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Volume 26 Issue 4
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GENERAL
New Periodic Solution to Jacobi Elliptic Functions of a (2+1)-Dimensional BKP Equation and a Generalized Klein-Gordon Equation
Ma Hong-Cai, Deng Ai-Ping, Qin Zhen-Yun
Chin. Phys. Lett. 2009, 26 (4): 040201 .   DOI: 10.1088/0256-307X/26/4/040201
Abstract   PDF(pc) (442KB) ( 818 )
With the help of the homogeneous balance method, the Jacobi elliptic expansion method and the auxiliary equation method, the first elliptic function equation is used to obtain the Jacobi doubly periodic wave solutions of the (2+1)-dimensional B-type Kadomtsev-Petviashvili (BKP) equation and the generalized Klein-Gordon equation. The method is also valid for other (1+1)-dimensional and higher dimensional systems.
Approximate Homotopy Direct Reduction Method: Infinite Series Reductions to Perturbed mKdV Equations
JIAO Xiao-Yu, YAO Ruo-Xia, , LOU Sen-Yu,
Chin. Phys. Lett. 2009, 26 (4): 040202 .   DOI: 10.1088/0256-307X/26/4/040202
Abstract   PDF(pc) (241KB) ( 570 )
An approximate homotopy direct reduction method is proposed and applied to two perturbed modified Korteweg-de Vries (mKdV) equations with fourth-order dispersion and second-order dissipation. The similarity reduction equations are derived to arbitrary orders. The method is valid not only for single soliton solutions but also for the Painlevé II waves and periodic waves expressed by Jacobi elliptic functions for both fourth-order dispersion and second-order dissipation. The method is also valid for strong perturbations.
Homoclinic Breather-Wave with Convective Effect for the (1+1)-Dimensional Boussinesq Equation
DAI Zheng-De, XIAN Da-Quan, LI Dong-Long
Chin. Phys. Lett. 2009, 26 (4): 040203 .   DOI: 10.1088/0256-307X/26/4/040203
Abstract   PDF(pc) (410KB) ( 553 )
A new type of two-wave solution, i.e. a homoclinic breather-wave solution with convective effect, for the (1+1)-dimensional Boussinesq equation is obtained using the extended homoclinic test method. Moreover, the mechanical feature of the wave solution is investigated and the phenomenon of homoclinic convection of the two-wave is exhibited on both sides of the equilibrium. These results enrich the dynamical behavior of (1+1)-dimensional nonlinear wave fields.
The generation of Entangled Qudits and their Application in Probabilistic Superdense Coding
Lin Qing
Chin. Phys. Lett. 2009, 26 (4): 040301 .   DOI: 10.1088/0256-307X/26/4/040301
Abstract   PDF(pc) (214KB) ( 517 )
A scheme of the generation of entangled qutrits is presented, and then is generalized to entangled ququads and entangled qudits. With the entangled qutrits, an experimental scheme of probability superdense coding with only linear optical elements is proposed. It is shown that this scheme will be suitable for the entangled ququads, even for the entangled qudits if some nonlinearity is used. This scheme is feasible in the laboratory with the current experimental technology.
Entanglement Evolution of a Two-Qubit System beyond Rotating-Wave Approximation
YANG Qing, YANG Ming, CAO Zhuo-Liang
Chin. Phys. Lett. 2009, 26 (4): 040302 .   DOI: 10.1088/0256-307X/26/4/040302
Abstract   PDF(pc) (1205KB) ( 513 )
Two noninteracting qubits, initially entangled in Bell states, are coupled to a one-mode cavity and evolve under its influence. The entanglement evolution of the two qubits is investigated beyond the rotating-wave approximation. It is shown that the counter-rotating wave terms have a great influence on the disentanglement behavior.
An Inequality Concerning Quantitative Duality in an Asymmetry Two-Way Interferometer
HAN Yang, WU Chun-Wang, WU Wei, CHEN Ping-Xing, LI Cheng-Zu
Chin. Phys. Lett. 2009, 26 (4): 040303 .   DOI: 10.1088/0256-307X/26/4/040303
Abstract   PDF(pc) (240KB) ( 423 )
We reinvestigate the measures concerning the notion of duality of a quantum system (the ``quanton'') in an asymmetry two-way interferometer. A new measure of the which-way information is introduced, which is based on the fidelity F instead of the trace distance Q of the final states of the which-way detector. An improved inequality is derived to be V2≤(R02- P2)(1-F)2, which is more stringent than the previous one of V2≤q(1-P2)(1-Q2).
A simple Scheme for Generating an n-Qubit W State in a Trapped-Ion System without a Lamb-Dicke Limit
ZHENG Xiao-Juan, XU Xue-Mei, OUYANG Fang-Ping, XU Hui,
Chin. Phys. Lett. 2009, 26 (4): 040304 .   DOI: 10.1088/0256-307X/26/4/040304
Abstract   PDF(pc) (241KB) ( 465 )
A simple and scalable scheme is proposed to generate a n-qubit W state in a trapped-ion system without the Lamb--Dicke limit. The n-qubit W state can be generated by the interaction between the ions and the laser field if the collective mode is initially prepared in the single-phonon state and each ion is in the ground state. The scheme only requires a single laser and avoids laser manipulation of the individual ion. The time required to complete the process decreases with the number of ions. The present scheme is not limited to small values of the LD parameter, which greatly enhances operation speeds.
Controlling Chaos Probability of a Bose-Einstein Condensate in a Weak Optical Superlattice
XU Jun, LUO Xiao-Bing
Chin. Phys. Lett. 2009, 26 (4): 040305 .   DOI: 10.1088/0256-307X/26/4/040305
Abstract   PDF(pc) (318KB) ( 421 )
The spatial chaos probability of a Bose--Einstein condensate perturbed by a weak optical superlattice is studied. It is demonstrated that the spatial chaotic solution appears with a certain probability in a given parameter region under a random boundary condition. The effects of the lattice depths and wave vectors on the chaos probability are illustrated, and different regions associated with different chaos probabilities are found. This suggests a feasible scheme for suppressing and strengthening chaos by adjusting the optical superlattice experimentally.
Statistical-Mechanical Entropy of a Black Hole with a Global Monopole to All Orders in Planck Length
HE Feng, ZHAO Fan
Chin. Phys. Lett. 2009, 26 (4): 040401 .   DOI: 10.1088/0256-307X/26/4/040401
Abstract   PDF(pc) (170KB) ( 474 )
Considering corrections to all orders in the Planck length on the quantum state density from the generalized uncertainty principle, we calculate the statistical entropy of the scalar field in the global monopole black hole spacetime without any artificial cutoff. It is shown that the entropy is proportional to the horizon area.
Spontaneous Emission of an Atom in a Spacetime with Two Parallel Reflecting Boundaries
HUANG Tie-Tie, , ZHU Zhi-Ying, ZHU Yun-Feng, YU Hong-Wei,
Chin. Phys. Lett. 2009, 26 (4): 040402 .   DOI: 10.1088/0256-307X/26/4/040402
Abstract   PDF(pc) (237KB) ( 378 )
We consider an inertial two-level atom in interaction with a real massless scalar quantum field in a spacetime between two parallel reflecting plane boundaries, and calculate the contributions of vacuum fluctuations and radiation reaction to the rate of change of the atomic energy. Our results show that there exists a regime of the separation L between the two boundaries such that the excited atom's spontaneous emission is impossible. There also exist certain values of the atom's position such that the corrections due to the presence of boundaries balance each other, so that the atom's spontaneous emission rate is the same as if there were no boundaries at all.
Measurement of Magnetic Properties of an Inertial Sensor with a Torsion Balance
TU Hai-Bo, BAI Yan-Zheng, ZHOU Ze-Bing, LIANG Yu-Rong, LUO Jun
Chin. Phys. Lett. 2009, 26 (4): 040403 .   DOI: 10.1088/0256-307X/26/4/040403
Abstract   PDF(pc) (391KB) ( 441 )
A torsion balance is constructed to accurately measure the magnetic properties of the real proof mass of the inertial sensor. The magnetic susceptibility and remnant moment of a titanium proof mass are measured in the first experiment, and further improvements and the potential sensitivity are also discussed. This is significant for choosing the material of the proof mass and investigating the magnetic disturbances acting on the proof mass.
Periodic, Quasiperiodic and Chaotic Discrete Breathers in a Parametrical Driven Two-Dimensional Discrete Klein-Gordon Lattice
XU Quan, TIAN Qiang
Chin. Phys. Lett. 2009, 26 (4): 040501 .   DOI: 10.1088/0256-307X/26/4/040501
Abstract   PDF(pc) (415KB) ( 416 )
We study a two-dimensional lattice of anharmonic oscillators with only quartic nearest-neighbor interactions, in which discrete breathers can be explicitly constructed by an exact separation of their time and space dependence. DBs can stably exist in the two-dimensional Klein-Gordon lattice with hard on-site potential. When a parametric driving term is introduced in the factor multiplying the harmonic part of the on-site potential of the system, we can obtain the stable quasiperiodic discrete breathers and chaotic discrete breathers by changing the amplitude of the driver.
Rectification Efficiency of Two Harmonically Coupled Particles
SUN Lian-Xiu
Chin. Phys. Lett. 2009, 26 (4): 040502 .   DOI: 10.1088/0256-307X/26/4/040502
Abstract   PDF(pc) (228KB) ( 501 )
Transportation properties of two harmonically coupled particles moving in a flashing or rocking ratchet potential are investigated in terms of Langevin simulation. The efficiency for rectification of non-equilibrium fluctuation is calculated by using a new definition. The results show that both the average current and efficiency of two coupled particles in the flashing ratchet are larger than that of a single particle and these quantities are non-monotonous functions of the potential remaining time
Frequency Sensitivity of Signal Detection in Scale-Free Networks
LU Fa-Ming, LIU Zong-Hua
Chin. Phys. Lett. 2009, 26 (4): 040503 .   DOI: 10.1088/0256-307X/26/4/040503
Abstract   PDF(pc) (488KB) ( 609 )
It has been recently reported that scale-free topology favors the detection of a weak signal because of the higher amplification at the hub node than that at other nodes [Phys. Ref. E 78(2008)046111]. We investigate the corresponding synchronization behaviors and find that the favorite detection depends not only on the coupling and noise strengths but also on the frequency of the external signal. We reveal theoretically and numerically that the amplification effect of the hub node will decrease monotonously with the external frequency, which is useful to understand the high sensitivity of animal visual and auditory systems to weak external signals.
Adaptive Function Projective Synchronization of Discrete-Time Chaotic Systems
LI Yin, LI Biao, CHEN Yong,
Chin. Phys. Lett. 2009, 26 (4): 040504 .   DOI: 10.1088/0256-307X/26/4/040504
Abstract   PDF(pc) (566KB) ( 537 )
By backstepping control law and the active control method, adaptive function projective synchronization of 2D and 3D discrete-time chaotic systems with uncertain parameters are investigated. To illustrate the effectiveness of the new scheme, some numerical examples are given.
Point Spread Function Estimation for a Turbulence-Degenerated Image Based on Àtrous Wavelet Transform
CHEN Bo, GENG Ze-Xun, SHEN Jun, YANG Yang
Chin. Phys. Lett. 2009, 26 (4): 040701 .   DOI: 10.1088/0256-307X/26/4/040701
Abstract   PDF(pc) (529KB) ( 670 )
The observed object images are seriously blurred because of the influence of atmospheric turbulence. The restoration is required for the reconstruction of turbulence degraded images. Point spread function (PSF) estimation, an essential part of image restoration, has no accurate estimation algorithm at present. Based on the àtrous wavelet, we deduce a novel PSF estimation algorithm. First, the àtrous wavelet at varying scales is transformed. Then, on the basis of the relation among the local maxima of the modulus of the wavelet coefficients at different scales, the Lipschitz exponent of the wavelet coefficients is computed, thus the variance of a PSF is estimated. From this estimated variance, one is able to obtain the PSF. Consequently, the object image can be restored. Experimental results show that the proposed method is highly effective with good performance.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
A Light-Cone QCD Inspired Effective Hamiltonian Model with SU(3) Flavor Mixing
GUO Xiao-Bo, TAO Jun, LI Lei, ZHOU Shan-Gui, WANG Shun-Jin,
Chin. Phys. Lett. 2009, 26 (4): 041201 .   DOI: 10.1088/0256-307X/26/4/041201
Abstract   PDF(pc) (282KB) ( 436 )
The effective light-cone Hamiltonian is extended to include the SU(3) flavor mixing interaction besides the confining potential. Solving the coupled J=0 mass eigen equations for the up, down, and strange quark components numerically, the masses of π0 and η, their radial wave functions, and rms radii are obtained in agreement with the experimental data.
Misidentification or Identification Rates for Four Kinds of Particles on BES-II
LIU Hui-Hui, LI Xin-Zhong, CHEN Jiang-Chuan
Chin. Phys. Lett. 2009, 26 (4): 041202 .   DOI: 10.1088/0256-307X/26/4/041202
Abstract   PDF(pc) (446KB) ( 400 )
Using the data samples collected at and around the center-of-mass energies of 3.097GeV and 3.773GeV with the BES-II detector at the BEPC collider, we select the pure particle samples of muon, electron, kaon and pion, and their mutual (mis)identification rates are also obtained.
Nuclear -K Bound States in 4He and 3He
LI Yi-He, WU Shi-Shu
Chin. Phys. Lett. 2009, 26 (4): 041301 .   DOI: 10.1088/0256-307X/26/4/041301
Abstract   PDF(pc) (200KB) ( 425 )
We construct a phenomenological -KN interaction which reproduces the two resonances: the energy of the first resonance is 1420MeV and the other is
1392MeV. The λ(1405) is found by a superposition of the two resonances with appropriate weights. Within the framework of the Brueckner-Hartree-Fock theory, we have studied K--3He(T=0) and K--4He(T=1/2). The binding energy BK- is 93MeV(72MeV) and the width Γ is 13MeV(25MeV) for K--3He(T=0) (K--4He(T=1/2)).
J/ψ Inclusive Photon Spectrum at BESIII
BIAN Jian-Ming, SHEN Xiao-Yan, LI Wei-Guo
Chin. Phys. Lett. 2009, 26 (4): 041302 .   DOI: 10.1088/0256-307X/26/4/041302
Abstract   PDF(pc) (294KB) ( 414 )
With a 15M J/ψ inclusive Monte Carlo sample, the absolute branching fraction of J/ψ→γ\η' from the J/ψ inclusive photon spectrum is measured to be Br(J/ψ→γ\η')=(4.68±0.08±0.27)×10-3, which is in good agreement with the input value. The J/ψ→γfJ(2220) is also searched for using the same sample. Under our assumptions, the statistical significances of J/ψ→γfJ(2220) are larger than 7\σ.
NUCLEAR PHYSICS
Ion Beam Analysis of the Annealing Behavior of Helium in Ti Films
HE Zhi-Jiang, SHI Li-Qun, LIU Chao-Zhuo, ZHANG Lei, LU Yong-Fang, ZHANGBin
Chin. Phys. Lett. 2009, 26 (4): 042501 .   DOI: 10.1088/0256-307X/26/4/042501
Abstract   PDF(pc) (429KB) ( 470 )
We present a theoretical calculation finding that a spectrum from ion beam analysis will change at different stopping cross sections. This is more visible at a deeper place in the sample. Helium-contained Ti films annealed at different temperatures are prepared to gain different stopping cross sections whereby the stopping cross section will change with the helium phase states and the pressure of helium bubbles. Then ion beam analysis is used to measure the concentration of helium. It is found that the concentration curve rises greatly after the sample is annealed at 673K which reflects the increasing size of the helium bubble. The results are consistent with that of positron annihilation radiation spectra which are performed by using a changeable energy positron beam.
Effect of Anode Floating Voltage and its Applications in Characterizing Silicon Drift Detectors
WU Guang-Guo, LI Hong-Ri, LIANG Kun, YANG Ru, CAO Xue-Lei, WANGHuan-Yu, AN Jun-Ming, HU Xiong-Wei, HAN De-Jun
Chin. Phys. Lett. 2009, 26 (4): 042901 .   DOI: 10.1088/0256-307X/26/4/042901
Abstract   PDF(pc) (430KB) ( 529 )
Anode floating voltage is predicted and investigated for silicon drift detectors (SDDs) with an active area of 5mm2 fabricated by a double-side parallel technology. It is demonstrated that the anode floating voltage increases with the increasing inner ring voltage, and is almost unchanged with the external ring voltage. The anode floating voltage will not be affected by the back electrode biased voltage until it reaches the full-depleted voltage (-50V) of the SDD. Theoretical analysis and experimental results show that the anode floating voltage is equal to the sum of the inner ring voltage and the built-in potential between the p+ inner ring and the n+ anode. A fast checking method before detector encapsulation is proposed by employing the anode floating voltage along with checking the leakage current, potential distribution and drift properties.
ATOMIC AND MOLECULAR PHYSICS
Effect of Electron Correlations and Breit Interactions on Ground-State Fine-Structures along the Nitrogen-Like Isoelectronic Sequence
WANG Xiao-Lu, LU Wen-Lai, GAO Xiang, LI Jia-Ming,
Chin. Phys. Lett. 2009, 26 (4): 043101 .   DOI: 10.1088/0256-307X/26/4/043101
Abstract   PDF(pc) (342KB) ( 559 )
The accurate atomic data of nitrogen and nitrogen-like ions have an importance role in fusion plasma studies and astrophysics studies. The recise calculation of fine-structures is required to obtain such atomic data. Along the whole nitrogen isoelectronic sequence, the contributions of the
electron correlations, the Breit interactions and the quantum electrodynamics corrections on the ground-state fine-structures are elucidated. When Z is low, the electron correlations are important, and the Breit interactions, which cannot be neglected cause interesting anomalous fine-structure splittings. When Z is high, the electron correlations are less important, and the Breit interactions are important in addit
Electron-Helium Scattering in a Bichromatic Laser Field in the Second-Order Born Approximation
ZHOU Bin, LI Shu-Min,
Chin. Phys. Lett. 2009, 26 (4): 043401 .   DOI: 10.1088/0256-307X/26/4/043401
Abstract   PDF(pc) (281KB) ( 539 )
The elastic scattering of electrons in atomic helium assisted by a bichromatic laser field is investigated in the second order Born approximation. The target atom is approximated by a simple screening potential. The dependence of the differential cross section on the relative phase between the two laser components is calculated, and compared with the recent results of first order Born approximation [Sun J F, Liang M C and Zhu Z L 2007 Chin. Phys. Lett. 24 2572].
Three-Dimensional Array for 40Ca+ Ion Trapping
WAN Jin-Yin, LIU Liang
Chin. Phys. Lett. 2009, 26 (4): 043701 .   DOI: 10.1088/0256-307X/26/4/043701
Abstract   PDF(pc) (450KB) ( 416 )
We present a three-dimensional scalable linear ion trap scheme for ion trapping and discuss its applications for the optical frequency standard and scalable quantum information processing with its parallel strings of trapped 40Ca+ ions. The geometry here contains nine equal-distance parallel rods driven by rf, which form trapping potentials for radial confinement and two end ring electrodes biased at a few volts for axial confinement. Its feasibility is calculated by using the finite element analysis method.
FUNDAMENTAL AREAS OF PHENOMENOLOGY(INCLUDING APPLICATIONS)
Microwave Absorption and Response Modeling of Nanocomposites Embedded SiC Nanoparticles
LU Ran, FANG Xiao-Yong, KANG Yu-Qing, YUAN Jie, CAO Mao-Sheng
Chin. Phys. Lett. 2009, 26 (4): 044101 .   DOI: 10.1088/0256-307X/26/4/044101
Abstract   PDF(pc) (387KB) ( 700 )
We study the mechanism of microwave response properties of SiCp/paraffin nanocomposites and propose a microwave absorption model of nanocomposites based on the conservation law of energy and the theory of electromagnetic scattering. Using the model we calculate the reflectivity of SiCp/paraffin nanocomposites ranging from 2GHz to 18GHz. The calculated results are very consistent with the experimental data in the frequency range investigated.
Tunable Effect of Double-Connective Dendritic Left-Handed Metamaterials Based on Electrorheological Fluids
GUO Ji-Quan, LUO Chun-Rong, ZHAO Xiao-Peng
Chin. Phys. Lett. 2009, 26 (4): 044102 .   DOI: 10.1088/0256-307X/26/4/044102
Abstract   PDF(pc) (493KB) ( 430 )
We present double-connective dendritic unit pairs which exhibit the left-handed property for electromagnetic wave normal incidence. Based on the tunable characteristics of electrorheological fluids (ERF) as the electric field, we experimentally study the influence of the distance of electrodes, the number of stacked layers, and the intensity of the external electric field upon the ERF to the left-handed transmission peak of the double-connective dendritic structure. The results show that the transmission could be enhanced with the increase of distance or the number of layers. Furthermore, by changing the intensity of the electric fields, the left-handed transmission peak can be modulated actively, and the maximum shift is up to 160MHz.
Numerical Simulations on the Formation of Speckles in Nanofluids Illuminated by a TEM00 Laser Beam
YAN Qin, QIAN Ming, NI Xiao-Wu, LU Jian, LI Qiang, XUAN Yi-Min
Chin. Phys. Lett. 2009, 26 (4): 044201 .   DOI: 10.1088/0256-307X/26/4/044201
Abstract   PDF(pc) (792KB) ( 566 )
On the basis of a Rayleigh scattering model for a single nanoparticle illuminated by a TEM00 laser beam, we theoretically and numerically study the speckle formation when nanofluids are illuminated by a TEM00 laser beam. The results show that the laser speckles possess a Gaussian distribution, which are in agreement with the experimental results. The results may be useful for using a laser speckle velocimetry to determine the velocitiies of nanoparticles in nanofluids.
Coherent Beam Combining of Three Watt-Level Fiber Amplifiers Using a DSP-Based Stochastic Parallel Gradient Descent Algorithm
ZHOU Pu, LIU Ze-Jin, WANG Xiao-Lin, MA Yan-Xing, LI Xiao, XU Xiao-Jun, GUO Shao-Feng
Chin. Phys. Lett. 2009, 26 (4): 044202 .   DOI: 10.1088/0256-307X/26/4/044202
Abstract   PDF(pc) (445KB) ( 653 )
We present an experimental study on coherent beam combining of three watt-level fiber amplifiers using a stochastic parallel gradient descent (SPGD) algorithm. Phase controlling is performed by running the SPGD algorithm on a digital-signal-processor (DSP) chip with a voltage updating rate of 16500 times per second. Energy encircled in the target pinhole is 2.62 times more than that in an open loop. The combining efficiency is as high as 87%.
A Continuous-Wave Ho:YAlO3 Laser with Output 8.5W Pumped by a 1.91μm Laser at Room Temperature
YAO Bao-Quan, YANG Xiao-Tao, DUAN Xiao-Ming, WANG Tian-Heng, JU You-Lun, WANG Yue-Zhu
Chin. Phys. Lett. 2009, 26 (4): 044203 .   DOI: 10.1088/0256-307X/26/4/044203
Abstract   PDF(pc) (345KB) ( 472 )
A cw high efficient Ho:YAlO3 laser pumped by 1.91μm diode-pumped Tm:YLF laser at room temperature is realized. The maximum output power reaches 8.5W when the incident pump power is 15.6W. The slope efficiency is 63.7%, and the Tm:YLF to Ho:YAP optical conversion efficiency is 54.5%. The laser wavelength is 2118.3nm when the transmission of output coupler is 30%. The beam quality factor is M2~1.39 measured by the traveling knife-edge method.
Coherent Beam Combination of Three Fiber Amplifiers with Multi-dithering Technique
MA Yan-Xing, LIU Ze-Jin, ZHOU Pu, WANG Xiao-Lin, MA Hao-Tong, LI Xiao, XU Xiao-Jun, SI Lei
Chin. Phys. Lett. 2009, 26 (4): 044204 .   DOI: 10.1088/0256-307X/26/4/044204
Abstract   PDF(pc) (555KB) ( 831 )
Coherent beam combination of three W-level fiber amplifiers with multi-dithering technique is demonstrated. The multi-dithering technique is used for phase control in two channels. In the experiment, two channels are modulated by sine wave with 70kHz and 100kHz respectively, and two regular commercial DSP lock-in amplifiers and an industrial computer are used for electric signal processing in the feedback loop. The fringe contrast is advanced from 12% to 81%, and 78% coherent combination efficiency is obtained when the feedback loop is closed.
Ultra-Stable Rubidium-Stabilized External-Cavity Diode Laser Based on the Modulation Transfer Spectroscopy Technique
QI Xiang-Hui, CHEN Wen-Lan, YI Lin, ZHOU Da-Wei, ZHOU Tong, XIAO Qin, DUAN Jun, ZHOU Xiao-Ji, CHEN Xu-Zong
Chin. Phys. Lett. 2009, 26 (4): 044205 .   DOI: 10.1088/0256-307X/26/4/044205
Abstract   PDF(pc) (359KB) ( 1100 )
We construct an ultra-stable external-cavity diode laser via modulation transfer spectroscopy referencing on a hyperfine component of the 87Rb D2 lines at 780nm. The Doppler-free dispersion-like modulation transfer signal is obtained with high signal-to-noise-ratio. The instability of the laser frequency is measured by beating with an optical frequency comb which is phase-locked to an ultra-stable oven controlled crystal oscillator. The Allan deviation is 3.9×10-13 at 1s averaging time and 9.8×10-14 at 90s averaging time.
Optimal Truncation of Element Beam in a Coherent Fiber Laser Array
ZHOU Pu, WANG Xiao-Lin, MA Yan-Xing, MA Hao-Tong, LIU Ze-Jin, XU Xiao-Jun
Chin. Phys. Lett. 2009, 26 (4): 044206 .   DOI: 10.1088/0256-307X/26/4/044206
Abstract   PDF(pc) (532KB) ( 965 )
The beam quality of a coherent fiber laser array often suffers from the low fill factor of the Gaussian laser array. One simple and effective approach to improve the fill factor is to truncate the array element properly. An analytical expression for far-field intensity distribution of a truncated coherent fiber laser array is derived. Optimal truncation of the element beam in different coherent fiber laser arrays is obtained by using energy encircled in the far-field central-lobe as the beam quality criterion. By optimal truncation, energy encircled in the central-lobe can be 97% compared with the ideal case. The shift in optimal truncation parameter in the case of phase noise is also
analyzed.
An Array of One-Dimensional Porous Silicon Photonic Crystal Reflector Islands for a Far-Infrared Image Detector
MIAO Feng-Juan, ZHANG Jie, XU Shao-Hui, WANG Lian-Wei, CHU Jun-Hao, CAO Zhi-Shen, ZHAN Peng, WANG Zhen-Lin
Chin. Phys. Lett. 2009, 26 (4): 044207 .   DOI: 10.1088/0256-307X/26/4/044207
Abstract   PDF(pc) (957KB) ( 442 )
With the aid of photolithography, an array of one-dimensional porous silicon photonic crystal reflector islands for a far infrared image detector ranging from 10μm to 14μm is successfully fabricated. Silicon nitride formed by low pressure chemical vapor deposition (LPCVD) was used as the masking layer for the island array formation. After etching, the microstructures were examined by a scanning electron microscope and the optical properties were studied by Fourier transform infrared spectroscopy, the result indicates that the multilayer structure could be obtained in the perpendicular direction via periodically alternative etching current in each pre-pattern. At the same time, the island array has a well-proportioned lateral etching effect, which is very useful for the thermal isolation in lateral orientation of the application in devices. It is concluded that regardless of the absorption of the deposition layer on the substrate, the localized photonic crystalline islands have higher reflectivity. The designed islands structure not only prevents the cracking of the porous silicon layers but is also useful for the application in the cold part for the sensor devices and the interconnection of each pixel.
Generation of a Sub-10fs Laser Pulse by a Ring Oscillator with a High Repetition Rate
ZHANG Qing, ZHAO Yan-Ying, WEI Zhi-Yi
Chin. Phys. Lett. 2009, 26 (4): 044208 .   DOI: 10.1088/0256-307X/26/4/044208
Abstract   PDF(pc) (275KB) ( 983 )
A compact femtosecond Ti:sapphire ring oscillator composed of chirped mirrors is designed. By accurately optimizing the intra-cavity dispersion and the mode locking range of the ring configuration, we generate laser pulses as short as 7.7fs with a repetition rate as high as 745MHz. The spectrum spans from 660nm to 940nm and the average output power is 480mW under the cw pump laser of 7.5W.
Photonic Crystal Fiber Source of Quantum Correlated Photon Pairs in the 1550nm Telecom Band
CUI Liang, LI Xiao-Ying, FAN Hai-Yang, YANG Lei, MA Xiao-Xin
Chin. Phys. Lett. 2009, 26 (4): 044209 .   DOI: 10.1088/0256-307X/26/4/044209
Abstract   PDF(pc) (273KB) ( 583 )
A source of quantum correlated photon pairs in the 1550nm telecom band obtained by a pumping 11m photonic crystal fiber with 10ps pulse trains is experimentally demonstrated. We investigate how the birefringence of the fiber influences the purity of the photon pairs. We also present the frequency correlation of the signal and idler photon pairs. The experimental results are useful for developing a compact source of photon pairs well suited for quantum communication.
Transmission Bandwidth Tunability of a Liquid-Filled Photonic Bandgap Fiber
ZOU Bing, LIU Yan-Ge, DU Jiang-Bing, WANG Zhi, HAN Ting-Ting, XU Jian-Bo, LI Yuan, LIU Bo
Chin. Phys. Lett. 2009, 26 (4): 044210 .   DOI: 10.1088/0256-307X/26/4/044210
Abstract   PDF(pc) (457KB) ( 646 )
A temperature tunable photonic bandgap fiber (PBGF) is demonstrated by an index-guiding photonic crystal fiber filled with high-index liquid. The temperature tunable characteristics of the fiber are experimentally and numerically investigated. Compression of transmission bandwidth of the PBGF is demonstrated by changing the temperature of part of the fiber. The tunable transmission bandwidth with a range of 250nm is achieved by changing the temperature from 30°C to 90°C.
Investigation on Characteristics and the Improving Method of Double Loop Optical Buffer
WANG Yong-Jun, WU Chong-Qing, WANG Zhi, YANG Shuang-Shou, ZHAO Shuang, WANG Ya-Ping, SHU Da, ZHAO Xi
Chin. Phys. Lett. 2009, 26 (4): 044211 .   DOI: 10.1088/0256-307X/26/4/044211
Abstract   PDF(pc) (716KB) ( 458 )
We establish an equivalent cascaded semiconductor optical amplifier system model to analyze the characteristics of the double loop optical buffer (DLOB). The theoretical analysis finds that the performance of the DLOB can be improved by inserted amplifying process in an interval of some cycles. The experiment demonstrates that the buffered cycles can be improved from 20 to 50 and the bit error rate is less than 10-9 by inserting amplifying process in an interval of about 10 cycles.
Ground State of Jaynes-Cummings Model: Comparison of Solutions with and without the Rotating-Wave Approximation
LI Xiao-Hong, WANG Ke-Lin, LIU Tao
Chin. Phys. Lett. 2009, 26 (4): 044212 .   DOI: 10.1088/0256-307X/26/4/044212
Abstract   PDF(pc) (369KB) ( 609 )
The eigenenergy spectrum of the Jaynes--Cummings (JC) model with and without the rotating-wave approximation (RWA) is investigated. The numerical analysis indicates that the non-RWA spectrum can only be approximated by the RWA in the range of sufficiently small coupling constant and detuning. In other region, the counter-rotating terms remarkably change the nature of the RWA energy spectrum. A simple expression with high accuracy for ground eigenenergy and eigenvector for non-RWA is available. The ground eigenvector for non-RWA shows that the ground state is not a dark state and very different from that of RWA which is a dark state.
Intermediate Self-similar Solutions of the Nonlinear Schrödinger Equation with an Arbitrary Longitudinal Gain Profile
ZHAO Wei, LU Ke-Qing, ZHANG Yi-Qi, YANG Yan-Long, WANG Yi-Shan, LIUXue-Ming
Chin. Phys. Lett. 2009, 26 (4): 044213 .   DOI: 10.1088/0256-307X/26/4/044213
Abstract   PDF(pc) (321KB) ( 492 )
We study pulse propagation in a normal-dispersion optical fibre amplifier with an arbitrary longitudinal gain profile by self-similarity techniques. We show the functional form of the development of low-amplitude wings on the parabolic pulse, which are associated with the evolution of an arbitrary input pulse to the asymptotic parabolic pulse solution. It is found that for the increasing gain the amplifier output corresponding to the input Gaussian pulse converges to the asymptotic parabolic pulse solution more quickly than the output obtained with the input hyperbolic secant pulse, whereas for the decreasing gain the input pulse profiles have nearly no effect on the speed of convergence to the parabolic pulse solution. These theoretical results are confirmed by numerical simulations.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
Calculated Optical Properties of Dielectric Shell Coated Gold Nanorods
CAO Min, WANG Meng, GU Ning
Chin. Phys. Lett. 2009, 26 (4): 045201 .   DOI: 10.1088/0256-307X/26/4/045201
Abstract   PDF(pc) (328KB) ( 869 )
Optical absorption spectra of dielectric shell coated gold nanorods are simulated using the discrete dipole approximation method. The influence of the aspect ratio, shell thickness, dielectric constant of the shell, and surrounding medium on the longitudinal resonance mode is investigated. It is found that the coated dielectric shell does not affect the trend in the dependence of resonance position on the aspect ratio, while it broadens the resonant line width and reduces the sensitivity of plasmon resonance in response to changes of the surrounding medium. Furthermore, the difference of dielectric constants between the shell and surrounding medium plays an important role in determining the resonance position. The screening effect of the dielectric shell tends to be less apparent for a thicker shell thickness.
Numerical Investigation of Finite k Effect on Damping Rate of Geodesic Acoustic Mode in Collisionless Plasmas
GUO Wen-Feng, WANG Shao-Jie, LI Jian-Gang
Chin. Phys. Lett. 2009, 26 (4): 045202 .   DOI: 10.1088/0256-307X/26/4/045202
Abstract   PDF(pc) (275KB) ( 383 )
Numerical method is applied to the investigation of the GAM damping rate with the finite k effects included. It is found that generally the damping rate given by the analytical method is smaller than that given by the numerical method, and the analytical damping rate has good approximation in the high q region (q>4). The difference between the analytical and numerical damping rates increases with the increasing k\ρi. However, for the short-wavelength case (k\ρi =0.2), the analytical methods are only good enough around q=4 because of the slow convergence of Bessel function with the large variable.
Nonplanar Ion-Acoustic Solitons in Electron-Positron-Ion Quantum Plasmas
S. A. Khan, S. Mahmood, Arshad M. Mirza
Chin. Phys. Lett. 2009, 26 (4): 045203 .   DOI: 10.1088/0256-307X/26/4/045203
Abstract   PDF(pc) (241KB) ( 1003 )
The propagation of nonplanar quantum ion-acoustic solitary waves in a dense, unmagnetized electron-positron-ion (e-p-i) plasma are studied by using the Korteweg-de Vries (KdV) model. The quantum hydrodynamic (QHD) equations are used taking into account the quantum diffraction and quantum statistics corrections. The analytical and numerical solutions of KdV equation reveal that the nonplanar ion-acoustic solitons are modified significantly with quantum corrections and positron concentration, and behave differently in different
geometries.
Structure and Spectrum of Binary Classic Systems Confined in a Parabolic Trap
YANG Wen, ZENG Zhi
Chin. Phys. Lett. 2009, 26 (4): 045204 .   DOI: 10.1088/0256-307X/26/4/045204
Abstract   PDF(pc) (240KB) ( 403 )
The static and dynamic properties of the two-dimensional classic system of two-species interacting charged particles in a parabolic trap are studied. The ground state energy and configuration for different kinds of binary systems are obtained by Monte Carlo simulation and Newton optimization. The
spectrum and normal modes vectors can be gained by diagonalizing the ynamical matrix of the system. It is found that the total particle number, particle number and mass-to-charge ratio of each species are decisive factors for the system structure and spectrum. The three intrinsic normal modes of single species Coulomb clusters are inherent, concluded from our numerical simulations and analytical results.
CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES
Defects in Si-Rich SiO2 Films Prepared by Radio-Frequency Magnetron Co-sputtering Using Variable Energy Positron Annihilation Spectroscopy
HAO Xiao-Peng, ZHOU Chun-Lan, WANG Bao-Yi, WEI Long
Chin. Phys. Lett. 2009, 26 (4): 046101 .   DOI: 10.1088/0256-307X/26/4/046101
Abstract   PDF(pc) (524KB) ( 633 )
Si-rich SiO2 films prepared by rf magnetron co-sputtering method are studied by slow positron beams. The negatively charge point defects (probably Pb centres or peroxy radicals) at the silicon nanocluster (nc-Si)/SiO2 interface are observed by Doppler broadening spectra. Coincidence Doppler-broadening spectra show that positrons have a higher annihilation probability with core electrons nearby oxygen atoms than silicon atoms. The formation of N-related bonds may be the reason for the prevention of the migration reaction of Si and O atoms, hence nc-Si formation is inhibited by annealing in nitrogen compared to in vacuum.
High-Density Stacked Ru Nanocrystals for Nonvolatile Memory Application
MAO Ping, ZHANG Zhi-Gang, PAN Li-Yang, XU Jun, CHEN Pei-Yi
Chin. Phys. Lett. 2009, 26 (4): 046102 .   DOI: 10.1088/0256-307X/26/4/046102
Abstract   PDF(pc) (579KB) ( 419 )
Stacked ruthenium (Ru) nanocrystals (NCs) are formed by rapid thermal annealing for the whole gate stacks and embedded in memory structure, which is compatible with conventional CMOS technology. Ru NCs with high density (3×1012cm-2), small size (2-4nm) and good uniformity both in aerial distribution and morphology are formed. Attributed to the higher surface trap density, a memory window of 5.2V is obtained with stacked Ru NCs in comparison to that of 3.5V with single-layer samples. The stacked Ru NCs device also exhibits much better retention performance because of Coulomb blockade and vertical uniformity between stacked Ru NCs.
Identification of Acceptor States in Li-N Dual-Doped p-Type ZnO Thin Films
ZHANG Yin-Zhu, LU Jian-Guo, YE Zhi-Zhen, HE Hai-Ping, CHEN Lan-Lan, ZHAO Bing-Hui
Chin. Phys. Lett. 2009, 26 (4): 046103 .   DOI: 10.1088/0256-307X/26/4/046103
Abstract   PDF(pc) (395KB) ( 535 )
Li-N dual-doped p-type ZnO (ZnO:(Li,N)) thin films are prepared by pulsed laser deposition. The optical properties are studied using temperature-dependent photoluminescence. The LiZn-NO complex acceptor with an energy level of 138meV is identified from the free-to-neutral-acceptor (e, A0) emission. The Haynes factor is about 0.087 for the LiZn-NO complex acceptor, with the acceptor bound-exciton binding energy of 12meV. Another deeper acceptor state located at 248meV, also identified from the (e, A0) emission, is attributed to zinc vacancy acceptor. The two acceptor states might both contribute to the observed p-type conductivity in ZnO:(Li,N).
Raman Investigation of BaWO4-II Phase under Hydrostatic Pressures up to 14.8GPa
TAN Da-Yong, XIAO Wan-Sheng, ZHOU Wen-Ge, SONG Mao-Shuang, XIONG Xiao-Lin, CHEN Ming
Chin. Phys. Lett. 2009, 26 (4): 046301 .   DOI: 10.1088/0256-307X/26/4/046301
Abstract   PDF(pc) (330KB) ( 518 )
The BaWO4-II phase is synthesized at 5.0GPa and 610°C with a cubic-anvil apparatus and identified by XRD. Raman scattering measurement is carried out to investigate the phase behaviour of a pure BaWO4-II phase (space group P21/n, Z=8) under hydrostatic pressures up to 14.8GPa at ambient temperature. In each spectrum recorded for this phase, 27 Raman modes are observed, and all bands shift toward higher wavenumber with a pressure dependence ranging from 3.8 to 0.2cm-1/GPa. No pressure-driven phase transition occurs in the entire pressure range in this study. Our results indicate that the previously reported high pressure phase of BaWO4 at pressure above about 10GPa and room temperature (Errandonea et al. Phys. Rev. B 73(2006)224103) is not the BaWO4-II phase.
Theoretical Study of Elastic Properties of Tungsten Disilicide
XU Guo-Liang, ZHANG Dong-Ling, XIA Yao-Zheng, LIU Xue-Feng, LIU Yu-Fang, ZHANG Xian-Zhou
Chin. Phys. Lett. 2009, 26 (4): 046302 .   DOI: 10.1088/0256-307X/26/4/046302
Abstract   PDF(pc) (380KB) ( 618 )
The plane-wave pseudopotential method using the generalized gradient approximation within the framework of density functional theory is applied to analyse the lattice parameters, elastic constants, bulk moduli, shear moduli and Young's moduli of WSi2. The quasi-harmonic Debye model, using a set of total energy versus cell volume obtained with the plane-wave pseudopotential method, is applied to the study of the elastic properties and vibrational effects. The athermal elastic constants of WSi2 are calculated as a function of pressure up to 35GPa. The relationship between bulk modulus and temperature up to 1200K is also obtained. Moreover, the Debye temperature is determined from the non-equilibrium Gibbs function. The calculated results are in good agreement with the experimental data.
A New Method for Determination of Sublimation Energy
CHEN Hua, TANG Wen-Hui, RAN Xian-Wen
Chin. Phys. Lett. 2009, 26 (4): 046401 .   DOI: 10.1088/0256-307X/26/4/046401
Abstract   PDF(pc) (193KB) ( 768 )
Sublimation energy is the latent heat of phase transition from solid state directly to gas state, but it is difficult to measure experimentally. We propose a new method to determine the sublimation energy of materials by using the experimental data of blow-off impulse induced by electron beam and the computer program DRAM. With this new method, the sublimation energy of polyester is finally determined to be about 1.1kJ/g.
Phase Transition and EOS of Cinnabar (α-HgS) at High Pressure and High Temperature
FAN Da-Wei, ZHOU Wen-Ge, LIU Cong-Qiang, WAN Fang, XING Yin-Suo, LIU Jing, LI Yan-Chun, XIE Hong-Sen
Chin. Phys. Lett. 2009, 26 (4): 046402 .   DOI: 10.1088/0256-307X/26/4/046402
Abstract   PDF(pc) (450KB) ( 567 )

Phase relations and equation of state (EOS) of natural cinnabar (α-HgS) are investigated by high-pressure and high-temperature synchrotron x-ray powder diffraction. The unambiguous cinnabar-rocksalt structure phase boundaries are determined to be Plower(GPa)=15.54-0.014T°C and Pupper(GPa)=23.84-0.014T(°C) at 300-623K. With K' fixed at 4, we obtain K0= 37(4)GPa, (∂K/∂ T)P=-0.025(2)GPaK-1, and α_{0}=3.79(20)×10-5K-1 for the cinnabar phase of α-HgS. The (K/∂T)P and α0 of cinnabar phase are obtained for the first time. A nearly isotropic compression of cinnabar phase is observed by linear regressions.

Fabrication and Characterization of Si Nanocrystals Synthesized by Electron Beam Evaporation of Si and SiO2 Mixture
LI Wei-Long, JIA Rui, LIU Ming, CHEN Chen, XIE Chang-Qing, ZHU Chen-Xin, LI Hao-Feng, ZHANG Pei-Wen, YE Tian-Chun
Chin. Phys. Lett. 2009, 26 (4): 046801 .   DOI: 10.1088/0256-307X/26/4/046801
Abstract   PDF(pc) (1147KB) ( 597 )
Silicon nanocrystals synthesized by electron beam (e-beam) evaporation of Si and SiO2 mixture are studied. Rutherford backscattering spectrometry of the as-deposited Si-rich silicon dioxide or oxide (SRO) thin film shows that after evaporation, the Si and SiO2 concentration is well kept, indicating that the e-beam evaporation is suitable for evaporating mixtures of Si and SiO2. The SRO thin films are annealed at different temperatures for two hours to synthesize silicon nanocrystals. For the sample annealed at 1050°C, silicon nanocrystals with different sizes and the mean diameter of 4.5nm are evidently observed by high resolution transmission electron microscopy (HRTEM). Then the Raman scattering and photoluminescence spectra arising from silicon nanocrystals are further confirmed the above results
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
Site Preference and Alloying Effect of Excess Ni in Ni-Mn-Ga Shape Memory Alloys
CHEN Jie, LI Yan, SHANG Jia-Xiang, XU Hui-Bin
Chin. Phys. Lett. 2009, 26 (4): 047101 .   DOI: 10.1088/0256-307X/26/4/047101
Abstract   PDF(pc) (423KB) ( 458 )
The formation energies and electronic structures of Ni-rich Ni-Mn-Ga alloys have been investigated by first-principles calculations using the pseudopotential plane wave method based on density functional theory. The results show that the alloying Ni prefers to occupy the Mn site directly in Ni9Mn3Ga4 and to occupy the Mn site and drive the displaced Mn atom to the Ga site in Ni9Mn4Ga3, which is in accordance with the experimental result. According to the lattice constants and the density of states analyses, these site preference behaviours are closely related to the smaller lattice distortion and the lower-energy electronic structure when the excess Ni occupies the Mn site. The effect of Ni alloying on martensitic transformation is discussed and the enhancement of martensitic transformation temperature by Ni alloying is estimated by the calculated formation energy difference between austenite and martensite phases.
Temperature-Dependent Defect-Induced New Emission in ZnSe Crystal
SHU Shi-Wei, MA Guo-Hong
Chin. Phys. Lett. 2009, 26 (4): 047102 .   DOI: 10.1088/0256-307X/26/4/047102
Abstract   PDF(pc) (285KB) ( 694 )
The temperature-dependent photoluminescence behaviour of chemical vapour transport (CVT)-grown ZnSe crystal is investigated. A new emission band appears when temperature is reduced to 155K. It is shown that the new emission band is strongly related to defect emission peaked at around 2.1eV. The emergence of the new emission band is accompanied by decreasing emission intensity of free exciton, as well as redshift of defect emission with temperature decreases. The activated energy of the defect state is estimated to be 60.6meV, which is approximately equal to the energy difference between the new emission and the free exciton emission at 155K.
Phase Interference in a Multi-level Quantum-Dot System
ZHANG Xu-Ming, CHEN Xiao-Shuang, LU Wei
Chin. Phys. Lett. 2009, 26 (4): 047301 .   DOI: 10.1088/0256-307X/26/4/047301
Abstract   PDF(pc) (283KB) ( 450 )
Considering phase interference, we investigate coherent transport in a quantum dot by using a thermopower. In the single process of the electronic transport through the quantum dot, it is shown that the phase interference between the levels of a quantum dot is like the Aharonov-Bohm effect. The result indicates that the thermopower is very sensitive to phase interference. It is also found that the phase-difference change of the different levels of the quantum dot can determine the shape of the thermopower.
Spin Accumulation in a Double Quantum Dot Aharonov-Bohm Interferometer
YIN Hai-Tao, LÜ, Tian-Quan, LIU Xiao-Jie, XUE Hui-Jie
Chin. Phys. Lett. 2009, 26 (4): 047302 .   DOI: 10.1088/0256-307X/26/4/047302
Abstract   PDF(pc) (312KB) ( 460 )
We investigate the spin accumulation in a double quantum dot Aharonov-Bohm (AB) interferometer in which both the Rashba spin--orbit (RSO) interaction and intradot Coulomb interaction are taken into account. Due to the existence of the RSO interaction, the electron, flowing through different arms of the AB ring, will acquire a spin-dependent phase factor in the tunnel-coupling strengths. This phase factor will induce various interesting interference phenomena. It is found that the electrons of the different spin directions can accumulate in the two dots by properly adjusting the bias and the intradot level with a fixed RSO interaction strength. Moreover, both the magnitude and direction of the spin accumulation in each dot can be conveniently controlled and tuned by the gate voltage acting on the dot or the bias on the lead.
Magneto-optical and Microwave Properties of LuBiIG Thin Films Prepared by Liquid Phase Epitaxy Method from Lead-Free Flux
YANG Qing-Hui, ZHNAG Huai-Wu, WEN Qi-Ye, LIU Ying-Li, Ihor M. Syvorotka, Ihor I. Syvorotka
Chin. Phys. Lett. 2009, 26 (4): 047401 .   DOI: 10.1088/0256-307X/26/4/047401
Abstract   PDF(pc) (619KB) ( 629 )
Lu2.1Bi0.9Fe5O12 (LuBiIG) garnet films are prepared by liquid phase epitaxy (LPE) method on gadolinium gallium garnet (GGG) substrates from lead-free flux. Three-inch single crystal garnet films with (444) orientation and good surface are successfully fabricated. The lattice mismatch to the GGG(111) substrate is as small as 0.08%. The ferromagnetic resonance (FMR) linewidth of the film is 2∆ H=2.8-5.1Oe, the Faraday rotation is 1.64deg/μm at 633nm at room temperature and the optical absorption coefficient of the film is 600cm-1 in visible range and about 100-170cm-1 when the wavelength is larger than 800nm. The epitaxy film possesses dominating in-plane magnetization with a saturation magnetization of about 1562G. These superior optical, magnetic-optical (MO) and microwave properties of our garnet films have potential applications in both MO and microwave devices.
Training Effect and Hysteretic Behaviour of Angular Dependence of Exchange Bias in Co/IrMn Bilayers
ZHANG Jing, DU Jun, BAI Xiao-Jun, YOU Biao, ZHANG Wei, HU An
Chin. Phys. Lett. 2009, 26 (4): 047501 .   DOI: 10.1088/0256-307X/26/4/047501
Abstract   PDF(pc) (349KB) ( 496 )
The training effect and the hysteresis behaviour of the angular dependence of exchange bias are extensively investigated upon the variation of the IrMn layer thickness tIrMn in a series of Co/IrMn bilayers. When tIrMn is very small, both of them are negligible. Then they increase very sharply with increasing tIrMn and then reach maxima at almost the same value of tIrMn. Finally they both decrease when tIrMn is further increased. The similar variation trends suggest that these phenomena arise from irreversible change of antiferromagnet spin orientations, according to the thermal activation model.
Relaxation of Dielectric Loss Peak over Intermediate Temperature Range in Bi5TiNbWO15 Intergrowth
WANG Wei, WANG Xiao-Juan, ZHU Jun, MAO Xiang-Yu, CHEN Xiao-Bing
Chin. Phys. Lett. 2009, 26 (4): 047701 .   DOI: 10.1088/0256-307X/26/4/047701
Abstract   PDF(pc) (551KB) ( 396 )
A dielectric loss peak with relaxation-type characteristic is observed in Bi5TiNbWO15 over 200-400°C. The modified Cole-Cole relation by introducing relaxation strength as another important fitting parameter is used to describe this temperature-dependent behaviour of dielectric relaxation process. This peak is considered to be associated with the oxygen vacancies inside the grains and with its activation energy by relaxation determined to be 0.76eV. The obtained broadening factor α is around 0.4, which indicates a strong correlation between those relaxation units. It is confirmed that the behaviour of this peak is due to the combined effects of the dielectric relaxation and electrical conduction by the thermal motion of oxygen vacancies. These results are further confirmed in Bi5TiNbWO15 samples through oxidization atmosphere treatment and Nd modification respectively.
Ferroelectric Properties of Bi3.25La0.75Ti3O12 Thin Films Crystallized inDifferent N2/O2 Ambients
LI Jian-Jun, YU Jun, LI Jia, YANG Wei-Ming, ZHOU Bin, GAO Jun-Xiong, WANG Yun-Bo
Chin. Phys. Lett. 2009, 26 (4): 047702 .   DOI: 10.1088/0256-307X/26/4/047702
Abstract   PDF(pc) (797KB) ( 579 )
Bi3.25La0.75Ti3O12 (BLT) ferroelectric thin films are deposited by sol-gel method and annealed for crystallizaion in total 1sccm N2/O2 mixed gas with various ratio at 750°C for 30min. The effect of crystallization ambient on the structural and ferroelectric properties of the BLT films is studied. The growth direction and grain size of BLT film are revealed to affect ferroelectric properties. After the BLT film is annealed in 20% O2, the largest Pr value is obtained, which is ascribed to an increase of random orientation and large grain size. The fatigue property is improved with the concentration of oxygen in the ambient increasing, which is ascribed to annealing in the ambient with high concentrated oxygen adequately decreasing the defects related to lack of oxygen.
Luminescent Characteristics of LiSrBO3:Eu3+ Phosphor for White Light Emitting Diode
LI Pan-Lai, WANG Zhi-Jun, YANG Zhi-Ping, GUO Qing-Lin
Chin. Phys. Lett. 2009, 26 (4): 047801 .   DOI: 10.1088/0256-307X/26/4/047801
Abstract   PDF(pc) (331KB) ( 524 )
LiSrBO3:Eu3+ phosphor is synthesized by a high solid-state reaction method, and its luminescent characteristics are investigated. The emission and excitation spectra of LiSrBO3:Eu3+ phosphors exhibit that the phosphors can be effectively excited by near ultraviolet (401nm) and blue (471nm) light, and emit 615nm red light. The effect of Eu3+ concentration on the emission spectrum of LiSrBO3:Eu3+ phosphor is studied; the results show that the emission intensity increases with increasing Eu3+ concentration, and then decreases because of concentration quenching. It reaches the maximum at 3mol%, and the concentration self-quenching mechanism is the dipole-dipole interaction according to the Dexter theory. Under the conditions of charge compensation Li+, Na+ or K+ incorporated in LiSrBO3, the luminescent intensities of LiSrBO3:Eu3+ phosphor are enhanced.
Interfaces in InAs/GaSb Superlattices Grown by Molecular Beam Epitaxy
GUO Jie, SUN Wei-Guo, PENG Zhen-Yu, ZHOU Zhi-Qiang, XU Ying-Qiang, NIU Zhi-Chuan
Chin. Phys. Lett. 2009, 26 (4): 047802 .   DOI: 10.1088/0256-307X/26/4/047802
Abstract   PDF(pc) (505KB) ( 803 )
Short period InAs(4ML)/GaSb(8ML) superlattices (SLs) with InSb- and mixed-like (or Ga1-xInxAs1-ySby-like) interfaces (IFs) are grown by molecular-beam epitaxy (MBE) on (001) GaSb substrates at optimized growth temperature. Raman scattering reveals that two kinds of IFs can be formed by controlling shutter sequences. X-ray diffraction (XRD) and atomic force microscopy (AFM) demonstrate that SLs with mixed-like IFs are more sensitive to growth temperature than that with InSb-like IFs. The photoluminescence (PL) spectra of SLs with mixed-like IFs show a stronger intensity and narrower line width than with InSb-like IFs. It is concluded that InAs/GaSb SLs with mixed-like IFs have better crystalline and optical properties.
Fe-Doped Polycrystalline CeO2 as Terahertz Optical Material
WEN Qi-Ye, ZHANG Huai-Wu, YANG Qing-Hui, LI Sheng, XU De-Gang, YAOJian-Quan
Chin. Phys. Lett. 2009, 26 (4): 047803 .   DOI: 10.1088/0256-307X/26/4/047803
Abstract   PDF(pc) (639KB) ( 792 )
Fe-doped CeO2 is synthesized by ceramic method and the effects of Fe doping on the structure and properties are characterized by ordinary methods and terahertz-time domain spectrometer (THz-TDS) technique. Our results show that pure CeO2 only has a small dielectric constant ε of 4, while a small amount of Fe (0.9at.%) doping into CeO2 promotes densification and induces a large ε of 23. From the THz spectroscopy, it is found that for undoped CeO2 both the power absorption and the index of refraction increase with frequency, while for Fe-doped CeO2 we measure a remarkable transparency together with a flat index curve. The absorption coefficient of Fe-doped CeO2 at frequency ranging from 0.2 to 1.8THz is less than 0.35cm-1, implying that Fe-doped CeO2 is a potential THz optical material.
Impurity Activation in MBE-Grown As-Doped HgCdTe by Modulated Photoluminescence Spectra
YUE Fang-Yu, CHEN Lu, WU Jun, HU Zhi-Gao, LI Ya-Wei, YANG Ping-Xiong, CHU Jun-Hao,
Chin. Phys. Lett. 2009, 26 (4): 047804 .   DOI: 10.1088/0256-307X/26/4/047804
Abstract   PDF(pc) (386KB) ( 459 )
Modulated photoluminescence spectra have been performed to investigate the impurity activation in MBE-grown As-doped Hg1-xCdxTe (x≈0.3). The results show that the doped As mainly acting as donors in the as-grown samples can be fully activated as AsTe by two-stage anneals of 285°C/16h + 240°C/48h, of which the ionization energy has been determined to be about 10.5meV, slightly smaller than that of intrinsic VHg (about 14.5meV). However, the higher activation temperature (e.g. 400°C) at the first-stage can produce large numbers of excessive VHg and seriously deteriorate the quality of epilayers. This could give a brief guideline for preparing extrinsic
p-type HgCdTe materials or devices.
A Defect Effect to Light Transmission through Acute Bending Coupled Cavity Waveguide in a Two-Dimensional Photonic Crystal
HUANG Yin, LU Yan-Wu
Chin. Phys. Lett. 2009, 26 (4): 047805 .   DOI: 10.1088/0256-307X/26/4/047805
Abstract   PDF(pc) (701KB) ( 404 )
Light propagation through a coupled-defect waveguide with a 63.5° bend in a two-dimensional (2D) photonic crystal is investigated. The waveguide modes are non-degenerate monopole state and dipole defect state of a square lattice for two different branches. To increase the transmission in the bending waveguide, we propose a method to rotate the localized state by introducing a new type defect with a sheared square rod into coupled cavity. The higher coupling efficiency and transmission in the bending waveguide are obtained with proper shear shift.
Efficient Fibre Amplifiers Based on a Highly Er3+/Yb3+ Codoped Phosphate Glass-Fibre
XU Shan-Hui, YANG Zhong-Min, FENG Zhou-Ming, ZHANG Qin-Yuan, JIANG Zhong-Hong, XU Wen-Cheng
Chin. Phys. Lett. 2009, 26 (4): 047806 .   DOI: 10.1088/0256-307X/26/4/047806
Abstract   PDF(pc) (394KB) ( 688 )
Highly Er3+/Yb3+-codoped single-mode phosphate glass fibre is fabricated by the rod-in-tube technique. The performances of high-concentration Er3+/Yb3+-codoped phosphate glass fibre amplifiers are investigated and discussed. An efficient optical fibre amplifier with a gain of 12.6dB based on a 3.0cm long Er3+/Yb3+-codoped phosphate glass fibre is demonstrated under a dual-pump configuration with two 976nm fibre-pigtail laser diodes, which make it attractive for compact Er3+-doped fibre amplifiers. The obtained noise figures of signal wavelength from 1525 to 1565nm are less than 6.0dB. Gain saturation behaviour at 1535nm is also investigated, and the obtained saturation output power is larger than 10dBm.
CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
Structural and Thermodynamic Properties of M3W3N (M=Fe, Co, Ni)
CHEN Yi, SHEN Jiang, CHEN Nan-Xian
Chin. Phys. Lett. 2009, 26 (4): 048101 .   DOI: 10.1088/0256-307X/26/4/048101
Abstract   PDF(pc) (345KB) ( 492 )
Ternary transition metal nitrides, Fe3W3N, Co3W3N, and Ni3W3N, are studied by the use of interatomic potentials acquired from lattice inversion. The study indicates that Fe3W3N would be more stable than the other compounds in the family of intermetallic tungsten nitrides. The investigation of phonon density of states indicates that the lower frequency modes are mostly excited by the metal atoms, and the higher frequency modes are mostly excited by the nitrogen atoms. A qualitative analysis is carried out with the relevant potentials for the phase stability and vibrational modes.
HPHT Synthesis of Different Shape Coarse-Grain Diamond Single Crystals
ZHOU Sheng-Guo, ZANG Chuan-Yi, MA Hong-An, HU Qiang, LI Xiao-Lei, LI Shang-Sheng, ZHANG He-Min, JIA Xiao-Peng,
Chin. Phys. Lett. 2009, 26 (4): 048102 .   DOI: 10.1088/0256-307X/26/4/048102
Abstract   PDF(pc) (567KB) ( 657 )
Synthesis of coarse-grain diamond crystals is studied in a China-type SPD6×1670T cubic high-pressure apparatus with high exact control system. To
synthesize high quality coarse-grain diamond crystals, advanced indirect heat assembly, powder catalyst technology and optimized synthesis craft are used. At last, three kinds of coarse-grain diamond (about 0.85mm) single crystals with hexahedron, hex-octahedron and octahedron are synthesized successfully under HPHT (about 5.4GPa, 1300-1450°). The growth characters
of different shape crystals are discussed. The results and techniques might be useful for the production of coarse-grain diamonds.
Highly Strained Si Films with Ultra-low Dislocation Density Grown on Virtual Substrates of Thin Thickness
YANG Hong-Bin, ZHANG Xiang-Jiu
Chin. Phys. Lett. 2009, 26 (4): 048103 .   DOI: 10.1088/0256-307X/26/4/048103
Abstract   PDF(pc) (894KB) ( 413 )
By using compositionally graded SiGe films as virtual substrates, tensile strained Si films with the strain of 1.5% and the threading dislocation density less than 1.0×105cm-2 are successfully grown in micron size windows by molecular beam epitaxy (MBE). The thickness of the virtual substrates was only 330nm. On the surface of the s-Si films no cross-hatched lines resulting from misfit dislocations could be observed. We attribute these results to the edge-induced strain relaxation of the epitaxial films in windows, and the patterned virtual substrates with compositionally graded SiGe films.
Fabrication and Frequency Response Characteristics of AlN-Based Solidly Mounted Resonator
XIONG Juan, GU Hao-Shuang, HU Kuan, HU Ming-Zhe
Chin. Phys. Lett. 2009, 26 (4): 048104 .   DOI: 10.1088/0256-307X/26/4/048104
Abstract   PDF(pc) (648KB) ( 631 )
Film bulk acoustic resonator (FBAR) with solidly mounted resonator (SMR)-type is carried out by rf magnetic sputtering. To fabricate SMR-type FBAR, alternative high and low acoustic impedance layers, Mo/Ti multilayer, are adopted as Bragg reflector deposited by dc magnetron sputtering. The influences of sputtering pressure, substrate temperature and sputtering power on the surface roughness of Bragg reflector layer are discussed. From the atom force microscopy (AFM) analysis, the surface roughness of the Bragg reflector is improved remarkably by controlling deposition conditions. Under the appropriate sputtering condition, AlN thin films with highly c-axis-preferred orientation are deposited by rf magnetron sputtering. The performance of fabricated Mo/Ti SMR shows that the electromechanical coupling coefficient is 3.89%, the series and parallel resonant frequencies appear at 2.49 and 2.53GHz, with their quality factors 134.2 and 97.6, respectively.
Compression Enhanced Shear Yield Stress of Electrorheological Fluid
ZHANG Min-Liang, TIAN Yu, JIANG Ji-Le, ZHU Xu-Li, MENG Yong-Gang, WENShi-Zhu
Chin. Phys. Lett. 2009, 26 (4): 048301 .   DOI: 10.1088/0256-307X/26/4/048301
Abstract   PDF(pc) (381KB) ( 453 )
Shear tests of an electrorheological fluid with pre-applied electric field and compression along the field direction are carried out. The results show that pre-compressions can increase the shear yield stress up to ten times. Under the same external electric field strength, a higher compressive strain corresponds to a larger shear yield stress enhancement but with slight current density decrease, which shows that the particle interaction potentials are not increased by compressions but the compression-induced chain aggregation dominates the shear yield stress improvement. This pre-compression technique might be useful for developing high performance flexible ER or magnetorheological couplings.
Lattice Boltzmann Simulations of Particle-Particle Interaction in Steady Poiseuille Flow
YI Hou-Hui, FAN Li-Juan, YANG Xiao-Feng, LI Hua-Bing
Chin. Phys. Lett. 2009, 26 (4): 048701 .   DOI: 10.1088/0256-307X/26/4/048701
Abstract   PDF(pc) (411KB) ( 529 )
The moving behaviour of two- and three-particles in a pressure-driven flow is studied by the lattice Boltzmann simulation in two dimensions. The time-dependent values, including particles' radial positions, translational velocities, angular velocities, and the x-directional distance between the particles are analysed extensively. The effect of flow Reynolds number on particle motion is also investigated numerically. The simulation results show that the leading particle equilibrium position is closer to the channel centre while the trailing particle equilibrium position is closer to the channel wall. If Reynolds number Re is less than 85.30, the larger flow Reynolds number results in the smaller x-directional equilibrium distance, otherwise the x-directional distance increases almost linearly with the increase of time and the particles separate finally. The simulation results are helpful to understand the particle-particle
interaction in suspensions with swarms of particles.
Agreement Dynamics of Memory-Based Naming Game with Forgetting Curve of Ebbinghaus
SHI Xiao-Ming, ZHANG Jie-Fang
Chin. Phys. Lett. 2009, 26 (4): 048901 .   DOI: 10.1088/0256-307X/26/4/048901
Abstract   PDF(pc) (356KB) ( 678 )
We propose a memory-based naming game (MBNG) model with two-state variables in full-connected networks, which is like some previous opinion propagation models. It is found that this model is deeply affected by the memory decision parameter, and then its dynamical behaviour can be partly analysed by using numerical simulation and analytical argument. We also report a modified MBNG model with the forgetting curve of Ebbinghaus in the memory. With deletion of one parameter in the MBNG model, it can converge to success rate S(t)=1 and the average sum E(t) is decided by the size of network N.
Prisoner's Dilemma Game on Two Types of Positively Correlated Networks
LIU Yong-Kui, LI Zhi, CHEN Xiao-Jie, WANG Long,
Chin. Phys. Lett. 2009, 26 (4): 048902 .   DOI: 10.1088/0256-307X/26/4/048902
Abstract   PDF(pc) (378KB) ( 524 )
We study the effects of degree correlations on the evolution of cooperation in the prisoner's dilemma game with individuals located on two types of positively correlated networks. It is shown that the positive degree correlation can either promote or inhibit the emergence of cooperation depending on network configurations. Furthermore, we investigate the probability to cooperate as a function of connectivity degree, and find that high-degree individuals generally have a higher tendency to cooperate. Finally, it is found that small-degree individuals usually change their strategy
more frequently, and such change is shown to be unfavourable to cooperation for both kinds of networks.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
Contribution from the Earth's Bow Shock to Region 1 Current under Low Alfvén Mach Numbers
PENG Zhong, HU You-Qiu
Chin. Phys. Lett. 2009, 26 (4): 049401 .   DOI: 10.1088/0256-307X/26/4/049401
Abstract   PDF(pc) (243KB) ( 440 )
Using global MHD simulations of the solar wind-magnetosphere-ionosphere system, we investigate the dependence of the contribution from the Earth's bow shock (I1bs) to ionospheric region 1 field aligned current (FAC) (I1). It is found that I1bs increases with increasing southward interplanetary magnetic field (IMF) strength Bs, if the Alfvén Mach number MA of the solar wind exceeds 2, a similar result as obtained by previous authors. However, if MA becomes close to or falls below 2, I1bs will decrease with Bs in both magnitude and percentage (i.e., I1bs}/I1) because of the resultant reduction of the bow shock strength. Both the surface current density Jbs at the nose of the bow shock and the total bow shock current Ibs share nearly the same relationship with MA, and vary non-monotonically with MA or Bs. The maximum point is found to be located at MA = 2.7. Three conclusions are then made as follows: (1) The surface current density at the nose, which is much easier to be evaluated, may be used to largely describe the behaviour of the bow shock instead of the total bow shock current. (2) The peak of the total bow shock current is reached at about MA = 2.7 when only Bs is adjusted. (3) The non-monotonic variation of the bow shock current with MA causes a similar variation of its contribution to region 1 FAC. The turning point for such contribution is found to be nearly MA= 2. The implication of these conclusions to the saturation of the ionospheric transpolar potential is briefly discussed
Slim Discs with Varying Accretion Rates
JIAO Cheng-Liang, LU Ju-Fu
Chin. Phys. Lett. 2009, 26 (4): 049701 .   DOI: 10.1088/0256-307X/26/4/049701
Abstract   PDF(pc) (213KB) ( 422 )
It was revealed in our previous studies that there exists a maximal possible accretion rate for slim discs with constant accretion rates because the correctly calculated vertical gravitational force can only gather some limited amount of accreted matter. Here we show that when the accretion rate is not constant and instead decreases with decreasing radius because of outflows, such that the amount of accreted matter is adjusted to be within the allowed limit, global slim disc solutions can be constructed even for the case that accretion rates at large radii apparently exceed the maximal possible value. This result further demonstrates that outflows seem to be unavoidable for accretion flows with large accretion rates at large radii.
76 articles