission spectrum can be controlled by the period number. Therefore, various applications can be realized by optimizing the transmission spectrum by reasonably selecting the matched parameters.
 Select Fabrication of 32×32 Arrayed Waveguide Grating Using Fluorinated Polymers ZHANG Xi-Zhen, WANG Fei, ZHANG Hai-Ming, ZHANG Da-Ming, SUN Wei Chin. Phys. Lett. 2005, 22 (8): 1955-1957 .   Abstract   PDF(pc) (284KB) ( 918 ) We investigate the optical properties of ZIP49 and ZIP51. The thickness and the refractive index of the polymer film are measured using an ellipsometer to be from 2μm to 10μm and from 1.49 to 1.51, respectively. A 32×32 arrayed waveguide grating is fabricated using the reactive ion etching technique. The curing temperature is increased to 270°C in nitrogen atmosphere. The etching rate is about 0.067μm/min. Using re-solution technique, the surface roughness of polymer film was reduced to less than 0.4nm after spin coating. The insertion loss of the arrayed waveguide grating is about 10dB and the crosstalk is about -20dB.
 Select Experimental and Theoretical Research on the Vibrational Gaps in Two-Dimensional Three-Component Composite Thin Plates YU Dian-Long, LIU Yao-Zong, QIU Jing, ZHAO Hong-Gang, LIU Zhi-Ming, Chin. Phys. Lett. 2005, 22 (8): 1958-1960 .   Abstract   PDF(pc) (263KB) ( 584 ) We investigate the vibrational band gaps in a thin plate of two-dimensional phononic crystals with the locally resonant structure in theory and experiment. The experimental sample is optimized based on the simple analytical model. The experimental results are in good agreement with the theoretical calculation by the finite element method. The findings will be significant for applications of phononic crystals in the field of vibration isolation.
 Select Experimental Observation of Kink in a Perfect Bidimensional Granular System ZHANG Peng, MIAO Guo-Qing, HUANG Kai, YUN Yi, WEI Rong-Jue Chin. Phys. Lett. 2005, 22 (8): 1961-1963 .   Abstract   PDF(pc) (523KB) ( 700 ) The kink formation in a vertical vibrated granular layer has been widely studied in three-dimensional systems, but there are few if any experimental reports on bidimensional granular layers. We report the kink formation newly found in a perfect bidimensional granular system. We measure the range of the driving frequencies and dimensionless accelerations for kinks. Furthermore, we observe a heaping process, which is caused by co-operative action of the kink-associated convection and the sidewall-associated convection.
 Select A Global Stability Analysis of the Wake behind a Rotating Circular Cylinder MA Dong-Jun, SUN De-Jun, YIN Xie-Yuan Chin. Phys. Lett. 2005, 22 (8): 1964-1967 .   Abstract   PDF(pc) (209KB) ( 1004 ) A new high resolution approach based on spectral element method is proposed to analyse the complex global stability for the non-parallel flow passing a rotating and translating circular cylinder. The studies presented here predict the variation of Strouhal number St as the spin parameter α increases from 0.0 to 1.4, for the Reynolds number Re=60. The direct numerical simulation shows a small increase of vortex shedding frequency at α<1.1, and a slight decrease as α approaches the critical spin parameter α=1.37. The trend of variation of eigen-frequency with α obtained by linear stability analysis is opposite to those obtained by direct numerical simulation for Re=60, although they achieve the same frequency at the onset of vortex shedding.
 Select Detecting Multi-Scale Coherent Eddy Structures and Intermittency in Turbulent Boundary Layer by Wavelet Analysis JIANG Nan, ZHANG Jin Chin. Phys. Lett. 2005, 22 (8): 1968-1971 .   Abstract   PDF(pc) (300KB) ( 522 ) Multi-scale decomposition by wavelet transform has been performed to velocity time sequences obtained by fine measurements of turbulent boundary layer flow. A conditional sampling technique for detecting multi-scale coherent eddy structures in turbulent field is proposed by using multi-scale instantaneous intensity factor and flatness factor of wavelet coefficients. Although the number of coherent eddy structures in the turbulent boundary layer is very small, their energy percentage with respect to the turbulence kinetic energy is high. Especially in buffer layer, the energy percentages of coherent structures are significantly higher than those in the logarithmic layer, indicating that the buffer layer is the most active region in the turbulent boundary layer. These multi-scale coherent eddy structures share some common dynamical characteristics and are responsible for the anomalous scaling law in the turbulent boundary layer.
 Select X-Ray Emission Spectra of Ni-Like Gold Ions under Coronal Plasma Condition ZENG Jiao-Long, ZHAO Gang, YUAN Jian-Min, Chin. Phys. Lett. 2005, 22 (8): 1972-1975 .   Abstract   PDF(pc) (223KB) ( 533 ) The strong x-ray line emission of n=4→n=3 and n=5→n=3 transitions of Ni-like Au has been investigated under a coronal plasma condition. A complete set of atomic data, including energy level, transition probability and collision strength, has been obtained to simulate the emission spectra. Under a typical coronal equilibrium (electron temperature of 2500eV and density of 1.0×1015), the predicted strongest line is due to the transition of (3d3/2-14f5/2)1 → (3d10)0. Extensive studies show that the relative intensity is insensitive to temperature and density over a wide plasma condition.
 Select Effect of Guiding Magnetic Field on Weibel Instability LI Ji-Wei, PEI Wen-Bing Chin. Phys. Lett. 2005, 22 (8): 1976-1979 .   Abstract   PDF(pc) (264KB) ( 910 ) We derive a linear dispersion relation in the presence of a constant uniform guiding magnetic field parallel to the beam velocity direction, which shows a strong background magnetic field suppresses or even stabilizes the Weibel instability produced by two counter streams in electron-ion plasmas. The simulation results are in good agreement with the analytical ones. Also observed in the simulations are the suppression of electrostatic field, a higher level of saturation of self-generated magnetic field, and the apparent difference in phase space compared with those in the absence of guiding magnetic field.
 Select A Novel Atmospheric Pressure Plasma Fluidized Bed and Its Application in Mutation of Plant Seeds CHEN Guang-Liang, FAN Song-Hua, LI Chun-Ling, GU Wei-Chao, FENG Wen-Ran, ZHANG Gu-Ling, WANG Jiu-Li, Latif K, ZHANG Shu-Gen, WANG Zhen-Quan, HAN Er-Li, FU Ya-Bo, YANG Si-Ze Chin. Phys. Lett. 2005, 22 (8): 1980-1983 .   Abstract   PDF(pc) (877KB) ( 843 ) An atmospheric pressure plasma fluidized bed (APPFB) is designed to generate plasma using a dielectric barrier discharge (DBD) with one liquid electrode. In the APPFB system, the physical properties of DBD discharge and its application in plant-seed mutating are studied fundamentally. The results show that the generated plasma is a typical glow discharge free from filament and arc plasma, and the macro-temperature of the plasma fluidized bed is nearly at room temperature. There are no obvious changes in the pimientos when their seeds are treated by APPFB, but great changes are found for coxcombs.
 Select A Practical Guide for X-Ray Diffraction Characterization of Ga(Al, In)N Alloys ZHOU Sheng-Qiang, WU Ming-Fang, YAO Shu-De Chin. Phys. Lett. 2005, 22 (8): 1984-1986 .   Abstract   PDF(pc) (227KB) ( 1179 ) Ga(In, Al)N alloys are used as an active layer or cladding layer in light emitting diodes and laser diodes. x-ray diffraction is extensively used to evaluate the crystalline quality, the chemical composition and the residual strain in Ga(Al,In)N thin films, which directly determine the emission wavelength and the device performance. Due to the minor mismatch in lattice parameters between Ga(Al, In)N alloy and a GaN virtual substrate, x-ray diffraction comes to a problem to separate the signal from Ga(Al,In)N alloy and GaN. We give a detailed comparison on different diffraction planes. In order to balance the intensity and peak separation between Ga(Al,In)N alloy and GaN, (0004) and $(10\bar 15)$ planes make the best choice for symmetric scan and asymmetric scan, respectively.
 Select Ab Initio Molecular Dynamics Simulations on Structural Properties of ZHAO Gang, LIU Chang-Song, ZHU Zhen-Gang Chin. Phys. Lett. 2005, 22 (8): 1987-1990 .   Abstract   PDF(pc) (250KB) ( 416 ) Ab initio molecular dynamics simulations on liquid In20Sn80 alloy are carried out at six different temperatures from 798K to 1193K. The temperature dependences of binding energy, volume, pair-correlation function and structure factor are studied. The first-peak position of our calculated pair correlation function is in agreement with the experimental data. A shoulder is reproduced in the high wave number side of the first peak in our calculated structure factor, implying the existence of the residual directional bonds of Sn atoms in liquid In20Sn80 alloy. The first-peak height of our calculated structure factor and the coordination number of Sn atom decrease more sharply in the low-temperature region from 798K to 986K than that in the high-temperature region from 986K to 1193K, suggesting that a discontinuous structural change may occur at around 986K in liquid In20Sn80 alloy.
 Select Structural Characteristics of Liquid Sn WU Ai-Qing, GUO Li-Jun, LIU Chang-Song, ZHU Zhen-Gang Chin. Phys. Lett. 2005, 22 (8): 1991-1993 .   Abstract   PDF(pc) (210KB) ( 922 ) We investigate the structural properties of liquid Sn. With the help of the internal friction (tanФ) method, it is found that a peak appears in the tan Ф-T curve, suggesting that an anomalous discontinuous temperature-induced structure change may take place in liquid Sn. From the experimental data of pair distribution functions, we calculate the viscosity η and the excess entropy S and it is found that there are a peak of viscosity in the η-T curve and a bend of excess entropy in the S-T curve, which give a positive support to the appearance of the internal-friction peak in the tan Ф-T curve.
 Select Migration Enthalpy of Thermal Vacancies by Positron Spectroscopy Emad A. Badawi Chin. Phys. Lett. 2005, 22 (8): 1998-2001 .   Abstract   PDF(pc) (215KB) ( 521 ) The trapping of positrons at vacancy site in some materials provide a new and sensitive method for the equilibrium determination of point defect migration enthalpy. Data are presented for commercial Al--Mg alloys and fitted to a model allowing presentation in the form of Arrhenius plots, hence the migration enthalpy Hivm can be determined by the positron annihilation lifetime technique. The results show that the value of Hivm increases as the concentration of Mg increases.
 Select A Direct Comparison between Static and Dynamic Melting Temperature Determinations below 100GPa SUN Yu-Huai, HUANG Hai-Jun, LIU Fu-Sheng, YANG Mei-Xia, JING Fu-Qian, Chin. Phys. Lett. 2005, 22 (8): 2002-2004 .   Abstract   PDF(pc) (231KB) ( 620 ) A preliminary experiment of sound velocity measurements for porous iron with initial average density of 6.275g/cm3 has been performed at pressures below 100GPa, in order to clarify a long-standing problem that the static melting temperature Tm, mostly below 100GPa due to its technical limitations, is notably lower than the extrapolated melting data inferred from the shock wave experiments made above 200GPa, for the sake of making a direct comparison between the experimental static and dynamic melting temperatures in the same pressure region. With the lately proposed Hugoniot sound velocity data analysis technique [Chin. Phys. Lett. 22 (2005) 863], the results deduced from this Hugoniot sound velocity measurement is Tm=3200K at 87GPa and Tm=3080K at 80GPa, which are in good agreement with the two latest static data of Tm=3510K at 105GPa and Tm=2750K at 58GPa, which utilized modern improved double-side laser heating and in situ accurate x-ray diffraction techniques in experiments. It can be concluded that consensus Tm data would be obtained from static and shock wave experiments in the case that the recently improved techniques are adopted in investigations.
 Select Equation of State of the Fluid He--Ne Binary Mixtures at High Pressures and High Temperatures Chen Qi-Feng, CAI Ling-Cang, JING Fu-Qian, CHEN Dong-Quan Chin. Phys. Lett. 2005, 22 (8): 2005-2008 .   Abstract   PDF(pc) (387KB) ( 767 ) The fluid variational free energy model is applied to calculate the equation of state (EOS) of the fluid (Ne/3,2He/3) mixtures at 296K. The pair potential is used to describe the He--Ne interaction. The calculated EOSs at 296K are compared with the experiments for solid Ne(He)2. The validity of the potential and the calculated model is verified by comparison. The present model is extended to calculate the equation of state of the fluid He--Ne mixtures with different He:Ne compositions in the pressure 0--160GPa and temperature up to 10000K.
 Select Operatorization and Unitary Transformation Approaches to Product Jahn--Teller Problems QIU Qing-Chun Chin. Phys. Lett. 2005, 22 (8): 2009-2011 .   Abstract   PDF(pc) (187KB) ( 404 ) The product Jahn--Teller (JT) system with two doubly-degenerate electronic open shells coupling to a single e-mode is studied using an operatorization approach followed by unitary transformation. It is found that the structure of the adiabatic potential energy surface can give anyone of the two different troughs based on the coupling constants, and the symmetry of the product JT system EoplusE can be decomposed into EoplusA1oplus A2. The present approach is conceptually simple and can be extended to other product JT systems.
 Select Combined Effect of Surface Tension, Gravity and van der Waals Force Induced by a Non-Contact Probe Tip on the Shape of Liquid Surface LIU Nan, BAI Yi-Long, XIA Meng-Fen, KE Fu-Jiu, Chin. Phys. Lett. 2005, 22 (8): 2012-2015 .   Abstract   PDF(pc) (232KB) ( 804 ) Aiming at understanding how a liquid film on a substrate affects the atomic force microscopic image in experiments, we present an analytical representation of the shape of liquid surface under van der Waals interaction induced by a non-contact probe tip. The analytical expression shows good consistence with the corresponding numerical results. According to the expression, we find that the vertical scale of the liquid dome is mainly governed by a combination of van der Waals force, surface tension and probe tip radius, and is weekly related to gravity. However, its horizontal extension is determined by the capillary length.
 Select A 10-GHz Bandwidth Electroabsorption Modulated Laser by Ultra-Low-Pressure Selective Area Growth ZHAO Qian, PAN Jiao-Qing, ZHOU Fan, WANG Bao-Jun, WANG Lu-Feng, WANG Wei Chin. Phys. Lett. 2005, 22 (8): 2016-2019 .   Abstract   PDF(pc) (231KB) ( 411 ) A novel integration technique has been developed using band-gap energy control of InGaAsP/InGaAsP multi-quantum-well (MQW) structures during simultaneous ultra-low-pressure (22 mbar) selective-area-growth (SAG) process in metal-organic chemical vapour deposition. A fundamental study of the controllability of band gap energy by the SAG method is performed. A large band-gap photoluminescence wavelength shift of 83nm is obtained with a small mask width variation (0--30μm). The method is then applied to fabricate an MQW distributed-feedback laser monolithically integrated with an electroabsorption modulator. The experimental results exhibit superior device characteristics with low threshold of 19mA, over 24dB extinction ratio when coupled into a single mode fibre. More than 10GHz modulation bandwidth is also achieved, which demonstrates that the ultra-low-pressure SAG technique is a promising approach for high-speed transmission photonic integrated circuits.
 Select High Performance P-Channel Schottky Barrier MOSFETs with Self-Aligned PtSi Source/Drain on Thin Film SOI Substrate ZHU Shi-Yang, LI Ming-Fu Chin. Phys. Lett. 2005, 22 (8): 2020-2022 .   Abstract   PDF(pc) (280KB) ( 467 ) P-channel metal-oxide-semiconductor field-effect transistors (MOSFETs) with PtSi Schottky barrier source/drain, high-k gate dielectric and metal gate electrode were fabricated on a thin p-type silicon-on-insulator (SOI) substrate using a simplified low temperature process. The device works on a fully-depleted accumulation-mode and has an excellent electrical performance. It reaches Ion/Ioff ratio of about 107, subthreshold swing of 65mV/decade and saturation drain current of Idx = 8.8μA/μm at |Vg- Vth|= |Vd| = 1V for devices with the channel length 4.0μm and the equivalent oxide thickness 2.0nm. Compared to the corresponding bulk-Si counterparts, SOI p-SBMOSFETs have smaller off-state current due to reduction of the PtSi/Si contact area.
 Select Analysis of Polaron Band Formation with the One-Dimensional Holstein Model GE Ming, QIN Gan, WAN Shao-Long Chin. Phys. Lett. 2005, 22 (8): 2023-2026 .   Abstract   PDF(pc) (220KB) ( 413 ) We present an analytic result of the polaronic band structure by using the one-dimensional Holstein model on an infinite lattice. The single-phonon effect is used to investigate the ground state properties, such as the polaronic band structure, ground state energy, phonon distribution and effective mass, which agree with the numerical and analytic results obtained recently in the region from the weak coupling to the intermediate coupling.
 Select Improvement of Performance of Organic Thin-Film Transistors through Zone Annealing DONG Gui-Fang, LIU Qing-Di, WANG Li-Duo, QIU Yong Chin. Phys. Lett. 2005, 22 (8): 2027-2030 .   Abstract   PDF(pc) (379KB) ( 459 ) A zone annealing process is adopted to improve the performance of pentacene organic thin film transistors. The process is completed in a glove box full of dry nitrogen gas and with a heating wire (Ф0.1mm tungsten wire) inside. The device have the structure of glass/ITO (150nm)/Ta2O5 (60nm)/pentacene (60nm)/Au (20nm). Under the gate--source voltage -60V and the drain--source voltage -60V, the source--drain current, the mobility, and the on/off current ratio increase from 4×10-7A to 2.0×10-6A, 2.9×10-3cm2V-1s-1 to 1.6×10 2cm2V-1s-1, and 2×103 to 5.33×103, respectively. It is found that the distance between the pentacene grain boundaries decreases and an obvious layer structure can be formed in grains after annealing. According to the transport of carriers in the polycrystalline film, these changes of the pentacene film can improve the source--drain current and the mobility.
 Select Effect of Ag Doping on Optical and Electrical Properties of ZnO Thin Films XU Jin, ZHANG Zi-Yu, ZHANG Yang, LIN Bi-Xia, FU Zhu-Xi Chin. Phys. Lett. 2005, 22 (8): 2031-2034 .   Abstract   PDF(pc) (234KB) ( 1414 ) ZnO thin films were prepared on p-type Si (100) substrates by the sol-gel process. The influence of Ag doping at a content of 0.002 % on the photoluminescence and current-voltage (I-V) characteristics of ZnO thin films has been investigated. It is found that Ag doping leads to a pronounced increase in the intensity of near band edge emission at 3.23eV and a remarkable red shift of the visible broadband at room temperature. The I-V characteristics of ZnO/p-Si heterojunctions are also changed. These results could be explained by Ag substituting for Zn in Ag doped ZnO thin films.
 Select Spin and Charge Currents through a Quantum Dot Connected to Ferromagnetic Leads CHI Feng, LI Shu-Shen Chin. Phys. Lett. 2005, 22 (8): 2035-2038 .   Abstract   PDF(pc) (235KB) ( 477 ) We investigate the spin polarized current through a quantum dot connected to ferromagnetic leads in the presence of a finite spin-dependent chemical potential. The effects of the spin polarization of the leads p and the external magnetic field B are studied. It is found that both the magnitude and the symmetry of the current are dependent on the spin polarization of the leads. When the two ferromagnetic leads are in parallel configuration, the spin polarization p has an insignificant effect on the spin current, and an accompanying charge current appears with the increase of p. When the leads are in antiparallel configuration, however, the effect of p is distinct. The charge current is always zero regardless of the variation of p in the absence of B. The peaks appearing in the pure spin current are greatly suppressed and become asymmetric as p is increased. The applied magnetic field B results in an accompanying charge current in both the parallel and antiparallel configurations of the leads. The characteristics of the currents are explained in terms of the density of states of the quantum dot.
 Select Dynamical Transport Property through an Interacting Quantum Wire CHENG Fang, ZHOU Guang-Hui, Chin. Phys. Lett. 2005, 22 (8): 2039-2042 .   Abstract   PDF(pc) (217KB) ( 373 ) Using the equation of motion, we investigate theoretically the dynamical ac conductance of a clean Luttinger-liquid quantum wire adiabatically coupled to Fermi liquid electron reservoirs in the presence of short-ranged electron-electron interactions. For a perfect single mode quantum wire, in the limit of zero-ranged interaction we conclude that the static dc conductance of ω→0 is e2/h, which is independent of the electron interactions. While in the dynamical case of ω≠0, the ac conductance oscillates with the amplitude e2/h and the period which depends on the interaction strength and the driving frequency as well as the position in the wire.
 Select Magnetic Tunnel Junctions with MgO/Al--O Composite Barriers LI Fei-Fei, JIANG Li-Xian, SHARIF Rehana, ZHANG Xie-Qun, FENG Yu-Qing, HAN Xiu-Feng Chin. Phys. Lett. 2005, 22 (8): 2043-2046 .   Abstract   PDF(pc) (260KB) ( 502 ) Magnetic tunnel junctions (MTJs) with structures of Ta(5nm)/Cu(30nm)/Ta(5nm)/Ni79Fe21(5nm)/Ir22Mn78 (12nm)/Co62Fe20B18(4nm)/MgO(d)/Al(0.8nm)-oxide/Co62Fe20B18(6nm)/Cu(30nm)/Ta(5nm) on a thermally oxidized Si wafer substrate were fabricated by magnetron sputtering and photolithographic patterning method. The tunnel magnetoresistance (TMR) and the bias dependence of TMR at room temperature for the MTJs with different thickness d of MgO are investigated. TMR values of over 50% as high as those of the MTJs with pure Al--O barrier and the TMR-voltage curve asymmetries, which vary with the increase of d, are observed in the MTJs with hybrid barriers after annealing at 265°C for an hour. The dependences of TMR, resistance and coercivity of the MTJs with composite barriers on temperature are also investigated.
 Select The Branch Process of Skyrmions in the Fractional Quantum Hall Effect DUAN Yi-Shi, ZHANG Xiu-Ming, TIAN Miao Chin. Phys. Lett. 2005, 22 (8): 2047-2051 .   Abstract   PDF(pc) (216KB) ( 507 ) The branch process of the skyrmions in the fractional quantum Hall effect is studied from the Ф-mapping topological current. It is shown that there exists a field zeta whose Hopf indices and Brouwer degrees characterize the topological structure of the skyrmions. Based on the bifurcation theory of the Ф-mapping theory, it is found that the skyrmions can be generated or annihilated at the limit points and they encounter, split or merge at the bifurcation points of the new field zeta.
 Select Shapiro Steps in Flux-Trapped Surface Intrinsic Junctions of Bi2Sr2CaCu2O8+δ WEI Yan-Feng, ZHAO Shi-Ping, ZHU Xiao-Bo, CHEN Geng-Hua, REN Yu-Feng, YU Hong-Wei, YANG Qian-Sheng, HU Yun Chin. Phys. Lett. 2005, 22 (8): 2051-2054 .   Abstract   PDF(pc) (424KB) ( 432 ) Microwave-field responses of the surface intrinsic Josephson junctions (IJJs) of Bi2Sr2CaCu2O8+δ superconductors are investigated. The IJJs are fabricated using an in situ low-temperature cleavage technique, which leads to the well-characterized surface CuO2 double layers and surface junctions. For the surface junctions in the large-junction limit, usually no Shapiro steps appear when a microwave field is applied. It is found that when the junctions are in a flux-trapped state, which is produced by a pulsed current and in which the critical current is significantly suppressed, clear Shapiro steps can be observed. These results are important for the study of the microwave-field properties of vortex-carrying IJJs and may find their use in device applications.
 Select Electronic Structure and Magnetism in Sm(Co,Cu)7 ZHANG Chang-Wen, LI Hua, DONG Jian-Min, GUO Yong-Quan, LI Wei Chin. Phys. Lett. 2005, 22 (8): 2055-2058 .   Abstract   PDF(pc) (257KB) ( 420 ) The electronic density of states, spin-splittings and atomic magnetic moments of SmCo7-xCux are studied by means of the spin-polarized multi-scattering Xα method. The results show that a few of the electrons can transfer to the Sm $5d^{0}$ orbital due to orbital hybridization between Sm and Co. The exchange interactions between 3d and 5d electrons lead to the magnetic coupling between Sm and Co, and therefore result in the long-range ferromagnetic order in SmCo7-xCux. The Curie temperature of SmCo7-xCux is generally lower than that of the corresponding pure Co, which may be explained by the weaker average strength of coupling between Co lattices due to some negative exchange couplings mainly from the 2e site. The calculated results for the Sm5Co30Cu4 cluster may lead to a better understanding of why SmCo7-xCux is stable phase. Since the negative coupling of the 2e sites becomes small and the d bond at EF becomes stronger in contrast to SmCo7, which results in decrease of the free energy of the system, the stable ferromagnetic order forms in SmCo7-xCux.
 Select Magnetic Behaviour of Iron Oxychloride and Its Organometallic Intercalation Compounds Studied by Möossbauer Spectroscopy DAI Yao-Dong, HAN Wei, ZHENG Likun, XIA Yuan-Fu Chin. Phys. Lett. 2005, 22 (8): 2059-2062 .   Abstract   PDF(pc) (249KB) ( 626 ) Metallocene intercalate compounds with iron oxychloride, FeOCl(FeCp2)0.16 and FeOCl(CoCp2)0.36 with Cp being cyclopentadienyl group, are synthesized and characterized. Magnetism and the structure--property relations are investigated by magnetic measurement and 57Fe Mössbauer spectroscopy. The results show that the through-space dipolar interactions play a critical role in three-dimensional magnetic ordering of such layered compounds.
 Select Calculation of Resistivity of the Insulating Layer in Tunnelling-Magnetoresistive Head by Fast Green Function Method WEI Dan, PIAO Kun, QIN Jian, DONG Zhong Chin. Phys. Lett. 2005, 22 (8): 2063-2065 .   Abstract   PDF(pc) (314KB) ( 467 ) We calculate the resistivity of the insulating layer in a tunnelling-magnetoresistive (TMR) magnetic head by using the Landauer--Büttiker formula with a fast Green function method, where a recursive process with a faster simulation speed and higher accuracy is carried out to substitute the inversion of Green’s matrix. A tight-binding model with an energy barrier ΔE is utilized to simulate the magnetoresistive tunnelling junction in the TMR head. The resistivity of the insulating layer is 2.6×105μΩcm with two oxygen-ion layers and ΔE=2.5eV, which agrees with the experimental data.
 Select Form Birefringence in Thin Films with Oblique Columnar Structures WANG Jian-Guo, SHAO Jian-Da, WANG Su-Mei, HE Hong-Bo, FAN Zheng-Xiu Chin. Phys. Lett. 2005, 22 (8): 2066-2068 .   Abstract   PDF(pc) (720KB) ( 686 ) Effective medium theory is useful for designing optical elements with form birefringent subwavelength structures. Thin films fabricated by oblique deposition are similar to the two-dimensional surface relief subwavelength gratings. We use the effective medium theory to calculate the anisotropic optical properties of the thin films with oblique columnar structures. The effective refractive indices and the directions are calculated from effective medium theory. It is shown that optical thin films with predetermined refractive indices and birefringence may be engineered.
 Select Anomalous Positive Refraction in an Anisotropic Left-Handed Medium HU Wei, LUO Hai-Lu, CAO Jing-Xiao Chin. Phys. Lett. 2005, 22 (8): 2069-2072 .   Abstract   PDF(pc) (240KB) ( 502 ) We investigate the refraction phenomena of extraordinary light at a planar interface associated with a uniaxial left-handed medium. It is found that the anomalous positive refraction can occur at the interface from an isotropic right-handed medium to a uniaxially anisotropic left-handed medium. When the optical axis of a uniaxial left-handed medium is not normal or parallel to the interface, the refraction of the Poynting vector for the extraordinary waves can be either positive or negative depending on the incident angles, while the refraction of the wave vector is always negative. The physical essential of the anomalous positive refraction results from the anisotropy of uniaxial crystals.
 Select Verification and Calculation of Negative Refractive Indices of a Meta-Material by Numerical Method SUI Qiang, LIU Ci-Xiang, LI Chao, LI Fang Chin. Phys. Lett. 2005, 22 (8): 2073-2076 .   Abstract   PDF(pc) (723KB) ( 408 ) The verification and calculation of the negative refractive index of a meta-material is carried out by the finite-difference time-domain method. A slab and a prism of the meta-material are simulated. A genuine plane wave is generated by a two-direction periodic boundary condition (PBC) in the slab model. Based on an advanced phase extraction technique, the negative refractive index of the meta-material is verified by phase velocity measurement in the slab and prism measurement. From our results, not only the phenomenon of backward phase propagation but also the negative refraction is clearly observed. The index is also calculated precisely. The results from the two models are consistent.
 Select Intraband Relaxation and Its Influences on Quantum Dot Lasers DENG Sheng-Ling, HUANG Yong-Zhen, YU Li-Juan Chin. Phys. Lett. 2005, 22 (8): 2077-2080 .   Abstract   PDF(pc) (280KB) ( 354 ) A comprehensive two-level numerical model is developed to describe carrier distribution in a quantum-dot laser. Light-emission spectra with different intraband relaxation rates (2ps, 7.5ps and 20ps) are calculated and analysed to investigate the influence of relaxation rates on performance of the quantum-dot laser. The results indicate that fast intraband relaxation favours not only the ground state single mode operation but also the higher injection efficiency.
 Select Optical Properties of Phase-Separated GaN1-xPx Alloys Grown by Light-Radiation Heating Metal-Organic Chemical Vapour Deposition LU Li-Wu, CHEN Ting-Jie, SHEN Bo, WANG Jiang-Nong, GE Wei-Kun Chin. Phys. Lett. 2005, 22 (8): 2081-2083 .   Abstract   PDF(pc) (222KB) ( 512 ) Based on the results of the temperature-dependent photoluminescence (PL) measurements, the broad PL emission in the phase-separated GaNP alloys with P compositions of 0.03, 0.07, and 0.15 has investigated. The broad PL peaks at 2.18, 2.12 and 1.83eV are assigned to be an emission from the optical transitions from several trap levels, possibly the iso-electronic trap levels related to nitrogen. With the increasing P composition (from 0.03 to 0.15), these iso-electronic trap levels are shown to become resonant with the conduction band of the alloy and thus optically inactive, leading to the apparent red shift (80--160meV) of the PL peak energy and the trend of the red shift is strengthened. No PL emission peak is observed from the GaN-rich GaNP region, suggesting that the photogenerated carriers in the GaN-rich GaNP region may recombine with each other via non-radiation transitions.
 Select Synthesis and Optical Properties of ZnO Nanostructures WANG Duo-Fa, LIAO Lei, LI Jin-Chai, FU Qiang, PENG Ming-Zeng, ZHOU Jun-Ming Chin. Phys. Lett. 2005, 22 (8): 2084-2087 .   Abstract   PDF(pc) (409KB) ( 473 ) ZnO nanostructures with different morphologies were fabricated by changing the partial oxygen pressure. The structures, morphologies and optical properties of ZnO nanostructures were investigated by x-ray diffraction, field emission scanning electron microscopy and photoluminescence (PL) spectra at room temperature. All the samples show preferred orientation along the c-axis. The oxygen partial pressure and the annealing atmosphere have important effect on the PL property of ZnO nanostructures. The high oxygen partial pressure during growth of samples and high-temperature annealing of the ZnO samples in oxygen can increase oxygen vacancies and can especially increase antisite oxygen (Ozn) defects, which degraded the near band-edge emission. However, the annealing in H2 can significantly modify the NBE emission.
 Select Optical Properties of Highly Strained GaInAs/GaAs Quantum Wells Grown by Sb Assistance QU Yu-Hua, JIANG De-Sheng, WU Dong-Hai, NIU Zhi-Chuan, SUN Zheng Chin. Phys. Lett. 2005, 22 (8): 2088-2091 .   Abstract   PDF(pc) (416KB) ( 765 ) Optical properties of highly strained GaInAs/GaAs quantum wells (QWs) grown by molecular beam epitaxy with Sb assistance are investigated. The samples grown by Sb incorporation and Sb pre-deposition methods display high room-temperature photoluminescence (PL) intensity at extended long wavelength. This result is explained by the surfactant effects of Sb during the growth of GaInAs/GaAs QW systems. An abnormal S-shaped temperature dependence of the PL peak position is found in the In0.42Ga0.58As/GaAs triple QWs sample grown with Sb pre-deposition. By investigating the transmission electron microscope images and time-resolved PL spectra, it is found that the S-shaped temperature dependence of the PL peak position originates from the exciton localization effect brought by the Sb-rich clusters on the QW interface.
 Select Photoluminescence Mechanism of ZnO:Zn Investigated by Microwave Dielectric Spectrometry DONG Guo-Yi, ZHENG Yi-Bo, LIN Lin, DOU Jun-Hong, WEI Zhi-Ren, YANG Shao-Peng, FU Guang-Sheng, LI Xiao-Wei Chin. Phys. Lett. 2005, 22 (8): 2092-2095 .   Abstract   PDF(pc) (227KB) ( 550 ) We investigate the decay process of photoelectrons from a luminescent material of ZnO:Zn using a microwave dielectric spectrometry. Electrons in the conduction band are found to decay exponentially and the lifetime is 781ns, while the time interval of decay from the maximum to half of this value is 470ns. ZnO:Zn is a green luminescent material at its central wavelength of 510nm. Compared to the decay of electrons in the conduction band, the decay process of the luminescence is faster, and the time interval of decay from the maximum to half of the maximum is about 100ns. We believe that the mechanism of the ZnO:Zn visible luminescence is recombination luminescence, and find that our theoretical simulation is in agreement with the experimental results.
 Select Photoluminescence Investigation of Two-Dimensional Electron Gas in an Undoped AlxGa1-xN/GaN Heterostructure HAN Xiu-Xun, WU Jie-Jun, LI Jie-Min, CONG Guang-Wei, LIU Xiang-Lin, ZHU Qin-Sheng, WANG Zhan-Guo Chin. Phys. Lett. 2005, 22 (8): 2096-2099 .   Abstract   PDF(pc) (251KB) ( 621 ) Low-temperature photoluminescence measurement is performed on an undoped AlxGa1-xN/GaN heterostructure. Temperature-dependent Hall mobility confirms the formation of two-dimensional electron gas (2DEG) near the heterointerface. A weak photoluminescence (PL) peak with the energy of ～79meV lower than the free exciton (FE) emission of bulk GaN is related to the radiative recombination between electrons confined in the triangular well and the holes near the flat-band region of GaN. Its identification is supported by the solution of coupled one-dimensional Poisson and Schrödinger equations. When the temperature increases, the red shift of the 2DEG related emission peak is slower than that of the FE peak. The enhanced screening effect coming from the increasing 2DEG concentration and the varying electron distribution at two lowest subbands as a function of temperature account for such behaviour.
 Select A Quasi-Symmetric Coupled Quantum Well and Its Electric-Optical Properties XU Zhi-Xin, JIANG Xiao-Qing, WANG Ming-Hua Chin. Phys. Lett. 2005, 22 (8): 2100-2102 .   Abstract   PDF(pc) (205KB) ( 548 ) We propose a novel coupled quantum well structure, i.e. a quasi-symmetric coupled quantum well (QSCQW). Based on the demands of optical switching devices for quantum well materials, the QSCQW configuration is further optimized. Consequently, in the case of low applied electric field 25kV/cm and low absorption loss 100cm-1, a large field-induced refractive index change (for TE mode, n=0.0106; for TM mode, n=0.0115) is obtained in the QSCQW structure at the operation wavelength 1550nm. The value is in one or two order of magnitude larger than that in a rectangular quantum well and about 50% larger than that of five-step asymmetric coupled quantum well structure under the same working conditions. The refractive index change obtained with the optimized QSCQW under so low absorption loss and applied electric field is very attractive for semiconductor optical switching devices. This manifests that the QSCQW structure has a great potential for applications in ultra-fast and low-voltage optical switches and in travelling wave modulators.
 Select High Thermoelectric Properties of PbTe Doped with Bi2Te3 and Sb2Te3 ZHU Pin-Wen, IMAI Yoshio, ISODA Yukihiro, SHINOHARA Yoshikazi, JIA Xiao-Peng, ZOU Guang-Tian Chin. Phys. Lett. 2005, 22 (8): 2103-2105 .   Abstract   PDF(pc) (212KB) ( 857 ) The composition-dependent thermoelectric properties of lead telluride (PbTe) doped with bismuth telluride (Bi2Te3), antimony telluride (Sb2Te3) and (BiSb)2Te3 have been studied at room temperature. All the samples exhibit small thermal conductivity. The figures of merit, 7.63, 1.03 and 8.97×10-4, have been obtained in PbTe with these dopants, respectively. These values are several times higher than those of PbTe containing other dopants with small grain sizes. The high thermoelectric performance is explained by electronic topological transition induced by alloying. The results indicate that these dopants are effective to enhance the thermoelectric performance of PbTe.
 Select Fabrication and Characterization of Ni Thin Films Using Direct-Current Magnetron Sputtering WANG Hong-Chang, WANG Zhan-Shan, ZHANG Shu-Min, WU Wen-Juan, ZHANG Zhong, GU Zhong-Xiang, XU Yao, WANG Feng-Li, CHENG Xin-Bin, WANG Bei, QIN Shu-Ji, CHEN Ling-Yan Chin. Phys. Lett. 2005, 22 (8): 2106-2108 .   Abstract   PDF(pc) (385KB) ( 490 ) Ni films are deposited by using ultra high vacuum dc magnetron sputtering onto silicon substrates at room temperature, and the high-quality and high-density films are prepared. The parameters, such as thickness, density and surface roughness, are obtained by using small-angle x-ray diffraction (XRD) analyses with the Marquardt gradient-expansion algorithm. The deposition rate is calculated and the Ni single layer can be fabricated precisely. Based on the fitting results, we can find that the surface roughness of the Ni films is about 0.7nm, the densities of Ni films are around 97% and the deposition rate is 0.26nm/s. The roughness of the surface is also characterized by using an atomic force microscope (AFM). The changing trend of the surface roughness in the simulation of XRD is in good agreement with the AFM measurement.
 Select High Precise Internal Friction Calculation for Force Vibration Mode LIANG Li-Min, FEI Guang-Tao, SHUI Jia-Peng, CUI Ping, WU Bing, CHEN Xiao-Ming, LUI Ke-Tao Chin. Phys. Lett. 2005, 22 (8): 2109-2111 .   Abstract   PDF(pc) (188KB) ( 507 ) For the necessity of measuring the small phase difference of internal friction, a detailed comparison is carried out among the fast Fourier transformation (FFT), correlation function and three-parameter sine wave curve-fit methods. The comparison shows that the three-parameter sine wave curve-fit method can obtain more precise phase angle difference than correlation methods. Compared with the FFT algorithm, the three-parameter sine wave curve-fit method can obtain more precise frequency values.
 Select Computation of the Fractal Pattern in Manganese Dendrites Z. Merdan, M. Bayirli Chin. Phys. Lett. 2005, 22 (8): 2112-2115 .   Abstract   PDF(pc) (516KB) ( 513 ) The images of manganese flowers (clusters) on the surface of the natural magnesium silicate substance are scanned and the pictures of them are transferred to computer atmosphere. By using these scanning parameters, the exponents of density correlation function and fractal dimension values are calculated. For all different groups between the least and the most dense in the samples, the correlation function exponents may range from 0.141 to 0.178 and the fractal dimension values may vary between 1.61 and 1.88. In addition, the manganese flowers are divided into seven different groups according to their smallest- and largest-density features. The formation of the natural manganese clusters (flowers, dendrites) on the surface of the magnesium silicate substance can be defined by using the deposition, diffusion and aggregation model.
 Select Quasi-Solid-State Dye-Sensitized Solar Cells based on Mesoporous Silica SBA-15 Framework Materials YANG Hong, CHENG Yun-Fei, LI Fu-You, ZHOU Zhi-Guo, YI Tao, HUANG Chun-Hui, JIA Neng-Qin Chin. Phys. Lett. 2005, 22 (8): 2116-2118 .   Abstract   PDF(pc) (198KB) ( 866 ) We develop a novel and efficient quasi-solid-state electrolyte based on the mesoporous silica SBA-15 as a framework material for a dye sensitized nanocrystalline TiO2 solar cell. A solar energy-to-electricity conversion efficiency of 4.34% is achieved under AM 1.5 illumination (100mW/cm2).
 Select Towards an Understanding of the Influence of Sedimentation on Colloidal Aggregation by Peclet Number SUN Zhi-Wei, LIU Jie, XU Sheng-Hua Chin. Phys. Lett. 2005, 22 (8): 2119-2122 .   Abstract   PDF(pc) (217KB) ( 819 ) The Peclet number is a useful index to estimate the importance of sedimentation as compared to the Brownian motion. However, how to choose the characteristic length scale for the Peclet number evaluation is rather critical because the diffusion length increases as the square root of the time whereas the drifting length is linearly related to time. Our Brownian dynamics simulation shows that the degree of sedimentation influence on the coagulation decreases when the dispersion volume fraction increases. Therefore using a fixed length, such as the diameter of particle, as the characteristic length scale for Peclet number evaluation is not a good choice when dealing with the influence of sedimentation on coagulation. The simulations demonstrated that environmental factors in the coagulation process, such as dispersion volume fraction and size distribution, should be taken into account for more reasonable evaluation of the sedimentation influence.
 Select Characteristics of THz Emission from GaAs Crystal Excited by 400nm and 800nm Optical Pulses YANG Yu-Ping, XU Xin-Long, YAN Wei, WANG Li Chin. Phys. Lett. 2005, 22 (8): 2123-2126 .   Abstract   PDF(pc) (302KB) ( 469 ) THz emission spectroscopy is used to study the generation mechanism dependent behaviour of terahertz (THz) electromagnetic waves from the GaAs crystal under excitation by 400nm and 800nm femtosecond (fs) pulses, respectively. The wavelength dependence of the emission spectrum under two types of THz generation mechanisms is analysed. Under the optical rectification mechanism, a slight enhancement of the spectral amplitude in the high-frequency regime is observed in a GaAs(110) crystal by the excitation of a 400-nm optical pulse compared with that of 800nm. Whereas an obvious red shift of the amplitude spectrum occurs in the GaAs(100) sample under the transient photoconduction mechanism. These phenomena are explained in detail by the duration of the optical pump pulse and the band structure of GaAs, respectively.
 Select Effect of Reverse Substrate Bias on Degradation of Ultra-Thin Gate-Oxide n-Channel Metal--Oxide--Semiconductor Field-Effect Transistors under Different Stress Modes ZHAO Yao, XU Ming-Zhen, TAN Chang-Hua Chin. Phys. Lett. 2005, 22 (8): 2127-2129 .   Abstract   PDF(pc) (226KB) ( 421 ) Degradation of ultra-thin gate-oxide n-channel metal--oxide--semiconductor field-effect transistors with the halo structure has been studied under different stress modes with a reverse substrate bias. The device degradation under the same stress mode with different reverse substrate voltages has been characterized by monitoring the substrate current in a stressing process, which follows a simple power law. When the gate voltage is less than the critical value, the device degradation will first decrease and then increase with the increasing reverse substrate voltage, otherwise, the device degradation will increase continuously. The critical value can be obtained by measuring the substrate current variation with the increases of reverse substrate voltage and gate voltage. The experimental results indicate that the stress mode with enhanced injection efficiency and smaller device degradation can be obtained when the gate voltage is less than the critical value with a proper reverse substrate voltage chosen.
 Select Thermal Behaviour for InGaAsP/InP Multi-Quantum-Well Superluminescent Diodes LI Lan, FU Li-Wei, YANG Rui-Xia, LI Guang-Min, TAO Yi, ZHANG Na, ZHANG Xiao-Song Chin. Phys. Lett. 2005, 22 (8): 2130-2132 .   Abstract   PDF(pc) (247KB) ( 516 ) Using a two-dimensional thermal flow model, we calculate the thermal resistance and the temperature distribution of InGaAsP/InP multi-quantum-well superluminescent diodes. The influence of lateral chip size and composition are evaluated. The results reveal that when the injection power reaches 1W, temperatures in the active region rises up to almost 50K. The width and length of the chip also have strong influence on the thermal resistance that can reach two orders of magnitude. The thermal resistance will change from 290K/W to 68K/W when the chip width increases from 500μm to 2500μm, and a similar result exists for the length. There is small effect on thermal resistance for active width. In view of the characteristics of output power versus the input current under pulsed and continues currents, the fitted experimental thermal resistance matches well with the measured results.
 Select Designability of Protein Structures on the Hexagonal Lattice Model ZHANG Wei, SUN Zhi-Bo, ZOU Xian-Wu Chin. Phys. Lett. 2005, 22 (8): 2133-2136 .   Abstract   PDF(pc) (249KB) ( 498 ) In view of the bonding angle and the number of neighbouring sites, the hexagonal lattice model is preferred to investigate the designability of protein structures. Here we simulate the designable structures by the simplified HP model in a two-dimensional hexagonal lattice with an unrestricted boundary. The result shows that the structures with a large number of core sites correspond to the high designability and have circular-like profiles. The maximum and average designabilities for the hexagonal lattice model are much higher than those for the square lattice mode, and the maximum and average designabilities for the square lattice model are much higher than those for the triangle lattice model.
 Select Phase Transition Dynamics of Collective Decision in Scale-Free Networks DUAN Wen-Qi, CHEN Zhong, LIU Zeng-Rong, Chin. Phys. Lett. 2005, 22 (8): 2137-2139 .   Abstract   PDF(pc) (201KB) ( 620 ) A strategic collective decision model is introduced to investigate the role of decision transmission mechanism and interaction networks in determining the collective decision dynamics. Assuming that agents are located in a scale-free network and their decisions are interdependent of each other. In our model, it is found that the effective decision transmission rate λ exists a threshold λc=1, which marks the transition between the two regimes, i.e. the decision spreading and the decision disappearing in the population. Furthermore, λ is mainly determined by the decision transmission mechanism and interaction network's topology.
 Select Electrical Properties of Natural Pyroxenite YI Li, WANG Duo-Jun, LI He-Ping Chin. Phys. Lett. 2005, 22 (8): 2140-2142 .   Abstract   PDF(pc) (245KB) ( 775 ) The complex electrical properties of natural pyroxenite were measured over a frequency range from 0.01 to 106Hz, at 3.0GPa and 1266--1504K, using the solid buffers (Mo--MoO2) to control the oxygen fugacity. The frequency dependence of electrical properties for the natural pyroxenite is investigated. Two distinct conduction mechanisms of the natural pyroxenite are observed: grain interior and grain boundary conduction. Grain interior transport controls the response above 100Hz, whereas grain boundary transport dominates between ～ 100 and 0.01Hz. Electrical response of natural pyroxenite is modelled with an equivalent circuit in which parallel RC circuit elements representing grain interior and grain boundary responses act in series. The grain boundaries do not enhance the total conductivity of natural pryoxenite. The total electrical conductivity of natural pyroxenite is lower than either grain interior or grain boundary conductivity alone.
88 articles