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CN 11-5639/O4
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  • A revised version of the program VEC (visual computing in electron crystallography)

    Li Xue-Ming, Li Fang-Hua, Fan Hai-Fu
    Chin. Phys. B 2009, 18 (6): 2459-2463
    The program package VEC (Visual computing in Electron Crystallography) has been revised such that (i) a program converting one-line symbols to two-line symbols of (3+1)-dimensional superspace groups has been incorporated into VEC so that the latter can interpret both kinds of symbols; (ii) a bug in ...

     
  • Competitions of magnetism and superconductivity in FeAs-based materials

    Yang Shuo, You Wen-Long, Gu Shi-Jian, Lin Hai-Qing
    Chin. Phys. B 2009, 18 (6): 2545-2550
    Using the numerical unrestricted Hartree--Fock approach, we study the ground state of a two-orbital model describing newly discovered FeAs-based superconductors. We observe the competition of a (0, π) mode spin-density wave and the superconductivity as the doping concentration changes. There might b...

     
Chin. Phys. B  
  Chin. Phys. B--2009, Vol.18, No.6
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GENERAL

Symmetry and general symmetry groups of the coupled Kadomtsev--Petviashvili equation

Wang Jia, Li Biao
Chin. Phys. B, 2009, 18 (6): 2109-2114 doi: 10.1088/1674-1056/18/6/001
Full Text: [PDF 178 KB] (Downloads:1229)
Show Abstract
In this paper, the Lie symmetry algebra of the coupled Kadomtsev--Petviashvili (cKP) equation is obtained by the classical Lie group method and this algebra is shown to have a Kac--Moody--Virasoro loop algebra structure. Then the general symmetry groups of the cKP equation is also obtained by the symmetry group direct method which is proposed by Lou et al。 From the general symmetry groups, the Lie symmetry group can be recovered and a group of discrete transformations can be derived simultaneously. Lastly, from a known simple solution of the cKP equation, we can easily obtain two new solutions by the general symmetry groups.

Modelling the spread of sexually transmitted diseases on scale-free networks

Liu Mao-Xing, Ruan Jiong
Chin. Phys. B, 2009, 18 (6): 2115-2120 doi: 10.1088/1674-1056/18/6/002
Full Text: [PDF 182 KB] (Downloads:834)
Show Abstract
In this paper a new model for the spread of sexually transmitted diseases (STDs) is presented. The dynamic behaviors of the model on a heterogenous scale-free (SF) network are considered, where the absence of a threshold on the SF network is demonstrated, and the stability of the disease-free equilibrium is obtained. Three immunization strategies, uniform immunization, proportional immunization and targeted immunization, are applied in this model. Analytical and simulated results are given to show that the proportional immunization strategy in the model is effective on SF networks.

Effects of dust size distribution on nonlinear waves in a dusty plasma

Chen Jian-Hong
Chin. Phys. B, 2009, 18 (6): 2121-2128 doi: 10.1088/1674-1056/18/6/003
Full Text: [PDF 247 KB] (Downloads:779)
Show Abstract
For two-dimensional unmagnetized dusty plasmas with many different dust grain species, a Kadomtsev--Petviashvili (KP) equation, a modified KP (mKP) equation and a coupled KP(cKP) equation for small, but finite amplitude dust-acoustic solitary waves are obtained for different physical conditions respectively. The influence of an arbitrary dust size distribution described by a polynomial expressed function on the properties of dust-acoustic solitary waves is investigated numerically. How dust size distribution affects the sign and the magnitude of nonlinear coefficient A (D) of KP (mKP) equation is also discussed in detail. It is noted that whether a compressive or a rarefactive solitary wave exists depends on the dust size distribution in some dusty plasmas.

New two-mode intermediate momentum-coordinate representation with quantum entanglement and its application

Xu Shi-Min, Xu Xing-Lei, Li Hong-Qi, Wang Ji-Suo
Chin. Phys. B, 2009, 18 (6): 2129-2136 doi: 10.1088/1674-1056/18/6/004
Full Text: [PDF 202 KB] (Downloads:692)
Show Abstract
We construct four linear composite operators for a two-particle system and give common eigenvectors of those operators. The technique of integration within an ordered product (IWOP) of operators is employed to prove that those common eigenvectors are complete and orthonormal. Therefore, a new two-mode intermediate momentum-coordinate representation which involves quantum entanglement for a two-particle system is proposed and applied to some two-body dynamic problems. Moreover, the pure-state density matrix | ξ 12 >C,DC,D< ξ 12 | is a Radon transform of Wigner operator.

Multiparty quantum secret conference based on quantum encryption with pure entangled states

Gu Bin, Li Chuan-Qi, Chen Yu-Lin
Chin. Phys. B, 2009, 18 (6): 2137-2142 doi: 10.1088/1674-1056/18/6/005
Full Text: [PDF 165 KB] (Downloads:713)
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We present a scheme for multiparty quantum remote secret conference (MQRSC) with pure entangled states, not maximally entangled multipartite quantum systems. The conferees first share a private quantum key, a sequence of pure entangled states and then use them to encode and decode the secret messages. The conferees exploit the decoy-photon technique to ensure the security of the transmission of qubits. This MQRSC scheme is more feasible and efficient than others.

Quantum key distribution series network protocol with M-classical Bobs

Zhang Xian-Zhou, Gong Wei-Gui, Tan Yong-Gang, Ren Zhen-Zhong, Guo Xiao-Tian
Chin. Phys. B, 2009, 18 (6): 2143-2148 doi: 10.1088/1674-1056/18/6/006
Full Text: [PDF 280 KB] (Downloads:926)
Show Abstract
Secure key distribution among classical parties is impossible both between two parties and in a network. In this paper, we present a quantum key distribution (QKD) protocol to distribute secure key bits among one quantum party and numerous classical parties who have no quantum capacity. We prove that our protocol is completely robust, i.e., any eavesdropping attack should be detected with nonzero probability. Our calculations show that our protocol may be secure against Eve's symmetrically individual attack.

Enhancing the security of quantum secret sharing against multiphoton attack

Zhang Bin-Bin, Wang Da-Qing, Huang Shan-Shan, Liu Yu
Chin. Phys. B, 2009, 18 (6): 2149-2153 doi: 10.1088/1674-1056/18/6/007
Full Text: [PDF 150 KB] (Downloads:633)
Show Abstract
It is generally believed that nonorthogonal operations which can realize the state transformation between two nonorthogonal bases may ensure the security of many quantum communication protocols. However, in this paper, we present a powerful attack against quantum secret sharing protocols of these kinds. Applying entangled photons as fake signals, Eve can successfully steal the exact information without being revealed. We also give our effective modification to improve it. Under the suggested checking strategy, even to Eve's most general attack, it is robust and secure.

A new method of researching fermion tunneling from the Vaidya--Bonner de Sitter black hole

Lin Kai, Yang Shu-Zheng
Chin. Phys. B, 2009, 18 (6): 2154-2158 doi: 10.1088/1674-1056/18/6/008
Full Text: [PDF 170 KB] (Downloads:737)
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Using the general tortoise coordinate transformation, we research the fermion tunneling of the Vaidya--Bonner de Sitter black hole via a semi-classical method and finally obtain the right surface gravity, Hawking temperature and tunneling rate near the event horizon and cosmical horizon.

Thermal equation of state for lattice Boltzmann gases

Ran Zheng
Chin. Phys. B, 2009, 18 (6): 2159-2167 doi: 10.1088/1674-1056/18/6/009
Full Text: [PDF 185 KB] (Downloads:782)
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The Galilean invariance and the induced thermo-hydrodynamics of the lattice Boltzmann Bhatnagar--Gross--Krook model are proposed together with their rigorous theoretical background. From the viewpoint of group invariance, recovering the Galilean invariance for the isothermal lattice Boltzmann Bhatnagar--Gross--Krook equation (LBGKE) induces a new natural thermal-dynamical system, which is compatible with the elementary statistical thermodynamics.

Circuitry implementation of a novel four-dimensional nonautonomous hyperchaotic Liu system and its experimental studies on synchronization control

Luo Xiao-Hua, Zhou Wei, Li Rui, Liang Yi-Long, Luo Ming-Wei
Chin. Phys. B, 2009, 18 (6): 2168-2175 doi: 10.1088/1674-1056/18/6/010
Full Text: [PDF 3361 KB] (Downloads:927)
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Based on the three-dimensional Liu chaotic system, this paper appends a feedback variable to construct a novel hyperchaotic Liu system. Then, a control signal is further added to construct a novel nonautonomous hyperchaotic Liu system. Through adjusting the frequency of the control signal, the chaotic property of the system can be controlled to show some different dynamic behaviors such as periodic, quasi-periodic, chaotic and hyperchaotic dynamic behaviours. By numerical simulations, the Lyapunov exponent spectrums, bifurcation diagrams and phase diagrams of the two new systems are studied, respectively. Furthermore, the synchronizing circuits of the nonautonomous hyperchaotic Liu system are designed via the synchronization control method of single variable coupling feedback. Finally, the hardware circuits are implemented, and the corresponding waves of chaos are observed by an oscillograph.

Pinning control of complex Lur'e networks

Zhang Qing-Zhen, Li Zhong-Kui
Chin. Phys. B, 2009, 18 (6): 2176-2183 doi: 10.1088/1674-1056/18/6/011
Full Text: [PDF 884 KB] (Downloads:768)
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This paper addresses the control problem of a class of complex dynamical networks with each node being a Lur'e system whose nonlinearity satisfies a sector condition, by applying local feedback injections to a small fraction of the nodes. The pinning control problem is reformulated in the framework of the absolute stability theory. It is shown that the global stability of the controlled network can be reduced to the test of a set of linear matrix inequalities, which in turn guarantee the absolute stability of the corresponding Lur'e systems whose dimensions are the same as that of a single node. A circle-type criterion in the frequency domain is further presented for checking the stability of the controlled network graphically. Finally, a network of Chua's oscillators is provided as a simulation example to illustrate the effectiveness of the theoretical results.

Random shortcuts induce phase synchronization in complex Chua systems

Wei Du-Qu, Luo Xiao-Shu, Qin Ying-Hua
Chin. Phys. B, 2009, 18 (6): 2184-2187 doi: 10.1088/1674-1056/18/6/012
Full Text: [PDF 218 KB] (Downloads:801)
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This paper studies how phase synchronization in complex networks depends on random shortcuts, using the piecewise-continuous chaotic Chua system as the nodes of the networks. It is found that for a given coupling strength, when the number of random shortcuts is greater than a threshold the phase synchronization is induced. Phase synchronization becomes evident and reaches its maximum as the number of random shortcuts is further increased. These phenomena imply that random shortcuts can induce and enhance the phase synchronization in complex Chua systems. Furthermore, the paper also investigates the effects of the coupling strength and it is found that stronger coupling makes it easier to obtain the complete phase synchronization.

A novel four-dimensional autonomous hyperchaotic system

Liu Chong-Xin, Liu Ling
Chin. Phys. B, 2009, 18 (6): 2188-2193 doi: 10.1088/1674-1056/18/6/013
Full Text: [PDF 3466 KB] (Downloads:1155)
Show Abstract
A novel four-dimensional autonomous hyperchaotic system is reported in this paper. Some basic dynamical properties of the new hyperchaotic system are investigated in detail by means of a continuous spectrum, Lyapunov exponents, fractional dimensions, a strange attractor and Poincaré mapping. The dynamical behaviours of the new hyperchaotic system are proved by not only performing numerical simulation and brief theoretical analysis but also by conducting an electronic circuit experiment.

Small-time scale network traffic prediction based on a local support vector machine regression model

Meng Qing-Fang, Chen Yue-Hui, Peng Yu-Hua
Chin. Phys. B, 2009, 18 (6): 2194-2199 doi: 10.1088/1674-1056/18/6/014
Full Text: [PDF 238 KB] (Downloads:905)
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In this paper we apply the nonlinear time series analysis method to small-time scale traffic measurement data. The prediction-based method is used to determine the embedding dimension of the traffic data. Based on the reconstructed phase space, the local support vector machine prediction method is used to predict the traffic measurement data, and the BIC-based neighbouring point selection method is used to choose the number of the nearest neighbouring points for the local support vector machine regression model. The experimental results show that the local support vector machine prediction method whose neighbouring points are optimized can effectively predict the small-time scale traffic measurement data and can reproduce the statistical features of real traffic measurements.

Simulating train movement in railway traffic using a car-following model

Li Ke-Ping, Guan Li-Jia
Chin. Phys. B, 2009, 18 (6): 2200-2204 doi: 10.1088/1674-1056/18/6/015
Full Text: [PDF 184 KB] (Downloads:772)
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Based on a car-following model, in this paper, we propose a new traffic model for simulating train movement in railway traffic. In the proposed model, some realistic characteristics of train movement are considered, such as the distance headway and the safety stopping distance. Using the proposed traffic model, we analyse the space-time diagram of traffic flow, the trajectory of train movement, etc. Simulation results demonstrate that the proposed model can be successfully used for simulating the train movement. Some complex phenomena can be reproduced, such as the complex acceleration and deceleration of trains and the propagation of train delay.

Spin-filtering junctions with double ferroelectric barriers

Ju Yan, Xing Ding-Yu
Chin. Phys. B, 2009, 18 (6): 2205-2208 doi: 10.1088/1674-1056/18/6/016
Full Text: [PDF 180 KB] (Downloads:654)
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An FS/FE/NS/FE/FS double tunnel junction is suggested to have the ability to inject, modulate and detect the spin-polarized current electrically in a single device, where FS is the ferromagnetic semiconductor electrode, NS is the nonmagnetic semiconductor, and FE the ferroelectric barrier. The spin polarization of the current injected into the NS region can be switched between a highly spin-polarized state and a spin unpolarized state. The high spin polarization may be detected by measuring the tunneling magnetoresistance ratio of the double tunnel junction.

Synchronization speed of identical oscillators on community networks

Zhang Zhi, Fu Zhong-Qian, Yan Gang
Chin. Phys. B, 2009, 18 (6): 2209-2212 doi: 10.1088/1674-1056/18/6/017
Full Text: [PDF 171 KB] (Downloads:881)
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Synchronizability of complex oscillators networks has attracted much research interest in recent years. In contrast, in this paper we investigate numerically the synchronization speed, rather than the synchronizability or synchronization stability, of identical oscillators on complex networks with communities. A new weighted community network model is employed here, in which the community strength could be tunable by one parameter δ. The results showed that the synchronization speed of identical oscillators on community networks could reach a maximal value when δ is around 0.1. We argue that this is induced by the competition between the community partition and the scale-free property of the networks. Moreover, we have given the corresponding analysis through the second least eigenvalue λ2 of the Laplacian matrix of the network which supports the previous result that the synchronization speed is determined by the value of λ2.
NUCLEAR PHYSICS

Monte Carlo simulation of exposure factor

Zhang Tao, Liu Yi-Bao, Yang Bo, Wu He-Xi, Gu Jin-Hu
Chin. Phys. B, 2009, 18 (6): 2217-2222 doi: 10.1088/1674-1056/18/6/019
Full Text: [PDF 625 KB] (Downloads:722)
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In this paper, we simulate the exposure factor by a simple model of a free-air ionization chamber with the Monte Carlo programme Geant4. Special emphasis is placed on the discussion of the exposure factor related to parameters of the chamber model. The reason for the variation in exposure factor with incident ray energy is also analysed in terms of reaction cross section for different types of reactions. The obtained results indicate that our simulation is accurate in the calculation of the exposure factor and can serve as a reference in designing air ionization chambers.

Characteristic analysis of the optical delay in frequency response of resonant cavity enhanced (RCE) photodetectors

Guo Jian-Chuan, Zuo Yu-Hua, Zhang Yun, Ding Wu-Chang, Cheng Bu-Wen, Yu Jin-Zhong, Wang Qi-Ming
Chin. Phys. B, 2009, 18 (6): 2223-2228 doi: 10.1088/1674-1056/18/6/020
Full Text: [PDF 605 KB] (Downloads:681)
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With consideration of the modulation frequency of the input lightwave itself, we present a new model to calculate the quantum efficiency of RCE p-i-n photodetectors (PD) by superimposition of multiple reflected lightwaves. For the first time, the optical delay, another important factor limiting the electrical bandwidth of RCE p-i-n PD excluding the transit time of the carriers and RCd response of the photodetector, is analyzed and discussed in detail. The optical delay dominates the bandwidth of RCE p-i-n PD when its active layer is thinner than several 10~nm. These three limiting factors must be considered exactly for design of ultra-high-speed RCE p-i-n PD.
CLASSICAL AREAS OF PHENOMENOLOGY

Theoretical studies on the one- and two-photon absorption properties of azulenylporphyrins and azulene-fused porphyrins

Li Wen-Chao, Feng Ji-Kang, Ren Ai-Min, Zhang Xiang-Biao, Sun Chia-Chung
Chin. Phys. B, 2009, 18 (6): 2271-2281 doi: 10.1088/1674-1056/18/6/027
Full Text: [PDF 2474 KB] (Downloads:805)
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The electronic structures, one-photon absorption (OPA) and two-photon absorption (TPA) properties of the azulenylporphyrins and azulene-fused porphyrins have been comparatively studied by using DFT/B3LYP/6-31G(d) and the ZINDO/SDCI method. With the number of azulenyl groups increasing, the OPA wavelengths of all molecules are red-shifted in 400--600~nm and the two-photon absorption cross section is gradually enlarged. The azulene-fused structures facilitate an expanding conjugated area and increasing TPA cross section. The origin of TPA properties of studied compounds is studied with a two-level model. In summary, the azulene-fused porphyrins exhibit strong two-photon absorption.

Manipulation of multiple electromagnetically induced two-photon transparency in a six-level atomic system

Jia Wen-Zhi, Wang Shun-Jin
Chin. Phys. B, 2009, 18 (6): 2282-2287 doi: 10.1088/1674-1056/18/6/028
Full Text: [PDF 193 KB] (Downloads:983)
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In the five-level K-type atomic system, by using another control field to couple the excited level of the coupling transition to the sixth higher excited level, a six-level atomic system is constructed. In this system, the multiple electromagnetically induced two-photon transparency has been investigated. What is more, if choosing the parameters of the control fields properly the triple transparency window will reduce to a double one which means that the multiple electromagnetically induced two-photon transparency can be manipulated in this system. The physical interpretation of these phenomena is given in terms of the dressed states and the dark states.

Entanglement and coherence of a three-level atom in Λ configuration interacting with two fields

Zhang Jian-Song, Xu Jing-Bo
Chin. Phys. B, 2009, 18 (6): 2288-2293 doi: 10.1088/1674-1056/18/6/029
Full Text: [PDF 239 KB] (Downloads:996)
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We investigate the entanglement of a three-level atom in λ configuration interacting with two quantized field modes by using logarithmic negativity. Then, we study the relationship of the atomic coherence and the entanglement between two fields which are initially prepared in vacuum or thermal states. We find that if the two fields are prepared in thermal states, the atomic coherence can induce the entanglement between two thermal fields. However, there is no coherence-induced entanglement between two vacuum fields.

Influence of the virtual photon field on the squeezing properties of atom laser

Zhao Jian-Gang, Sun Chang-Yong, Wen Ling-Hua, Liang Bao-Long
Chin. Phys. B, 2009, 18 (6): 2294-2299 doi: 10.1088/1674-1056/18/6/030
Full Text: [PDF 757 KB] (Downloads:715)
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This paper investigates the squeezing properties of an atom laser without rotating-wave approximation in the system of a binomial states field interacting with a two-level atomic Bose--Einstein condensate. It discusses the influences of atomic eigenfrequency, the interaction intensity between the optical field and atoms,parameter of the binomial states field and virtual photon field on the squeezing properties. The results show that two quadrature components of an atom laser can be squeezed periodically. The duration and the degree of squeezing an atom laser have something to do with the atomic eigenfrequency and the parameter of the binomial states field, respectively. The collapse and revival frequency of atom laser fluctuation depends on the interaction intensity between the optical field and atoms. The effect of the virtual photon field deepens the depth of squeezing an atom laser.

Quasiprobability distributions of a new kind of even and odd nonlinear coherent states

Meng Xiang-Guo, Wang Ji-Suo, Liang Bao-Long
Chin. Phys. B, 2009, 18 (6): 2300-2306 doi: 10.1088/1674-1056/18/6/031
Full Text: [PDF 1061 KB] (Downloads:529)
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Using a numerical computational method, quasiprobability distributions of new kinds of even and odd nonlinear coherent states (EONLCS) are investigated. The results show that the distributions of the new even nonlinear coherent states (NLCS) are distinct from those of the new odd NLCS and imply that the new EONLCS always exhibit some different nonclassical effects. Finally, with the aid of newly introduced intermediate coordinate-momentum representation in quantum optics, the tomograms of the new EONLCS are calculated. This is a new way of obtaining the tomogram function.

Optimal entropy squeezing sudden generation and its control for an effective two-level moving atom entanglement with the two-mode coherent fields

Liu Xiao-Juan, Zhou Yuan-Jun, Fang Mao-Fa
Chin. Phys. B, 2009, 18 (6): 2307-2313 doi: 10.1088/1674-1056/18/6/032
Full Text: [PDF 854 KB] (Downloads:691)
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From the viewpoint of quantum information, this paper proposes a concept and a definition of the atomic optimal entropy squeezing sudden generation (AOESSG) for the system of an effective two-level moving atom which entangles with the two-mode coherent fields. It also researches the relationship between the AOESSG and entanglement sudden death of the atom-fields, and discusses the influences of atomic initial state on the AOESSG and obtains the system parameter which controls the AOESSG.

Quantization of the radiation field in an anisotropic dielectric medium

Li Wei, Liu Shi-Bing, Yang Wei
Chin. Phys. B, 2009, 18 (6): 2314-2318 doi: 10.1088/1674-1056/18/6/033
Full Text: [PDF 148 KB] (Downloads:664)
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There are both loss and dispersion characteristics for most dielectric media. In quantum theory the loss in medium is generally described by Langevin force in the Langevin noise (LN) scheme by which the quantization of the radiation field in various homogeneous absorbing dielectrics can be successfully actualized. However, it is invalid for the anisotropic dispersion medium. This paper extends the LN theory to an anisotropic dispersion medium and presented the quantization of the radiation field as well as the transformation relation between the homogeneous and anisotropic dispersion media.

Quantum superdense coding via cavity-assisted interactions

Pan Guo-Zhu, Yang Ming, Cao Zhuo-Liang
Chin. Phys. B, 2009, 18 (6): 2319-2323 doi: 10.1088/1674-1056/18/6/034
Full Text: [PDF 653 KB] (Downloads:948)
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Quantum superdense coding (QSC) is an example of how entanglement can be used to minimize the number of carriers of classical information. This paper proposes two schemes for implementing QSC by means of cavity assisted interactions with single-photon pulses. The schemes are insensitive to the cavity decay and the thermal field, thus it might be realizable based on the current cavity QED techniques.

Influence of laser linewidth on external-cavity frequency doubling efficiency of a 1.56μm master oscillator fiber power amplifier

Tian Xiu-Tao, Li Yong-Min, Liu Qin, Zhang Kuan-Shou
Chin. Phys. B, 2009, 18 (6): 2324-2327 doi: 10.1088/1674-1056/18/6/035
Full Text: [PDF 299 KB] (Downloads:721)
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By using an external-cavity frequency-doubling master oscillator fiber power amplifier (MOPA), a 700~mW continuous-wave single-frequency laser source at 780~nm is produced. It is shown that the frequency doubling efficiency is improved when the seed diode laser is optically locked to a resonant frequency of a confocal Fabry--Perot (F-P) cavity. This phenomenon can be attributed to the narrowing of the 1.56~μ m laser linewidth and explained by our presented theoretical model. The experimental results are found to be in good agreement with the theoretical predictions.

Pulse-train nonuniformity in an all-fiber ring laser passively mode-locked by nonlinear polarization rotation

Luo Zhi-Chao, Xu Wen-Cheng, Song Chuang-Xing, Luo Ai-Ping, Chen Wei-Cheng
Chin. Phys. B, 2009, 18 (6): 2328-2333 doi: 10.1088/1674-1056/18/6/036
Full Text: [PDF 1676 KB] (Downloads:1018)
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This paper reports the periodic power variation of the pulse-train in a passively mode-locked soliton fiber ring laser. It can obtain either the uniform or nonuniform pulse-train output by simply rotating the polarization controllers. The experimental results show that the pulse-train nonuniformity is caused by the interaction between the nonuniform polarization states of the soliton pulses and the passive polarizer in the cavity.

Vibration insensitive optical ring cavity

Miao Jin, Jiang Yan-Yi, Fang Su, Bi Zhi-Yi, Ma Long-Sheng
Chin. Phys. B, 2009, 18 (6): 2334-2339 doi: 10.1088/1674-1056/18/6/037
Full Text: [PDF 1177 KB] (Downloads:816)
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The mounting configuration of an optical ring cavity is optimized for vibration insensitivity by finite element analysis. A minimum response to vertical accelerations is found by simulations made for different supporting positions.

Phase dispersion of Raman and Rayleigh-enhanced four-wave mixings in femtosecond polarization beats

Zhao Yan, Nie Zhi-Qiang, Li Chang-Biao, Zhang Yan-Peng, Gan Chen-Li, Zheng Huai-Bin, Li Yuan-Yuan, Lu Ke-Qing
Chin. Phys. B, 2009, 18 (6): 2340-2351 doi: 10.1088/1674-1056/18/6/038
Full Text: [PDF 854 KB] (Downloads:884)
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Based on color-locking noisy field correlation in three Markovian stochastic models, phase dispersions of the Raman- and Rayleigh-enhanced four-wave mixing (FWM) have been investigated. The phase dispersions are modified by both linewidth and time delay for negative time delay, but only by linewidth for positive time delay. Moreover, the results under narrowband condition are close to the nonmodified nonlinear dispersion and absorption of the material. Homodyne and heterodyne detections of the Raman, the Rayleigh and the mixing femtosecond difference-frequency polarization beats have also been investigated, separately.

Solutions to the equations describing materials with competing quadratic and cubic nonlinearities

Zhao Li-Na, Tong Zi-Shuang, Lin Ji
Chin. Phys. B, 2009, 18 (6): 2352-2358 doi: 10.1088/1674-1056/18/6/039
Full Text: [PDF 914 KB] (Downloads:583)
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The Lie group theoretical method is used to study the equations describing materials with competing quadratic and cubic nonlinearities. The equations share some of the nice properties of soliton equations. From the elliptic functions expansion method, we obtain large families of analytical solutions, in special cases, we have the periodic, kink and solitary solutions of the equations. Furthermore, we investigate the stability of these solutions under the perturbation of amplitude noises by numerical simulation.

Dark incoherent spatial solitons in logarithmically saturable nonlinear media

Zhang Yi-Qi, Lu Ke-Qing, Zhang Mei-Zhi, Li Ke-Hao, Liu Shuang, Zhang Yan-Peng
Chin. Phys. B, 2009, 18 (6): 2359-2363 doi: 10.1088/1674-1056/18/6/040
Full Text: [PDF 793 KB] (Downloads:767)
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This paper studies numerically the dark incoherent spatial solitons propagating in logarithmically saturable nonlinear media by using a coherent density approach and a split-step Fourier approach for the first time. Under odd and even initial conditions, a soliton triplet and a doublet are obtained respectively for given parameters. Simultaneously, coherence properties associated with the soliton triplet and doublet are discussed. In addition, if the values of the parameters are properly chosen, five and four splittings from the input dark incoherent spatial solitons can also form. Lastly, the grayness of the soliton triplet and that of the doublet are studied, in detail.

Similarity of interactions between (3+1)D spatiotemporal optical solitons in both the dispersive medium with cubic-quintic nonlinearity and the saturable medium

Peng Jin-Zhang, Yang Hong, Tang Yi
Chin. Phys. B, 2009, 18 (6): 2364-2371 doi: 10.1088/1674-1056/18/6/041
Full Text: [PDF 6987 KB] (Downloads:654)
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By making use of the split-step Fourier method, this paper numerically simulates dynamical behaviors, including repulsion, fusion, scattering and spiraling of colliding (3+1)D spatiotemporal solitons in both the dispersive medium with cubic-quintic and the saturable medium. Careful comparison of the colliding behaviors in these two media is presented. Although the origin of the nonlinearities is different in these two media, the obtained results show that the dynamical behaviors are very similar. This presents additional evidence to support the supposition of universality of interactions between solitons.

OH-1 absorption bands of LiNbO3 with varying composition

Chen Hong-Jian, Shi Li-Hong, Yan Wen-Bo, Chen Gui-Feng, Shen Jun, Li Yang-Xian
Chin. Phys. B, 2009, 18 (6): 2372-2376 doi: 10.1088/1674-1056/18/6/042
Full Text: [PDF 458 KB] (Downloads:698)
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This paper reports that OH-1 absorption bands of lithium niobate crystal have been measured at room temperature, and the band shape depending on the crystal composition has been observed. The OH-1 absorption bands are fitted with three Lorentzian peaks by varying position, halfwidth, and height. Nearly constant peak positions (3468, 3481 and 3490~cm-1) are obtained for all samples. It shows that the height and area of the decomposed peaks vary with the Li composition in a complex way. However, the combinations of these fitting parameters show a linear dependence on the composition up to nearly 50~mol%, which is very useful for the composition determination in a wide range. The linear relationships between the parameter combinations and Li composition are also presented quantitatively. In addition, the explanations were given for the excellent composition linearity of parameter combinations.

Transmission spectra through photonic double quantum well system

Fei Hong-Ming, Jiang Yuan-Kai, Liang Jiu-Qing, Lin Duo-Liang
Chin. Phys. B, 2009, 18 (6): 2377-2382 doi: 10.1088/1674-1056/18/6/043
Full Text: [PDF 217 KB] (Downloads:652)
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By means of the modal expansion method with an R-matrix propagation algorithm, effects of the coupling between resonance photonic states on the resonance tunneling through a double quantum well structure are investigated. We examine the effects on the transmission spectra due to variation of the second well width and middle barrier thickness. Drastic change of the tunneling spectra is found and analyzed when the wells are filled with left-hand media.

Fabrication of high-quality three-dimensional photonic crystal heterostructures

Liu Zheng-Qi, Feng Tian-Hua, Dai Qiao-Feng, Wu Li-Jun, Lan Sheng
Chin. Phys. B, 2009, 18 (6): 2383-2388 doi: 10.1088/1674-1056/18/6/044
Full Text: [PDF 2014 KB] (Downloads:853)
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Three-dimensional photonic crystal (PC) heterostructures with high quality are fabricated by using a pressure controlled isothermal heating vertical deposition technique. The formed heterostructures have higher quality, such as deeper band gaps and sharper band edges, than the heterostructures reported so far. Such a significant improvement in quality is due to the introduction of a thin TiO2 buffer layer between the two constitutional PCs. It is revealed that the disorder caused by lattice mismatch is successfully removed if the buffer layer is used once. As a result, the formed heterostructures possess the main features in the band gap of constitutional PCs. The crucial role of the thin buffer layer is also verified by numerical simulations based on the finite-difference time-domain technique.

Applied electric field to fabricate colloidal crystals with the photonic band-gap in communication waveband

Yan Hai-Tao, Wang Ming, Ge Yi-Xian, Yu Ping
Chin. Phys. B, 2009, 18 (6): 2389-2392 doi: 10.1088/1674-1056/18/6/045
Full Text: [PDF 1442 KB] (Downloads:690)
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The macropore silica colloidal crystal templates were assembled orderly in a capillary glass tube by an applied electric field method to control silica deposition. In order to achieve the photonic band gap (PBG) of colloidal crystal in optical communication waveband, the diameter of silica microspheres is selected by Bragg diffraction formula. An experiment was designed to test the bandgap of the silica crystal templates. This paper discusses the formation process and the close-packed fashion of the silica colloidal crystal templates was discussed. The surface morphology of the templates was also analyzed. The results showed that the close-packed fashion of silica array templates was face-centered cubic (FCC) structure. The agreement is very good between the experimental data and the theoretical calculation.

High-performance evanescently-coupled uni-traveling-carrier photodiodes

Zhang Yun-Xiao, Liao Zai-Yi, Wang Wei
Chin. Phys. B, 2009, 18 (6): 2393-2397 doi: 10.1088/1674-1056/18/6/046
Full Text: [PDF 460 KB] (Downloads:629)
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A new evanescently-coupled uni-traveling-carrier photodiode (EC-UTC PD) based on a multimode diluted waveguide (MDW) structure is fabricated, analysed and characterized. Optical and electrical characteristics of the device are investigated. The excellent characteristics are demonstrated such as a responsivity of 0.36~A/W, a bandwidth of 11.5~GHz and a small-signal 1-dB compression current greater than 18~mA at 10~GHz. The saturation current is significantly improved compared with those of similar evanescently-coupled pin photodiodes. The radio frequency (RF) bandwidth can be further improved by eliminating RF losses induced by the cables, the probe and the bias tee between the photodiode and the spectrum analyzer.

Mode-field half widths of Gaussian approximation for fundamental mode of two kinds of optical waveguides

Li Lian-Huang, Guo Fu-Yuan
Chin. Phys. B, 2009, 18 (6): 2398-2403 doi: 10.1088/1674-1056/18/6/047
Full Text: [PDF 390 KB] (Downloads:892)
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This paper analyzes the characteristic of matching efficiency between the fundamental mode of two kinds of optical waveguides and its Gaussian approximate field.Then, it presents a new method where the mode-field half-width of Gaussian approximation for the fundamental mode should be defined according to the maximal matching efficiency method. The relationship between the mode-field half-width of the Gaussian approximate field obtained from the maximal matching efficiency and normalized frequency is studied; furthermore, two formulas of mode-field half-widths as a function of normalized frequency are proposed.

Theoretical and experimental investigations of flexural wave propagation in periodic grid structures designed with the idea of phononic crystals

Wen Ji-Hong, Yu Dian-Long, Liu Jing-Wen, Xiao Yong, Wen Xi-Sen
Chin. Phys. B, 2009, 18 (6): 2404-2411 doi: 10.1088/1674-1056/18/6/048
Full Text: [PDF 4892 KB] (Downloads:909)
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The propagation characteristics of flexural waves in periodic grid structures designed with the idea of phononic crystals are investigated by combining the Bloch theorem with the finite element method. This combined analysis yields phase constant surfaces, which predict the location and the extension of band gaps, as well as the directions and the regions of wave propagation at assigned frequencies. The predictions are validated by computation and experimental analysis of the harmonic responses of a finite structure with 11× 11 unit cells. The flexural wave is localized at the point of excitation in band gaps, while the directional behaviour occurs at particular frequencies in pass bands. These studies provide guidelines to designing periodic structures for vibration attenuation.
ATOMIC AND MOLECULAR PHYSICS

Energy level analyses of even-parity J = 1 and 2 Rydberg states of Sn I by multichannel quantum defect theory

You Shuai, Feng Yan-Yan, Dai Zhen-Wen
Chin. Phys. B, 2009, 18 (6): 2229-2237 doi: 10.1088/1674-1056/18/6/021
Full Text: [PDF 787 KB] (Downloads:609)
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This paper analyzes the energy levels along the even-parity J=1 and 2 Rydberg series of Sn I by multichannel quantum defect theory. A good agreement between theoretical and experimental energy levels was achieved. Below 59198~cm-1, a total of 85 and 23 new energy levels, respectively, in the J=1 and J=2 series, which cannot be measured previously by experiments, are predicted in this work. Based on the calculated admixture coefficients of each channel, interchannel interactions were discussed in detail. The results are helpful to understand the characteristics of configuration interaction among even-parity levels in Sn I.

Ground state energy of He isoelectronic sequence treated variationally via Hylleraas-like wavefunction

Serpil ?akiro?lu, Kadir Akgüng?r, ?smail S?kmen
Chin. Phys. B, 2009, 18 (6): 2238-2243 doi: 10.1088/1674-1056/18/6/022
Full Text: [PDF 173 KB] (Downloads:870)
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In this study, the energy for the ground state of helium and a few helium-like ions (Z=1--6) is computed variationally by using a Hylleraas-like wavefunction. A four-parameters wavefunction, satisfying boundary conditions for coalescence points, is combined with a Hylleraas-like basis set which explicitly incorporates r12 interelectronic distance. The main contribution of this work is the introduction of modified correlation terms leading to the definition of integral transforms which provide the calculation of expectation value of energy to be done analytically over single-particle coordinates instead of Hylleraas coordinates.

Oscillator strengths for 22S--n2P transitions of the lithium isoelectronic sequence from Z = 11 to 20

Hu Mu-Hong, Wang Zhi -Wen
Chin. Phys. B, 2009, 18 (6): 2244-2249 doi: 10.1088/1674-1056/18/6/023
Full Text: [PDF 196 KB] (Downloads:822)
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The dipole-length, dipole-velocity and dipole-acceleration absorption oscillator strengths for the 1s22s--1s2np (3 ≤ n ≤ 9) transitions of lithium-like systems from Z=11 to 20 are calculated by using the energies and the multiconfiguration interaction wave functions obtained from a full core plus correlation method, in which relativistic and mass-polarization effects on the energy, as the first-order perturbation corrections, are included. The results of three forms are in good agreement with each other, and closely agree with the experimental data available in the literature. Based on the quantum defects obtained with quantum defect theory (QDT), the discrete oscillator strengths for the transitions from the ground state to highly excited states 1s2np (n ≥ 10) and oscillator strength densities corresponding to the bound-free transitions are obtained for these ions.

Elastic collisions between Si and D atoms at low temperatures and accurate analytic potential energy function and molecular constants of the SiD(X2П) radical

Shi De-Heng, Zhang Jin-Ping, Sun Jin-Feng, Zhu Zun-Lue
Chin. Phys. B, 2009, 18 (6): 2250-2257 doi: 10.1088/1674-1056/18/6/024
Full Text: [PDF 228 KB] (Downloads:653)
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Interaction potential of the SiD(X2П) radical is constructed by using the CCSD(T) theory in combination with the largest correlation-consistent quintuple basis set augmented with the diffuse functions in the valence range. Using the interaction potential, the spectroscopic parameters are accurately determined. The present D0, De, Re, ω e, α e and Be values are of 3.0956~eV, 3.1863~eV, 0.15223~nm, 1472.894~cm-1, 0.07799~cm-1 and 3.8717~cm-1, respectively, which are in excellent agreement with the measurements. A total of 26 vibrational states is predicted when J = 0 by solving the radial Schr?dinger equation of nuclear motion. The complete vibrational levels, classical turning points, initial rotation and centrifugal distortion constants when J=0 are reported for the first time, which are in good accord with the available experiments. The total and various partial-wave cross sections are calculated for the elastic collisions between Si and D atoms in their ground states at 1.0× 10-11--1.0× 10-3~a.u. when the two atoms approach each other along the SiD(X2П) potential energy curve. Four shape resonances are found in the total elastic cross sections, and their resonant energies are of 1.73× 10-5, 4.0× 10-5, 6.45× 10-5 and 5.5× 10-4~a.u., respectively. Each shape resonance in the total elastic cross sections is carefully investigated. The results show that the shape of the total elastic cross sections is mainly dominated by the s partial wave at very low temperatures. Because of the weakness of the shape resonances coming from the higher partial waves, most of them are passed into oblivion by the strong s partial-wave elastic cross sections.

Size dependence of biexciton binding energy in single InAs/GaAs quantum dots

Dou Xiu-Ming, Sun Bao-Quan, Huang She-Song, Ni Hai-Qiao, Niu Zhi-Chuan, Yang Fu-Hua, Jia Rui
Chin. Phys. B, 2009, 18 (6): 2258-2263 doi: 10.1088/1674-1056/18/6/025
Full Text: [PDF 1967 KB] (Downloads:805)
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This paper studies the size dependence of biexciton binding energy in single quantum dots (QDs) by using atomic force microscopy and micro-photoluminescence measurements. It finds that the biexciton binding energies in the QDs show ``binding'' and ``antibinding'' properties which correspond to the large and small sizes of QDs, respectively. The experimental results can be well interpreted by the biexciton potential curve, calculated from the exciton molecular model and the Heitler--London method.

Appearance of metallic features in small tungsten clusters

Lei Xue-Ling, Wang Xian-Ming, Zhu Heng-Jiang, Luo You-Hua
Chin. Phys. B, 2009, 18 (6): 2264-2270 doi: 10.1088/1674-1056/18/6/026
Full Text: [PDF 1524 KB] (Downloads:732)
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The structures and properties of Wn (n=2--14) clusters were studied by using the density functional theory (DFT) at LSDA level. The most stable structures of Wn (n=2--14) clusters with global minimum were determined. The average binding energy (Eb), the first and second difference of total energy (\itδ E, \itδ2E), the vertical detachment energy (VDE), and the HOMO-LUMO gap versus the size were also discussed. The abrupt decrease of VDE and HOMO-LUMO gap at size n=8 and 10 implied that tungsten clusters of W8 and W10 appeared to have metallic features. These changes were also accompanied by the delocalization of electron charge density and the strong hybridization between 5d and 6s orbits in W8 and W_10 clusters. Our results are in good agreement with the available experimental data.
CROSS DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

Structure optimization by heuristic algorithm in a coarse-grained off-lattice model

Liu Jing-Fa
Chin. Phys. B, 2009, 18 (6): 2615-2621 doi: 10.1088/1674-1056/18/6/082
Full Text: [PDF 175 KB] (Downloads:611)
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A heuristic algorithm is presented for a three-dimensional off-lattice AB model consisting of hydrophobic (A) and hydrophilic (B) residues in Fibonacci sequences. By incorporating extra energy contributions into the original potential function, we convert the constrained optimization problem of AB model into an unconstrained optimization problem which can be solved by the gradient method. After the gradient minimization leads to the basins of the local energy minima, the heuristic off-trap strategy and subsequent neighborhood search mechanism are then proposed to get out of local minima and search for the lower-energy configurations. Furthermore, in order to improve the efficiency of the proposed algorithm, we apply the improved version called the new PERM with importance sampling (nPERMis) of the chain-growth algorithm, pruned-enriched-Rosenbluth method (PERM), to face-centered-cubic (FCC)-lattice to produce the initial configurations. The numerical results show that the proposed methods are very promising for finding the ground states of proteins. In several cases, we found the ground state energies are lower than the best values reported in the present literature.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS

Experimental sensitivity on searching for CP violation at BES-III

Zhao Ming-Gang, Rong Gang, Ma Hai-Long, Zhang Da-Hua
Chin. Phys. B, 2009, 18 (6): 2213-2216 doi: 10.1088/1674-1056/18/6/018
Full Text: [PDF 174 KB] (Downloads:612)
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The CP violation in the D system is predicted to be an unobserved level in the Standard Model. In this paper, we describe the method of searching for CP violation decay processes with the coherently produced D0\bar D0 mesons from the ψ(3770) decay. The CP violation decay processes can be searched for at the BES-III experiment. The experimental sensitivity for searching for the CP violation can reach about a 10-4 level with a ψ(3770) data sample of about 20 fb-1.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

Self-consistent three-dimensional modeling and simulation of large-scale rectangular surface-wave plasma source

Lan Chao-Hui, Lan Chao-Zhen, Hu Xi-Wei, Chen Zhao-Quan, Liu Ming-Hai
Chin. Phys. B, 2009, 18 (6): 2412-2419 doi: 10.1088/1674-1056/18/6/049
Full Text: [PDF 2044 KB] (Downloads:815)
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A self-consistent and three-dimensional (3D) model of argon discharge in a large-scale rectangular surface-wave plasma (SWP) source is presented in this paper, which is based on the finite-difference time-domain (FDTD) approximation to Maxwell's equations self-consistently coupled with a fluid model for plasma evolution. The discharge characteristics at an input microwave power of 1200~W and a filling gas pressure of 50~Pa in the SWP source are analyzed. The simulation shows the time evolution of deposited power density at different stages, and the 3D distributions of electron density and temperature in the chamber at steady state. In addition, the results show that there is a peak of plasma density approximately at a vertical distance of 3~cm from the quartz window.

Electric fields inside and outside an anisotropic dielectric sphere

Li Ying-Le, Wang Ming-Jun
Chin. Phys. B, 2009, 18 (6): 2420-2425 doi: 10.1088/1674-1056/18/6/050
Full Text: [PDF 351 KB] (Downloads:910)
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Analytical expressions of electric fields inside and outside an anisotropic dielectric sphere are presented by transforming an anisotropic medium into an isotropic one based on the multi-scale transformation of electromagnetic theory. The theoretical expressions are consistent with those in the literature. The inside electric field, the outside electric field and the angle between their directions are derived in detail. Numerical simulations show that the direction of the outside field influences the magnitude of the inside field, while the dielectric constant tensor greatly affects its direction.

Dynamics simulation on interaction of intense laser pulses with atomic clusters

Du Hong-Chuan, Zhu Peng-Jia, Sun Shao-Hua, Liu Zuo-Ye, Li Lu, Ma Ling-Ling, Hu Bi-Tao
Chin. Phys. B, 2009, 18 (6): 2426-2431 doi: 10.1088/1674-1056/18/6/051
Full Text: [PDF 681 KB] (Downloads:672)
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Under classical particle dynamics, the interaction process between intense femtosecond laser pulses and icosahedral noble-gas atomic clusters was studied. Our calculated results show that ionization proceeds mainly through tunnel ionization in the combined field from ions, electrons and laser, rather than the electron-impact ionization. With increasing cluster size, the average and maximum kinetic energy of the product ion increases. According to our calculation, the expansion process of the clusters after laser irradiation is dominated by Coulomb explosion and the expansion scale increases with increasing cluster size. The dependence of average kinetic energy and average charge state of the product ions on laser wavelength is also presented and discussed. The dependence of average kinetic energy on the number of atoms inside the cluster was studied and compared with the experimental data. Our results agree with the experimental results reasonably well.

The stability margin on EAST tokamak

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Chin. Phys. B, 2009, 18 (6): 2432-2440 doi: 10.1088/1674-1056/18/6/052
Full Text: [PDF 5615 KB] (Downloads:705)
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The experimental advanced superconducting tokamak (EAST) is the first full superconducting tokamak with a D-shaped cross-sectional plasma presently in operation. Its poloidal coils are relatively far from the plasma due to the necessary thermal isolation from the superconducting magnets, which leads to relatively weaker coupling between plasma and poloidal field. This may cause more difficulties in controlling the vertical instability by using the poloidal coils. The measured growth rates of vertical stability are compared with theoretical calculations, based on a rigid plasma model. Poloidal beta and internal inductance are varied to investigate their effects on the stability margin by changing the values of parameters α n and γ n(Howl et al 1992 Phys. Fluids B4 1724), with plasma shape fixed to be a configuration with k = 1.9 and δ = 0.5. A number of ways of studying the stability margin are investigated. Among them, changing the values of parameters к and li is shown to be the most effective way to increase the stability margin. Finally, a guideline of stability margin Ms (к ,li ,A) to a new discharge scenario showing whether plasmas can be stabilized is also presented in this paper.

Prediction of the plasma distribution using artificial neural network

Li Wei, Chen Jun-Fang, Wang Teng
Chin. Phys. B, 2009, 18 (6): 2441-2444 doi: 10.1088/1674-1056/18/6/053
Full Text: [PDF 588 KB] (Downloads:947)
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In this work, an artificial neural network (ANN) model is established using a back-propagation training algorithm in order to predict the plasma spatial distribution in an electron cyclotron resonance (ECR) --- plasma-enhanced chemical vapor deposition (PECVD) plasma system. In our model, there are three layers: the input layer, the hidden layer and the output layer. The input layer is composed of five neurons: the radial position, the axial position, the gas pressure, the microwave power and the magnet coil current. The output layer is our target output neuron: the plasma density. The accuracy of our prediction is tested with the experimental data obtained by a Langmuir probe, and ANN results show a good agreement with the experimental data. It is concluded that ANN is a useful tool in dealing with some nonlinear problems of the plasma spatial distribution.

7.8GHz power generation device design using a rectangular dielectric-loaded waveguide

Lu Zhi-Gang, Gong Yu-Bin, Wei Yan-Yu, Xu Jin, Gao Peng, Wang Wen-Xiang
Chin. Phys. B, 2009, 18 (6): 2445-2451 doi: 10.1088/1674-1056/18/6/054
Full Text: [PDF 711 KB] (Downloads:809)
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In this paper, we present a design where a bunched relativistic electron beam traversing inside the rectangular dielectric-loaded (DL) waveguide is used as a high power microwave generation device. Two kinds of methods of calculating the electromagnetic (EM) field excited by a bunched beam are introduced, and in the second method the calculation of EM pulse length is discussed in detail. The desired operating mode is the LSM_11 due to its strong interaction with the electron beam. For the designed 7.8~GHz operating frequency, with a 100~nC/bunch drive train of electron bunches separated by 0.769~ns, we find that high gradient (>30~MV/m) and high power (>160~MW) can be generated. An output coupler is also designed which is able to extract the generated power to standard waveguides with a 94% coupling efficiency.

Three-dimensional simulation of Ka-band relativistic Cherenkov source with metal photonic-band-gap structures

Gao Xi, Yang Zi-Qiang, Qi Li-Mei, Lan Feng, Shi Zong-Jun, Li Da-Zhi, Liang Zheng
Chin. Phys. B, 2009, 18 (6): 2452-2458 doi: 10.1088/1674-1056/18/6/055
Full Text: [PDF 2286 KB] (Downloads:784)
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This paper presents a three-dimensional particle-in-cell (PIC) simulation of a Ka-band relativistic Cherenkov source with a slow wave structure (SWS) consisting of metal photonic band gap (PBG) structures. In the simulation, a perfect match layer boundary is employed to absorb passing band modes supported by the PBG lattice with an artificial metal boundary. The simulated axial field distributions in the cross section and surface of the SWS demonstrate that the device operates in the vicinity of the П point of a TM01-like mode. The Fourier transformation spectra of the axial fields as functions of time and space show that only a single frequency appears at 36.27~GHz, which is in good agreement with that of the intersection of the dispersion curve with the slow space charge wave generated on the beam. The simulation results demonstrate that the SWS has good mode selectivity.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

A revised version of the program VEC (visual computing in electron crystallography) Hot!

Li Xue-Ming, Li Fang-Hua, Fan Hai-Fu
Chin. Phys. B, 2009, 18 (6): 2459-2463 doi: 10.1088/1674-1056/18/6/056
Full Text: [PDF 2194 KB] (Downloads:462)
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The program package VEC (Visual computing in Electron Crystallography) has been revised such that (i) a program converting one-line symbols to two-line symbols of (3+1)-dimensional superspace groups has been incorporated into VEC so that the latter can interpret both kinds of symbols; (ii) a bug in calculating structure factors of one-dimensionally incommensurate modulated crystals has been fixed. The correction has been verified by successfully matching the experimental electron microscopy image of an incommensurate crystal with a series of simulated images. The precompiled revised version of VEC and relevant materials are available on the Web at http://cryst.iphy.ac.cn.

Experimental verification of Foreman dislocation model

Zhao Chun-Wang, Xing Yong-Ming, Bai Pu-Cun
Chin. Phys. B, 2009, 18 (6): 2464-2468 doi: 10.1088/1674-1056/18/6/057
Full Text: [PDF 4373 KB] (Downloads:741)
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We present a strain analysis of an edge dislocation core, and a detailed discussion of the Foreman dislocation model. In order to examine the model, the quantitative measurement of strain field around an edge dislocation in aluminum is performed, and high-resolution transmission electron microscopy and geometric phase analysis are employed to map the strain field of the edge dislocation core in aluminum. The strain measurements are compared with the Foreman dislocation model, showing that they are in good agreement with each other when 0.7 ≤ a ≤ 1.5.

Periodic, quasiperiodic and chaotic discrete breathers in a parametrical driven two-dimensional discrete diatomic Klein--Gordon lattice

Xu Quan, Tian Qiang
Chin. Phys. B, 2009, 18 (6): 2469-2474 doi: 10.1088/1674-1056/18/6/058
Full Text: [PDF 2893 KB] (Downloads:572)
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We study a two-dimensional (2D) diatomic lattice of anharmonic oscillators with only quartic nearest-neighbor interactions, in which discrete breathers (DBs) can be explicitly constructed by an exact separation of their time and space dependence. DBs can stably exist in the 2D discrete diatomic Klein--Gordon lattice with hard and soft on-site potentials. 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 (QDBs) and chaotic discrete breathers (CDBs) by changing the amplitude of the driver. But the DBs and QDBs with symmetric and anti-symmetric profiles that are centered at a heavy atom are more stable than at a light atom, because the frequencies of the DBs and QDBs centered at a heavy atom are lower than those centered at a light atom.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

Single-particle spectral function of the Hubbard chain: frustration induced

Wang Jing, Enrico Arrigoni
Chin. Phys. B, 2009, 18 (6): 2475-2480 doi: 10.1088/1674-1056/18/6/059
Full Text: [PDF 300 KB] (Downloads:613)
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The one-electron spectral function of a frustrated Hubbard chain is computed by making use of the cluster perturbation theory. The spectral weight we found turns out to be strongly dependent on the frustrating next-nearest-neighbor hopping t'. A frustration induced pseudogap arises when the system evolves from a gapful Mott insulator to a gapless conductor for an intermediate value of the frustration parameter |t'|. Furthermore, the opening of a pseudogap in the density of states already in the metallic side leads to a continuous opening of the true gap in the insulator. For the hole-doped case, the pseudogap is pinned at the Fermi energy, while the Mott gap is shifted in energy with increasing Hubbard interaction U. The separation of the pseudogap and Mott gap in the hole-doped system demonstrates the validity of the existence of a pseudogap.

Ab initio prediction on ferrotoroidic and electronic properties of olivine Li4MnFeCoNiP4O16

Feng Hong-Jian, Liu Fa-Min
Chin. Phys. B, 2009, 18 (6): 2481-2486 doi: 10.1088/1674-1056/18/6/060
Full Text: [PDF 979 KB] (Downloads:790)
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First-principles calculations predict that olivine Li4MnFeCoNiP4O16 has a large toroidal moment and ferrimagnetic configuration with a magnetic moment of 1.99μB per formula unit. Density functional theory plus U (DFT+U) shows an indirect band gap of 0.65~eV in this hypothetical material. The band gap is not simply related to the electronic conductivity when it is used as cathode material in rechargeable Li-ion batteries. Based on the orbital-resolved density of states for the transition-metal ions in the hypothetical material, Co, Ni and Mn are in the high-spin configuration while Fe is in the low-spin configuration, which leads to a large resulting toroidal moment deriving from the Co and Ni ions. The spin configuration of the transition-metal ions in the system breaks the space- and time-inversion symmetry and leads to the magnetoelectric property simultaneously. The ferrotoroidic domain, the fourth form of ferroic, is observed in this new material, as in the case of LiCoPO_4 reported recently.

Ab initio study on magnetoelectric and electronic properties in Pb2TiVO6

Feng Hong-Jian, Liu Fa-Min
Chin. Phys. B, 2009, 18 (6): 2487-2491 doi: 10.1088/1674-1056/18/6/061
Full Text: [PDF 217 KB] (Downloads:892)
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First principles calculations within the projected augmented-wave (PAW) method, using the local spin density approximation plus U (LSDA+U) scheme, show that the tetragonal Pb2TiVO6 is a potential multiferroic material with antiferromagnetic (AFM) spin configuration. It has a magnetic moment of 1μB in a one unit cell originating from the non-bonding orbital dxy in a majority spin channel and a band gap of 1.45~eV with proper U. The large BEC (Born effective charge) of Pb and Ti shows that the stereochemical activity of Pb and Ti may provide the possibility of switchable paths for the ferroelectricity in this hypothetical material. The insulating property and the lower resistivity in the recent prepared PbVO3 can be significantly improved by adopting the Ti.

Ab initio studies on n-type and p-type Li4Ti5O12

Zhong Zhi-Yong, Nie Zheng-Xin, Du Yan-Lan, Ouyang Chu-Ying, Shi Si-Qi, Lei Min-Sheng
Chin. Phys. B, 2009, 18 (6): 2492-2497 doi: 10.1088/1674-1056/18/6/062
Full Text: [PDF 1398 KB] (Downloads:2009)
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This paper studies the structure and electronic properties of Li4Ti5O12, as anode material for lithium ion batteries, from first principles calculations. The results suggest that there are two kinds of unit cell of Li4Ti5O12: n-type and p-type. The two unit cells have different structures and electronic properties: the n-type with two 16d site Li ions is metallic by electron, while the p-type with three 16d Li ions is metallic by hole. However, the Li4Ti5O12 is an insulator. It is very interesting that one n-type cell and two p-type cells constitute one Li4Ti5O12 supercell which is insulating. The results show that the intercalation potential obtained with a p-type unit cell with one additional electron is quite close to the experimental value of 1.5~V.

Transport properties of a random binary side-coupled chain

Hu Dong-Sheng, Lu Xiu-Juan, Zhang Yong-Mei, Zhu Chen-Ping
Chin. Phys. B, 2009, 18 (6): 2498-2501 doi: 10.1088/1674-1056/18/6/063
Full Text: [PDF 171 KB] (Downloads:662)
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We investigate the transport properties of a random binary side-coupled chain by using the transfer-matrix technique. It is found that there are resonant states in the systems with short-range correlations between the host chain atoms and the side-coupled atoms. The analytic expressions for the extended states are also presented in the systems with the side couplings between like atoms and between unlike atoms.

Transport properties of boron nanotubes investigated by ab initio calculation

Guo Wei, Hu Yi-Bin, Zhang Yu-Yang, Du Shi-Xuan, Gao Hong-Jun
Chin. Phys. B, 2009, 18 (6): 2502-2507 doi: 10.1088/1674-1056/18/6/064
Full Text: [PDF 699 KB] (Downloads:880)
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We investigate atomic and electronic structures of boron nanotubes (BNTs) by using the density functional theory (DFT). The transport properties of BNTs with different diameters and chiralities are studied by the Keldysh nonequilibrium Green function (NEGF) method. It is found that the cohesive energies and conductances of BNTs decrease as their diameters decrease. It is more difficult to form (N, 0) tubes than (M, M) tubes when the diameters of the two kinds of tubes are comparable. However, the (N, 0) tubes have a higher conductance than the (M, M) tubes. When the BNTs are connected to gold electrodes, the coupling between the BNTs and the electrodes will affect the transport properties of tubes significantly.

First-principles study of the electronic and optical properties of ZnO nanowires

Zhang Fu-Chun, Zhang Zhi-Yong, Zhang Wei-Hu, Yan Jun-Feng, Yong Jiang-Ni
Chin. Phys. B, 2009, 18 (6): 2508-2513 doi: 10.1088/1674-1056/18/6/065
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The geometric, energetic, electronic structures and optical properties of ZnO nanowires (NWs) with hexagonal cross sections are investigated by using the first-principles calculation of plane wave ultra-soft pseudo-potential technology based on the density functional theory (DFT). The calculated results reveal that the initial Zn-O double layers merge into single layers after structural relaxations, the band gap and binding energies decrease with the increase of the ZnO nanowire size. Those properties show great dimension and size dependence. It is also found that the dielectric functions of ZnO NWs have different peaks with respect to light polarization, and the peaks of ZnO NWs exhibit a significant blueshift in comparison with those of bulk ZnO. Our results gives some reference to the thorough understanding of optical properties of ZnO, and also enables more precise monitoring and controlling during the growth of ZnO materials to be possible.

Current-voltage characteristics of individual conducting polymer nanotubes and nanowires

Long Yun-Ze, Yin Zhi-Hua, Li Meng-Meng, Gu Chang-Zhi, Duvail Jean-Luc, Jin Ai-Zi, Wan Mei-Xiang
Chin. Phys. B, 2009, 18 (6): 2514-2522 doi: 10.1088/1674-1056/18/6/066
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We report the current-voltage (I--V) characteristics of individual polypyrrole nanotubes and poly(3,4-ethylenedioxythiophene) (PEDOT) nanowires in a temperature range from 300~K to 2~K. Considering the complex structures of such quasi-one-dimensional systems with an array of ordered conductive regions separated by disordered barriers, we use the extended fluctuation-induced tunneling (FIT) and thermal excitation model (Kaiser expression) to fit the temperature and electric-field dependent I--V curves. It is found that the I--V data measured at higher temperatures or higher voltages can be well fitted by the Kaiser expression. However, the low-temperature data around the zero bias clearly deviate from those obtained from this model. The deviation (or zero-bias conductance suppression) could be possibly ascribed to the occurrence of the Coulomb-gap in the density of states near the Femi level and/or the enhancement of electron-electron interaction resulting from nanosize effects, which have been revealed in the previous studies on low-temperature electronic transport in conducting polymer films, pellets and nanostructures. In addition, similar I--V characteristics and deviation are also observed in an isolated K0.27MnO2 nanowire.

Dynamics of electron in a surface quantum well

Wang Li-Fei, Yang Guang-Can
Chin. Phys. B, 2009, 18 (6): 2523-2528 doi: 10.1088/1674-1056/18/6/067
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This paper studies the quantum dynamics of electrons in a surface quantum well in the time domain with autocorrelation of wave packet. The evolution of the wave packet for different manifold eigenstates with finite and infinite lifetimes is investigated analytically. It is found that the quantum coherence and evolution of the surface electronic wave packet can be controlled by the laser central energy and electric field. The results show that the finite lifetime of excited states expedites the dephasing of the coherent electronic wave packet significantly. The correspondence between classical and quantum mechanics is shown explicitly in the system.

Propagation properties of a modified surface plasmonic waveguide with an arc slot

Xue Wen-Rui, Guo Ya-Nan, Zhang Wen-Mei
Chin. Phys. B, 2009, 18 (6): 2529-2534 doi: 10.1088/1674-1056/18/6/068
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We introduce a modified surface plasmonic waveguide with an arc slot. The dependences of distribution of energy flux density, effective index, propagation length and mode area of the symmetric mode supported by this waveguide on geometrical parameters and working wavelength are analysed by using the finite-difference frequency-domain (FDFD) method. Results show that the energy flux density distributes mainly in four corners which are formed by two arcs, and the closer to the corners it is, the stronger the energy flux density will be. The effective index, the propagation length and the mode area are influenced by geometrical parameters, including the width, the thickness and the arc radius of the surface plasmonic waveguide, as well as the working wavelength. It has been shown that the surface plasmonic waveguide with an arc slot has better propagation properties than the surface plasmonic waveguide with a straight slot. This work may be helpful for applying the slot surface plasmonic waveguide to integrated photonics.

The topological structure of the integral quantum Hall effect in magnetic semiconductor-superconductor hybrids

Ren Ji-Rong, Zhu Hui
Chin. Phys. B, 2009, 18 (6): 2535-2541 doi: 10.1088/1674-1056/18/6/069
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An unconventional integer quantum Hall regime was found in magnetic semiconductor-superconductor hybrids. By making use of the decomposition of the gauge potential on a U(1) principal fibre bundle over k-space, we study the topological structure of the integral Hall conductance. It is labeled by the Hopf index β and the Brouwer degree η. The Hall conductance topological current and its evolution is discussed.

Zero biased Ge-on-Si photodetector with a bandwidth of 4.72~GHz at 1550~nm

Xue Hai-Yun, Xue Chun-Lai, Cheng Bu-Wen, Yu Yu-De, Wang Qi-Ming
Chin. Phys. B, 2009, 18 (6): 2542-2544 doi: 10.1088/1674-1056/18/6/070
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High quality Ge was epitaxially grown on Si using ultrahigh vacuum/chemical vapor deposition (UHV/CVD). This paper demonstrates efficient germanium-on-silicon p-i-n photodetectors with 0.8~μm Ge, with responsivities as high as 0.38 and 0.21~A/W at 1.31 and 1.55~μ m, respectively. The dark current density is 0.37~mA/cm2 and 29.4~mA/cm2 at 0~V and a reverse bias of 0.5~V. The detector with a diameter of 30~μ m, a 3~dB-bandwidth of 4.72~GHz at an incident wavelength of 1550~nm and zero external bias has been measured. At a reverse bias of 3~V, the bandwidth is 6.28~GHz.

Competitions of magnetism and superconductivity in FeAs-based materials Hot!

Yang Shuo, You Wen-Long, Gu Shi-Jian, Lin Hai-Qing
Chin. Phys. B, 2009, 18 (6): 2545-2550 doi: 10.1088/1674-1056/18/6/071
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Using the numerical unrestricted Hartree--Fock approach, we study the ground state of a two-orbital model describing newly discovered FeAs-based superconductors. We observe the competition of a (0, π) mode spin-density wave and the superconductivity as the doping concentration changes. There might be a small region in the electron-doping side where the magnetism and superconductivity coexist. The superconducting pairing is found to be spin singlet, orbital even, and coexisting sxy + dx2-y2 wave (even parity).

First-principles investigation of the electronic structure and magnetism of eskolaite

Shen Jing-Qin, Shi Si-Qi, Ouyang Chu-Ying, Lei Min-Sheng, Tang Wei-Hua
Chin. Phys. B, 2009, 18 (6): 2551-2556 doi: 10.1088/1674-1056/18/6/072
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Due to the fault of the author(s), the article entitled “First-principles investigation of the electronic structure and magnetism of eskolaite”, published in Chinese Physics B, 2009, Vol.18, Issue 6, pp 2551-2556, has been clarified to be copied from the article published in Physical Review B, 2009, Vol.79, Issue 10, article No.104404. So the above article in Chinese Physics B has been withdrawn from the publication. [16 December 2009]

The electronic structure and magnetism of eskolaite are studied by using first-principles calculations where the on-site Coulomb interaction and the exchange interaction are taken into account and the LSDA+U method is used. The calculated energies of magnetic configurations are very well fitted by the Heisenberg Hamiltonian with interactions in five neighbour shells; interaction with two nearest neighbours is found to be dominant. The Néel temperature is calculated in the spin-3/2 pair-cluster approximation. It is found that the measurements are in good agreement with the calculations of lattice parameters, density of states, band gap, local magnetic moment, and the Néel temperature for the values of U and J that are close to those obtained within the constrained occupation method. The band gap is of the Mott--Hubbard type.

Ferroelectricity in diatomic Ising chain as investigated by elastic Ising model

Guo Yun-Jun, Wang Ke-Feng, Liu Jun-Ming
Chin. Phys. B, 2009, 18 (6): 2557-2564 doi: 10.1088/1674-1056/18/6/073
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An elastic Ising model for a one-dimensional diatomic spin chain is proposed to explain the ferroelectricity induced by the collinear magnetic order with a low-excited energy state. A statistical theory based on this model is developed to calculate the electrical and magnetic properties of Ca3CoMnO6, a typical quasi-one-dimensional diatomic spin chain system. The calculated ferroelectric polarization and dielectric susceptibility show a good agreement with recently reported data on Ca3Co2-xMnxO6 (x ≈0.96) (Phys. Rev. Lett. 100 047601 (2008)), although the predicted magnetic susceptibility does not coincide well with experiment. We also address the rationality and deficiency of this model by including a first-order correction which improves the consistency between the model and experiment.

Influence of Fe cap layer on the structural and magnetic properties of Fe49Pt51/Fe bi-layers

Duan Chao-Yang, Ma Bin, Wei Fu-Lin, Zhang Zong-Zhi, Jin Qing-Yuan
Chin. Phys. B, 2009, 18 (6): 2565-2570 doi: 10.1088/1674-1056/18/6/074
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The influences of an Fe cap layer on the structural and magnetic properties of FePt/Fe bi-layers are investigated. Compared with single FePt alloy films, a thin Fe layer can affect the crystalline orientation and improve the chemical ordering of L10 FePt films. Moreover, the coercivity increases when a thin Fe layer covers the FePt layer. Beyond a critical thickness, however, the Fe cover layer quickens the magnetization reversal of Fe49Pt51/Fe bi-layers by their exchange coupling.

Microstructural and electromagnetic properties of MnO2 coated nickel particles with submicron size

Tang Bao-Lin, He Jun, Ji Tian-Hao, Wang Xin-Lin
Chin. Phys. B, 2009, 18 (6): 2571-2575 doi: 10.1088/1674-1056/18/6/075
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Nickel particles with submicron size are prepared by using the solvothermal method. These spheres are then coated with a layer of MnO2 using the soft chemical method. The microstructure is characterized by x-ray diffraction, transmission electron microscopy, and scanning electron microscopy. Energy x-ray dispersive spectrometry and high-resolution images show that the granular composites have a classical core/shell structure with an MnO2 superficial layer, no more than 10~nm in thickness. The hysteresis measurements indicate that these submicron-size Ni composite powders have small remanence and moderate coercivity. The electromagnetic properties of the powders measured by a vector network analyzer in a frequency range of 2--18~GHz are also reported in detail.

The electrical transport behavior of Zn-treated Zn1-xMnxO bulks

Peng Xian-De, Zhu Tao, Wang Fang-Wei, Huang Wan-Guo, Cheng Zhao-Hua
Chin. Phys. B, 2009, 18 (6): 2576-2581 doi: 10.1088/1674-1056/18/6/076
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Zn1-xMnxO bulks have been prepared by the solid state reaction method. Zn vapor treatment has been carried out to adjust the carrier concentration. For the Zn treated Zn1-xMnxO bulks, analysis of the temperature dependence of resistance and the field dependence of magnetoresistance demonstrates that the bound magnetic polarons (BMPs) play an important role in the electrical transport behavior. The hopping of BMPs dominates the electrical conduction behavior when temperature is below 170~K. At low temperature, paramagnetic Zn1-xMnxO bulks show a large magnetoresistance effect, which indicates that the large magnetoresistance effect in transition-metal doped ZnO dilute magnetic semiconductors is independent of their magnetic states.

Simulation of magnetization behaviours of Sm(Co,Fe,Cu,Zr)z magnet with low Cu content

Chen Ren-Jie, Zhang Hong-Wei, Shen Bao-Gen, Yan A-Ru, Chen Li-Dong
Chin. Phys. B, 2009, 18 (6): 2582-2588 doi: 10.1088/1674-1056/18/6/077
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The effects of microstructure, cell orientation and temperature on magnetic properties and the coercivity mechanism in Sm(Co,Fe,Cu,Zr)z with low Cu content are studied by using the micromagnetic finite element method in this paper. The simulations of the demagnetization behaviours indicate that the pinning effect weakens gradually with the thickness of cell boundary decreasing and strengthens gradually with the cell size decreasing. Because of the intergrain exchange coupling, the coercivity mechanism is determined by the difference in magnetocrystalline anisotropy between the cell phase and the cell boundary phase. And the coercivity mechanism is related to not only the cells alignment but also temperature. With temperature increasing, a transformation of the demagnetization mechanism occurs from the domain pinning to the uniform magnetization reversal mode and the transformation temperature is about 650~K.

The magnetoresistive effect induced by stress in spin-valve structure

Qian Li-Jie, Xu Xiao-Yong, Hu Jing-Guo
Chin. Phys. B, 2009, 18 (6): 2589-2595 doi: 10.1088/1674-1056/18/6/078
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Using a method of free energy minimization, this paper investigates the magnetization properties of a ferromagnetic (FM) monolayer and an FM/antiferromagnetic (AFM) bilayer under a stress field, respectively. It then investigates the magnetoresistance (MR) of the spin-valve structure, which is built by an FM monolayer and an FM/AFM bilayer, and its dependence upon the applied stress field. The results show that under the stress field, the magnetization properties of the FM monolayer is obviously different from that of the FM/AFM bilayer, since the coupled AFM layer can obviously block the magnetization of the FM layer. This phenomenon makes the MR of the spin-valve structure become obvious. In detail, there are two behaviors for the MR of the spin-valve structure dependence upon the stress field distinguished by the coupling (FM coupling or AFM coupling) between the FM layer and the FM/AFM bilayer. Either behavior of the MR of the spin-valve structure depends on the stress field including its value and orientation. Based on these investigations, a perfect mechanical sensor at the nano-scale is suggested to be devised experimentally.

Structural and electrical properties of Nd ion modified lead zirconate titanate nanopowders and ceramics

Wang Da-Wei, Zhang De-Qing, Yuan Jie, Zhao Quan-Liang, Liu Hong-Mei, Wang Zhi-Ying, Cao Mao-Sheng
Chin. Phys. B, 2009, 18 (6): 2596-2602 doi: 10.1088/1674-1056/18/6/079
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A modified sol-gel method is used for synthesizing Nd ion doped lead zirconate titanate nanopowders Pb1 - 3x/2NdxZr0.52Ti0.48O3 (PNZT) in an ethylene glycol system with zirconium nitrate as zirconium source. The results show that it is critical to add lead acetate after the reaction of zirconium nitrate with tetrabutyl titanate in the ethylene glycol system for preparing PNZT with an exact fraction of titanium content. It has been observed that the dopant of excess Nd ions can effectively improve the sintered densification and activity of the PNZT ceramics. Piezoelectric, dielectric and ferroelectric properties of the PNZT ceramics are remarkably enhanced as compared with those of monolithic lead zirconate titanate (PZT). Especially, the supreme values of piezoelectric constant (d33) and dielectric constant (\it ε) for the PNZT are both about two times that of the monolithic PZT and moreover, the remnant polarization (Pr) also increases by 30%. According to the analysis of the structures and properties, we attribute the improvement in electrical properties to the lead vacancies caused by the doping of Nd ions.

Strain effects on the polarized optical properties of InGaN with different In compositions

Tao Ren-Chun, Yu Tong-Jun, Jia Chuan-Yu, Chen Zhi-Zhong, Qin Zhi-Xin, Zhang Guo-Yi
Chin. Phys. B, 2009, 18 (6): 2603-2609 doi: 10.1088/1674-1056/18/6/080
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Strain effects on the polarized optical properties of c-plane and m-plane Inx1-xN were discussed for different In compositions (x=0, 0.05, 0.10, 0.15) by analyzing the relative oscillator strength (ROS) and energy level splitting of the three transitions related to the top three valence bands (VBs). The ROS was calculated by applying the effective-mass Hamiltonian based on k. p perturbation theory. For c-plane InxGa1-xN, it was found that the ROS of | X > and | Y >-like states were superposed with each other. Especially, under compressive strain, they dominated in the top VB whose energy level also went up with strain, while the ROS of the | Z >-like state decreased in the second band. For m-plane InxGa1-xN under compressive strain, the top three VBs were dominated by | X >, | Z >, and | Y >-like states, respectively, which led to nearly linearly-polarized light emissions. For the top VB, ROS difference between | X > and | Z >-like states became larger with compressive strain. It was also found that such tendencies were more evident in layers with higher In compositions. As a result, there would be more TE modes in total emissions from both c-plane and m-plane InGaN with compressive strain and In content, leading to a larger polarization degree. Experimental results of luminescence from InGaN/GaN quantum wells (QWs) showed good coincidence with our calculations.

Effect of annealing on structural, optical and electrical properties of ZnS/porous silicon composites

Wang Cai-Feng, Li Qing-Shan, Hu Bo, Li Wei-Bing
Chin. Phys. B, 2009, 18 (6): 2610-2615 doi: 10.1088/1674-1056/18/6/081
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ZnS films were prepared by pulsed laser deposition (PLD) on porous silicon (PS) substrates. This paper investigates the effect of annealing temperature on the structural, morphological, optical and electrical properties of ZnS/PS composites by x-ray diffraction (XRD), scanning electron microscope (SEM), photoluminescence (PL) and I--V characteristics. It is found that the ZnS films deposited on PS substrates were grown in preferred orientation along β-ZnS (111) direction, and the intensity of diffraction peak increases with increasing annealing temperature, which is attributed to the grain growth and the enhancement of crystallinity of ZnS films. The smooth and uniform surface of the as-prepared ZnS/PS composite becomes rougher through annealing treatment, which is related to grain growth at the higher annealing temperature. With the increase of annealing temperature, the intensity of self-activated luminescence of ZnS increases, while the luminescence intensity of PS decreases, and a new green emission located around 550~nm appeared in the PL spectra of ZnS/PS composites which is ascribed to the defect-center luminescence of ZnS. The I--V characteristics of ZnS/PS heterojunctions exhibited rectifying behavior, and the forward current increases with increasing annealing temperature.
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