#### Current Issue

Volume 22 Issue 9
Online Date:
Original Articles
 Select Creation of Multipartite Entanglement and Entanglement Transfer via Heisenberg Interaction ZHANG Yong, CAO Wan-Cang, LONG Gui-Lu, Chin. Phys. Lett. 2005, 22 (9): 2143-2146 .   Abstract   PDF(pc) (288KB) ( 694 ) We discuss how to create multipartite entanglement. By coupling a new particle with entangled particles via Heisenberg interaction between two particles, we can prepare three-particle entangled states. For some special coupling strength, entanglement transfer can be achieved from entangled pair AB to particles A and C that never interact by coupling particle C with particle B, which can be used to create entanglement between two separated particles.
 Select Two-Qubit Quantum Logic Gate in Molecular Magnets HOU Jing-Min, TIAN Li-Jun, GE Mo-Lin Chin. Phys. Lett. 2005, 22 (9): 2147-2150 .   Abstract   PDF(pc) (258KB) ( 512 ) We propose a scheme to realize a controlled-NOT quantum logic gate in a dimer of exchange coupled single-molecule magnets, [Mn4]2. We chosen the ground state and the three low-lying excited states of a dimer in a finite longitudinal magnetic field as the quantum computing bases and introduced a pulsed transverse magnetic field with a special frequency. The pulsed transverse magnetic field induces the transitions between the quantum computing bases so as to realize a controlled-NOT quantum logic gate. The transition rates between a pair of the four quantum computing bases and between the quantum computing bases and excited states are evaluated and analysed.
 Select Entanglement in Anisotropic Heisenberg Model with Non-Uniform External Fields WANG Yuan-Feng, CAO Jun-Peng, WANG Yu-Peng Chin. Phys. Lett. 2005, 22 (9): 2151-2153 .   Abstract   PDF(pc) (206KB) ( 561 ) We study entanglement properties of the three-qubit anisotropic Heisenberg model with both uniform and non-uniform external magnetic fields. Analytic expressions for the measures of entanglement at the ground state are obtained. We show that the pairwise entanglement and global entanglement of the system at the ground state clearly depend on the strength and configuration of external fields. The entanglement between some pairs can be enhanced by non-uniform external fields.
 Select Surface Gravity on the Horizon of η-ξ Spacetime LI Zi-Jing, GUI Yuan-Xing, ZHANG Su-Hong, YU Hong Chin. Phys. Lett. 2005, 22 (9): 2154-2156 .   Abstract   PDF(pc) (201KB) ( 698 ) We investigate the two methods of defining the surface gravity k on the horizon, which are the metric definition and the definition given by the spacetime conformal method. It is found that the latter is of greater generality. By this method, we find that k of η-ξ spacetime is equal to the exponent factor α in the coordinate transformation, which confirms the argument that η-ξ spacetime can be considered as the background spacetime for finite-temperature field theories. The reasons why the metric definition of k can not be applied in η-ξ spacetime are presented.
 Select Utilization of Electromagnetic Detector for Selection and Detection of High-Frequency Relic Gravitational Waves LI Fang-Yu, CHEN Zhen-Ya, YI Ying Chin. Phys. Lett. 2005, 22 (9): 2157-2160 .   Abstract   PDF(pc) (236KB) ( 508 ) It is shown that the coupling system between fractal membranes and a Gaussian beam passing through a static magnetic field has strong selection capability for the stochastic relic gravitational wave (GW) background. The relic GW components propagating along the positive direction of the symmetrical axis of the Gaussian beam might generate an optimal electromagnetic perturbation, while the perturbation produced by the relic GW components propagating along the negative and perpendicular directions to the symmetrical axis will be much less than the former, and the influence of the random fluctuation of the relic GWs to such effect can be neglected. The high-frequency relic GWs satisfying the parameters requirement (h～10-31 or larger), frequency resonance and direction coupling'', in principle, would be selectable and measurable in seconds.
 Select Relic Gravitational Waves and Trans-Planckian Physics WU Pu-Xun, YU Hong-Wei Chin. Phys. Lett. 2005, 22 (9): 2161-2164 .   Abstract   PDF(pc) (229KB) ( 350 ) Assuming that the effects of trans-Planckian physics are encoded in the choice of initial conditions, mode by mode, for vacuum states at the time when its wavelength becomes equal to the scale of new physics (Planck’s scale for example), we calculate the spectrum of energy densities of total relic gravitational waves from de Sitter inflation to the matter dominated universe. Our results show that the spectrum acquires corrections due to the consideration of trans-Planckian physics and these corrections depend sensitively on the vacuum state that was actually realized at the beginning of the inflation.
 Select Random Motion of a Charged Test Particle with a Constant Classical Velocity in a Spacetime with a Plane Boundary TAN Mei-Hua, YU Hong-Wei Chin. Phys. Lett. 2005, 22 (9): 2165-2168 .   Abstract   PDF(pc) (198KB) ( 587 ) We study the random motion of a charged test particle coupled to electromagnetic vacuum fluctuations near a perfectly reflecting plane boundary with a nonzero classical constant velocity in a direction parallel to the plane. We calculate the mean squared fluctuations in the velocity and position of the test particle taking into account both fluctuating electric and magnetic forces. Our results show that the influence of fluctuating magnetic fields is, in general, of the higher order than that caused by fluctuating electric fields and is thus negligible.
 Select Precise Determination of Period of a Torsion Pendulum in Measurement of Gravitational Constant LUO Jie, WANG Dian-Hong, LIU Qi, SHAO Cheng-Gang Chin. Phys. Lett. 2005, 22 (9): 2169-2172 .   Abstract   PDF(pc) (243KB) ( 773 ) The period of a torsion pendulum would vary under the disturbances of environmental noise factors. In order to subtract the period of the pendulum from external influence, we employ the correlation method to determine the period with a high precision. Theoretical analysis shows that the relative precision is improved to be proportional to 1/m3/2 with the number of the period m, compared with the conventional statistical mean that is proportional to 1/m1/2, which is significant for the determination of gravitational constant with the swing time method.
 Select Complete Synchronization in Coupled Chaotic HR Neurons with Symmetric Coupling Schemes WANG Hai-Xia, LU Qi-Shao, WANG Qing-Yun Chin. Phys. Lett. 2005, 22 (9): 2173-2175 .   Abstract   PDF(pc) (239KB) ( 690 ) Chaos synchronization in an array of coupled chaotic neurons with symmetric coupling is investigated. A criterion for the stability of the synchronization manifold is deduced by transforming the variational equation of the coupled system into a block diagonal one, and the critical coupling strengths for synchronization in different coupled cases are given. As examples for illustration, the HR neurons with the open-ended (i.e. chain), ring, star and all-to-all (i.e. global) coupling schemes are considered. It is shown that the coupling scheme plays an important role in synchronization and information transmission of neurons.
 Select Evolution of Spiral Waves under Modulated Electric Fields MA Jun, YING He-Ping, PAN Guo-Wei, PU Zhong-Sheng Chin. Phys. Lett. 2005, 22 (9): 2176-2179 .   Abstract   PDF(pc) (1355KB) ( 515 ) Spirals generated from the excitable media within the Barkley model is investigated under the gradient electric fields by a numerical simulation. The spiral drift and spiral break up are observed when the amplitude of the electric fields is modulated by a constant signal or a chaotic signal. It is also verified that, even in the presence of the white noise, the whole system can reach homogeneous states after the spiral breakup, by using an adaptive strategy.
 Select Control of Beam Halo-Chaos by Soliton BAI Long, WENG Jia-Qiang, FANG Jin-Qing Chin. Phys. Lett. 2005, 22 (9): 2180-2182 .   Abstract   PDF(pc) (227KB) ( 607 ) The Kapchinsky--Vladimirsky beam through an alternating-gradient quadrupole magnetic field is studied using the particle-core model. The beam halo-chaos is found, and the soliton controller is proposed based on the mechanism of halo formation and strategy of controlling halo-chaos. We perform a multiparticle simulation to control the halo by soliton controller, and find that the halo-chaos and its regeneration can be eliminated. It is shown that our control method is effective.
 Select Chaos Synchronization in Complex Networks YANG Jun-Zhong, ZHANG Mei Chin. Phys. Lett. 2005, 22 (9): 2183-2185 .   Abstract   PDF(pc) (268KB) ( 715 ) We employ several simple numerical experiments to show that the statements that short mean path length or low heterogeneity enhances synchronizability in complex networks could be misleading. Furthermore, we point out that the impacts of the structural parameters on the synchronizability are complicated even if we could change one structural parameter independently.
 Select Contrast Reversal of Topography Artifacts in a Transmission SNOM LI Zhi, WANG Shu-Feng, ZHANG Jia-Sen, GONG Qi-Huang Chin. Phys. Lett. 2005, 22 (9): 2186-2189 .   Abstract   PDF(pc) (1207KB) ( 402 ) We demonstrate the contrast reversal behaviour of topography artifacts by changing the diameter of the collection diaphragm in a transmission scanning near-field optical microscopy (SNOM). This originates from the change of the approach curves. Such contrast reversal phenomenon is used to distinguish the artifact signal from the true optical signal of the SNOM image. We also show that continuously changing the diaphragm to a proper diameter can greatly reduce topography artifacts.
 Select Casimir effect for a Cavity in the Spacetime with an Extra Dimension CHENG Hong-Bo Chin. Phys. Lett. 2005, 22 (9): 2190-2193 .   Abstract   PDF(pc) (215KB) ( 446 ) We reexamine the Casimir effect for the rectangular cavity with two or three equal edges in the presence of compactified universal extra dimension. We derive the expressions for the Casimir energy and discuss the nature of Casimir force. We show analytically the extra-dimension corrections to the standard Casimir effect to put forward a new method of exploring the existence of extra dimensions of the Universe.
 Select Soliton Solution of SU(3) Gauge Fields at Finite Temperature WANG Dian-Fu, SONG He-Shan Chin. Phys. Lett. 2005, 22 (9): 2194-2197 .   Abstract   PDF(pc) (208KB) ( 524 ) Starting from a soliton model of SU(3) gauge fields, we investigate the behaviour of the model at finite temperature. it is found that colour confinement at zero temperature can be melted away under high temperatures.
 Select Quenched Charmed Meson Spectra Using Tadpole Improved Quark Action on Anisotropic Lattices LIU Liu-Ming, SU Shi-Quan, LI Xin, LIU Chuan Chin. Phys. Lett. 2005, 22 (9): 2198-2200 .   Abstract   PDF(pc) (236KB) ( 371 ) Charmed meson charmonium spectra are studied with improved quark actions on anisotropic lattices. We measured the pseudo-scalar and vector meson dispersion relations for four lowest lattice momentum modes with quark mass values ranging from the strange quark to charm quark with three different values of gauge coupling β and four different values of bare speed of light v. With the bare speed of light parameter v tuned in a mass-dependent way, we study the mass spectra of D, Ds, ηc, D*, Dx* and J/ψ mesons. The results extrapolated to the continuum limit are compared with the experiment, and a qualitative agreement is found.
 Select Lepton Polarization Asymmetry in B→+- Decay beyond the Standard Model V. Bashiry Chin. Phys. Lett. 2005, 22 (9): 2201-2203 .   Abstract   PDF(pc) (608KB) ( 654 ) The lepton polarization asymmetry in the B→e+e- decay, when one of the leptons is polarized, is investigated by using the most general form of the effective Hamiltonian. We find allowed regions for the new scalar Wilson coefficients, assuming that the experimental branching ratio is measured within 10% percent uncertainty. Then using these restrictions to the new coefficients the sensitivity of the lepton polarization asymmetry to them is studied. Moreover, it is observed that there are regions of terms describing the scalar interactions, where lepton polarization asymmetry differs from zero, which can serve as a good test for searching new physics beyond the standard model.
 Select Dibaryon Structure in Extended Chiral SU(3) Quark Model DAI Lian-Rong Chin. Phys. Lett. 2005, 22 (9): 2204-2206 .   Abstract   PDF(pc) (221KB) ( 700 ) The structure of ΔΔ dibaryon is studied in the extended chiral SU(3) quark model in which vector meson exchanges are included. The effect of the vector meson fields is very similar to that of the one-gluon exchange (OGE) interaction. Both in the chiral SU(3) quark model and in the extended chiral SU(3) quark model, the resultant mass of the ΔΔ dibaryon is lower than the threshold of the ΔΔ channel but higher than that of the ΔNπ channel.
 Select Charge Density of 23,24O with Isoscalar--Isovector Coupling Terms JIANG Wei-Zhou Chin. Phys. Lett. 2005, 22 (9): 2207-2210 .   Abstract   PDF(pc) (249KB) ( 504 ) The nonlinear isoscalar--isovector terms which are used to simulate the density dependence of the symmetry energy are considered in the relativistic mean field model. The charge density distributions of 23,24O are investigated by considering the contribution from the isoscalar--isovector couplings. Contrarily to the uncertainty of the neutron radius of 208Pb, a considerable uncertainty exists for the charge radii of 23,24O. The data-to-data correlation between the neutron thickness of 208Pb and that of 23,24O is enhanced by the inclusion of the ρNN tensor coupling. This enhancement is closely related to the structural factor, the 2s1/2 occupation of the out-layer neutrons.
 Select Identification of New β-Delayed γ Rays and a Low-Spin Isomer in 176Ir WANG Hua-Lei, ZHANG Yu-Hu, ZHOU Xiao-Hong, GUO Ying-Xiang, LEI Xiang-Guo, XU Shu-Wei, XIE Yuan-Xiang, LIU Min-Liang, ZHENG Yong, XING Ye-Bing, XIE Cheng-Ying, SONG Li-Tao, LUO Peng, YU Hai-Ping, GUO Wen-Tao Chin. Phys. Lett. 2005, 22 (9): 2211-2214 .   Abstract   PDF(pc) (303KB) ( 512 ) The β+/EC decay of doubly odd nucleus 176Ir has been studied via the 146Nd(35Cl, 5nγ) heavy ion fusion evaporation reaction at 210MeV bombarding energy. With the aid of a helium-jet recoil fast tape transport system, the reaction products were transported to a low-background location for measurement. Based on the data analysis, the previously known γ rays from the decay of 176Ir are proven. Moreover, three new excited levels and ten new γ rays are assigned to 176Os. The time spectra of typical γ rays clearly indicate a long-lived low-spin isomer in 176Ir.
 Select Theoretical Prediction with Monte Carlo Simulation for pp→nK+Σ+ through Δ++ Resonance Production XIE Ju-Jun, ZOU Bing-Song, , LIU Bo-Chao, Chin. Phys. Lett. 2005, 22 (9): 2215-2218 .   Abstract   PDF(pc) (291KB) ( 401 ) The pp → nK+Σ+ reaction is a very good isospin 3/2 filter for studying Δ++ decaying to K+Σ+. The proton beam experiment with a scheduled 4π hadron detector at Lanzhou Cooler Storage Ring (CSR) will make the study of this reaction possible. Here, based on very limited available knowledge on the relevant ingredients for this reaction, we give theoretical prediction with Monte Carlo simulation for various observables for this reaction. This could serve as a reference for building the scheduled hadron detector and for identifying new physics in the following-on experiments at CSR.
 Select Measurement of 2H(8Li,9Be)n Reaction Relevant to Primordial Nucleosynthesis ZENG Sheng, LIU Wei-Ping, LI Zhi-Hong, BAI Xi-Xiang, YAN Sheng-Quan, WANG Bao-Xiang, LIAN Gang, SU Jun Chin. Phys. Lett. 2005, 22 (9): 2219-2221 .   Abstract   PDF(pc) (309KB) ( 806 ) The angular distribution of the 2H(8Li, 9Be)n (ground state) reaction, important to primordial nucleosynthesis in the inhomogeneous model, has been measured at Ec.m=8.1MeV using a secondary 8Li beam. Cross section of this reaction was determined to be 9.0±3.4mb. According to the cross section, the astrophysical S-factor was calculated to be 272±103keV b. It is shown that 2H(8Li, 9Be)n (ground state) reaction is important for creating 9Be, but less important for destroying 8Li in primordial nucleosynthesis.
 Select Shape Evolution of the Compound Nucleus in the Superheavy Element Synthesis Reaction via the BUU Model WEI Liang, LIU Yu-Xin, , Chin. Phys. Lett. 2005, 22 (9): 2222-2225 .   Abstract   PDF(pc) (669KB) ( 438 ) By taking the BUU model, we simulate the superheavy element synthesis reaction. With the rotation effect being included in the BUU model, the effect of the non-centrality of the reaction 48Ca + 238U → 286112 is studied. It is shown that the promising impact parameter in the synthesis process can be released from zero to a value little smaller than the radius of the smaller nucleus involved in the reaction. Meanwhile, the compound nucleus may involve rich shape phases.
 Select Correlation between Symmetry Energy and Collective Flow in Heavy-Ion Collisions Induced by High Energy Radioactive Beams YONG Gao-Chan, LI Bao-An, ZUO Wei, Chin. Phys. Lett. 2005, 22 (9): 2226-2229 .   Abstract   PDF(pc) (261KB) ( 541 ) Using an isospin- and momentum-dependent hadronic transport model, we investigate effects of the symmetry energy on several collective flows in heavy-ion collisions induced by radioactive beams at intermediate energies. It is found that the neutron-proton differential directed flow and the neutron-proton differential elliptic flow are strongly correlated with the symmetry energy, while the position averaged radial flow is weakly correlated with the symmetry energy.
 Select Profound Carrier-Envelope-Phase-Difference Effect on Photoionization Rate: Numerical Results on a Model Hydrogen Atom ZHOU Yu, ZHANG Gui-Zhong, XIANG Wang-Hua, W. T. Hill III Chin. Phys. Lett. 2005, 22 (9): 2230-2232 .   Abstract   PDF(pc) (207KB) ( 443 ) We discuss importance of the carrier-envelope phase difference (CEPD) effect which would be encountered in real short laser pulses. By numerically simulating photoionization rate of a one-dimensional atomic hydrogen model irradiated by short light pulses, a profound CEPD effect on the photoionization rate is revealed, which might shed light on laser-atom interaction investigation. We also suggest that photoionization process might be exploited in return to measure CEPD values.
 Select Photodetachment of H- in a Static Electric Field near a Surface YANG Guang-Can, LIU Yong, CHI Xian-Xing Chin. Phys. Lett. 2005, 22 (9): 2233-2236 .   Abstract   PDF(pc) (227KB) ( 456 ) The photodetachment of H- in a static electric field near a surface is investigated based on the closed orbit theory. It is found the distance between the ion and the surface modulates the cross section of photodetachment. For an elastic surface perpendicular to electric field, the detachment spectrum displays a staircase structure, in contrast with the smooth oscillation when only the electric field exists.
 Select A New Method of Measuring Electron Emission Induced by Low Energy Ions from Solids ZHANG Heng-Da, A. Breskin, R.Chechik, S. Shckemelinin, E. Cheifetz Chin. Phys. Lett. 2005, 22 (9): 2237-2240 .   Abstract   PDF(pc) (222KB) ( 806 ) A new mathematical method of measuring electron emission induced by low energy ions from solids is described and used to calculate secondary electron emission according to the recorded pulse-height spectra of ions and ultraviolet (UV) photons. Using the UV single secondary electron spectra, we predict the shape of many secondary electron distributions under consideration of detection efficiency of MCP detector. These calculated distributions allow us to characterize the secondary electrons yield, and to give a secondary electron distribution for measured data. It seems rather feasible to determine secondary electron yield emitted by low energy ions at very low ion fluxes.
 Select Carrier Envelope Phase Controlled High-Order Harmonic Generation in Ultrashort Laser Pulse WANG Bing-Bing, CHEN Jing, LIU Jie, LI Xiao-Feng, FU Pan-Ming Chin. Phys. Lett. 2005, 22 (9): 2237-2240 .   Abstract   PDF(pc) (243KB) ( 575 ) We investigate the carrier envelope phase (CEP) effects on high-order harmonic generation (HHG) in ultrashort pulses with the pulse duration 2.5fs when the laser intensity is high enough so that the initial state is ionized effectively during the laser pulse but remains about 20% population at the end of the laser pulse. We find that the ionization process of the initial state is very sensitive to the CEP during the laser pulse. The ionization process of the initial state determines the continuum state population and hence influences dramatically the weights of the classical trajectories that contribute to HHG. In such a case we can not predict the cutoff and the structure of the harmonic spectrum only by the number and the kinetic energy of the classical trajectories. The harmonic spectrum exhibits abundant characters for different CEP cases. As a result, we can control the cutoff frequency and the plateau structure of the harmonic spectrum with CEP by controlling the time behaviour of the ionization of the initial state.
 Select L\$-Shell Ionization Cross Section Measurements of Dysprosium and Samarium by Low-Energy Electron Impact GOU Cheng-Jun, WU Zhang-Wen, YANG Dai-Lun, HE Fu-Qing, PENG Xiu-Feng, AN Zhu, LUO Zheng-Ming Chin. Phys. Lett. 2005, 22 (9): 2244-2247 .   Abstract   PDF(pc) (275KB) ( 491 ) The Lα, Lβ and Lγ x-ray production cross sections of Dy and Sm by electron impact are measured at energies from near threshold to tens of keV. In the experiments, thin targets with thick substrates are used. Meanwhile, the electron transport bipartition model is used to eliminate the influence of electrons reflected from the thick substrates on measurements. The measured x-ray production cross sections are also compared with the theoretical predictions by Gryzinski and McGuire.
 Select Photon Angular Distribution and Polarization of Radiative Recombination OU Wei-Ying, SHEN Tian-Ming, CHEN Chong-Yang, Roger Hutton, ZOU Ya-Ming, Chin. Phys. Lett. 2005, 22 (9): 2248-2251 .   Abstract   PDF(pc) (254KB) ( 703 ) A systematic study is carried out on the angular distribution and polarization of photons emitted following radiative-recombination of bare and He-like ions of Ne, Ar, Ni and Mo with a unidirectional electron beam. In order to incorporate the screening effect due to inner-shell electrons, a distorted wave method is used. Scaling rules for polarization of the photon following radiative recombination to both bare and He-like ions are given for the incident energy regions up to six times the ionization threshold energy of the final state.
 Select Measurement of Integrated Stokes Parameters for He 3 3P State Excited by Spin-Polarized Electrons DING Hai-Bing, PANG Wen-Ning, LIU Yi-Bao, SHANG Ren-Cheng Chin. Phys. Lett. 2005, 22 (9): 2252-2254 .   Abstract   PDF(pc) (209KB) ( 400 ) Integrated Stokes parameters Pi (i=1,2, 3) for the He 3 3P → 2 3S1 (388.9nm) transition after excitation from the ground state to the 3 3P state by a transversely spin-polarized electron beam are measured in near threshold energy region. The experimental results are presented. The linear-polarization P2 are consistent with zero over the incident energy range, providing evidence for the LS coupling mechanism of the 3 3P state. The measured circular polarization P3 are non-zero, indicating strong electron-electron exchange effects in the spin-polarized electron-atom collision process.
 Select Typical Microstructures of Chinese Medicines with X-Ray Microscopy in Phase Contrast WEI Xun, XIAO Ti-Qiao, LIU Li-Xiang, DU Guo-Hao, CHEN Min, LUO Yu-Yu, XU Hong-Jie Chin. Phys. Lett. 2005, 22 (9): 2255-2258 .   Abstract   PDF(pc) (1263KB) ( 514 ) Due to the low absorption contrast of plant tissues, traditional x-ray radiography has not been included in the microscopic techniques used in the identification of traditional Chinese medicines (TCMs). With the development of x-ray phase contrast imaging (XPCI) in recent years, weakly absorbing materials could also be imaged by x-rays. Here we investigate microstructures of TCMs utilizing XPCI based on a nano-focus x-ray tube. The results demonstrated that XPCI is capable of revealing the microstructures of TCMs used as judging criteria in the identification of TCMs. The major advantages of the new method are nondestructivity, no special demand for sample preparation and suitability for thick samples.
 Select Spectral Anomalies in the Fraunhofer Diffraction Pattern PU Ji-Xiong, CAI Chao, HU Xian-Dai, LIU Xiao-Yun Chin. Phys. Lett. 2005, 22 (9): 2259-2261 .   Abstract   PDF(pc) (286KB) ( 654 ) We study the spectral characteristics theoretically and experimentally in the Fraunhofer diffraction pattern formed by the diffraction of a spatially coherent, polychromatic light through a slit. It is found that the spectrum in some diffraction directions close to the singular direction is redshifted, compared to the spectrum of the incident polychromatic light, and blueshifted in other directions, and splits into two lines at the singular direction. We show that the experimental results are consistent with the theoretical expectations.
 Select Uniform Diffraction Efficiency for Three-Dimensional Dynamic-Static Speckle Multiplexing Holographic Storage MA Xiao-Su, HE Qing-Sheng, JIN Guo-Fan Chin. Phys. Lett. 2005, 22 (9): 2262-2265 .   Abstract   PDF(pc) (1568KB) ( 591 ) We analyse and optimize the exposure-schedule of three-dimensional dynamic-static speckle multiplexing (DSSM) schemes. The uniform diffraction efficiency for the DSSM volume holographic storage system is realized in an ion and indium doped LiNbO3 crystal. An overlap-factor matrix is introduced into the system to compensate for the complex erasure effects caused by the static speckle multiplexing. We obtain 100 holograms demonstrating the exposure-schedule theory. The uniformity of the diffraction efficiency is improved by about 8%.
 Select Scheme for Preparation of the W State via Cavity QED ZHAN Zhi-Ming, LI Jia-Hua, LUO Jin-Ming Chin. Phys. Lett. 2005, 22 (9): 2266-2268 .   Abstract   PDF(pc) (202KB) ( 663 ) We put forward a scheme for preparation of an entangled multiparty W state between different modes of radiation field inside high-Q cavity QED. Our scheme is based on the interaction of a two-level atom with the cavity field with the assistance of a strong classical driving field for precalculated interaction time. In principle, the scheme can be extended to prepare an N-party W state. The required experimental techniques are within the scope of what can be obtained in the microwave cavity QED setup.
 Select Low-Threshold-Current and High-out-Power 660nm Laser Diodes with a p-GaAs Current Blocking Layer for DVD-RAM/R ZHENG Kai, MA Xiao-Yu, LIN Tao, WANG Jun, LIU Su-Ping, ZHANG Guang-Ze Chin. Phys. Lett. 2005, 22 (9): 2269-2272 .   Abstract   PDF(pc) (388KB) ( 1083 ) We investigate a new structure of high-power 660-nm AlGaInP laser diodes. In the structure, a p-GaAs layer is grown on the ridge waveguide serving as the current-blocking layer, and nonabsorbing windows are only fabricated near the cavity facets to increase the catastrophic-optical-damage level. Stable fundamental mode operation was achieved at up to 80mW without kinks, and the maximum output power was 184mW at 22°C. The threshold current was 40mA.
 Select Coherent Beam Combination of Two Polarization Maintaining Ytterbium Fibre Amplifiers HOU Jing, XIAO Rui, JIANG Zong-Fu, CHENG Xiang-Ai, SHU Bai-Hong, CHEN Jin-Bao, LIU Ze-Jin Chin. Phys. Lett. 2005, 22 (9): 2273-2275 .   Abstract   PDF(pc) (210KB) ( 654 ) We investigate coherent beam combination of fibre laser beams by phase locking. Phase noise of a polarization maintaining ytterbium fibre amplifier is inspected with a fibre interferometer. In a feed back control loop, two fibre polarization maintaining ytterbium amplifiers are phase locked and coherent combined when the phase noise is properly controlled by a LiNO3 phase modulator.
 Select Diode Stack End-Pumped Nd:GdVO4 Continuous Wave Slab Laser ZHANG Heng-Li, ZHANG Huai-Jin, LI Dai-Jun, WANG Ji-Yang, SHI Peng, Haas R\"udiger, LI Hong-Xia, JIANG Min-Hua, DU Keming Chin. Phys. Lett. 2005, 22 (9): 2276-2277 .   Abstract   PDF(pc) (301KB) ( 561 ) We report a diode stack end-pumped Nd:GdVO4 slab laser with a near-diffraction-limited beam. The output power of 45.8W at 1064nm is obtained under the pumping power of 147W, with the optical-optical conversion efficiency of 31.2%, and the slope efficiency is 39.6%.
 Select Polarization Self-Modulation Phenomenon in a Free Oscillated Nd:YAG Laser YANG Qian-Suo, LUO Geng-Xing, ZOU Nian-Yu, YANG Guo-Wei, ZHU Nai-Yi Chin. Phys. Lett. 2005, 22 (9): 2278-2281 .   Abstract   PDF(pc) (287KB) ( 797 ) Polarization self-modulation effect in a free oscillated Nd:YAG laser is investigated after a quarter wave plate is introduced independently in the two positions of the cavity. As described in the previous experiments, the intensity components in the orthogonal directions are modulated with a period of the round-trip time or twice. Different pulse shapes reveal that the seed field from the spontaneous emission is not uniform and seems to be stochastic for each pulse.
 Select Large Third-Order Optical Nonlinearity and Fast Response of a Squarylium Dye LI Zhong-Yu, JIN Zhao-Hui, KASATANI Kazuo, OKAMOTO Hiroaki Chin. Phys. Lett. 2005, 22 (9): 2282-2285 .   Abstract   PDF(pc) (394KB) ( 526 ) The third-order optical nonlinearities and responses of a squarylium dye, 2,4-di-3-guaiazulenyl-1,3-dihydroxycyclo\-butenediylium dihydroxide, in tetrahydrofuran (THF) solution and in polystyrene (PS) coating films are measured by the femtosecond degenerate four-wave mixing technique under resonant conditions. The molecular hyperpolarizability g of the squarylium dye in the THF solution is determined to be 3.0 × 10-29,esu at 764nm, and its electronic component γe is determined to be 1.1 × 10-29esu. The third-order nonlinear susceptibility x(3) of one of the present PS coating films containing the squarylium dye is as high as 3.1 × 10-8esu at 800nm, and its electronic component x(3)-e is 1.3 × 10-8esu.
 Select A Sign Alternation of Nonlinear Absorption in Gold Composite Films in Z-Scan CHEN Dai-Jian, DING Sha, HAN Jun-Bo, ZHOU Hui-Jun, XIAO Si, XIONG Gui-Guang, WANG Qu-Quan, Chin. Phys. Lett. 2005, 22 (9): 2286-2289 .   Abstract   PDF(pc) (531KB) ( 507 ) Au--TiO2 composite films with Au atom content varying from about 15% to 82% are prepared by co-sputtering technique. Both open- and closed-aperture Z-scan of the samples are performed in the femtosecond time region. A conversion of the nonlinear absorption from negative to positive is observed as the Au atom content increases due to the saturation of reverse saturable absorption. The nonlinear refractive index γ and effective nonlinear absorption coefficient βeff at the Au atom content of 54% are measured to be 1.6×10-2cm2/GW and -2.6×103cm/GW, respectively. The corresponding third-order optical nonlinearity x(3) is about 6.3×10-8esu.
 Select Two-Dimensional Photonic Band-Gap Defect Modes with Deformed Lattice CAI Xiang-Hua, ZHENG Wan-Hua, MA Xiao-Tao, REN Gang, XIA Jian-Bai Chin. Phys. Lett. 2005, 22 (9): 2290-2293 .   Abstract   PDF(pc) (1109KB) ( 679 ) A numerical study of the defect modes in two-dimensional photonic crystals with deformed triangular lattice is presented by using the supercell method and the finite-difference time-domain method. We find the stretch or shrink of the lattice can bring the change not only on the frequencies of the defect modes but also on their magnetic field distributions. We obtain the separation of the doubly degenerate dipole modes with the change of the lattice and find that both the stretch and the shrink of the lattice can make the dipole modes separate large enough to realize the single-mode emission. These results may be advantageous to the manufacture of photonic crystal lasers and provide a new way to realize the single-mode operation in photonic crystal lasers.
 Select Phase Effect on Guided Resonance in Photonic Crystal Slabs LIU Ken Chin. Phys. Lett. 2005, 22 (9): 2294-2297 .   Abstract   PDF(pc) (483KB) ( 703 ) Phase effect on the guided resonances in photonic crystal slabs is analysed. We present an analysis in the case of a mirror symmetric system and an asymmetric system irradiated from both sides, as well as the more realistic and interesting case of a system bounded from one side by a perfect mirror. Gain is incorporated in the system, mainly to exemplify the results. Finally we find that phase effects persist in the asymmetric system resulting in a periodic response for the reflectivity versus the distance from the mirror, which is the main parameter controlling the phase relationship between the two incident waves.
 Select Electroluminescence of an n-ZnO/p-GaN Heterojunction under Forward and Reverse Biases QIN Qi, GUO Li-Wei, ZHOU Zhong-Tang, CHEN Hong, DU Xiao-Long, MEI Zeng-Xia, JIA Jin-Feng, XUE Qi-Kun, ZHOU Jun-Ming Chin. Phys. Lett. 2005, 22 (9): 2298-2301 .   Abstract   PDF(pc) (245KB) ( 521 ) Electroluminescent characteristics of n-ZnO/p-GaN heterojunctions under forward and reverse biases are studied. Emissions at 389nm and 570nm are observed under forward bias. An unusual emission at 390nm appears under reverse bias, and is attributed to the recombination in the p-GaN side of the heterojunction. The yellow emission peaked at 570nm is suppressed under reverse bias. The light intensity exponentially depends on the reverse current. The emission under reverse bias is correlated to tunnelling carrier transport in the heterostructure. Our results also support that the well-known yellow band of GaN comes from the transitions between some near-conduction-band-edge states and deep localized acceptor states.
 Select An Ultra-Broadband Single-Polarization Single-Mode Photonic Crystal Fibre LOU Shu-Qin, JIAN Wei, REN Guo-Bin, JIAN Shui-Sheng Chin. Phys. Lett. 2005, 22 (9): 2302-2304 .   Abstract   PDF(pc) (317KB) ( 876 ) An ultra broadband single-polarization single-mode (SPSM) photonic crystal fibre (PCF) is proposed and analysed by using the plane-wave expansion method and the beam propagation method. Numerical results demonstrate that the SPSM wavelength region nearly at 580nm in width from 1.46μm to 2.04μm is obtained in this PCF. The start wavelength of the SPSM region is close to the hole pitch, and the width of the SPSM region increases with the increasing hole pitch. Effects of dopant concentration on SPSM properties are investigated. The confinement loss decreases and the width of SPSM region widens slightly with the increasing dopant concentration. These results offer a new possibility of fabricating active doped SPSM PCFs with high performance that is crucial for improving the performance of linearly polarized fibre lasers.
 Select Homogenization of Two-Dimensional Phononic Crystals at Low Frequencies NI Qing, CHENG Jian-Chun Chin. Phys. Lett. 2005, 22 (9): 2305-2308 .   Abstract   PDF(pc) (307KB) ( 601 ) Effective velocities of elastic waves propagating in two-dimensional phononic crystal at low frequencies are analysed theoretically, and exact analytical formulas for effective velocities of elastic waves are derived according to the method presented by Krokhin et al. [Phys. Rev. Lett. 91 (2003) 264302]. Numerical calculations for phononic crystals consisted of array of Pb cylinders embedded in epoxy show that the composites have distinct anisotropy at low filling fraction. The anisotropy increases as the filling fraction increases, while as the filling fraction closes to the limitation, the anisotropy decreases.
 Select Thermal Properties of Materials Characterized by Scanning Electron-Acoustic Microscopy GAO Chun-Ming, ZHANG Shu-Yi, ZHANG Zhong-Ning, SHUI Xiu-Ji, JIANG Tao Chin. Phys. Lett. 2005, 22 (9): 2309-2312 .   Abstract   PDF(pc) (244KB) ( 519 ) A modified technique of scanning electron-acoustic microscopy is employed to determine thermal diffusivity of materials. Using the dependence of the electron-acoustic signal on modulation frequency of the electron beam, the thermal diffusivity of materials is characterized based on a simplified thermoelastic theory. The thermal diffusivities of several metals characterized by the modified scanning electron-acoustic microscopy are in good agreement with the referential values of the corresponding materials, which proves that the scanning electron-acoustic microscopy can be used to characterize the thermal diffusivity of materials effectively. In addition, for micro-inhomogeneous materials, such as biological tissues, the macro-effective (average) thermal diffusivities are characterized by the technique.
 Select A New Lattice Boltzmann Model for KdV-Burgers Equation MA Chang-Feng Chin. Phys. Lett. 2005, 22 (9): 2313-2315 .   Abstract   PDF(pc) (224KB) ( 635 ) A new lattice Boltzmann model with amending-function for KdV-Burgers equation, ut+uux-α uxx+βuxxx=0, is presented by using the single-relaxation form of the lattice Boltzmann equation. Applying the proposed model, we simulate the solutions of a kind of KdV-Burgers equations, and the numerical results agree with the analytical solutions quite well.
 Select Fractional Fourier Transform of Cantor Sets LIAO Tian-He, GAO Qiong Chin. Phys. Lett. 2005, 22 (9): 2316-2319 .   Abstract   PDF(pc) (271KB) ( 829 ) A new kind of multifractal is constructed by fractional Fourier transform of Cantor sets. The wavelet transform modulus maxima method is applied to calculate the singularity spectrum under an operational definition of multifractal. In particular, an analysing procedure to determine the spectrum is suggested for practice. Nonanalyticities of singularity spectra or phase transitions are discovered, which are interpreted as some indications on the range of Boltzmann temperature q, on which the scaling relation of partition function holds.
 Select Carrier-Density-Dependent Electron Spin Relaxation in GaAs/AlGaAs Multi Quantum Wells SHOU Qian, WU Yu, LIU Lu-Ning, WEN Jin-Hui, LAI Tian-Shu, LIN Wei-Zhu Chin. Phys. Lett. 2005, 22 (9): 2320-2323 .   Abstract   PDF(pc) (252KB) ( 519 ) The carrier-density-dependent electron spin relaxation processes in GaAs/AlGaAs multi quantum wells are investigated by a femtosecond pump probe experiment. The spin relaxation time presents two distinguishable trends with the increasing excitation density. It increases from 60ps to 70ps with carrier densities from 1× 1017cm-3 to 5×1017cm-3 and gradually saturates up to ～80ps at 4×1018cm-3. The experimental results are attributed to the combined competition between collision intensification and scattering potential screening and provide a good experimental confirmation for the theoretical D’yakonov--Perel’ mechanism descriptions.
 Select Open M-shell Opacity of Bromine Plasma in Comparison of the Detailed Level Accounting Model with the Average Atom Model JIN Feng-Tao, YUAN Jian-Min Chin. Phys. Lett. 2005, 22 (9): 2324-2327 .   Abstract   PDF(pc) (236KB) ( 644 ) The open M-shell opacity of a hot bromine plasma has been calculated by using a detailed level accounting (DLA) model. One-electron orbitals obtained by solving the fully relativistic Dirac--Fock equations are used to obtain the atomic levels and the radiative transition oscillator strengths. Only the level mixing within the same electron configuration is considered to reduce the complexity of the calculations. Detailed comparisons have been made between the results of the DLA and average atom (AA) models. Good agreements are found for both the M-shell transition arrays and the Planck mean opacity but there are differences for the line positions in the 2p → 3d absorption region due to the statistical treatment for the one-electron orbitals in the AA model.
 Select Radiation Temperature Scaling Law for Gold Hohlraum Heated with Lasers at 0.35mm Wavelength JIANG Shao-En, SUN Ke-Xu, DING Yong-Kun, HUANG Tian-Xuan, CUI Yan-Li, CHEN Jiu-Sen Chin. Phys. Lett. 2005, 22 (9): 2328-2331 .   Abstract   PDF(pc) (241KB) ( 769 ) We have carried out the hohlraum experiments about radiation temperature scaling on the Shenguang-II (SG-II) laser facility with eight laser beams of 0.35μm, pulse duration of about 1.0ns and total energy of 2000J. The reradiated x-ray flux through the laser entrance hole was measured using a soft x-ray spectrometer. The measured peak radiation temperature was 170eV for the standard hohlraum and 150eV for the 1.5-scaled one. We have derived the radiation temperature scaling law, in which the laser hohlraum coupling efficiency is included. With an appropriate coupling efficiency, the coincidences between experimental and scaling hohlraum radiation temperatures are rather good.
 Select Deposition of Hydrogen-Free Silicon Nitride Thin Films by Microwave ECR plasma Enhanced Magnetron Sputtering at Room Temperature DING Wan-Yu, XU Jun, PIAO Yong, LI Yan-Qin, GAO Peng, DENG Xin-Lu, DONG Chuang Chin. Phys. Lett. 2005, 22 (9): 2332-2334 .   Abstract   PDF(pc) (224KB) ( 2948 ) Hydrogen-free silicon nitride (SiNx) films were deposited at room temperature by microwave electron cyclotron resonance (MW-ECR) plasma enhanced unbalance magnetron sputtering system. Both Fourier-transform infrared spectroscopy and x-ray photoelectron spectroscopy are used to study the bonding type and the change of bonding structures of the silicon nitride films. The results indicate that the chemical structure and composition of SiNx films deposited by this technique depend strongly on the Nx flow rates, the stoichiometric SiNx film, which has the highest hardness of 22.9GPa, could be obtained at lower Nx flow rate of 4sccm.
 Select Step Structure in Cold-Rolled Deformed Nanocrystalline Nickel ZHANG Xi-Yan, WU Xiao-Lei, XIA Bao-Yu, ZHOU Ming-Zhe, ZHOU Shi-Jie, JIA Chong Chin. Phys. Lett. 2005, 22 (9): 2335-2337 .   Abstract   PDF(pc) (361KB) ( 724 ) The microstructure characteristic of the cold-rolled deformed nanocrystalline nickel metal is studied by transmission electron microscopy. The results show that there are step structures nearby the grain boundary (GB), and the contrast of stress field in front of the step corresponds to the step in the shape. It is indicated that the interaction between twins and dislocations is not a necessary condition to realizing the deformation. In the later stage of the deformation when the grain size becomes about 100nm, the deformation can depend upon the moving of the boundary of the stack faults (SFs) which result from the partial dislocations emitted from GBs. However, when the size of SFs grows up, the local internal stress which is in front of the step gradually becomes higher. When this stress reaches a critical value which stops the gliding of the partial dislocations, the SFs will stop to grow up and leave a step structure behind.
 Select Reconsideration of Anelastic Relaxation Peaks in Pure Aluminium SHANG Li-Yan, SHUI Jia-Peng, CAI Bin, CUI Ping Chin. Phys. Lett. 2005, 22 (9): 2338-2341 .   Abstract   PDF(pc) (232KB) ( 502 ) The temperature dependence of internal friction (T-tan ψ curves) in pure aluminium (Al) is measured at sixteen different frequencies. Based on T-tan ψ curves, the frequency dependence of internal friction (f-tan ψ curves) is also obtained by the interpolation method. An internal friction peak is observed in both the T-tan ψ curves and the f-tan ψ curves. The activation energy of the peak in the f-tan ψ curves is found to be 2.08 ± 0.02eV and compared to the value of 1.60 ± 0.04eV in the T-tan ψ curves. It is suggested that the change of relaxation strength with temperature should be considered when one calculates the activation energy of the peak in T-tan ψ curves.
 Select Scholte Wave at Air--Metal Interface Generated by a Pulsed Disc-Like Source PENG Ruo-Long, QIAN Meng-Lu Chin. Phys. Lett. 2005, 22 (9): 2342-2345 .   Abstract   PDF(pc) (429KB) ( 391 ) The normal displacement and pressure of Scholte and Leaky Rayleigh waves at air--metal interface generated by a pulsed disc-like source are simulated theoretically by the Cagniard--de Hoop method and studied by laser ultrasound technique experimentally. It is found that the Scholte wave detected by a photorefractive interferometer is mainly contributed by the surface pressure and the Leaky Rayleigh wave is dominated by the surface displacement. It is also proven that the pulse width of these interface waves is mainly determined by the acoustic time delay on the generating source size under our experimental conditions.
 Select Calculation of Specific Heat for Aluminium Thin Films LU Yao, SONG Qing-Lin, XIA Shan-Hong Chin. Phys. Lett. 2005, 22 (9): 2346-2348 .   Abstract   PDF(pc) (312KB) ( 549 ) We employ Prasher’s non-dimensional form to analyse the size effects on specific heat of Al thin films. Compared the calculation results of pure aluminium film with the experimental data, it is found that the reduction of phonon states is not the main reason of the size effect on the specific heat Al thin films with thickness from 10nm to 370nm. However, the Al thin film in air usually has an oxidation layer and the specific heat of the layer is smaller than Al. By including the contribution of the oxidation layer to the thin-film specific heat, the calculation results are much closer to the experimental data. This may be a possible reason of the size effects on specific heat of Al thin films.
 Select Numerical Study of Luttinger Liquid Regime of Two-Leg Hubbard Ladders CHENG Kuan, LIU Yu-Liang Chin. Phys. Lett. 2005, 22 (9): 2349-2352 .   Abstract   PDF(pc) (251KB) ( 556 ) We investigate two-leg Hubbard ladders in the Luttinger liquid regime by the density-matrix renormalization group method. Applicability of the bond concept in this region is discussed in a quantitative comparison of power-law decay exponents, energy components and anti-bond occupations between ladders and chains. The interaction between bond and anti-bond bands induced by finite Hubbard repulsion U is emphasized by our numerical results. Our quantitative results are useful for the justification of the validity of various analytical approaches.
 Select Microstructural Properties of Single Crystalline PbTe Thin Films Grown on BaF2(111) by Molecular Beam Epitaxy SI Jian-Xiao, WU Hui-Zhen, XU Tian-Ning, CAO Chun-Fang, HUANG Zhan-Chao Chin. Phys. Lett. 2005, 22 (9): 2353-2356 .   Abstract   PDF(pc) (465KB) ( 788 ) Single crystal PbTe thin films have been grown on BaF2 (111) by using solid source molecular beam epitaxy. The studies of evolution of the surface morphology with the increasing growth temperature from 375 to 525°C by AFM show that PbTe epilayers exhibit smooth surface morphologies with atomic layer scale roughness and are crack free. It is found that for PbTe grown at 475°C, the morphology is dominated by triangles and the rms roughness is 3.987nm. Compared to the rms roughnesses of 0.432nm and 0.759nm for the samples grown at 375 and 525°C respectively, the surface of the PbTe layer grown at 475°C is much rougher. This roughening transition is due to the interaction between the elastic relaxation and the plastic relaxation during the strain relaxation process. In contrast to the result of the morphology that the PbTe epitaxial layer grown at 375°C has most smooth surface, as observed from the line width of x-ray diffraction curves at higher growth temperature improves the crystal quality of the single-crystalline PbTe layer.
 Select Atomic and Electronic Structures of Cd0.96Zn0.04Te(110) Surface ZHA Gang-Qiang, JIE Wan-Qi, ZHANG Wen-Hua, LI Qiang, XU Fa-Qiang Chin. Phys. Lett. 2005, 22 (9): 2357-2359 .   Abstract   PDF(pc) (307KB) ( 672 ) X-Ray diffraction is used to analyse the lattice structure of CdCd0.96Zn0.04Te (CZT), and the lattice constant is measured to be 0.647nm. The atomic structure of the clean CZT(110) surface obtained by Ar+ etching in vacuum is observed by low-energy electron diffraction, where no surface reconstruction is discovered. Angle-resolved photoemission spectroscopy was used to characterize the surface state of the clean CZT (110) surface, by which we find a 1.5-eV-wide surface band with the peak at 0.9eV below the Fermi energy containing about 6.9×1014 electrons/cm2, approximately one electron per surface atom.
 Select Dielectric Response of Graded Spherical Composites LI Zhi, WEI En-Bo, ZHANG Han-De, TIAN Ji-Wei Chin. Phys. Lett. 2005, 22 (9): 2360-2362 .   Abstract   PDF(pc) (218KB) ( 368 ) We investigate the effective dielectric responses of graded spherical composites under an external uniform electric field by taking the dielectric function of spherical inclusion, εi=crk eβr, where r is the inner distance of a point inside the particle from the centre of the spherical particle in the coordination. In the dilute limit, our exact result is used to test the validity of differential effective dipole approximation (DEDA) for estimating the effective response of graded spherical composites and it is shown that the DEDA is in excellent agreement with the exact result.
 Select Quantitative Mobility Spectrum Analysis for Determination of Electron and Magneto Transport Properties of Te-Doped GaSb S. Acar, M. Kasap, B. Y. Isik, S. Ö, zcelik, N. Tugluoglu, S. Karadeniz Chin. Phys. Lett. 2005, 22 (9): 2363-2366 .   Abstract   PDF(pc) (259KB) ( 490 ) Resistivity, magnetoresistivity and Hall effect measurements in n-type Te-doped GaSb grown by the liquid encapsuled Czochralsk technique are carried out as functions of temperature (35--350K) and magnetic field (0--1.35T). The power law model is used to explain the temperature-dependent resistivity. The magnetic-field-dependent data are analysed using the quantitative mobility spectrum analysis technique. The effect of individual band parameters (nL, nΓ, μL, μΓ, p and μp) on both the electron and magneto transports have been discussed. The EL-EG energy separation between the L and Γ conduction band edges is also derived.
 Select Polaron Energy and Effective Mass in Parabolic Quantum Wells WANG Zhi-Ping, LIANG Xi-Xia, Chin. Phys. Lett. 2005, 22 (9): 2367-2371 .   Abstract   PDF(pc) (225KB) ( 843 ) The energy and effective mass of a polaron in a parabolic quantum well are studied theoretically by using LLP-like transformations and a variational approach. Numerical results are presented for the polaron energy and effective mass in the GaAs/Al0.3Ga0.7As parabolic quantum well. The results show that the energy and the effective mass of the polaron both have their maxima in the finite parabolic quantum well but decrease monotonously in the infinite parabolic quantum well with the increasing well width. It is verified that the bulk longitudinal optical phonon mode approximation is an adequate formulation for the electron-phonon coupling in parabolic quantum well structures.
 Select Singlet-Triplet Transition in Quantum Dots Confined by Triangular and Bowl-Like Potentials: the Effect of Electric Fields SUN Lian-Liang, LI Shu-Shen Chin. Phys. Lett. 2005, 22 (9): 2371-2374 .   Abstract   PDF(pc) (406KB) ( 771 ) We theoretically investigate the energy spectra of two-electron two-dimensional (2e 2D) quantum dots (QDs) confined by triangular potentials and bowl-like potentials in a magnetic field by exact diagonalization in the framework of effective mass theory. An in-plane electric field is found to contribute to the singlet--triplet transition of the ground state of the 2e 2D QDs confined by triangular or bowl-like potentials in a perpendicular magnetic field. The stronger the in-plane electric field, the smaller the magnetic field for the total spin of the ground states in the dot systems to change from S=0 to S=1. However, the influence of an in-plane electric field on the singlet--triplet transition of the ground state of two electrons in a triangular QD modulated by a perpendicular magnetic field is quite small because the triangular potential just deviates from the harmonic potential well slightly. We find that the strength of the perpendicular magnetic field needed for the spin singlet--triplet transition of the ground state of the QD confined by a bowl-like potential is reduced drastically by applying an in-plane electric field.
 Select Geometrical Structure Effect on Localization Length of Carbon Nanotubes RAN Wen-Qi, CHANG Jun, LU Han-Tao, SU Yue-Hua, LUO Hong-Gang, XIANG Tao Chin. Phys. Lett. 2005, 22 (9): 2375-2378 .   Abstract   PDF(pc) (256KB) ( 409 ) The localization length and density of states of carbon nanotubes are evaluated within the tight-binding approximation. By comparison with the corresponding results for the square lattice tubes, it is found that the hexagonal structure affects strongly the behaviour of the density of states and localization lengths of carbon nanotubes.
 Select Figure of Merit for Detectors Based on Laser-Induced hermoelectric Voltages in La1-xCaxMnO3 and Ba2Cu3O7-σ Thin Films ZHANG Guo-Yong, ZHANG Peng-Xiang, ZHANG Hui, LEE Wing-Kee Chin. Phys. Lett. 2005, 22 (9): 2379-2381 .   Abstract   PDF(pc) (244KB) ( 474 ) A figure of merit (FOM) Z = Up/τr, where Up is the peak voltage, and τr is the rise time of the laser-induced thermoelectric voltage (LITV) signal, is defined for photodetector based on the LITV and the influence of the parameters on FOM is analysed based on the time dependence of LITVs in La1-xCaxMnO3 (LCMO) and YBa2Cu3O7-σ (YBCO) thin films grown on vicinal-cut substrates. We find that the FOM increases as the photon penetration depth decreases, and linearly increases with the thermal diffusion constant D. To achieve the highest FOM, the film thickness d has to be controlled to an optimum value. We also find that the FOM is directly proportional to the laser absorption coefficient α0, the laser energy density per pulse E, the illuminated length of film l, sin(2α) [αis the vicinal-cut angle], the Seebeck coefficient anisotropy (Sab - Sc ), and is inversely proportional to the mass density ρ and the specific heat c0.
 Select Magnetic and Thermal Behaviour of One-Dimensional Antiferromagnetic Spin-1 Ising Chain at Low Temperatures Ekrem Aydiner, Cenk Akyüz Chin. Phys. Lett. 2005, 22 (9): 2382-2385 .   Abstract   PDF(pc) (240KB) ( 1003 ) We investigate magnetic and thermal behaviours of one-dimensional antiferromagnetic spin-1 Ising chain with single-ion anisotropy at very low temperatures using the classical transfer matrix technique. Magnetic plateaus, phase diagram, specific heat, susceptibility of the spin chain have been evaluated numerically from the free energy. The results are in good agreement with the experimental data for the spin-1 compounds [Ni2(Medpt)2(μ-ox)(H2O)2](ClO4)22H2O, [Ni2(Medpt)2(μ-ox)(μ-N3)](ClO4)0.5H2O, Ni(C2H8N2)Ni(CN)4 and Ni(C10H8N2)2 Ni-(CN)4.H2O.
 Select Aligned Structures of Fe3O4 Nanoparticles in a Curable Polymer Carrier Induced by a Magnetic Field FANG Wen-Xiao, HE Zhen-Hui, XU Xue-Qing, SHEN Hui Chin. Phys. Lett. 2005, 22 (9): 2386-2389 .   Abstract   PDF(pc) (881KB) ( 375 ) To understand the interaction in dipolar systems, it is necessary to investigate the structures formed by the interacting particles. We introduce a polymer acrylic resin carrier to fix the structures in the magnetic fluid (Fe3O4). An aligned structure is investigated, which is formed under a magnetic field, and fixed in the cured acrylic resin film by evaporating the solvent at room temperature. The aligned structure is confirmed with the help of optical microscopy and optical diffraction for the cured film. Furthermore, we find substructures by using a scanning electronic microscope. Based on the curable and observable structures, a platform can be developed for investigating the aligned structures and configurations dominant by dipolar interaction. This is also helpful for the development of magnetic devices with orderly aligned structures.
 Select Pyroelectricity and Spontaneous Polarization in [111] Oriented 0.955Pb(Zn1/3Nb2/3)O3--0.045PbTiO3 Single Crystals SHEN Ming-Rong, YAO Dong-Lai, CAO Wen-Wu Chin. Phys. Lett. 2005, 22 (9): 2390-2393 .   Abstract   PDF(pc) (263KB) ( 742 ) We report that the measurements of the pyroelectric current of the pre-poled [111]-oriented 0.955Pb(Zn1/3Nb2/3)O3--0.045PbTiO3 (PZN-4.5%PT) single crystals can shed some light on the phase transition and spontaneous polarization characters of this material in a similar way to measures of remanent polarization and dielectric properties. The pyroelectric current is measured and the corresponding spontaneous polarization is calculated as a function of temperature with various poling fields added during cooling the sample from 200°C to room temperature. Critical electric field of 0.061kV/cm is found to be essential to induce the intermediate ferroelectric orthorhombic phase between the ferroelectric rhombohedral and tetragonal phases. Below the critical field, the polarization increases almost linearly with the increase of poling field. At the critical field, the polarization at 30°C increases abruptly from 14μC/cm2 for a poling field of 0.06kV/cm to 29.5μC/cm2 for a poling field of 0.061kV/cm, and afterwards, increases slowly and saturates to 31muC/cm2 for poling fields beyond 0.55kV/cm.
 Select A New Method to Analyse Two-Side Tapered Waveguides FAN Guo-Fang, NING Ji-Ping, SHANG Lian-Ju, HAN Qun, CHEN Zhi-Qiang Chin. Phys. Lett. 2005, 22 (9): 2394-2395 .   Abstract   PDF(pc) (222KB) ( 638 ) We discuss the characters of two-side tapered waveguides. Then, based on some approximations, a simple but practical and efficient method is developed to design the taper waveguide. The results are compared with other methods in a good agreement.
 Select Magneto-Optic Coupling Theory for Guided Optical Waves and Magnetostatic Waves Using an Arbitrarily Tilted Bias Magnetic Field WU Bao-Jian, QIU Kun Chin. Phys. Lett. 2005, 22 (9): 2396-2399 .   Abstract   PDF(pc) (268KB) ( 445 ) We report the magneto-optic (MO) coupling interaction of guided optical waves (GOWs) with magnetostatic waves (MSWs) in MO film waveguides using arbitrarily tilted bias magnetic fields. The universal MO coupled-mode equations are obtained and can be applied to the collinear or noncollinear interactions of the GOWs with magnetostatic forward volume wave (MSFVW), magnetostatic backward volume wave (MSBVW) and magnetostatic surface wave (MSSW). As a typical example, the noncollinear diffraction interaction of the GOW with the MSFVW excited by single-element microstrip line transducer in the yttrium-iron-garnet (YIG) film is analysed in detail. For the case of normal magnetization, the calculated plot is consistent with the experimental results in the first passband. By comparison, the diffraction efficiency (DE) can further be improved by optimizing the magnetization direction. The maximum DE gain can reach 5.7dB under the appropriately inclined bias magnetic field at ψ=180° and θ=9°.
 Select Raman Active Phonons in RCoO3 (R=La, Ce, Pr, Nd, Sm, Eu, Gd, and Dy) Perovskites WANG Wei-Ran, XU Da-Peng, SU Wen-Hui, , DING Zhan-Hui, XUE Yan-Feng, SONG Geng-Xin, Chin. Phys. Lett. 2005, 22 (9): 2400-2402 .   Abstract   PDF(pc) (345KB) ( 1376 ) We examine RCoO3 (R=La, Ce, Pr, Nd, Sm, Eu, Gd, and Dy) perovskites prepared with the solid-state reaction method by Raman spectroscopy, and report the Raman active phonons in the RCoO3 perovskites crystallized in cubic symmetry for RCoO3 (R=La, Ce, Pr and Nd) and orthorhombic symmetry for RCoO3 (R=Sm, Eu, Gd, and Dy). It is found that the Raman spectra of RCoO3 perovskites are strongly dependent on the ionic radius of the rare earth elements, and the frequency shift of the most intense modes of the orthorhombic samples are correlated with some structural parameters such as Co--O bond distances, ionic radius of the rare earth elements and Jahn--Teller distortion. It is clear that Raman spectroscopy has the advantage of sensitivity to structure distortion and oxygen motion.
 Select Interface Phonon Modes in Quantum Cascade Lasers YU Bing, CAO Jun-Cheng, FENG Song-Lin Chin. Phys. Lett. 2005, 22 (9): 2403-2406 .   Abstract   PDF(pc) (308KB) ( 435 ) We investigate the interface phonon assisted transition in GaAs/AlGaAs quantum cascade lasers (QCLs) by using the transfer matrix method based on the dielectric continuum model. Electron eigenvalues and eigenstates are calculated by solving Schrödinger equation and the Poisson equation self-consistently. The AlAs-like and upper GaAs-like interface phonon modes contribute most of the scattering rate. Interface phonon modes couple strongly with electrons at E2, and the magnitude of scattering rate between E2 and E1 is much larger than that between E3 and E1, which is helpful for the laser inversion between E3 and E2. The calculation can be easily applied to the design and simulation of QCLs.
 Select Oxygen Precipitation within Denuded Zone Founded by Rapid Thermal Processing in Czochralski Silicon Wafers CUI Can, YANG De-Ren, MA Xiang-Yang, FU Li-Ming, FAN Rui-Xin, QUE Duan-Lin Chin. Phys. Lett. 2005, 22 (9): 2407-2410 .   Abstract   PDF(pc) (451KB) ( 1596 ) Oxygen precipitation within the magic denuded zone (MDZ) founded by rapid thermal processing in Czochralski silicon (CZ-Si) wafers is investigated. After the standard MDZ process, the CZ-Si wafers are further subjected to two specific oxygen precipitation annealing, respectively. It is found that the MDZs in CZ-Si wafers shrunk notably because oxygen precipitation occurs within the MDZs. However, a width of substantial DZ still remains within the wafer. Therefore, it is believed that the outer region of the MDZs, which corresponds to the oxygen denuded zone formed in the course of rapid thermal process and high temperature annealing, is a substantial defect-free zone which acts as the active area for semiconductor devices.
 Select Synthesis and Field Emission of ZnO Nanostructures on CuO Catalyzed Porous Silicon Substrate YU Ke, ZHANG Yong-Sheng, OUYANG Shi-Xi, ZHANG Qing-Jie, LUO Lai-Qiang, ZHANG Qiu-Xiang, CHANG Zhong-Kun, LI Li-Jun, ZHU Zi-Qiang Chin. Phys. Lett. 2005, 22 (9): 2411-2414 .   Abstract   PDF(pc) (1296KB) ( 460 ) Mass production of ZnO nanobelts and hexagonal nanorods has been successfully synthesized on CuO catalyzed porous silicon (PS) using a simple vapour--solid (VS) growth method. A comparison of their morphologies is investigated by scanning electron microscopy (SEM). The transmission electron microscopy (TEM) confirms that ZnO nanobelts and nanorods are single crystalline with the growth direction of (0110) and (0001), respectively. Field emission tests indicate that the ZnO nanostructures on porous silicon have low turn-on field of about 3.6V/μm (at 1.0μA/cm2) and the threshold field of about 8.3V/μm (at 1.0mA/cm2), high emission site density (ESD) of approximately 104cm-2.
 Select Effect of Regrown Graphite on the Growth of Large Gem Diamonds by Temperature Gradient Method ZANG Chuan-Yi, JIA Xiao-Peng, MA Hong-An, TIAN Yu, XIAO Hong-Yu Chin. Phys. Lett. 2005, 22 (9): 2415-2417 .   Abstract   PDF(pc) (415KB) ( 602 ) Generally, when growing high-quality large gem diamond crystals by temperature gradient method under high pressure and high temperature, the crystal growth rate is only determined by the temperature gradient. However, we find that the seed crystal cannot completely absorb all the diffused carbon sources, when growing gem diamonds under a higher temperature gradient. Other influence factors appear, and the growth rate of growing diamonds is partly dependent on the crystalline form of superfluous unabsorbed carbon source, flaky regrown graphite or small diamond crystals nucleated spontaneously. The present form is determined by the growth temperature if the pressure is fixed. Different from spontaneous diamond nuclei, the appearance of regrown graphite in the diamond-stable region can retard the growth rate of gem diamonds substantially, even if the temperature gradient keeps unchanged. On the other hand, the formation mechanism of metastable regrown graphite in the diamond-stable region is also explained.
 Select Effect of Trimethyl Aluminium Surface Pretreatment on Atomic Layer Deposition Al2O3 Ultra-Thin Film on Si Substrate XU Min, LU Hong-Liang, DING Shi-Jin, SUN Liang, ZHANG Wei, WANG Li-Kang Chin. Phys. Lett. 2005, 22 (9): 2418-2421 .   Abstract   PDF(pc) (542KB) ( 1228 ) Ultra-thin Al2O3 dielectric films have been deposited on Si substrates by using trimethyl aluminium (TMA) and water as precursors in an atomic layer deposition (ALD) system. Growth of the interfacial layer between ultra-thin Al2O3 and the Si substrate is effectively suppressed by a long-time TMA surface pretreatment of the Si substrate prior to Al2O3 atomic layer deposition. High resolution transmission electron microscopy (TEM) images show that the thickness of the interfacial layer is reduced to be 0.5nm for the sample with TMA pretreatment lasting 3600s. The x-ray photoelectron spectroscopy results indicate that the Al2O3 film deposited on the TMA-pretreated Si surface exhibits very good thermal stability. However, a hysteresis of about 50mV is observed in the C--V curve of the samples with the TMA pretreatment.
 Select Effect of Precursor Mechanism on CO--NO Catalytic Reaction on Body-Centred Cubic Structure: Monte Carlo Simulation A. U. Qaisrani, M. Khalid, M. K. Khan Chin. Phys. Lett. 2005, 22 (9): 2422-2425 .   Abstract   PDF(pc) (231KB) ( 394 ) The CO--NO catalytic reaction on body-centred cubic (bcc) lattice is studied by Monte Carlo simulation. The simple Langmuir--Hinshelwood (LH) mechanism yields a steady reactive window, which is separated by continuous and discontinuous irreversible phase transitions. The effect of precursor mechanism on the phase diagram of the system is also studied. According to this mechanism, the precursor motion of CO molecules is considered only on the surface of bcc lattice. Some interesting observations are reported.
 Select Fibre-Coupling Zig-Zag Beam Deflection Technology for Investigation of Attenuation Process of Laser-Induced Shock Waves ZHANG Ping, BIAN Bao-Min, LI Zhen-Hua Chin. Phys. Lett. 2005, 22 (9): 2426-2428 .   Abstract   PDF(pc) (218KB) ( 516 ) A novel fibre-coupling zig-zag beam deflection technology is developed to investigate the attenuation process of laser-induced shock waves in air. Utilizing ordinal reflections of probe beams by a pair of parallel mirrors, a zig-zag beam field is formed, which has eleven probe beams in the horizontal plane. When a laser-induced shock wave propagates through the testing field, it causes eleven deflection signals one after another. The whole attenuation process of the shock wave in air can be detected and illuminated clearly on one experimental curve.
 Select Investigation of a Microcalorimeter for Thin-Film Heat Capacity Measurement YU Jun, TANG Zhen-An, ZHANG Feng-Tian, WEI Guang-Fen, WANG Li-Ding Chin. Phys. Lett. 2005, 22 (9): 2429-2432 .   Abstract   PDF(pc) (469KB) ( 841 ) A microcalorimeter is studied for testing heat capacity of thin films. The microcalorimeter is a suspended membrane supported by six microbridges, which is fabricated by the front-side surface micromachining. Compared to the bulk micro-machined one, the microcalorimeter has excellent mechanical strength and precisely controlled pattern size as well as good thermal characteristics that are essential to a microcalorimeter. The heating rate of the microcalorimeter is up to 2×105K/s with 4.5mW heating power in vacuum, and the heat capacity of the corresponding empty microcalorimeter is about 23.4nJ/K at 300K. By a pulse calorimetry, the heat capacity of Al thin films with thickness of 40--1150nm are measured in the temperature range from 300K to 420K in vacuum. The mass of each sample is evaluated and the specific heat capacity is calculated. The results show that specific heat capacity of the 1150-nm Al film agrees well with the data of bulk Al reported in the literature. For the thinner films, enhanced heat capacity is observed.
 Select A Quantitative Analysis of Modulation of the Fast Excitatory Postsynaptic Potential of Neurons in Rat Sympathetic Ganglia by a Low-Intensity Laser MO Hua, YANG Li-Jian, JIA Ya Chin. Phys. Lett. 2005, 22 (9): 2433-2436 .   Abstract   PDF(pc) (271KB) ( 616 ) We propose a mathematical model which can quantitatively describe the kinetics of postsynaptic membrane potential modulated by a low intensity laser. By virtue of the numerical computation, it is found that the height of peak of fast excitatory postsynaptic potential (f-EPSP) for intermediate laser power density (around 2mW/cm2) is higher than that for both small and large laser power densities, that is, of the f-EPSP peak height changes with the increasing laser power density (up to 5mW/cm2) in non-monotonic behaviour. The theoretical results are qualitatively consistent with the previous experimental data.
 Select Effects of Cross-Correlation Colour Noises on Tumour Growth Process WANG Xian-Ju, ZENG Chang-Chun, DENG Xiao-Yuan, LIU Song-Hao, LIU Liang-Gang Chin. Phys. Lett. 2005, 22 (9): 2437-2440 .   Abstract   PDF(pc) (236KB) ( 453 ) We present a tumour cell growth process model including a multiplicative coloured noise and an additive coloured noise correlated. How the noise cross-correlation intensity λ and correlation time τ can affect the steady state properties of tumour cell growth model are discussed by solving an approximative Fokker--Planck equation. It is found that the increase of noise correlation time τ can cause the tumour cell number increasing, but the increase of multiplicative noise intensity can cause the tumour cell number extinction. We also find that the increase of cross-correlation intensity λ in the case of 0 <λ<1 can cause the tumour cell number extinction, whereas increase of cross-correlation intensity λ in the case of λ < 0 can cause the tumour cell number increasing.
 Select How Is a Protein Molecule Nearsighted? GAO De, JI Qing, Lü Gang Chin. Phys. Lett. 2005, 22 (9): 2440-2442 .   Abstract   PDF(pc) (243KB) ( 521 ) The effect range of a local change of a protein molecule is calculated using a cluster method developed in this work based on the Gaussian software. This range is found to be about 8A, which gives a concrete estimation on the nearsightedness'' by Kohn for protein molecules. The cluster method can be applied to calculation of the electronic density of a large molecule such as a motor protein and can provide a basis for the dynamical analysis of a single protein molecule.
 Select Analysis of Near-Field Diffraction Pattern of a Metallic Probe Tip with the Boundary Diffraction Wave Method TANG Lin, GU Chun, CHEN Bo, WANG Pei, MING Hai, XIE Jian-Ping Chin. Phys. Lett. 2005, 22 (9): 2443-2446 .   Abstract   PDF(pc) (531KB) ( 619 ) The boundary diffraction wave theory is introduced to analyse a near-field diffraction (NFD) pattern of a metallic probe tip of apertureless scanning near-field microscopy. This method is simple and can give a clear physical picture. The polarization effect of the incident light and the different shapes of the metallic probe tip are simulated. The results show that the NFD pattern of the metallic probe tip is directly related to those factors.
 Select Dynamical Convergence Trajectory in Networks TAN Ning, ZHANG Yun-Jun, OUYANG Qi, GENG Zhi Chin. Phys. Lett. 2005, 22 (9): 2447-2450 .   Abstract   PDF(pc) (243KB) ( 545 ) It is well known that topology and dynamics are two major aspects to determine the function of a network. We study one of the dynamic properties of a network: trajectory convergence, i.e. how a system converges to its steady state. Using numerical and analytical methods, we show that in a logical-like dynamical model, the occurrence of convergent trajectory in a network depends mainly on the type of the fixed point and the ratio between activation and inhibition links. We analytically proof that this property is induced by the competition between two types of state transition structures in phase space: tree-like transition structure and star-like transition structure. We show that the biological networks, such as the cell cycle network in budding yeast, prefers the tree-like transition structures and suggest that this type of convergence trajectories may be universal.
 Select Excitation of Whistler-Mode (Chorus) Emissions during Terrestrial Substorms XIAO Fu-Liang, ZHAO Hua, HE Hui-Yong Chin. Phys. Lett. 2005, 22 (9): 2451-2454 .   Abstract   PDF(pc) (537KB) ( 522 ) The enhanced growth rate of whistler mode waves has been evaluated during an injection event associated with an isolated terrestrial substorm that occurred at 23:00 UT, on January 21, 1991. The electron phase space density observed by an LEPA instrument on the board of the CRRES spacecraft is modelled by using a bi-loss-cone distribution function (composed of a high anisotropic component and a quasi-isotropic component). During the injection event, the path integrated gain may increase by a factor of 5 over a frequency range near a few tenths of the electron gyrofrequency, which is consistent with the enhancement observed in the CRRES plasma wave experiment (PWE) emissions. Scattering of electrons by the enhanced whistler mode waves causes the pitch angle distribution of resonant electrons to a quasi isotropic (flat-top) distribution during the terrestrial substorm injection event.
 Select Connection of Screw Instability with Electric Current in an Accretion Disc around a Black Hole AN Xiao-Xia, WANG Ding-Xiong, GAN Zhao-Ming Chin. Phys. Lett. 2005, 22 (9): 2455-2458 .   Abstract   PDF(pc) (394KB) ( 511 ) The screw instability of the magnetic field is discussed based on its poloidal configuration generated by a single toroidal electric current flowing in the equatorial plane of a Kerr black hole (BH). The rotation of the BH relative to the disc induces an electromotive force, which in turn results in a poloidal electric current. By using Ampere's law, we calculate the toroidal component of the magnetic field and derive a criterion for the screw instability of the magnetic field connecting the rotating BH with its surrounding disc. It is determined that the screw instability is related to two parameters: the radius of the disc and the BH spin. The occurrence of screw instability is depicted in a parameter space. In addition, we discuss the effect of the screw instability on magnetic extraction of energy from the rotating BH.
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