Chin. Phys. B

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Perpendicular magnetic tunnel junction and its application in magnetic random access memory

Liu Hou-Fang, Syed Shahbaz Ali, Han Xiu-Feng

Chin. Phys. B, 2014, 23 (7): 077501 doi: 10.1088/1674-1056/23/7/077501
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Recent progresses in magnetic tunnel junctions with perpendicular magnetic anisotropy (PMA) are reviewed and summarized. At first, the concept and source of perpendicular magnetic anisotropy (PMA) are introduced. Next, a historical overview of PMA materials as magnetic electrodes, such as the RE-TM alloys TbFeCo and GdFeCo, novel tetragonal manganese alloys Mn-Ga, L1₀-ordered (Co, Fe)/Pt alloy, multilayer film [Co, Fe, CoFe/Pt, Pd, Ni, Au]N, and ultra-thin magnetic metal/oxidized barrier is offered. The other part of the article focuses on the optimization and fabrication of CoFeB/MgO/CoFeB p-MTJs, which is thought to have high potential to meet the main demands for non-volatile magnetic random access memory.

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Formation of multifunctional Fe₃O₄/Au composite nanoparticles for dual-mode MR/CT imaging applications

Hu Yong, Li Jing-Chao, Shen Ming-Wu, Shi Xiang-Yang

Chin. Phys. B, 2014, 23 (7): 078704 doi: 10.1088/1674-1056/23/7/078704
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Recent advances with iron oxide/gold (Fe₃O₄/Au) composite nanoparticles (CNPs) in dual-modality magnetic resonance (MR) and computed tomography (CT) imaging applications are reviewed. The synthesis and assembly of “dumbbell-like” and “core/shell” Fe₃O₄/Au CNPs is introduced. Potential applications of some developed Fe₃O₄/Au CNPs as contrast agents for dual-mode MR/CT imaging applications are described in detail.

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Nonequilibrium thermodynamics and fluctuation relations for small systems

Cao Liang, Ke Pu, Qiao Li-Yan, Zheng Zhi-Gang

Chin. Phys. B, 2014, 23 (7): 070501 doi: 10.1088/1674-1056/23/7/070501
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In this review, we give a retrospect of the recent progress in nonequilibrium statistical mechanics and thermodynamics in small dynamical systems. For systems with only a few number of particles, fluctuations and nonlinearity become significant and contribute to the nonequilibrium behaviors of the systems, hence the statistical properties and thermodynamics should be carefully studied. We review recent developments of this topic by starting from the Gallavotti-Cohen fluctuation theorem, and then to the Evans-Searles transient fluctuation theorem, Jarzynski free-energy equality, and the Crooks fluctuation relation. We also investigate the nonequilibrium free energy theorem for trajectories involving changes of the heat bath temperature and propose a generalized free-energy relation. It should be noticed that the non-Markovian property of the heat bath may lead to the violation of the free-energy relation.

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Level spacing statistics for two-dimensional massless Dirac billiards

Huang Liang, Xu Hong-Ya, Lai Ying-Cheng, Celso Grebogi

Chin. Phys. B, 2014, 23 (7): 070507 doi: 10.1088/1674-1056/23/7/070507
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Classical-quantum correspondence has been an intriguing issue ever since quantum theory was proposed. The searching for signatures of classically nonintegrable dynamics in quantum systems comprises the interesting field of quantum chaos. In this short review, we shall go over recent efforts of extending the understanding of quantum chaos to relativistic cases. We shall focus on the level spacing statistics for two-dimensional massless Dirac billiards, i.e., particles confined in a closed region. We shall discuss the works for both the particle described by the massless Dirac equation (orWeyl equation) and the quasiparticle from graphene. Although the equations are the same, the boundary conditions are typically different, rendering distinct level spacing statistics.

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Nonequilibrium work equalities in isolated quantum systems

Liu Fei, Ouyang Zhong-Can

Chin. Phys. B, 2014, 23 (7): 070512 doi: 10.1088/1674-1056/23/7/070512
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We briefly introduce the quantum Jarzynski and Bochkov-Kuzovlev equalities in isolated quantum Hamiltonian systems, including their origin, their derivations using a quantum Feynman-Kac formula, the quantum Crooks equality, the evolution equations governing the characteristic functions of the probability density functions for the quantum work, and recent experimental verifications. Some results are given here for the first time. We particularly emphasize the formally structural consistence between these quantum equalities and their classical counterparts, which are useful for understanding the existing equalities and pursuing new fluctuation relations in other complex quantum systems.

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Equivalent formulations of “the equation of life”

Ao Ping

Chin. Phys. B, 2014, 23 (7): 070513 doi: 10.1088/1674-1056/23/7/070513
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Motivated by progress in theoretical biology a recent proposal on a general and quantitative dynamical framework for nonequilibrium processes and dynamics of complex systems is briefly reviewed. It is nothing but the evolutionary process discovered by Charles Darwin and Alfred Wallace. Such general and structured dynamics may be tentatively named “the equation of life”. Three equivalent formulations are discussed, and it is also pointed out that such a quantitative dynamical framework leads naturally to the powerful Boltzmann-Gibbs distribution and the second law in physics. In this way, the equation of life provides a logically consistent foundation for thermodynamics. This view clarifies a particular outstanding problem and further suggests a unifying principle for physics and biology.

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Sub-diffusive scaling with power-law trapping times

Luo Liang, Tang Lei-Han

Chin. Phys. B, 2014, 23 (7): 070514 doi: 10.1088/1674-1056/23/7/070514
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Thermally driven diffusive motion of a particle underlies many physical and biological processes. In the presence of traps and obstacles, the spread of the particle is substantially impeded, leading to subdiffusive scaling at long times. The statistical mechanical treatment of diffusion in a disordered environment is often quite involved. In this short review, we present a simple and unified view of the many quantitative results on anomalous diffusion in the literature, including the scaling of the diffusion front and the mean first-passage time. Various analytic calculations and physical arguments are examined to highlight the role of dimensionality, energy landscape, and rare events in affecting the particle trajectory statistics. The general understanding that emerges will aid the interpretation of relevant experimental and simulation results.

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Effective temperature and fluctuation-dissipation theorem in athermal granular systems：A review

Chen Qiong, Hou Mei-Ying

Chin. Phys. B, 2014, 23 (7): 074501 doi: 10.1088/1674-1056/23/7/074501
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The definition and the previous measurements of a dynamics-relevant temperature-like quantity in granular media are reviewed for slow and fast particle systems. Especially, the validity of the fluctuation-dissipation theorem in such an athermal system is explored. Experimental evidences for the fluctuation-dissipation theorem relevant effect temperature support the athermal statistical mechanics, which has been widely explored in recent years by physicists. Difficulties encountered in defining temperature or establishing thermodynamics or statistical mechanics in non-equilibrium situations are discussed.

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Percolation on networks with dependence links

Li Ming, Wang Bing-Hong

Chin. Phys. B, 2014, 23 (7): 076402 doi: 10.1088/1674-1056/23/7/076402
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As a classical model of statistical physics, the percolation theory provides a powerful approach to analyze the network structure and dynamics. Recently, to model the relations among interacting agents beyond the connection of the networked system, the concept of dependence link is proposed to represent the dependence relationship of agents. These studies suggest that the percolation properties of these networks differ greatly from those of the ordinary networks. In particular, unlike the well known continuous transition on the ordinary networks, the percolation transitions on these networks are discontinuous. Moreover, these networks are more fragile for a broader degree distribution, which is opposite to the famous results for the ordinary networks. In this article, we give a summary of the theoretical approaches to study the percolation process on networks with inter- and inner-dependence links, and review the recent advances in this field, focusing on the topology and robustness of such networks.

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RNA structure prediction：Progress and perspective

Shi Ya-Zhou, Wu Yuan-Yan, Wang Feng-Hua, Tan Zhi-Jie

Chin. Phys. B, 2014, 23 (7): 078701 doi: 10.1088/1674-1056/23/7/078701
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Many recent exciting discoveries have revealed the versatility of RNAs and their importance in a variety of cellular functions which are strongly coupled to RNA structures. To understand the functions of RNAs, some structure prediction models have been developed in recent years. In this review, the progress in computational models for RNA structure prediction is introduced and the distinguishing features of many outstanding algorithms are discussed, emphasizing three-dimensional (3D) structure prediction. A promising coarse-grained model for predicting RNA 3D structure, stability and salt effect is also introduced briefly. Finally, we discuss the major challenges in the RNA 3D structure modeling.

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Collective behaviors of suprachiasm nucleus neurons under different light-dark cycles

Gu Chang-Gui, Zhang Xin-Hua, Liu Zong-Hua

Chin. Phys. B, 2014, 23 (7): 078702 doi: 10.1088/1674-1056/23/7/078702
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The principal circadian clock in the suprachiasm nucleus (SCN) regulates the circadian rhythm of physiological and behavioral activities of mammals. Except for the normal function of the circadian rhythm, the ensemble of SCN neurons may show two collective behaviors, i.e., a free running period in the absence of a light-dark cycle and an entrainment ability to an external T cycle. Experiments show that both the free running periods and the entrainment ranges may vary from one species to another and can be seriously influenced by the coupling among the SCN neurons. We here review the recent progress on how the heterogeneous couplings influence these two collective behaviors. We will show that in the case of homogeneous coupling, the free running period increases monotonically while the entrainment range decreases monotonically with the increase of the coupling strength. While in the case of heterogenous coupling, the dispersion of the coupling strength plays a crucial role. It has been found that the free running period decreases with the increase of the dispersion while the entrainment ability is enhanced by the dispersion. These findings provide new insights into the mechanism of the circadian clock in the SCN.

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Proteins：From sequence to structure

Zheng Wei-Mou

Chin. Phys. B, 2014, 23 (7): 078705 doi: 10.1088/1674-1056/23/7/078705
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Protein sequences as special heterogeneous sequences are rare in the amino acid sequence space. The specific sequential order of amino acids of a protein is essential to its 3D structure. On the whole, the correlation between sequence and structure of a protein is not so strong. How well would a protein sequence contain its structural information? How does a sequence determine its native structure? Keeping the globular proteins in mind, we discuss several problems from sequence to structure.

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Statistical physics of hard combinatorial optimization：Vertex cover problem

Zhao Jin-Hua, Zhou Hai-Jun

Chin. Phys. B, 2014, 23 (7): 078901 doi: 10.1088/1674-1056/23/7/078901
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Typical-case computation complexity is a research topic at the boundary of computer science, applied mathematics, and statistical physics. In the last twenty years, the replica-symmetry-breaking mean field theory of spin glasses and the associated message-passing algorithms have greatly deepened our understanding of typical-case computation complexity. In this paper, we use the vertex cover problem, a basic nondeterministic-polynomial (NP)-complete combinatorial optimization problem of wide application, as an example to introduce the statistical physical methods and algorithms. We do not go into the technical details but emphasize mainly the intuitive physical meanings of the message-passing equations. A nonfamiliar reader shall be able to understand to a large extent the physics behind the mean field approaches and to adjust the mean field methods in solving other optimization problems.

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Statistical physics of human beings in games：Controlled experiments

Liang Yuan, Huang Ji-Ping

Chin. Phys. B, 2014, 23 (7): 078902 doi: 10.1088/1674-1056/23/7/078902
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It is important to know whether the laws or phenomena in statistical physics for natural systems with non-adaptive agents still hold for social human systems with adaptive agents, because this implies whether it is possible to study or understand social human systems by using statistical physics originating from natural systems. For this purpose, we review the role of human adaptability in four kinds of specific human behaviors, namely, normal behavior, herd behavior, contrarian behavior, and hedge behavior. The approach is based on controlled experiments in the framework of market-directed resource-allocation games. The role of the controlled experiments could be at least two-fold: adopting the real human decision-making process so that the system under consideration could reflect the performance of genuine human beings; making it possible to obtain macroscopic physical properties of a human system by tuning a particular factor of the system, thus directly revealing cause and effect. As a result, both computer simulations and theoretical analyses help to show a few counterparts of some laws or phenomena in statistical physics for social human systems: two-phase phenomena or phase transitions, entropy-related phenomena, and a non-equilibrium steady state. This review highlights the role of human adaptability in these counterparts, and makes it possible to study or understand some particular social human systems by means of statistical physics coming from natural systems.

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A mini-review on econophysics：Comparative study of Chinese and western financial markets

Zheng Bo, Jiang Xiong-Fei, Ni Peng-Yun

Chin. Phys. B, 2014, 23 (7): 078903 doi: 10.1088/1674-1056/23/7/078903
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We present a review of our recent research in econophysics, and focus on the comparative study of Chinese and western financial markets. By virtue of concepts and methods in statistical physics, we investigate the time correlations and spatial structure of financial markets based on empirical high-frequency data. We discover that the Chinese stock market shares common basic properties with the western stock markets, such as the fat-tail probability distribution of price returns, the long-range auto-correlation of volatilities, and the persistence probability of volatilities, while it exhibits very different higher-order time correlations of price returns and volatilities, spatial correlations of individual stock prices, and large-fluctuation dynamic behaviors. Furthermore, multi-agent-based models are developed to simulate the microscopic interaction and dynamic evolution of the stock markets.

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Zero-determinant strategy：An underway revolution in game theory

Hao Dong, Rong Zhi-Hai, Zhou Tao

Chin. Phys. B, 2014, 23 (7): 078905 doi: 10.1088/1674-1056/23/7/078905
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Repeated games describe situations where players interact with each other in a dynamic pattern and make decisions according to outcomes of previous stage games. Very recently, Press and Dyson have revealed a new class of zero-determinant (ZD) strategies for the repeated games, which can enforce a fixed linear relationship between expected payoffs of two players, indicating that a smart player can control her unwitting co-player's payoff in a unilateral way [Proc. Acad. Natl. Sci. USA 109, 10409 (2012)]. The theory of ZD strategies provides a novel viewpoint to depict interactions among players, and fundamentally changes the research paradigm of game theory. In this brief survey, we first introduce the mathematical framework of ZD strategies, and review the properties and constrains of two specifications of ZD strategies, called pinning strategies and extortion strategies. Then we review some representative research progresses, including robustness analysis, cooperative ZD strategy analysis, and evolutionary stability analysis. Finally, we discuss some significant extensions to ZD strategies, including the multi-player ZD strategies, and ZD strategies under noise. Challenges in related research fields are also listed.

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Attractive target wave patterns in complex networks consisting of excitable nodes

Zhang Li-Sheng, Liao Xu-Hong, Mi Yuan-Yuan, Qian Yu, Hu Gang

Chin. Phys. B, 2014, 23 (7): 078906 doi: 10.1088/1674-1056/23/7/078906
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This review describes the investigations of oscillatory complex networks consisting of excitable nodes, focusing on the target wave patterns or say the target wave attractors. A method of dominant phase advanced driving (DPAD) is introduced to reveal the dynamic structures in the networks supporting oscillations, such as the oscillation sources and the main excitation propagation paths from the sources to the whole networks. The target center nodes and their drivers are regarded as the key nodes which can completely determine the corresponding target wave patterns. Therefore, the center (say node A) and its driver (say node B) of a target wave can be used as a label, (A,B), of the given target pattern. The label can give a clue to conveniently retrieve, suppress, and control the target waves. Statistical investigations, both theoretically from the label analysis and numerically from direct simulations of network dynamics, show that there exist huge numbers of target wave attractors in excitable complex networks if the system size is large, and all these attractors can be labeled and easily controlled based on the information given by the labels. The possible applications of the physical ideas and the mathematical methods about multiplicity and labelability of attractors to memory problems of neural networks are briefly discussed.

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Symmetries and variational calculationof discrete Hamiltonian systems

Xia Li-Li, Chen Li-Qun, Fu Jing-Li, Wu Jing-He

Chin. Phys. B, 2014, 23 (7): 070201 doi: 10.1088/1674-1056/23/7/070201
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We present a numerical simulation method of Noether and Lie symmetries for discrete Hamiltonian systems. The Noether and Lie symmetries for the systems are proposed by investigating the invariance properties of discrete Lagrangian in phase space. The numerical calculations of a two-degree-of-freedom nonlinear harmonic oscillator show that the difference discrete variational method preserves the exactness and the invariant quantity.

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Non-autonomous discrete Boussinesq equation：Solutions and consistency

Nong Li-Juan, Zhang Da-Juan

Chin. Phys. B, 2014, 23 (7): 070202 doi: 10.1088/1674-1056/23/7/070202
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A non-autonomous 3-component discrete Boussinesq equation is discussed. Its spacing parameters p_n and q_m are related to independent variables n and m, respectively. We derive bilinear form and solutions in Casoratian form. The plain wave factor is defined through the cubic roots of unity. The plain wave factor also leads to extended non-autonomous discrete Boussinesq equation which contains a parameter δ. Tree-dimendional consistency and Lax pair of the obtained equation are discussed.

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Rogue-wave pair and dark-bright-rogue wave solutions of the coupled Hirota equations Suggested by editors

Wang Xin, Chen Yong

Chin. Phys. B, 2014, 23 (7): 070203 doi: 10.1088/1674-1056/23/7/070203
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Novel explicit rogue wave solutions of the coupled Hirota equations are obtained by using the Darboux transformation. In contrast to the fundamental Peregrine solitons and dark rogue waves, we present an interesting rogue-wave pair that involves four zero-amplitude holes for the coupled Hirota equations. It is significant that the corresponding expressions of the rogue-wave pair solutions contain polynomials of the fourth order rather than the second order. Moreover, dark-bright-rogue wave solutions of the coupled Hirota equations are given, and interactions between Peregrine solitons and dark-bright solitons are analyzed. The results further reveal the dynamical properties of rogue waves for the coupled Hirota equations.

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Optimal switching policy for performance enhancement of distributed parameter systems based on event-driven control

Mu Wen-Ying, Cui Bao-Tong, Lou Xu-Yang, Li Wen

Chin. Phys. B, 2014, 23 (7): 070204 doi: 10.1088/1674-1056/23/7/070204
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This paper aims to improve the performance of a class of distributed parameter systems for the optimal switching of actuators and controllers based on event-driven control. It is assumed that in the available multiple actuators, only one actuator can receive the control signal and be activated over an unfixed time interval, and the other actuators keep dormant. After incorporating a state observer into the event generator, the event-driven control loop and the minimum inter-event time are ultimately bounded. Based on the event-driven state feedback control, the time intervals of unfixed length can be obtained. The optimal switching policy is based on finite horizon linear quadratic optimal control at the beginning of each time subinterval. A simulation example demonstrate the effectiveness of the proposed policy.

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Impulsive effect on exponential synchronization of neural networks with leakage delay under sampled-data feedback control Suggested by editors

S. Lakshmanan, Ju H. Park, Fathalla A. Rihan, R. Rakkiyappan

Chin. Phys. B, 2014, 23 (7): 070205 doi: 10.1088/1674-1056/23/7/070205
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We consider the impulsive effect on the exponential synchronization of neural networks with leakage delay under the sampled-data feedback control. We use an appropriate Lyapunov-Krasovskii functional combined with the input delay approach and some inequality techniques to derive sufficient conditions that ensure the exponential synchronization of the delayed neural network. The conditions are formulated in terms of the leakage delay, the sampling period, and the exponential convergence rate. Numerical examples are given to demonstrate the usefulness and the effectiveness of the results.

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Co-evolution of the brand effect and competitiveness in evolving networks

Guo Jin-Li

Chin. Phys. B, 2014, 23 (7): 070206 doi: 10.1088/1674-1056/23/7/070206
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The principle that ‘the brand effect is attractive’ underlies the preferential attachment. Here we show that the brand effect is just one dimension of attractiveness. Another dimension is competitiveness. We firstly introduce a general framework that allows us to investigate the competitive aspect of real networks, instead of simply preferring popular nodes. Our model accurately describes the evolution of social and technological networks. The phenomenon that more competitive nodes become richer can help us to understand the evolution of many competitive systems in nature and society. In general, the paper provides an explicit analytical expression of degree distributions of the network. In particular, the model yields a nontrivial time evolution of nodes' properties and the scale-free behavior with exponents depending on the microscopic parameters characterizing the competition rules. Secondly, through theoretical analyses and numerical simulations, we reveal that our model has not only the universality for the homogeneous weighted network, but also the character for the heterogeneous weighted network. Thirdly, we also develop a model based on the profit-driven mechanism. It can better describe the observed phenomenon in enterprise cooperation networks. We show that the standard preferential attachment, the growing random graph, the initial attractiveness model, the fitness model, and weighted networks can all be seen as degenerate cases of our model.

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An interpolating reproducing kernel particle method for two-dimensional scatter points

Qin Yi-Xiao, Liu Ying-Ying, Li Zhong-Hua, Yang Ming

Chin. Phys. B, 2014, 23 (7): 070207 doi: 10.1088/1674-1056/23/7/070207
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An interpolating reproducing kernel particle method for two-dimensional (2D) scatter points is introduced. It eliminates the dependency of gridding in numerical calculations. The interpolating shape function in the interpolating reproducing kernel particle method satisfies the property of the Kronecker delta function. This method offers a mathematics basis for recognition technology and simulation analysis, which can be expressed as simultaneous differential equations in science or project problems. Mathematical examples are given to show the validity of the interpolating reproducing kernel particle method.

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Average vector field methods for the coupled Schrödinger–KdV equations Suggested by editors

Zhang Hong, Song Song-He, Chen Xu-Dong, Zhou Wei-En

Chin. Phys. B, 2014, 23 (7): 070208 doi: 10.1088/1674-1056/23/7/070208
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The energy preserving average vector field (AVF) method is applied to the coupled Schrödinger-KdV equations. Two energy preserving schemes are constructed by using Fourier pseudospectral method in space direction discretization. In order to accelerate our simulation, the split-step technique is used. The numerical experiments show that the non-splitting scheme and splitting scheme are both effective, and have excellent long time numerical behavior. The comparisons show that the splitting scheme is faster than the non-splitting scheme, but it is not as good as the non-splitting scheme in preserving the invariants.

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Comparison between photon annihilation-then-creation and photon creation-then-annihilation thermal states：Non-classical and non-Gaussian properties

Xu Xue-Xiang, Yuan Hong-Chun, Wang Yan

Chin. Phys. B, 2014, 23 (7): 070301 doi: 10.1088/1674-1056/23/7/070301
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We investigate the nonclassical properties of arbitrary number photon annihilation-then-creation operation (AC) and creation-then-annihilation operation (CA) to the thermal state (TS), whose normalization factors are related to the polylogarithm function. Then we compare their quantum characters, such as photon number distribution, average photon number, Mandel Q-parameter, purity and the Wigner function. Because of the noncommutativity between the annihilation operator and the creation operator, the ACTS and the CATS have different nonclassical properties. It is found that nonclassical properties are exhibited more strongly after AC than after CA. In addition we also examine their non-Gaussianity. The result shows that the ACTS can present a slightly bigger non-Gaussianity than the CATS.

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Global entanglement in ground state of {Cu₃} single-molecular magnet with magnetic field

Li Ji-Qiang, Zhou Bin

Chin. Phys. B, 2014, 23 (7): 070302 doi: 10.1088/1674-1056/23/7/070302
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We investigate global entanglement in the ground state of single-molecular magnet Na₉[Cu₃Na₃(H₂ O)₉(α -AsW₉O₃₃)₂]· 26H₂O with an external magnetic field. The concurrence, tangle, and measure function Q, which characterize the pairwise entanglement, 3-party entanglement and total entanglement, respectively, are calculated numerically at zero temperature. The results show that the magnitude and direction of the applied magnetic field play a significant role in the properties of three kinds of entanglement measures. We give a physical interpretation of the variation of the global entanglement with the magnetic field. Finally, the phase diagram of the global entanglement characterized by the critical magnetic fields is presented.

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Rise of quantum correlations in non-Markovian environments in continuous-variable systems

Liu Xin, Wu Wei

Chin. Phys. B, 2014, 23 (7): 070303 doi: 10.1088/1674-1056/23/7/070303
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We investigate the time evolution of quantum correlations, which are measured by Gaussian quantum discord in a continuous-variable bipartite system subject to common and independent non-Markovian environments. Considering an initial two-mode Gaussian symmetric squeezed thermal state, we show that quantum correlations can be created during the non-Markovian evolution, which is different from the Markovian process. Furthermore, we find that the temperature is a key factor during the evolution in non-Markovian environments. For common reservoirs, a maximum creation of quantum correlations may occur under an appropriate temperature. For independent reservoirs, the non-Markovianity of the total system corresponds to the subsystem whose temperature is higher. In both common and independent environments, the Gaussian quantum discord is influenced by the temperature and the photon number of each mode.

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Optimal 1→M phase-covariant cloning in three dimensions

Zhang Wen-Hai, Yu Long-Bao, Cao Zhuo-Liang, Ye Liu

Chin. Phys. B, 2014, 23 (7): 070304 doi: 10.1088/1674-1056/23/7/070304
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In this paper, we derive the explicit transformations of the optimal 1→3, 4, 5 phase-covariant cloning in three dimensions, and then generalize them to the cases of 1→M = 3n, 3n+1, 3n+2 (n≥1 integer) cloning. The clone fidelities are coincident with the theoretical bounds found.

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Symmetric quantum discord for a two-qubit state

Wang Zhong-Xiao, Wang Bo-Bo

Chin. Phys. B, 2014, 23 (7): 070305 doi: 10.1088/1674-1056/23/7/070305
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We discuss the symmetric quantum discord (SQD) for an arbitrary two-qubit state consisting of subsystems A and B and give the analysis formula of the symmetric quantum discord for the arbitrary two-qubit state. We also give the optimization process of the symmetric quantum discord for some states and obtain the symmetric quantum discord. We compare the quantum discord (QD) with the symmetric quantum discord, and find that the symmetric quantum discord is greater than the quantum discord. We also find that the symmetric quantum discord can be unequal to the quantum discord when the right quantum discord (measure on subsystem B) is equal to the left quantum discord (measure on subsystem A).

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Quantum correlations in a two-qubit anisotropic Heisenberg XYZ chain with uniform magnetic field

Li Lei, Yang Guo-Hui

Chin. Phys. B, 2014, 23 (7): 070306 doi: 10.1088/1674-1056/23/7/070306
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Quantum correlations in an anisotropic Heisenberg XYZ chain is investigated by use of concurrence C and measurement-induced disturbance (MID). We show that the behaviors of the MID are remarkably different from the concurrence. Firstly, it is shown that there is a revival phenomenon in the concurrence but not in the MID, which is suitable for both the ground state case and the finite temperature case. Based on the analysis of the ground-state C and MID structures, we illustrate the reason why the ground-state MID does not show a revival phenomenon in detail. Then we explore different effects of the external and self parameters on entanglement and MID behaviors. It can be shown that the region of MID is evidently larger than the case of concurrence, and that the concurrence signals a quantum phase transition even at finite T while MID does not. Cases where the concurrence finally maintains one nonzero constant value regardless of the value of the variable B for a constant J_z, while MID decreases monotonously to zero with increasing B. We also show that if B can take a proper range of values, the concurrence decreases with the improvement of the anisotropic parameter γ, whereas an opposite effect for MID behaviors is presented.

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Adiabatic tunneling of Bose-Einstein condensates with modulated atom interaction in a double-well potential

Xin Xiao-Tian, Huang Fang, Xu Zhi-Jun, Li Hai-Bin

Chin. Phys. B, 2014, 23 (7): 070307 doi: 10.1088/1674-1056/23/7/070307
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We study the adiabatic tunneling of Bose-Einstein condensates in a symmetric double-well potential when the interaction strength between the atoms is modulated linearly or in a cosine periodic form. It is shown that the system evolves along a nonlinear eigenstate path. In the case of linear modulation under the adiabatic approximation conditions, the tunneling probability of the condensate atoms to the other potential well is half. However, when the system is periodically scanned in the adiabatic process, we find an interesting phenomenon. A small change in the cycle period can lead to the condensate atoms returning to the right well or tunneling to the left well. The system comes from a linear eigenstate back to a nonlinear one, which is completely different from the linear eigenstate evolution. We explain the results by using the energy level and the phase diagram.

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Ground state of rotating ultracold quantum gases with anisotropic spin–orbit coupling and concentrically coupled annular potential

Wang Xin, Tan Ren-Bing, Du Zhi-Jing, Zhao Wen-Yu, Zhang Xiao-Fei, Zhang Shou-Gang

Chin. Phys. B, 2014, 23 (7): 070308 doi: 10.1088/1674-1056/23/7/070308
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[PDF 673 KB] (Downloads:441)

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Motivated by recent experimental realization of synthetic spin-orbit coupling in neutral quantum gases, we consider the quasi-two-dimensional rotating two-component Bose-Einstein condensates with anisotropic Rashba spin-orbit coupling subject to concentrically coupled annular potential. For experimentally feasible parameters, the rotating condensate exhibits a variety of rich ground state structures by varying the strengths of the spin-orbit coupling and rotational frequency. Moreover, the phase transitions between different ground state phases induced by the anisotropic spin-orbit coupling are obviously different from the isotropic one.

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Delay-dependent asymptotic stability of mobile ad-hoc networks：A descriptor system approach

Yang Juan, Yang Dan, Huang Bin, Zhang Xiao-Hong, Luo Jian-Lu

Chin. Phys. B, 2014, 23 (7): 070502 doi: 10.1088/1674-1056/23/7/070502
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[PDF 538 KB] (Downloads:354)

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In order to analyze the capacity stability of the time-varying-propagation and delay-dependent of mobile ad-hoc networks (MANETs), in this paper, a novel approach is proposed to explore the capacity asymptotic stability for the delay-dependent of MANETs based on non-cooperative game theory, where the delay-dependent conditions are explicitly taken into consideration. This approach is based on the Lyapunov-Krasovskii stability theory for functional differential equations and the linear matrix inequality (LMI) technique. A corresponding Lyapunov-Krasovskii functional is introduced for the stability analysis of this system with use of the descriptor and “neutral-type” model transformation without producing any additional dynamics. The delay-dependent stability criteria are derived for this system. Conditions are given in terms of linear matrix inequalities, and for the first time referred to neutral systems with the time-varying propagation and delay-dependent stability for capacity analysis of MANETs. The proposed criteria are less conservative since they are based on an equivalent model transformation. Furthermore, we also provide an effective and efficient iterative algorithm to solve the constrained stability control model. Simulation experiments have verified the effectiveness and efficiency of our algorithm.

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Mapping equivalent approach to analysis and realization of memristor-based dynamical circuit

Bao Bo-Cheng, Hu Feng-Wei, Liu Zhong, Xu Jian-Ping

Chin. Phys. B, 2014, 23 (7): 070503 doi: 10.1088/1674-1056/23/7/070503
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[PDF 1057 KB] (Downloads:614)

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A novel mapping equivalent approach is proposed in this paper, which can be used for analyzing and realizing a memristor-based dynamical circuit equivalently by a nonlinear dynamical circuit with the same topologies and circuit parameters. A memristor-based chaotic circuit and the corresponding Chua's chaotic circuit with two output differentiators are taken as examples to illustrate this approach. Equivalent dynamical analysis and realization of the memristor-based chaotic circuit are performed by using Chua's chaotic circuit. The results indicate that the outputs of memristor-based chaotic circuit and the corresponding outputs of Chua's chaotic circuit have identical dynamics. The proposed approach verified by numerical simulations and experimental observations is useful in designing and analyzing memristor-based dynamical circuits.

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Signal reconstruction in wireless sensor networks based on a cubature Kalman particle filter

Huang Jin-Wang, Feng Jiu-Chao

Chin. Phys. B, 2014, 23 (7): 070504 doi: 10.1088/1674-1056/23/7/070504
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[PDF 250 KB] (Downloads:337)

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For solving the issues of the signal reconstruction of nonlinear non-Gaussian signals in wireless sensor networks (WSNs), a new signal reconstruction algorithm based on a cubature Kalman particle filter (CKPF) is proposed in this paper. We model the reconstruction signal first and then use the CKPF to estimate the signal. The CKPF uses a cubature Kalman filter (CKF) to generate the importance proposal distribution of the particle filter and integrates the latest observation, which can approximate the true posterior distribution better. It can improve the estimation accuracy. CKPF uses fewer cubature points than the unscented Kalman particle filter (UKPF) and has less computational overheads. Meanwhile, CKPF uses the square root of the error covariance for iterating and is more stable and accurate than the UKPF counterpart. Simulation results show that the algorithm can reconstruct the observed signals quickly and effectively, at the same time consuming less computational time and with more accuracy than the method based on UKPF.

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Space–time fractional KdV–Burgers equation for dust acoustic shock waves in dusty plasma with non-thermal ions

Emad K. El-Shewy, Abeer A. Mahmoud, Ashraf M. Tawfik, Essam M. Abulwafa, Ahmed Elgarayhi

Chin. Phys. B, 2014, 23 (7): 070505 doi: 10.1088/1674-1056/23/7/070505
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[PDF 266 KB] (Downloads:866)

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The KdV-Burgers equation for dust acoustic waves in unmagnetized plasma having electrons, singly charged non-thermal ions, and hot and cold dust species is derived using the reductive perturbation method. The Boltzmann distribution is used for electrons in the presence of the cold (hot) dust viscosity coefficients. The semi-inverse method and Agrawal variational technique are applied to formulate the space-time fractional KdV-Burgers equation which is solved using the fractional sub-equation method. The effect of the fractional parameter on the behavior of the dust acoustic shock waves in the dusty plasma is investigated.

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PC synchronization of a class of chaotic systems via event-triggered control

Luo Run-Zi, He Long-Min

Chin. Phys. B, 2014, 23 (7): 070506 doi: 10.1088/1674-1056/23/7/070506
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[PDF 406 KB] (Downloads:387)

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The PC synchronization of a class of chaotic systems is investigated in this paper. The drive system is assumed to have only one state variable available. By constructing proper observers, some novel criteria for PC synchronization are proposed via event-triggered control scheme. The Lü system and Chen system are taken as examples to demonstrate the efficiency of the proposed approach.

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Partial and complete periodic synchronization in coupled discontinuous map lattices

Yang Ke-Li, Chen Hui-Yun, Du Wei-Wei, Jin Tao, Qu Shi-Xian

Chin. Phys. B, 2014, 23 (7): 070508 doi: 10.1088/1674-1056/23/7/070508
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[PDF 1461 KB] (Downloads:341)

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The partial and complete periodic synchronization in coupled discontinuous map lattices consisting of both discontinuous and non-invertible maps are discussed. We classify three typical types of periodic synchronization states, which give rise to different spatiotemporal patterns including static partial periodic synchronization, dynamically periodic synchronization, and complete periodic synchronization patterns. A special prelude dynamics of partial and complete periodic synchronization motion, which is shown by five separated concave curves in the time series plots of the order parameters, is observed. The detailed analysis shows that the special prelude dynamics is induced by the competition between two synchronized clusters, and the analytical expression for the corresponding order parameter is obtained.

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Distributed formation control for a multi-agent system with dynamic and static obstacle avoidances

Cao Jian-Fu, Ling Zhi-Hao, Yuan Yi-Feng, Gao Chong

Chin. Phys. B, 2014, 23 (7): 070509 doi: 10.1088/1674-1056/23/7/070509
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[PDF 589 KB] (Downloads:429)

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Formation control and obstacle avoidance for multi-agent systems have attracted more and more attention. In this paper, the problems of formation control and obstacle avoidance are investigated by means of a consensus algorithm. A novel distributed control model is proposed for the multi-agent system to form the anticipated formation as well as achieve obstacle avoidance. Based on the consensus algorithm, a distributed control function consisting of three terms (formation control term, velocity matching term, and obstacle avoidance term) is presented. By establishing a novel formation control matrix, a formation control term is constructed such that the agents can converge to consensus and reach the anticipated formation. A new obstacle avoidance function is developed by using the modified potential field approach to make sure that obstacle avoidance can be achieved whether the obstacle is in a dynamic state or a stationary state. A velocity matching term is also put forward to guarantee that the velocities of all agents converge to the same value. Furthermore, stability of the control model is proven. Simulation results are provided to demonstrate the effectiveness of the proposed control.

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Fault-tolerant topology in the wireless sensor networks for energy depletion and random failure

Liu Bin, Dong Ming-Ru, Yin Rong-Rong, Yin Wen-Xiao

Chin. Phys. B, 2014, 23 (7): 070510 doi: 10.1088/1674-1056/23/7/070510
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[PDF 256 KB] (Downloads:432)

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Nodes in the wireless sensor networks (WSNs) are prone to failure due to energy depletion and poor environment, which could have a negative impact on the normal operation of the network. In order to solve this problem, in this paper, we build a fault-tolerant topology which can effectively tolerate energy depletion and random failure. Firstly, a comprehensive failure model about energy depletion and random failure is established. Then an improved evolution model is presented to generate a fault-tolerant topology, and the degree distribution of the topology can be adjusted. Finally, the relation between the degree distribution and the topological fault tolerance is analyzed, and the optimal value of evolution model parameter is obtained. Then the target fault-tolerant topology which can effectively tolerate energy depletion and random failure is obtained. The performances of the new fault tolerant topology are verified by simulation experiments. The results show that the new fault tolerant topology effectively prolongs the network lifetime and has strong fault tolerance.

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Nonequilibrium behavior of the kinetic metamagnetic spin-5/2 Blume-Capel model

Ümüt Temizer

Chin. Phys. B, 2014, 23 (7): 070511 doi: 10.1088/1674-1056/23/7/070511
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[PDF 861 KB] (Downloads:488)

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The dynamic magnetic behavior of the kinetic metamagnetic spin-5/2 Blume-Capel model is examined, within a mean-field approach, under a time-dependent oscillating magnetic field. To describe the kinetics of the system, Glauber-type stochastic dynamics has been utilized. The mean-field dynamic equations of the model are obtained from the Master equation. Firstly, these dynamic equations are solved to find the phases in the system. Then, the dynamic phase transition temperatures are obtained by investigating the thermal behavior of dynamic sublattice magnetizations. Moreover, from this investigation, the nature of the phase transitions (first- or second-order) is characterized. Finally, the dynamic phase diagrams are plotted in five different planes. It is found that the dynamic phase diagrams contain the paramagnetic (P), antiferromagnetic (AF_5/2, AF_3/2, AF_1/2) phases and five different mixed phases. The phase diagrams also display many dynamic critical points, such as tricritical point, triple point, quadruple point, double critical end point and separating point.

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Ferromagnetic materials under high pressure in a diamond-anvil cell：A magnetic study Suggested by editors

Wang Xin, Hu Tian-Li, Han Bing, Jin Hui-Chao, Li Yan, Zhou Qiang, Zhang Tao

Chin. Phys. B, 2014, 23 (7): 070701 doi: 10.1088/1674-1056/23/7/070701
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[PDF 728 KB] (Downloads:367)

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A magnetic-parameter measurement system for study of ferromagnetic materials under high pressure using a diamond-anvil cell is built. The factors affecting the measurement sensitivity are analyzed and the possibility of improving the sensitivity is mentioned. Based on the system, the magnetization curves of iron as a function of pressure are obtained. The start point and end point of pressure-induced magnetic transition of iron are observed at room temperature.

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Mutator for transferring a memristor emulator into meminductive and memcapacitive circuits

Yu Dong-Sheng, Liang Yan, Herbert H. C. Iu, Hu Yi-Hua

Chin. Phys. B, 2014, 23 (7): 070702 doi: 10.1088/1674-1056/23/7/070702
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[PDF 550 KB] (Downloads:887)

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In this paper, a concise but effective interface circuit for transforming a memristor into meminductive and memcapacitive systems is designed. This newly proposed interface circuit, constructed by only two current conveyors, is equipped with three available ports, which can provide six connecting combinations in terms of one resistor, one capacitor, and one memristor. For the sake of confirming the design effectiveness, theoretical and simulation discussions are hence introduced and all the experimental waveforms provide conclusive evidence to validate the correctness of these new mutators. The most attractive features of this new interface circuit are the floating terminals and convenient practical implementation.

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A double toroidal analyzer for scanning probe electron energy spectrometer Suggested by editors

Xu Chun-Kai, Zhang Pan-Ke, Li Meng, Chen Xiang-Jun

Chin. Phys. B, 2014, 23 (7): 073402 doi: 10.1088/1674-1056/23/7/073402
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[PDF 1509 KB] (Downloads:315)

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An ultra-high vacuum (UHV) compatible electron spectrometer employing a double toroidal analyzer has been developed. It is designed to be combined with a custom-made scanning tunneling microscope (STM) to study the spatially localized electron energy spectrum on a surface. A tip-sample system composed of a piezo-driven field-emission tungsten tip and a sample of highly ordered pyrolytic graphite (HOPG) is employed to test the performance of the spectrometer. Two-dimensional images of the energy-resolved and angle-dispersed electrons backscattered from the surface of HOPG are obtained, the performance is optimized and the spectrometer is calibrated. A complete electron energy loss spectrum covering the elastic peak to the secondary electron peaks for the HOPG surface, acquired at a tip voltage of -140 V and a sample current of 0.5 pA, is presented, demonstrating the viability of the spectrometer.

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Multiferroic properties in terbium orthoferrite Suggested by editors

Song Yu-Quan, Zhou Wei-Ping, Fang Yong, Yang Yan-Ting, Wang Liao-Yu, Wang Dun-Hui, Du You-Wei

Chin. Phys. B, 2014, 23 (7): 077505 doi: 10.1088/1674-1056/23/7/077505
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[PDF 472 KB] (Downloads:758)

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Multiferroic properties in a polycrystalline terbium orthoferrite are investigated. Different thermomagnetic behaviors are observed in different magnetic fields, which is attributed to the suppression of the low temperature magnetic phase by an external magnetic field. Further studies reveal that the ferroelectricity originates from the spin configuration below 3.5 K. In addition, the magnetic field control of electric polarization and dielectric constant is observed, which suggests a magnetoelectric effect in TbFeO₃. The origin of ferroelectricity in this rare-earth orthoferrite is discussed.

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A typical slow reaction H(²S)+S₂(X³Σ_g^-)→SH(X²∏)+S(³P) on a new surface：Quantum dynamics calculations

Wei Wei, Gao Shou-Bao, Sun Zhao-Peng, Song Yu-Zhi, Meng Qing-Tian

Chin. Phys. B, 2014, 23 (7): 073101 doi: 10.1088/1674-1056/23/7/073101
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[PDF 298 KB] (Downloads:370)

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Quantum dynamics calculations for the title reaction H(²S)+S₂(X³Σ_g^-)→SH(X²∏)+S(³P) are performed by using a globally accurate double many-body expansion potential energy surface [J. Phys. Chem. A 115 5274 (2011)]. The Chebyshev real wave packet propagation method is employed to obtain the dynamical information, such as reaction probability, initial state-specified integral cross section, and thermal rate constant. It is found not only that there is a reaction threshold near 0.7 eV in both reaction probabilities and integral cross section curves, but also that both the probability and cross section increase firstly and then decrease as the collision energy increases. The existence of the resonance structure in both the probability and cross section curves is ascribed to the deep potential well. The calculation of the rate constant reveals that the reaction occurring on the potential energy surface of the ground-state HS₂ is slow to take place.

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On-chip optical pulse shaper for arbitrary waveform generation

Liao Sha-Sha, Yang Ting, Dong Jian-Ji

Chin. Phys. B, 2014, 23 (7): 073201 doi: 10.1088/1674-1056/23/7/073201
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[PDF 453 KB] (Downloads:339)

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We propose and demonstrate a silicon-on-insulator (SOI) on-chip optical pulse shaper based on four-tap finite impulse response. Due to different width designs in phase region of each tap, the phase differences for all taps are controlled by an external thermal source, resulting in an optical pulse shaper. We further demonstrate optical arbitrary waveform generation based on the optical pulse shaper assisted by an optical frequency comb injection. Four different optical waveforms are generated when setting the central wavelengths at 1533.78 nm and 1547.1 nm and setting the thermal source temperatures at 23 ℃ and 33 ℃, respectively. Our scheme has distinct advantages of compactness, capability for integrating with electronics since the integrated silicon waveguide is employed.

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Dynamical correlation between quantum entanglement and intramolecular energy in molecular vibrations：An algebraic approach

Feng Hai-Ran, Meng Xiang-Jia, Li Peng, Zheng Yu-Jun

Chin. Phys. B, 2014, 23 (7): 073301 doi: 10.1088/1674-1056/23/7/073301
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[PDF 378 KB] (Downloads:395)

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The dynamical correlation between quantum entanglement and intramolecular energy in realistic molecular vibrations is explored using the Lie algebraic approach. The explicit expression of entanglement measurement can be achieved using algebraic operations. The common and different characteristics of dynamical entanglement in different molecular vibrations are also provided. The dynamical study of quantum entanglement and intramolecular energy in small molecular vibrations can be helpful for controlling the entanglement and further understanding the intramolecular dynamics.

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Potential energy curves and spectroscopic properties of X²Σ⁺ and A²Π states of ¹³C¹⁴N

Liao Jian-Wen, Yang Chuan-Lu

Chin. Phys. B, 2014, 23 (7): 073401 doi: 10.1088/1674-1056/23/7/073401
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[PDF 215 KB] (Downloads:455)

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The potential energy curves (PECs) of X²Σ⁺ and A²Π states of the CN molecule have been calculated with the multi-reference configuration interaction method and the aug-cc-pwCV5Z basis set. Based on the PECs, all of the vibrational and rotational levels of the ¹³C¹⁴N molecule are obtained by solving the Schrödinger equation of the molecular nuclear motion. The spectroscopic parameters are determined by fitting the Dunham coefficients with the levels. Both the levels and the spectroscopic parameters are in good qualitative agreement with the experimental data available. The analytical potential energy functions are also deduced from the calculated PECs. The present results can provide a helpful reference for future spectroscopy experiments or dynamical calculations of the molecule.

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A progressive processing method for breast cancer detection via UWB based on an MRI-derived model

Xiao Xia, Song Hang, Wang Zong-Jie, Wang Liang

Chin. Phys. B, 2014, 23 (7): 074101 doi: 10.1088/1674-1056/23/7/074101
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[PDF 2008 KB] (Downloads:457)

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Ultra-wideband (UWB) microwave imaging is a promising method for breast cancer detection based on the large contrast of electric parameters between the malignant tumor and its surrounded normal breast organisms. In the case of multiple tumors being present, the conventional imaging approaches may be ineffective to detect all the tumors clearly. In this paper, a progressive processing method is proposed for detecting more than one tumor. The method is divided into three stages: primary detection, refocusing and image optimization. To test the feasibility of the approach, a numerical breast model is developed based on the realistic magnetic resonance image (MRI). Two tumors are assumed embedded in different positions. Successful detection of a 3.6 mm-diameter tumor at a depth of 42 mm is achieved. The correct information of both tumors is shown in the reconstructed image, suggesting that the progressive processing method is promising for multi-tumor detection.

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Solar-blind ultraviolet band-pass filter based on metal-dielectric multilayer structures

Wang Tian-Jiao, Xu Wei-Zong, Lu Hai, Ren Fang-Fang, Chen Dun-Jun, Zhang Rong, Zheng You-Dou

Chin. Phys. B, 2014, 23 (7): 074201 doi: 10.1088/1674-1056/23/7/074201
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[PDF 361 KB] (Downloads:604)

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Solar-blind ultraviolet (UV) band-pass filter has significant value in many scientific, commercial, and military applications, in which the detection of weak UV signal against a strong background of solar radiation is required. In this work, a solar-blind filter is designed based on the concept of “transparent metal”. The filter consisting of Al/SiO₂ multilayers could exhibit a high transmission in the solar-blind wavelength region and a wide stopband extending from near-ultraviolet to infrared wavelength range. The central wavelength, bandwidth, Q factor, and rejection ratio of the passband are numerically studied as a function of individual layer thickness and multilayer period.

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Scintillation of partially coherent Gaussian-Schell model beam propagation in slant atmospheric turbulence considering inner- and outer-scale effects

Li Ya-Qing, Wu Zhen-Sen, Zhang Yuan-Yuan, Wang Ming-Jun

Chin. Phys. B, 2014, 23 (7): 074202 doi: 10.1088/1674-1056/23/7/074202
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[PDF 1990 KB] (Downloads:777)

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Based on the modified Rytov theory and the international telecommunication union-radio (ITU-R) slant atmospheric structure constant model, the uniform scintillation index of partially coherent Gaussian-Schell model (GSM) beam propagation in the slant path is derived from weak- to strong-turbulence regions considering inner- and outer-scale effects. The effects of wavelength of beams and inner- and outer-scale of turbulence on scintillation are analyzed numerically. Comparison between the scintillation of GSM beams under the von Karman spectrum and that of beams under the modified Hill spectrum is made. The results obtained show that the scintillation index obtained under the von Karman spectrum is smaller than that under the modified Hill spectrum. This study can find theory bases for the experiments of the partially coherent GSM beam propagation through atmospheric turbulence.

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Entropy squeezing and atomic inversion in the k-photon Jaynes-Cummings model in the presence of the Stark shift and a Kerr medium：A full nonlinear approach

H R Baghshahi, M K Tavassoly, A Behjat

Chin. Phys. B, 2014, 23 (7): 074203 doi: 10.1088/1674-1056/23/7/074203
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[PDF 8349 KB] (Downloads:353)

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The interaction between a two-level atom and a single-mode field in the k-photon Jaynes-Cummings model (JCM) in the presence of the Stark shift and a Kerr medium is studied. All terms in the Hamiltonian, such as the single-mode field, its interaction with the atom, the contribution of the Stark shift and the Kerr medium effects are considered to be f-deformed. In particular, the effect of the initial state of the radiation field on the dynamical evolution of some physical properties such as atomic inversion and entropy squeezing are investigated by considering different initial field states (coherent, squeezed and thermal states).

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Electromagnetically induced grating in a four-level tripod-type atomic system Suggested by editors

Dong Ya-Bin, Guo Yao-Hua

Chin. Phys. B, 2014, 23 (7): 074204 doi: 10.1088/1674-1056/23/7/074204
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[PDF 229 KB] (Downloads:396)

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An electromagnetically induced grating in a four-level tripod-type atomic system is studied theoretically. By virtue of a weak standing-wave signal field, the phase modulation effectively diffracts a weak probe field into the first-order direction. By changing the weak signal field, the diffraction of the weak probe field can be modulated in real time, and a first-order diffraction efficiency of more than 32% can be obtained with proper parameters. Such a system has a potential application in an all-optical switch controlled by a weak optical signal.

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Application of thermal stress model to paint removal by Q-switched Nd：YAG laser

Zou Wan-Fang, Xie Ying-Mao, Xiao Xing, Zeng Xiang-Zhi, Luo Ying

Chin. Phys. B, 2014, 23 (7): 074205 doi: 10.1088/1674-1056/23/7/074205
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[PDF 603 KB] (Downloads:345)

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In this paper, we demonstrate that thermal stress is the main mechanism in the process of paint removal by Q-switched Nd:YAG laser (λ =1064 nm, τ=10 ns). A theoretical model of paint removal by short-pulse laser is established from the perspective of thermal stress. Thermal stress is generated by thermal expansion, and the temperatures of different samples are calculated according to the one-dimensional (1D) heat conduction equation. The theoretical cleaning threshold can be obtained by comparing thermal stress with the adhesion of paint, and the theoretical damage threshold is obtained by calculating the temperature. Moreover, the theoretical calculations are verified by experimental results. It is shown that the thermal stress model of the laser cleaning is very useful to choose the appropriate laser fluence in the practical applications of paint removal by Q-switched Nd: YAG laser because our model can validly balance the efficiency of laser cleaning and the safety of the substrate.

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All optical method for measuring the carrier envelope phase from half-cycle cutoffs Suggested by editors

Li Qian-Guang, Chen Huan, Zhang Xiu, Yi Xu-Nong

Chin. Phys. B, 2014, 23 (7): 074206 doi: 10.1088/1674-1056/23/7/074206
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[PDF 310 KB] (Downloads:336)

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An all optical method is demonstrated for measuring the carrier-envelope phase (CEP) of few-cycle laser pulses. It is found that, in the few-cycle regime, the high harmonic spectrum generated from asymmetric molecules shows several half-cycle cutoffs that change their positions as the CEP varies. Such half-cycle cutoffs represent the fingerprint of different quantum trajectories and the waveform of the driving pulse. In this case, the CEP can be accurately measured from the half-cycle cutoffs.

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Spectral energetic properties of the X-ray-boosted photoionization by an intense few-cycle laser Suggested by editors

Ge Yu-Cheng, He Hai-Ping

Chin. Phys. B, 2014, 23 (7): 074207 doi: 10.1088/1674-1056/23/7/074207
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[PDF 1398 KB] (Downloads:398)

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We report a discovery that an intense few-cycle laser pulse passing through gas leaves a fingerprint of its field envelope on the photoelectron energy spectrum, which involves continuous X-ray radiations. The spectrum resulting from the photoionization processes includes significant quantum enhancement and interference and exhibits interesting energetic properties. The spectral cut-off energies reflect the strength, time, and interference of the laser field modulation on the photoelectron energy. These energetic properties suggest a new method for precise intense-laser-pulse measurement in situ. The method has the advantages of accuracy, simplicity, speed, and large dynamic ranges (up to many orders of intensity).

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Transversal reverse transformation of anomalous hollow beams in strongly isotropic nonlocal media

Dai Zhi-Ping, Yang Zhen-Jun, Zhang Shu-Min, Pang Zhao-Guang, You Kai-Ming

Chin. Phys. B, 2014, 23 (7): 074208 doi: 10.1088/1674-1056/23/7/074208
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[PDF 1910 KB] (Downloads:302)

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Based on the nonlocal nonlinear Schrödinger equation, the propagation properties of anomalous hollow beams in strongly isotropic nonlocal media are investigated. The analytical expressions of the beam propagation, the on-axis intensity and the beam width are obtained. The results show that the evolution of the beam is periodical and the input power is the most important parameter. The input power determines the variation of the period. Furthermore, it is found that there exists a critical input power in the x direction and in the y direction separately when the initial beam widths in the two transversal directions are unequal. The beam width remains invariant in the corresponding transversal direction when the input power equals the critical power in one of the transversal directions. Selecting a proper input power, the beam can be broadened or compressed in the two transversal directions at the same time. In particular, the beam can be broadened (compressed) in one transversal direction, whereas in the other transversal direction, it is compressed (broadened), i.e., the transversal reverse transformation.

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Phase transition model of water flow irradiated by high-energy laser in a chamber

Wei Ji-Feng, Sun Li-Qun, Zhang Kai, Hu Xiao-Yang

Chin. Phys. B, 2014, 23 (7): 074209 doi: 10.1088/1674-1056/23/7/074209
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[PDF 1456 KB] (Downloads:422)

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In the absorption chamber of a high-energy laser energy meter, water is directly used as an absorbing medium and the interaction of the high-power laser and the water flow can produce a variety of physical phenomena such as phase transitions. The unit difference method is adopted to deduce the phase transition model for water flow irradiated by a high-energy laser. In addition, the model is simulated and verified through experiments. Among them, the experimental verification uses the photographic method, shooting the distribution and the form of the air mass of water flow in different operating conditions, which are compared with the simulation results. The research shows that it is achievable to reduce the intensity of the phase transition by increasing the water flow, reducing the power intensity of the beam, shortening the distance the beam covers, reducing the initial water temperature or adopting a shorter wavelength laser. The study's results will provide the reference for the design of a water-direct-absorption-type high-energy laser energy meter as well as an analysis of the interaction processes of other similar high-power lasers and water flow.

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Nonlinear impedances of thermoacoustic stacks with ordered and disordered structures Suggested by editors

Ge Huan, Fan Li, Xia Jie, Zhang Shu-Yi, Tao Sha, Yang Yue-Tao, Zhang Hui

Chin. Phys. B, 2014, 23 (7): 074301 doi: 10.1088/1674-1056/23/7/074301
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[PDF 407 KB] (Downloads:364)

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Nonlinear impedances of two thermoacoustic stacks with ordered structures (plate-type and pipe-type) and one with a disordered structure (copper mesh) are studied. The linear resistances, nonlinear coefficients and effective acoustic masses of the stacks are extracted from the experimental results based on an analogical model of nonlinear impedances of porous materials. The resistance and nonlinear coefficient of the disordered stack are found to be much larger than those of the ordered stacks, which have similar volume porosities. In the ordered stacks, the resistance is only marginally influenced by the length of the stack, while in the disordered stack, the resistance increases significantly with the length. These characteristics of the impedances of ordered and disordered stacks are explained with the minor loss theory and the tortuosity of a stack.

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Integrated physics package of a chip-scale atomic clock Suggested by editors

Li Shao-Liang, Xu Jing, Zhang Zhi-Qiang, Zhao Lu-Bing, Long Liang, Wu Ya-Ming

Chin. Phys. B, 2014, 23 (7): 074302 doi: 10.1088/1674-1056/23/7/074302
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[PDF 1676 KB] (Downloads:698)

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The physics package of a chip-scale atomic clock (CSAC) has been successfully realized by integrating vertical cavity surface emitting laser (VCSEL), neutral density (ND) filter, λ/4 wave plate, ⁸⁷Rb vapor cell, photodiode (PD), and magnetic coil into a cuboid metal package with a volume of about 2.8 cm³. In this physics package, the critical component, ⁸⁷Rb vapor cell, is batch-fabricated based on MEMS technology and in-situ chemical reaction method. Pt heater and thermistors are integrated in the physics package. A PTFE pillar is used to support the optical elements in the physics package, in order to reduce the power dissipation. The optical absorption spectrum of ⁸⁷Rb D1 line and the microwave frequency correction signal are successfully observed while connecting the package with the servo circuit system. Using the above mentioned packaging solution, a CSAC with short-term frequency stability of about 7× 10^-10τ^-1/2 has been successfully achieved, which demonstrates that this physics package would become one promising solution for the CSAC.

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Flow and heat transfer of a nanofluid over a hyperbolically stretching sheet

A. Ahmad, S. Asghar, A. Alsaedi

Chin. Phys. B, 2014, 23 (7): 074401 doi: 10.1088/1674-1056/23/7/074401
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This article explores the boundary layer flow and heat transfer of a viscous nanofluid bounded by a hyperbolically stretching sheet. Effects of Brownian and thermophoretic diffusions on heat transfer and concentration of nanoparticles are given due attention. The resulting nonlinear problems are computed for analytic and numerical solutions. The effects of Brownian motion and thermophoretic property are found to increase the temperature of the medium and reduce the heat transfer rate. The thermophoretic property thus enriches the concentration while the Brownian motion reduces the concentration of the nanoparticles in the fluid. Opposite effects of these properties are observed on the Sherwood number.

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Three-dimensional magnetohydrodynamics axisymmetric stagnation flow and heat transfer due to an axisymmetric shrinking/stretching sheet with viscous dissipation and heat source/sink

Dinesh Rajotia, R. N. Jat

Chin. Phys. B, 2014, 23 (7): 074701 doi: 10.1088/1674-1056/23/7/074701
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The present work is concerned with the effects of viscous dissipation and heat source/sink on a three-dimensional magnetohydrodynamic boundary layer axisymmetric stagnation flow, and the heat transfer of an electrically conducting fluid over a sheet, which shrinks or stretches axisymmetrically in its own plane where the line of the symmetry of the stagnation flow and that of the shrinking (stretching) sheet are, in general, not aligned. The governing equations are transformed into ordinary differential equations by using suitable similarity transformations and then solved numerically by a shooting technique. This investigation explores the conditions of the non-existence, existence and uniqueness of the solutions of the similar equations numerically. It is noted that the range of the velocity ratio parameter, where the similarity solution exists, is increased with the increase of the value of the magnetic parameter. Furthermore, the study reveals that the non-alignment function affects the shrinking sheet more than the stretching sheet. In addition, the numerical results of the velocity profile, temperature profile, skin-friction coefficient, and rate of heat transfer at the sheet are discussed in detail with different parameters.

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Molecular dynamics simulations of the nano-droplet impact process on hydrophobic surfaces

Hu Hai-Bao, Chen Li-Bin, Bao Lu-Yao, Huang Su-He

Chin. Phys. B, 2014, 23 (7): 074702 doi: 10.1088/1674-1056/23/7/074702
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Large-scale molecular dynamics simulations are used to study the dynamic processes of a nano-droplet impacting on hydrophobic surfaces at a microscopic level. Both the impact phenomena and the velocity distributions are recorded and analyzed. According to the simulation results, similar phenomena are obtained to those in macro-experiments. Impact velocity affects the spread process to a greater degree than at a level of contact angle when the velocity is relatively high. The velocity distribution along the X axis during spread is wave-like, either W- or M-shaped, and the velocity at each point is oscillatory; while the edges have the highest spread velocity and there are crests in the distribution curve which shift toward the edges over time. The distribution along the Y axis is <- or >-shaped, and the segments above the middle have the lowest decrease rate in the spreading process and the highest increase rate in the retraction process.

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Influence of limestone fillers on combustion characteristics of asphalt mortar for pavements

Wu Ke, Zhu Kai, Wu Hao, Han Jun, Wang Jin-Chang, Huang Zhi-Yi, Liang Pei

Chin. Phys. B, 2014, 23 (7): 074703 doi: 10.1088/1674-1056/23/7/074703
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Asphalt materials will be ignited and release significant toxic fumes within tunnel fires. Thus, combustion characteristics of asphalt materials used in road tunnel should be studied in order to limit such an adverse effect. In the present work we study the influence of limestone fillers on combustion characteristics of asphalt mortar by thermogravimetric and kinetic analysis. It is shown that the combustion of asphalt mortar is not just a linear superposition of asphalt and limestone. The limestone will increase the ignition point and the activation energy of the primary volatile release, and will catalyze the char formation from the primary volatile release. Kinetic analysis shows that the primary volatile release stage of asphalt mortar combustion can be explained by a three-dimensional diffusion model, the secondary volatile release and char combustion stage can be explained by a model under the assumption of random nucleation and nuclei growth, whereas the limestone decomposition stage appears to follow the one-dimensional phase boundary model.

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Balmer-alpha and Balmer-beta Stark line intensity profiles for high-power hydrogen inductively coupled plasmas

Wang Song-Bai, Lei Guang-Jiu, Liu Dong-Ping, Yang Si-Ze

Chin. Phys. B, 2014, 23 (7): 075201 doi: 10.1088/1674-1056/23/7/075201
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We compare Balmer-alpha (H_α) and Balmer-beta (H_β) emissions from high-power (1.0-6.0 kW) hydrogen inductively coupled plasmas (ICPs), and propose region I (0.0-2.0 kW), region Ⅱ (2.0-5.0 kW), and region Ⅲ (5.0-6.0 kW). In region I, both H_α emission intensity (I_α) and H_β emission intensity (I_β) increase with radio frequency (RF) power, which is explained by the corona model and Boltzmann's law, etc. However, in region Ⅱ, I_α almost remains constant while I_β rapidly achieves its maximum value. In region Ⅲ, I_α slightly increases with RF power, while I_β decreases with RF power, which deviates significantly from the theoretical explanation for the H_α and H_β emissions in region I. It is suggested that two strong electric fields are generated in high-power (2.0-6.0 kW) hydrogen ICPs: one is due to the external electric field of high-power RF discharge, and the other one is due to the micro electric field of the ions and electrons around the exited state hydrogen atoms in ICPs. Therefore, the strong Stark effect can play an important role in explaining the experimental results.

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Mitigation of energetic ion debris from Gd plasma using dual laser pulses and the combined effect with ambient gas

Dou Yin-Ping, Sun Chang-Kai, Liu Chao-Zhi, Gao Jian, Hao Zuo-Qiang, Lin Jing-Quan

Chin. Phys. B, 2014, 23 (7): 075202 doi: 10.1088/1674-1056/23/7/075202
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For the next-generation beyond extreme ultraviolet lithography (EUVL) sources, gadolinium (Gd) plasma with emission wavelength at 6.7 nm seems to be the leading candidate. Similar to the Sn target 13.5 nm light source, ion debris mitigation is one of the most important tasks in the laser-produced Gd plasma EUV source development. In this paper, a dual-laser-pulse scheme, which uses a low energy pulse to produce a pre-plasma and a main pulse after a time delay to shoot the pre-plasma, is employed to mitigate the energetic ion generation from the source. Optimal conditions (such as pre-pulse energy and wavelength, and the time delay between the pre-pulse and the main pulse for mitigating the ion energy) are experimentally obtained, and with the optimal conditions, the peak of the ion energy is found to be reduced to 1/18 of that of a single laser pulse case. Moreover, the combined effect by applying ambient gas to the dual-pulse scheme for ion debris mitigation is demonstrated, and the result shows that the yield of Gd ions is further reduced to around 1/9 of the value for the case with dual laser pulses.

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Characteristics of wall sheath and secondary electron emission under different electron temperatures in a Hall thruster

Duan Ping, Qin Hai-Juan, Zhou Xin-Wei, Cao An-Ning, Chen Long, Gao Hong

Chin. Phys. B, 2014, 23 (7): 075203 doi: 10.1088/1674-1056/23/7/075203
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In this paper, a two-dimensional physical model is established in a Hall thruster sheath region to investigate the influences of the electron temperature and the propellant on the sheath potential drop and the secondary electron emission in the Hall thruster, by the particle-in-cell (PIC) method. The numerical results show that when the electron temperature is relatively low, the change of sheath potential drop is relatively large, the surface potential maintains a stable value and the stability of the sheath is good. When the electron temperature is relatively high, the surface potential maintains a persistent oscillation, and the stability of the sheath reduces. As the electron temperature increases, the secondary electron emission coefficient on the wall increases. For three kinds of propellants (Ar, Kr, and Xe), as the ion mass increases the sheath potentials and the secondary electron emission coefficients reduce in sequence.

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Atmospheric pressure plasma jet utilizing Ar and Ar/H₂O mixtures and its applications to bacteria inactivation

Cheng Cheng, Shen Jie, Xiao De-Zhi, Xie Hong-Bing, Lan Yan, Fang Shi-Dong, Meng Yue-Dong, Chu Paul K

Chin. Phys. B, 2014, 23 (7): 075204 doi: 10.1088/1674-1056/23/7/075204
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An atmospheric pressure plasma jet generated with Ar with H₂O vapor is characterized and applied to inactivation of Bacillus subtilis spores. The emission spectra obtained from Ar/H₂O plasma shows a higher intensity of OH radicals compared to pure argon at a specified H₂O concentration. The gas temperature is estimated by comparing the simulated spectra of the OH band with experimental spectra. The excitation electron temperature is determined from the Boltzmann's plots and Stark broadening of the hydrogen Balmer H_β line is applied to measure the electron density. The gas temperature, excitation electron temperature, and electron density of the plasma jet decrease with the increase of water vapor concentration at a fixed input voltage. The bacteria inactivation rate increases with the increase of OH generation reaching a maximum reduction at 2.6% (v/v) water vapor. Our results also show that the OH radicals generated by the Ar/H₂O plasma jet only makes a limited contribution to spore inactivation and the shape change of the spores before and after plasma irradiation is discussed.

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Effect of passive structure and toroidal rotation on resistive wall mode stability in the EAST tokamak

Liu Guang-Jun, Wan Bao-Nian, Sun You-Wen, Liu Yue-Qiang, Guo Wen-Feng, Hao Guang-Zhou, Ding Si-Ye, Shen Biao, Xiao Bing-Jia, Qian Jin-Ping

Chin. Phys. B, 2014, 23 (7): 075205 doi: 10.1088/1674-1056/23/7/075205
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If β_N exceeds β_N^no-wall, the plasma will be unstable because of external kink and resistive wall mode (RWM). In this article, the effect of the passive structure and the toroidal rotation on the RWM stability in the experimental advanced superconducting tokamak (EAST) are simulated with CHEASE and MARS codes. A model using a one-dimensional (1D) surface to present the effect of the passive plate is proved to be credible. The no wall β_N limit is about 3l_i, and the ideal wall β_N limit is about 4.5l_i on EAST. It is found that the rotation near the q=2 surface and the plasma edge affects the RWM more.

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Toroidicity and shape dependence of peeling mode growth rates in axisymmetric toroidal plasmas

Shi Bing-Ren

Chin. Phys. B, 2014, 23 (7): 075206 doi: 10.1088/1674-1056/23/7/075206
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The growth rate of the peeling mode instability with large toroidal mode number is calculated for general axisymmetric toroidal plasmas, including tokamaks and the spherical torus (ST) equilibia by using formalism presented by Connor et al. Analytic equilibia with non-zero edge current density and quasi-uniform current profiles are assumed. It is found that in sharp D-shape tokamak plasma, the derivative of the safety factor with respect to the poloidal flux becomes very large, making the perturbed poloidal motion very large, in turn making a significant reduction of the growth rate of the peeling mode, similar to the X-point effect in diverted plasma. The large aspect ratio effect is also studied, which reduces the growth rate further.

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DD proton spectrum for diagnosing the areal density of imploded capsules on Shenguang Ⅲ prototype laser facility

Teng Jian, Zhang Tian-Kui, Wu Bo, Pu Yu-Dong, Hong Wei, Shan Lian-Qiang, Zhu Bin, He Wei-Hua, Lu Feng, Wen Xian-Lun, Zhou Wei-Min, Cao Lei-Feng, Jiang Shao-En, Gu Yu-Qiu

Chin. Phys. B, 2014, 23 (7): 075207 doi: 10.1088/1674-1056/23/7/075207
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The primary DD proton spectrum is used for diagnosing the fuel-shell areal density ρR of imploded capsules on Shenguang Ⅲ (SG-Ⅲ) prototype laser facility for the first time. A charged particle spectrometer (CPS) with a CR39 nuclear track detector is used to measure the DD proton spectrum. The proton spectrum is determined from both the proton track and its size. A typical proton energy peak shift from 3.02 MeV to 2.6 MeV is observed in our experiment, which yields a maximum ρR larger than 6 mg/cm².

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Efficiency and stability enhancement of a virtual cathode oscillator

Fan Yu-Wei, Li Zhi-Qiang, Shu Ting, Liu Jing

Chin. Phys. B, 2014, 23 (7): 075208 doi: 10.1088/1674-1056/23/7/075208
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A virtual cathode oscillator (VCO) with a resonant cavity is presented and investigated numerically and theoretically, and its efficiency and stability are enhanced. An equivalent circuit method is introduced to analyze the resonant cavity composed of anode foil and feedback annulus, and a theoretical expression for the fundamental mode frequency of the resonant cavity is given. The VCO is investigated in detail with a particle-in-cell method. We obtain the microwave frequencies from simulation, theoretical expression, and relative references, and draw three important conclusions. First, the microwave frequency is a constant when the diode voltage is changed from 588 kV to 717 kV. Second, the fluctuation of the microwave frequency is very small when the AK gap is changed from 1.2 cm to 1.6 cm. Third, the microwave frequency agrees with the theoretical result. The relative error, which is calculated according to the theoretical and simulation frequencies, is only 1.7%.

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Mode transition in homogenous dielectric barrier discharge in argon at atmospheric pressure

Liu Fu-Cheng, He Ya-Feng, Wang Xiao-Fei

Chin. Phys. B, 2014, 23 (7): 075209 doi: 10.1088/1674-1056/23/7/075209
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The influence of driving frequency on the discharge regime of a homogenous dielectric barrier discharge in argon at atmospheric pressure is studied through a one-dimensional self-consistent fluid model. The simulation results show that the discharge exhibits five notable discharge modes, namely the Townsend mode, stable glow mode, chaotic mode, asymmetric glow, and multiple period glow mode in a broad frequency range. The transition mechanisms of these modes should be attributed to the competition between the applied voltage and the memory voltage induced by the surface charges.

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Shockwave-boundary layer interaction control by plasma aerodynamic actuation：An experimental investigation Suggested by editors

Sun Quan, Cui Wei, Li Ying-Hong, Cheng Bang-Qin, Jin Di, Li Jun

Chin. Phys. B, 2014, 23 (7): 075210 doi: 10.1088/1674-1056/23/7/075210
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The potential of controlling shockwave-boundary layer interactions (SWBLIs) in air by plasma aerodynamic actuation is demonstrated. Experiments are conducted in a Mach 3 in-draft air tunnel. The separation-inducing shock is generated with a diamond-shaped shockwave generator located on the wall opposite to the surface electrodes, and the flow properties are studied with schlieren imaging and static wall pressure probes. The measurements show that the separation phenomenon is weakened with the plasma aerodynamic actuation, which is observed to have significant control authority over the interaction. The main effect is the displacement of the reflected shock. Perturbations of incident and reflected oblique shocks interacting with the separation bubble in a rectangular cross section supersonic test section are produced by the plasma actuation. This interaction results in a reduction of the separation bubble size, as detected by phase-lock schlieren images. The measured static wall pressure also shows that the separation-inducing shock is restrained. Our results suggest that the boundary layer separation control through heating is the primary control mechanism.

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Small-angle X-ray analysis of the effect of grain size on the thermal damage of octahydro-1, 3, 5, 7-tetranitro-1, 3, 5, 7 tetrazocine-based plastic-bounded expolsives

Yan Guan-Yun, Tian Qiang, Liu Jia-Hui, Chen Bo, Sun Guang-Ai, Huang Ming, Li Xiu-Hong

Chin. Phys. B, 2014, 23 (7): 076101 doi: 10.1088/1674-1056/23/7/076101
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The microstructure evolution of plastic-bonded explosives (PBXs) after thermal stimulus plays a key role in PBX performance. In this paper, the nanoscale pores of thermal-treated octahydro-1,3,5,7-tetranitro-1,3,5,7 tetrazocine (HMX)-based PBXs with different HMX particle sizes [approximately 40 (FHP) and 100 μm (LHP)] were measured using small-angle X-ray scattering (SAXS). No obvious pore variations were found in the LHP samples heated at 160 ℃ for 6 h, whereas the amount of pores of FHP decreased when subjected to 160 ℃ for 6 h. At 180 ℃, the average pore radii of FHP and LHP decreased from approximately 45 nm to 25 nm, and the total pore volume increased distinctively because of phase transformation. The LHP sample reached a high level of pore content after being held at 180 ℃ for 1 h, whereas FHP required 3 h. Both FHP and LHP had relatively high pore volumes when subjected to 200 ℃ for 1 and 3 h.

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Quantum confinement and surface chemistry of 0.8-1.6 nm hydrosilylated silicon nanocrystals Suggested by editors

Pi Xiao-Dong, Wang Rong, Yang De-Ren

Chin. Phys. B, 2014, 23 (7): 076102 doi: 10.1088/1674-1056/23/7/076102
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In the framework of density functional theory (DFT), we have studied the electronic properties of alkene/alkyne-hydrosilylated silicon nanocrystals (Si NCs) in the size range from 0.8 nm to 1.6 nm. Among the alkenes with all kinds of functional groups considered in this work, only those containing -NH₂ and -C₄H₃S lead to significant hydrosilylation-induced changes in the gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of an Si NC at the ground state. The quantum confinement effect is dominant for all of the alkene-hydrosilylated Si NCs at the ground state. At the excited state, the prevailing effect of surface chemistry only occurs at the smallest (0.8 nm) Si NCs hydrosilylated with alkenes containing -NH₂ and -C₄H₃S. Although the alkyne hydrosilylation gives rise to a more significant surface chemistry effect than alkene hydrosilylation, the quantum confinement effect remains dominant for alkyne-hydrosilylated Si NCs at the ground state. However, at the excited state, the effect of surface chemistry induced by the hydrosilylation with conjugated alkynes is strong enough to prevail over that of quantum confinement.

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Spectroscopic and scanning probe analysis on large-area epitaxial graphene grown under pressure of 4 mbar on 4H-SiC (0001) substrates

Wang Dang-Chao, Zhang Yu-Ming

Chin. Phys. B, 2014, 23 (7): 076103 doi: 10.1088/1674-1056/23/7/076103
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We produced epitaxial graphene under a moderate pressure of 4 mbar (about 400 Pa) at temperature 1600 ℃. Raman spectroscopy and optical microscopy were used to confirm that epitaxial graphene has taken shape continually with slight thickness variations and regularly with a centimeter order of magnitude on 4H-SiC (0001) substrates. Then using X-ray photoelectron spectroscopy and Auger electron spectroscopy, we analyzed the chemical compositions and estimated the layer number of epitaxial graphene. Finally, an atomic force microscope and a scanning force microscope were used to characterize the morphological structure. Our results showed that under 4-mbar pressure, epitaxial graphene could be produced on a SiC substrate with a large area, uniform thickness but a limited morphological property. We hope our work will be of benefit to understanding the formation process of epitaxial graphene on SiC substrate in detail.

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Ferromagnetism on a paramagnetic host background in cobalt-doped Bi₂Se₃ topological insulator

Zhang Min, Lü Li, Wei Zhan-Tao, Yang Xin-Sheng, Zhao Yong

Chin. Phys. B, 2014, 23 (7): 076104 doi: 10.1088/1674-1056/23/7/076104
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Cobalt-doped Bi₂Se₃ topological insulators have been grown though melt-grown reaction. The Bi₂Se₃ matrix is diamagnetic and doped sample is a superposition of ferromagnetism (FM) and paramagnetism (PM) behavior at low temperature. The values of M_Smol, H_c, and M_r increase as the Co concentration increases. Two possible explanations have been proposed for the origin of ferromagnetism in Co-doped Bi₂Se₃. One is the magnetic ordering from nanoclusters of Co-Se compound in the crystals, and the other is Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between magnetic impurities.

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Physical properties of FePt nanocomposite doped with Ag atoms：First-principles study

Jia Yong-Fei, Shu Xiao-Lin, Xie Yong, Chen Zi-Yu

Chin. Phys. B, 2014, 23 (7): 076105 doi: 10.1088/1674-1056/23/7/076105
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L1₀ FePt nanocomposite with high magnetocrystalline anisotropy energy has been extensively investigated in the fields of ultra-high density magnetic recording media. However, the order-disorder transition temperature of the nanocomposite is higher than 600 ℃, which is a disadvantage for the use of the material due to the sustained growth of FePt grain under the temperature. To address the problem, addition of Ag atoms has been proposed, but the magnetic properties of the doped system are still unclear so far. Here in this paper, we use first-principles method to study the lattice parameters, formation energy, electronic structure, atomic magnetic moment and order-disorder transition temperature of L1₀ FePt with Ag atom doping. The results show that the formation energy of a Ag atom substituting for a Pt site is 1.309 eV, which is lower than that of substituting for an Fe site 1.346 eV. The formation energy of substituting for the two nearest Pt sites is 2.560 eV lower than that of substituting for the further sites 2.621 eV, which indicates that Ag dopants tend to segregate L1₀ FePt. The special quasirandom structures (SQSs) for the pure FePt and the FePt doped with two Ag atoms at the stable Pt sites show that the order-disorder transition temperatures are 1377 ℃ and 600 ℃, respectively, suggesting that the transition temperature can be reduced with Ag atom, and therefore the FePt grain growth is suppressed. The saturation magnetizations of the pure FePt and the two Ag atoms doped FePt are 1083 emu/cc and 1062 emu/cc, respectively, indicating that the magnetic property of the doped system is almost unchanged.

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Effect of size polydispersity on the structural and vibrational characteristics of two-dimensional granular assemblies Suggested by editors

Zhang Guo-Hua, Sun Qi-Cheng, Shi Zhi-Ping, Feng Xu, Gu Qiang, Jin Feng

Chin. Phys. B, 2014, 23 (7): 076301 doi: 10.1088/1674-1056/23/7/076301
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Two-dimensional disordered granular assemblies composed of 2048 polydispersed frictionless disks are simulated using the discrete element method. The height of the first peak of the pair correlation function, g₁, the local and global bond orientational parameters ψ₆^l and ψ₆^g, and the fluctuations of these parameters decrease with increasing polydispersity s, implying the transition from a polycrystalline state to an amorphous state in the system. As s increases, the peak position of the boson peak ω_BP shifts towards a lower frequency and the intensity of the boson peak D(ω_BP)/ω_BP increases, indicating that the position and the strength of the boson peak are controlled by the polydispersity of the system. Moreover, the inverse of the boson peak intensity ω_BP/D(ω_BP), the shear modulus G, and the basin curvature S_IS all have a similar dependence on s, implying that the s dependence of the vibrational density of states at low frequencies likely originates from the s dependence of the basin curvature.

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Characteristics of phase transitions via intervention in random networks

Jia Xiao, Hong Jin-Song, Yang Hong-Chun, Yang Chun, Shi Xiao-Hong, Hu Jian-Quan

Chin. Phys. B, 2014, 23 (7): 076401 doi: 10.1088/1674-1056/23/7/076401
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We present a percolation process in which the classical Erdös-Rényi (ER) random evolutionary network is intervened by the product rule (PR) from some moment t₀. The parameter t₀ is continuously tunable over the real interval [0, 1]. This model becomes the random network under the Achlioptas process at t₀= 0 and the ER network at t₀= 1. For the percolation process at t₀≤ 1, we introduce a relatively slow-growing point, after which the largest cluster begins growing faster than that in the ER model. A weakly discontinuous transition is generated in the percolation process at t₀ ≤ 0.5. We take the relatively slow-growing point as the lower pseudotransition point and the maximum gap point of the order parameter as the upper pseudotransition point. The critical point can be approximately predicted by each fitting function of the two points about t₀. This contributes to understanding the rapid mergence of the large clusters at the critical point. The numerical simulations indicate that the lower pseudotransition point and the upper pseudotransition point are equal in the thermodynamic limit. When t₀> 0.5, the percolation processes generate a continuous transition. The scaling analyses of several quantities are presented, including the relatively slow-growing point, the duration of the relatively slow-growing process, as well as the relatively maximum strength between the percolation percolation at t₀< 1 and the ER network about different t₀. The presented mechanism can be viewed as a two-stage percolation process that has many potential applications in the growth processes of real networks.

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Electrical and optical properties of indium tin oxide/epoxy composite film

Guo Xia, Guo Chun-Wei, Chen Yu, Su Zhi-Ping

Chin. Phys. B, 2014, 23 (7): 076403 doi: 10.1088/1674-1056/23/7/076403
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The electrical and optical properties of the indium tin oxide (ITO)/epoxy composite exhibit dramatic variations as functions of the ITO composition and ITO particle size. Sharp increases in the conductivity in the vicinity of a critical volume fraction have been found within the framework of percolation theory. A conductive and insulating transition model is extracted by the ITO particle network in the SEM image, and verified by the resistivity dependence on the temperature. The dependence of the optical transmittance on the particle size was studied. Further decreasing the ITO particle size could further improve the percolation threshold and light transparency of the composite film.

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Dynamic thermo-mechanical coupled response of random particulate composites：A statistical two-scale method

Yang Zi-Hao, Chen Yun, Yang Zhi-Qiang, Ma Qiang

Chin. Phys. B, 2014, 23 (7): 076501 doi: 10.1088/1674-1056/23/7/076501
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This paper focuses on the dynamic thermo-mechanical coupled response of random particulate composite materials. Both the inertia term and coupling term are considered in the dynamic coupled problem. The formulation of the problem by a statistical second-order two-scale (SSOTS) analysis method and the algorithm procedure based on the finite-element difference method are presented. Numerical results of coupled cases are compared with those of uncoupled cases. It shows that the coupling effects on temperature, thermal flux, displacement, and stresses are very distinct, and the micro-characteristics of particles affect the coupling effect of the random composites. Furthermore, the coupling effect causes a lag in the variations of temperature, thermal flux, displacement, and stresses.

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Fabrication of VO₂ thin film by rapid thermal annealing in oxygen atmosphere and its metal-insulator phase transition properties

Liang Ji-Ran, Wu Mai-Jun, Hu Ming, Liu Jian, Zhu Nai-Wei, Xia Xiao-Xu, Chen Hong-Da

Chin. Phys. B, 2014, 23 (7): 076801 doi: 10.1088/1674-1056/23/7/076801
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Vanadium dioxide thin films have been fabricated through sputtering vanadium thin films and rapid thermal annealing in oxygen. The microstructure and the metal-insulator transition properties of the vanadium dioxide thin films were investigated by X-ray diffraction, X-ray photoelectron spectroscopy, and a spectrometer. It is found that the preferred orientation of the vanadium dioxide changes from (111) to (011) with increasing thickness of the vanadium thin film after rapid thermal annealing. The vanadium dioxide thin films exhibit an obvious metal-insulator transition with increasing temperature, and the phase transition temperature decreases as the film thickness increases. The transition shows hysteretic behaviors, and the hysteresis width decreases as the film thickness increases due to the higher concentration carriers resulted from the uncompleted lattice. The fabrication of vanadium dioxide thin films with higher concentration carriers will facilitate the nature study of the metal-insulator transition.

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Interaction and spin-orbit effects on a kagome lattice at 1/3 filling ^Hot! Suggested by editors

Liu Hai-Di, Chen Yao-Hua, Lin Heng-Fu, Tao Hong-Shuai, Wu Jian-Hua

Chin. Phys. B, 2014, 23 (7): 077101 doi: 10.1088/1674-1056/23/7/077101
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We investigate the competing effects of spin-orbit coupling and electron-electron interaction on a kagome lattice at 1/3 filling. We apply the cellular dynamical mean-field theory and its real-space extension combined with the continuous time quantum Monte Carlo method, and obtain a phase diagram including the effects of the interaction and the spin-orbit coupling at T=0.1t, where T is the temperature and t is the hopping energy. We find that without the spin-orbit coupling, the system is in a semi-metal phase stable against the electron-electron interaction. The presence of the spin-orbit coupling can induce a topological non-trivial gap and drive the system to a topological insulator, and as the interaction increases, a larger spin-orbit coupling is required to reach the topological insulating phase.

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First-principles study of structural, electronic and optical properties of ZnF₂

Wu Jian-Bang, Cheng Xin-Lu, Zhang Hong, Xiong Zheng-Wei

Chin. Phys. B, 2014, 23 (7): 077102 doi: 10.1088/1674-1056/23/7/077102
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The structural, electronic, and optical properties of rutile-, CaCl₂-, and PdF₂-ZnF₂ are calculated by the plane-wave pseudopotential method within the density functional theory. The calculated equilibrium lattice constants are in reasonable agreement with the available experimental and other calculated results. The band structures show that the rutile-, CaCl₂-, and PdF₂-ZnF₂ are all direct band insulator. The band gaps are 3.63, 3.62, and 3.36 eV, respectively. The contribution of the different bands was analyzed by the density of states. The Mulliken population analysis is performed. A mixture of covalent and weak ionic chemical bonding exists in ZnF₂. Furthermore, in order to understand the optical properties of ZnF₂, the dielectric function, absorption coefficient, refractive index, electronic energy loss spectroscopy, and optical reflectivity are also performed in the energy range from 0 to 30 eV. It is found that the main absorption parts locate in the UV region for ZnF₂. This is the first quantitative theoretical prediction of the electronic and optical properties of ZnF₂ compound, and it still awaits experimental confirmation.

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Hybrid density functional studies of cadmium vacancy in CdTe

Xu Run, Xu Hai-Tao, Tang Min-Yan, Wang Lin-Jun

Chin. Phys. B, 2014, 23 (7): 077103 doi: 10.1088/1674-1056/23/7/077103
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[PDF 274 KB] (Downloads:393)

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The intrinsic defect of cadmium vacancy (V_Cd) in cadmium telluride (CdTe) has been studied by first-principles calculations using potentials with both the screened hybrid functional of Heyd, Scuseria, and Ernzerhof (HSE) approximation and the generalized gradient approximation of the Perdew-Burke-Ernzerhof form (PBE-GGA). Both results show that the T_d structure of the V_Cd defect for different charges is the most stable structure as compared with the distorted C_3v structure with one hole localized at one of the four nearest Te atoms. This indicates that the John-Teller distortion (C_3v) structure may be unstable in bulk CdTe crystal. The reason likely lies in the delocalized resonance nature of the t₂ state of the V_{m Cd} defect. Moreover, the formation energy obtained by the HSE method is about 0.6-0.8 eV larger than that obtained by the PBE method. The transition levels calculated by the PBE method and the HSE method are similar and well consistent with the experimental results.

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A theoretical investigation of the band alignment of type-I direct band gap dilute nitride phosphide alloy of GaN_xAs_yP_1-x-y/GaP quantum wells on GaP substrates

Ö L Ünsal, B Gönül, M Temiz

Chin. Phys. B, 2014, 23 (7): 077104 doi: 10.1088/1674-1056/23/7/077104
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[PDF 259 KB] (Downloads:372)

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The GaP-based dilute nitride direct band gap material Ga(NAsP) is gaining importance due to the monolithic integration of laser diodes on Si microprocessors. The major advantage of this newly proposed laser material system is the small lattice mismatch between GaP and Si. However, the large threshold current density of these promising laser diodes on Si substrates shows that the carrier leakage plays an important role in Ga(NAsP)/GaP QW lasers. Therefore, it is necessary to investigate the band alignment in this laser material system. In this paper, we present a theoretical investigation to optimize the band alignment of type-I direct band gap GaN_xAs_yP_1-x-y/GaP QWs on GaP substrates. We examine the effect of nitrogen (N) concentration on the band offset ratios and band offset energies. We also provide a comparison of the band alignment of type-I direct band gap GaN_xAs_yP_1-x-y/GaP QWs with that of the GaN_xAs_yP_1-x-y/Al_zGa_1-zP QWs on GaP substrates. Our theoretical calculations indicate that the incorporations of N into the well and Al into the barrier improve the band alignment compared to that of the GaAsP/GaP QW laser heterostructures.

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Influence of temperature on strain-induced polarization Coulomb field scattering in AlN/GaN heterostructure field-effect transistors

Lü Yuan-Jie, Feng Zhi-Hong, Lin Zhao-Jun, Guo Hong-Yu, Gu Guo-Dong, Yin Jia-Yun, Wang Yuan-Gang, Xu Peng, Song Xu-Bo, Cai Shu-Jun

Chin. Phys. B, 2014, 23 (7): 077105 doi: 10.1088/1674-1056/23/7/077105
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[PDF 269 KB] (Downloads:363)

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Electron mobility scattering mechanism in AlN/GaN heterostuctures is investigated by temperature-dependent Hall measurement, and it is found that longitudinal optical phonon scattering dominates electron mobility near room temperature while the interface roughness scattering becomes the dominant carrier scattering mechanism at low temperatures (～ 100 K). Based on measured current-voltage characteristics of prepared rectangular AlN/GaN heterostructure field-effect transistor under different temperatures, the temperature-dependent variation of electron mobility under different gate biases is investigated. The polarization Coulomb field (PCF) scattering is found to become an important carrier scattering mechanism after device processing under different temperatures. Moreover, it is found that the PCF scattering is not generated from the thermal stresses, but from the piezoelectric contribution induced by the electrical field in the thin AlN barrier layer. This is attributed to the large lattice mismatch between the extreme thinner AlN barrier layer and GaN, giving rise to a stronger converse piezoelectric effect.

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Design consideration and fabrication of 1.2-kV 4H-SiC trenched-and-implanted vertical junction field-effect transistors

Chen Si-Zhe, Sheng Kuang

Chin. Phys. B, 2014, 23 (7): 077201 doi: 10.1088/1674-1056/23/7/077201
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[PDF 783 KB] (Downloads:440)

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We present the design consideration and fabrication of 4H-SiC trenched-and-implanted vertical junction field-effect transistors (TI-VJFETs). Different design factors, including channel width, channel doping, and mesa height, are considered and evaluated by numerical simulations. Based on the simulation result, normally-on and normally-off devices are fabricated. The fabricated device has a 12 μm thick drift layer with 8× 10¹⁵ cm^-3 N-type doping and 2.6 μm channel length. The normally-on device shows a 1.2 kV blocking capability with a minimum on-state resistance of 2.33 mΩ · cm², while the normally-off device shows an on-state resistance of 3.85 mΩ ·cm². Both the on-state and the blocking performances of the device are close to the state-of-the-art values in this voltage range.

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A novel solution-based self-assembly approach to preparing ultralong titanyl phthalocyanine sub-micron wires Suggested by editors

Zhu Zong-Peng, Wei Bin, Zhang Jian-Hua, Wang Jun

Chin. Phys. B, 2014, 23 (7): 077202 doi: 10.1088/1674-1056/23/7/077202
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[PDF 1488 KB] (Downloads:295)

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Ultralong titanyl phthalocyanine (TiOPc) sub-micron wires have been synthesized by a novel solution-based self-assembly method. By using different solvents, changing the mass concentration and the solvent vapor pressure, the length and the shape of the wires can be adjusted. The mixed-phase properties of the TiOPc sub-micron wires were investigated by the ultraviolet-visible (UV-vis) absorption spectrum and X-ray diffraction. Organic transistors based on these wires were studied, which show the typical p-channel characteristics.

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Lattice structures and electronic properties of CIGS/CdS interface：First-principles calculations

Tang Fu-Ling, Liu Ran, Xue Hong-Tao, Lu Wen-Jiang, Feng Yu-Dong, Rui Zhi-Yuan, Huang Min

Chin. Phys. B, 2014, 23 (7): 077301 doi: 10.1088/1674-1056/23/7/077301
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[PDF 763 KB] (Downloads:1169)

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Using first-principles calculations within density functional theory, we study the atomic structures and electronic properties of the perfect and defective (2V_Cu+In_Cu) CuInGaSe₂/CdS interfaces theoretically, especially the interface states. We find that the local lattice structure of (2V_Cu+In_Cu) interface is somewhat disorganized. By analyzing the local density of states projected on several atomic layers of the two interfaces models, we find that for the (2V_Cu+In_Cu) interface the interface states near the Fermi level in CuInGaSe₂ and CdS band gap regions are mainly composed of interfacial Se-4p, Cu-3d and S-3p orbitals, while for the perfect interface there are no clear interface states in the CuInGaSe₂ region but only some interface states which are mainly composed of S-3p orbitals in the valance band of CdS region.

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Efficiency of electrical manipulation in two-dimensional topological insulators

Pang Mi, Wu Xiao-Guang

Chin. Phys. B, 2014, 23 (7): 077302 doi: 10.1088/1674-1056/23/7/077302
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[PDF 610 KB] (Downloads:322)

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We investigate the efficiency of electrical manipulation in a two-dimensional topological insulator by inspecting the electronic states of a lateral electrical potential superlattice in the system. The spatial distribution of the electron density in the system can be tuned by changing the strength of the externally applied lateral electrical superlattice potential. This provides us the information about how efficiently one can manipulate the electron motion inside a two-dimensional topological insulator. Such information is important in designing electronic devices, e.g., an electric field effect transistor made of the topological insulator. The electronic states under various conditions are examined carefully. It is found that the dispersion of the mini-band and the electron distribution in the potential well region both display an oscillatory behavior as the potential strength of the lateral superlattice increases. The probability of finding an electron in the potential well region can be larger or smaller than the average as the potential strength varies. These features can be attributed to the coupled multiple-band nature of the topological insulator. In addition, it is also found that these behaviors are not sensitive to the gap parameter of the two-dimensional topological insulator model. Our study suggests that the electron density manipulation via electrical gating in a two-dimensional topological insulator is less effective and more delicate than that in a traditional single-band semiconductor.

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Effect of annealing on performance of PEDOT：PSS/n-GaN Schottky solar cells

Feng Qian, Du Kai, Li Yu-Kun, Shi Peng, Feng Qing

Chin. Phys. B, 2014, 23 (7): 077303 doi: 10.1088/1674-1056/23/7/077303
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[PDF 967 KB] (Downloads:791)

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We develop a heterojunction-based Schottky solar cell consisting of n-type GaN and PEDOT:PSS and also investigate the effect of annealing on the performance of the solar cell. The results show that the open circuit voltage (V_oc) increases from 0.54 V to 0.56 V, 0.71 V and 0.82 eV while decreases to 0.69 eV after annealing at 100 ℃, 130 ℃, 160 ℃, and 200 ℃, respectively, which can be ascribed to the change of barrier height of PEDOT:PSS/GaN Schottky contact induced by variation of the work function of the PEDOT:PSS. Furthermore, the conductivity and surface roughness measurements of the PEDOT:PSS indicate that annealing can increase the grain size and improve the connectivity between PEDOT and PSS particles, and cause thermal degradation at the same time, which leads to the rise in short-circuit current density (I_sc) up to 160 ℃ and the dropoff in I_sc after annealing at 200 ℃.

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Non-recessed-gate quasi-E-mode double heterojunction AlGaN/GaN high electron mobility transistor with high breakdown voltage

Mi Min-Han, Zhang Kai, Chen Xing, Zhao Sheng-Lei, Wang Chong, Zhang Jin-Cheng, Ma Xiao-Hua, Hao Yue

Chin. Phys. B, 2014, 23 (7): 077304 doi: 10.1088/1674-1056/23/7/077304
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[PDF 433 KB] (Downloads:500)

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A non-recessed-gate quasi-E-mode double heterojunction AlGaN/GaN high electron mobility transistor (quasi-E-DHEMT) with a thin barrier, high breakdown voltage and good performance of drain induced barrier lowering (DIBL) was presented. Due to the metal organic chemical vapor deposition (MOCVD) grown 9-nm undoped AlGaN barrier, the effect that the gate metal depleted the two-dimensiomal electron gas (2DEG) was greatly impressed. Therefore, the density of carriers in the channel was nearly zero. Hence, the threshold voltage was above 0 V. Quasi-E-DHEMT with 4.1-μm source-to-drain distance, 2.6-μm gate-to-drain distance, and 0.5-μm gate length showed a drain current of 260 mA/mm. The threshold voltage of this device was 0.165 V when the drain voltage was 10 V and the DIBL was 5.26 mV/V. The quasi-E-DHEMT drain leakage current at a drain voltage of 146 V and a gate voltage of -6 V was below 1 mA/mm. This indicated that the hard breakdown voltage was more than 146 V.

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Effect of alumina thickness on Al₂O₃/InP interface with post deposition annealing in oxygen ambient

Yang Zhuo, Yang Jing-Zhi, Huang Yong, Zhang Kai, Hao Yue

Chin. Phys. B, 2014, 23 (7): 077305 doi: 10.1088/1674-1056/23/7/077305
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[PDF 297 KB] (Downloads:465)

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In this paper, the effect of alumina thickness on Al₂O₃/InP interface with post deposition annealing (PDA) in the oxygen ambient is studied. Atomic layer deposited (ALD) Al₂O₃ films with four different thickness values (5 nm, 7 nm, 9 nm, 11 nm) are deposited on InP substrates. The capacitance-voltage (C-V) measurement shows a negative correlation between the alumina thickness and the frequency dispersion. The X-ray photoelectronspectroscopy (XPS) data present significant growth of indium-phosphorus oxide near the Al₂O₃/InP interface, which indicates serious oxidation of InP during the oxygen annealing. The hysteresis curve shows an optimum thickness of 7 nm after PDA in an oxygen ambient at 500 ℃ for 10 min. It is demonstrated that both sides of the interface are impacted by oxygen during post deposition annealing. It is suggested that the final state of the interface is of reduced positively charged defects on Al₂O₃ side and oxidized InP, which degrades the interface.

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A low specific on-resistance SOI LDMOS with a novel junction field plate

Luo Yin-Chun, Luo Xiao-Rong, Hu Gang-Yi, Fan Yuan-Hang, Li Peng-Cheng, Wei Jie, Tan Qiao, Zhang Bo

Chin. Phys. B, 2014, 23 (7): 077306 doi: 10.1088/1674-1056/23/7/077306
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[PDF 451 KB] (Downloads:514)

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A low specific on-resistance SOI LDMOS with a novel junction field plate (JFP) is proposed and investigated theoretically. The most significant feature of the JFP LDMOS is a PP-N junction field plate instead of a metal field plate. The unique structure not only yields charge compensation between the JFP and the drift region, but also modulates the surface electric field. In addition, a trench gate extends to the buried oxide layer (BOX) and thus widens the vertical conduction area. As a result, the breakdown voltage (BV) is improved and the specific on-resistance (R_on,sp) is decreased significantly. It is demonstrated that the BV of 306 V and the R_on,sp of 7.43 mΩ · cm² are obtained for the JFP LDMOS. Compared with those of the conventional LDMOS with the same dimensional parameters, the BV is improved by 34.8%, and the R_on,sp is decreased by 56.6% simultaneously. The proposed JFP LDMOS exhibits significant superiority in terms of the trade-off between BV and R_on,sp. The novel JFP technique offers an alternative technique to achieve high blocking voltage and large current capacity for power devices.

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High dV/dt immunity MOS controlled thyristor using a double variable lateral doping technique for capacitor discharge applications

Chen Wan-Jun, Sun Rui-Ze, Peng Chao-Fei, Zhang Bo

Chin. Phys. B, 2014, 23 (7): 077307 doi: 10.1088/1674-1056/23/7/077307
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[PDF 870 KB] (Downloads:506)

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An analysis model of the dV/dt capability for a metal-oxide-semiconductor (MOS) controlled thyristor (MCT) is developed. It is shown that, in addition to the P-well resistance reported previously, the existence of the OFF-FET channel resistance in the MCT may degrade the dV/dt capability. Lower P-well and N-well dosages in the MCT are useful in getting a lower threshold voltage of OFF-FET and then a higher dV/dt immunity. However, both dosages are restricted by the requirements for the blocking property and the forward conduction capability. Thus, a double variable lateral doping (DVLD) technique is proposed to realize a high dV/dt immunity without any sacrifice in other properties. The accuracy of the developed model is verified by comparing the obtained results with those from simulations. In addition, this DVLD MCT features mask-saving compared with the conventional MCT fabrication process. The excellent device performance, coupled with the simple fabrication, makes the proposed DVLP MCT a promising candidate for capacitor discharge applications.

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Exotic electronic states in the world of flat bands：From theory to material

Liu Zheng, Liu Feng, Wu Yong-Shi

Chin. Phys. B, 2014, 23 (7): 077308 doi: 10.1088/1674-1056/23/7/077308
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[PDF 1690 KB] (Downloads:1035)

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It has long been noticed that special lattices contain single-electron flat bands (FB) without any dispersion. Since the kinetic energy of electrons is quenched in the FB, this highly degenerate energy level becomes an ideal platform to achieve strongly correlated electronic states, such as magnetism, superconductivity, and Wigner crystal. Recently, the FB has attracted increasing interest because of the possibility to go beyond the conventional symmetry-breaking phases towards topologically ordered phases, such as lattice versions of fractional quantum Hall states. This article reviews different aspects of FBs in a nutshell. Starting from the standard band theory, we aim to bridge the frontier of FBs with the textbook solidstate physics. Then, based on concrete examples, we show the common origin of FBs in terms of destructive interference, and discuss various many-body phases associated with such a singular band structure. In the end, we demonstrate real FBs in quantum frustrated materials and organometallic frameworks.

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Formation of epitaxial Tl₂Ba₂Ca₂Cu₃O₁₀ superconducting films by dc-magnetron sputtering and triple post-annealing method

Xie Wei, Wang Pei, Ji Lu, Ge De-Yong, Du Jia-Nan, Gao Xiao-Xin, Liu Xin, Song Feng-Bin, Hu Lei, Zhang Xu, He Ming, Zhao Xin-Jie

Chin. Phys. B, 2014, 23 (7): 077401 doi: 10.1088/1674-1056/23/7/077401
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[PDF 1147 KB] (Downloads:357)

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For obtaining pure phase Tl₂Ba₂Ca₂Cu₃O₁₀ (Tl-2223) films with good superconducting properties, the growth technique is improved by dc magnetron sputtering and a triple post-annealing process. The triple post-annealing process comprises annealing twice in argon and once in oxygen at different temperatures. In the first low-temperature annealing phase in argon, Tl₂Ba₂CaCu₂O₈ (Tl-2212) is obtained to effectively minimize evaporation in the next step. With the increase of temperature in the second annealing stage in argon, the previously prepared Tl-2212 inter-phase is converted into Tl-2223 phase. An additional annealing in oxygen is also adopted to improve the properties of Tl-2223 films, each containing an optimal oxygen content value. The results of X-ray diffraction (XRD) θ -2θ scans, ω scans and rotational ø scans show that each of the Tl-2223 films has a high phase purity and an epitaxial structure. Smooth films are observed by scanning electron microscopy (SEM). The critical temperatures T_c of the films are measured to be about 120 K and the critical current densities J_c can reach 4.0 MA/cm² at 77 K at self field.

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Modulation of magnetic properties and enhanced magnetoelectric effects in MnW_1-xMo_xO₄ compounds ^Hot! Suggested by editors

Fang Yong, Zhou Wei-Ping, Song Yu-Quan, Lü Li-Ya, Wang Dun-Hui, Du You-Wei

Chin. Phys. B, 2014, 23 (7): 077502 doi: 10.1088/1674-1056/23/7/077502
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[PDF 1141 KB] (Downloads:421)

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In this letter, we investigate the magnetic and ferroelectric properties of polycrystalline MnW_1-xMo_xO₄ (x = 0, 0.05, 0.10, 0.20) compounds. The substitution of nonmagnetic Mo⁶⁺ ions for W⁶⁺ ions modifies the magnetic transition temperatures of MnW_1-xMo_xO₄ by changing the Mn-O-Mn bond. As a result, distinct ferroelectric properties and enhanced magnetoelectric effects are observed in Mo⁶⁺-doped MnWO₄ compounds. The effects of substitution of Mo⁶⁺ ions on magnetic properties and magnetoelectric coupling are discussed.

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Substituting Al for Fe in Pr(Al_xFe_1-x)_1.9 alloys：Effects on magnetic and magnetostrictive properties Suggested by editors

Tang Yan-Mei, Chen Le-Yi, Wei Jun, Tang Shao-Long, Du You-Wei

Chin. Phys. B, 2014, 23 (7): 077503 doi: 10.1088/1674-1056/23/7/077503
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[PDF 313 KB] (Downloads:280)

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The magnetostrictive effects of substituting Al for Fe in Pr(Al_xFe_1-x)_1.9 (x=0.0, 0.02, 0.05, 0.10) alloys between 5 K and 300 K were investigated. The substitution decreases the Curie temperature and the value of λ₁₁₁. Fortunately, the substitution slightly increases the magnetostriction in a low magnetic field, which imbues these materials with potential advantages for applications. Rotation of the easy magnetization direction (EMD) from [111] to [100] in the Pr(Al_0.02Fe_0.98)_1.9 alloy as temperature decreases was detected by step scanned XRD reflections.

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Degradation of ferroelectric and weak ferromagnetic properties of BiFeO₃ films due to the diffusion of silicon atoms

Xiao Ren-Zheng, Zhang Zao-Di, Vasiliy O. Pelenovich, Wang Ze-Song, Zhang Rui, Li Hui, Liu Yong, Huang Zhi-Hong, Fu De-Jun

Chin. Phys. B, 2014, 23 (7): 077504 doi: 10.1088/1674-1056/23/7/077504
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[PDF 1006 KB] (Downloads:986)

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Crystalline BiFeO₃ (BFO) films each with a crystal structure of a distorted rhombohedral perovskite are characterized by X-ray diffraction (XRD) and high-resolution electron microscopy (HRTEM). The diffusion of silicon atoms from the substrate into the BiFeO₃ film is detected by Rutherford backscattering spectrometry (RBS). The element analysis is performed by energy dispersive X-ray spectroscopy (EDS). Simulation results of RBS spectrum show a visualized distribution of silicon. X-ray photoelectron spectroscopy (XPS) indicates that a portion of silica is formed in the diffusion process of silicon atoms. Ferroelectric and weak ferromagnetic properties of the BFO films are degraded due to the diffusion of silicon atoms. The saturation magnetization decreases from 6.11 down to 0.75 emu/g, and the leakage current density increases from 3.8 × 10^-4 up to 7.1 × 10^-4 A/cm^-2.

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An electron spin resonance study of Eu doping effect in La_4/3Sr_5/3Mn₂O₇ single crystal Suggested by editors

He Li-Min, Ji Yu, Wu Hong-Ye, Xu Bao, Sun Yun-Bin, Zhang Xue-Feng, Lu Yi, Zhao Jian-Jun

Chin. Phys. B, 2014, 23 (7): 077601 doi: 10.1088/1674-1056/23/7/077601
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[PDF 311 KB] (Downloads:387)

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The effect of Eu³⁺ ion doping in the La sites of single-crystal La_4/3Sr_5/3Mn₂O₇ was investigated. Electron spin resonance (ESR) was applied to La_4/3Sr_5/3Mn₂O₇ and (La_0.8Eu_0.2)_4/3Sr_5/3Mn₂O₇ single crystals. A phase separation and phase transitions were observed from the ESR spectra data. Between 350 K and 300 K, both paramagnetic resonance (PMR) and anisotropic ferromagnetic resonance (FMR) lines were observed in the ab plane and the c axis direction, suggesting a coexistence of the paramagnetic (PM) phase and the ferromagnetic (FM) phase. The magnetization measurement reveals a spin-glass-like behavior in single-crystal (La_0.8Eu_0.2)_4/3Sr_5/3Mn₂O₇ below the temperature of spin freezing T_f (～ 29.5 K).

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What has been measured by reflection magnetic circular dichroism in Ga_1-xMn_xAs/GaAs structures? ^Hot! Suggested by editors

He Zhen-Xin, Zheng Hou-Zhi, Huang Xue-Jiao, Wang Hai-Long, Zhao Jian-Hua

Chin. Phys. B, 2014, 23 (7): 077801 doi: 10.1088/1674-1056/23/7/077801
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[PDF 319 KB] (Downloads:379)

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An explicit expression of reflection magnetic circular dichroism (R_MCD) has been derived, taking into account the interference effect that arises from multiple internal reflections in an air/Ga_1-xMn_xAs/GaAs dielectric layered system. It unambiguously shows that the R_MCD signal is composed by three terms. In addition to the conventional term, which is sufficient in the absence of interference, an oscillatory term is required. Both of them are related to the imaginary part ε"_xy of the off-diagonal element of the dielectric tensor. One also becomes aware that in this case R_MCD is not actually determined only by the imaginary part ε"_xy of the off-diagonal element of the dielectric tensor, as has been widely accepted. In fact, the real part ε'_xy of the off-diagonal element will substantially mix into the measured R_MCD results by another oscillatory cosθ form. It can even reverse the sign of R_MCD, when the Ga_1-xMn_xAs layer becomes thicker. The main aspects of these predictions were used to reasonably explain the R_MCD results measured in three different types of samples. Our work will bring about a reconsideration of how to correctly explain R_MCD results.

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Pure blue and white light electroluminescence in a multilayer organic light-emitting diode using a new blue emitter Suggested by editors

Wei Na, Guo Kun-Ping, Zhou Peng-Chao, Yu Jian-Ning, Wei Bin, Zhang Jian-Hua

Chin. Phys. B, 2014, 23 (7): 077802 doi: 10.1088/1674-1056/23/7/077802
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[PDF 2175 KB] (Downloads:769)

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We characterized the 6,12-bis{[N-(3,4-dimethylphenyl)-N-(2,4,5-trimethylphenyl)]}amino chrysene (BmPAC), which has been proven to be a blue fluorescent emission with high EL efficiency. The blue fluorescent device exhibits good performance with an external quantum efficiency of 5.8% and current efficiency of 8.9 cd/A, respectively. Using BmPAC, we also demonstrate a hybrid phosphorescence/fluorescence white organic light-emitting device (WOLED) with high efficiency of 36.3 cd/A. In order to improve the relative intensity of blue light, we plus a blue light-emitting layer (BEML) in front of the orange light emitting layer (YEML) to take advantage of the excess singlet excitons. With the new emitting layer of BEML/YEML/BEML, we demonstrate the fluorescence/phosphorescence/fluorescence WOLED exhibits good performance with a current efficiency of 47 cd/A and an enhanced relative intensity of blue light.

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Self-organized voids revisited：Experimental verification of the formation mechanism Suggested by editors

Song Juan, Ye Jun-Yi, Qian Meng-Di, Luo Fang-Fang, Lin Xian, Bian Hua-Dong, Dai Ye, Ma Guo-Hong, Chen Qing-Xi, Jiang Yan, Zhao Quan-Zhong, Qiu Jian-Rong

Chin. Phys. B, 2014, 23 (7): 077901 doi: 10.1088/1674-1056/23/7/077901
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[PDF 1303 KB] (Downloads:363)

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We conduct several experiments to further clarify the formation mechanism of a self-organized void array induced by a single laser beam, including energy-related experiments, refractive-index-contrast-related experiments, depth-related experiments, and effective-numerical-aperture experiment. These experiments indicate that the interface spherical aberration is indeed responsible for the formation of void arrays.

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Microwave absorption properties of a double-layer absorber based on nanocomposite BaFe₁₂O₁₉/α -Fe and nanocrystalline α -Fe microfibers Suggested by editors

Shen Xiang-Qian, Liu Hong-Bo, Wang Zhou, Qian Xin-Ye, Jing Mao-Xiang, Yang Xin-Chun

Chin. Phys. B, 2014, 23 (7): 078101 doi: 10.1088/1674-1056/23/7/078101
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[PDF 557 KB] (Downloads:467)

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The nanocomposite BaFe₁₂O₁₉/α -Fe and nanocrystalline α -Fe microfibers with diameters of 1-5 μm, high aspect ratios and large specific areas are prepared by the citrate gel transformation and reduction process. The nanocomposite BaFe₁₂O₁₉/α -Fe microfibers show some exchange-coupling interactions largely arising from the magnetization hard (BaFe₁₂O₁₉) and soft (α -Fe) nanoparticles. For the microwave absorptions, the double-layer structures consisting of the nanocomposite BaFe₁₂O₁₉/α -Fe and α -Fe microfibers each exhibit a wide band and strong absorption behavior. When the nanocomposite BaFe₁₂O₁₉/α -Fe microfibers are used as a matching layer of 2.3 mm in thickness and α -Fe microfibers as an absorbing layer of 1.2 mm in thickness, the optimal reflection loss (RL) achieves -47 dB at 15.6 GHz, the absorption bandwidth is about 12.7 GHz ranging from 5.3 to 18 GHz, exceeding -20 dB, which covers 72.5% C-band (4.2-8.2 GHz) and whole X-band (8.2-12.4 GHz) and K_u-band (12.4-18 GHz). The enhanced absorption properties of these double-layer absorbers are mainly ascribed to the improvement in impedance matching ability and microwave multi-reflection largely resulting from the dipolar polarization, interfacial polarization, exchange-coupling interaction, and small size effect.

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Improved interfacial and electrical properties of GaSb metal oxide semiconductor devices passivated with acidic (NH₄)₂S solution

Zhao Lian-Feng, Tan Zhen, Wang Jing, Xu Jun

Chin. Phys. B, 2014, 23 (7): 078102 doi: 10.1088/1674-1056/23/7/078102
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[PDF 879 KB] (Downloads:363)

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Surface passivation with acidic (NH₄)₂S solution is shown to be effective in improving the interfacial and electrical properties of HfO₂/GaSb metal oxide semiconductor devices. Compared with control samples, the samples treated with acidic (NH₄)₂S solution show great improvements in gate leakage current, frequency dispersion, border trap density, and interface trap density. These improvements are attributed to the enhancing passivation of the substrates, according to analysis from the perspective of chemical mechanism, X-ray photoelectron spectroscopy, and high-resolution cross-sectional transmission electron microscopy.

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Hybrid phase-locked loop with fast locking time and low spur in a 0.18-μm CMOS process

Zhu Si-Heng, Si Li-Ming, Guo Chao, Shi Jun-Yu, Zhu Wei-Ren

Chin. Phys. B, 2014, 23 (7): 078401 doi: 10.1088/1674-1056/23/7/078401
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We propose a novel hybrid phase-locked loop (PLL) architecture for overcoming the trade-off between fast locking time and low spur. To reduce the settling time and meanwhile suppress the reference spurs, we employ a wide-band single-path PLL and a narrow-band dual-path PLL in a transient state and a steady state, respectively, by changing the loop bandwidth according to the gain of voltage controlled oscillator (VCO) and the resister of the loop filter. The hybrid PLL is implemented in a 0.18-μm complementary metal oxide semiconductor (CMOS) process with a total die area of 1.4× 0.46 mm². The measured results exhibit a reference spur level of lower than -73 dB with a reference frequency of 10 MHz and a settling time of 20 μs with 40 MHz frequency jump at 2 GHz. The total power consumption of the hybrid PLL is less than 27 mW with a supply voltage of 1.8 V.

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Four-dimensional parameter estimation of plane waves using swarming intelligence

Fawad Zaman, Ijaz Mansoor Qureshi, Fahad Munir, Zafar Ullah Khan

Chin. Phys. B, 2014, 23 (7): 078402 doi: 10.1088/1674-1056/23/7/078402
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This paper proposes an efficient approach for four-dimensional (4D) parameter estimation of plane waves impinging on a 2-L shape array. The 4D parameters include amplitude, frequency and the two-dimensional (2D) direction of arrival, namely, azimuth and elevation angles. The proposed approach is based on memetic computation, in which the global optimizer, particle swarm optimization is hybridized with a rapid local search technique, pattern search. For this purpose, a new multi-objective fitness function is used. This fitness function is the combination of mean square error and the correlation between the normalized desired and estimated vectors. The proposed hybrid scheme is not only compared with individual performances of particle swarm optimization and pattern search, but also with the performance of the hybrid genetic algorithm and that of the traditional approach. A large number of Monte-Carlo simulations are carried out to validate the performance of the proposed scheme. It gives promising results in terms of estimation accuracy, convergence rate, proximity effect and robustness against noise.

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Image reconstruction from few views by l₀-norm optimization

Sun Yu-Li, Tao Jin-Xu

Chin. Phys. B, 2014, 23 (7): 078703 doi: 10.1088/1674-1056/23/7/078703
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In the medical computer tomography (CT) field, total variation (TV), which is the l₁-norm of the discrete gradient transform (DGT), is widely used as regularization based on the compressive sensing (CS) theory. To overcome the TV model's disadvantageous tendency of uniformly penalizing the image gradient and over smoothing the low-contrast structures, an iterative algorithm based on the l₀-norm optimization of the DGT is proposed. In order to rise to the challenges introduced by the l₀-norm DGT, the algorithm uses a pseudo-inverse transform of DGT and adapts an iterative hard thresholding (IHT) algorithm, whose convergence and effective efficiency have been theoretically proven. The simulation demonstrates our conclusions and indicates that the algorithm proposed in this paper can obviously improve the reconstruction quality.

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Row-column visibility graph approach to two-dimensional landscapes

Xiao Qin, Pan Xue, Li Xin-Li, Mutua Stephen, Yang Hui-Jie, Jiang Yan, Wang Jian-Yong, Zhang Qing-Jun

Chin. Phys. B, 2014, 23 (7): 078904 doi: 10.1088/1674-1056/23/7/078904
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A new concept, called the row-column visibility graph, is proposed to map two-dimensional landscapes to complex networks. A cluster coverage is introduced to describe the extensive property of node clusters on a Euclidean lattice. Graphs mapped from fractals generated with the probability redistribution model behave scale-free. They have pattern-induced hierarchical organizations and comparatively much more extensive structures. The scale-free exponent has a negative correlation with the Hurst exponent, however, there is no deterministic relation between them. Graphs for fractals generated with the midpoint displacement model are exponential networks. When the Hurst exponent is large enough (e.g., H>0.5), the degree distribution decays much more slowly, the average coverage becomes significant large, and the initially hierarchical structure at H<0.5 is destroyed completely. Hence, the row-column visibility graph can be used to detect the pattern-related new characteristics of two-dimensional landscapes.

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Experimental verification of the parasitic bipolar amplification effect in PMOS single event transients

He Yi-Bai, Chen Shu-Ming

Chin. Phys. B, 2014, 23 (7): 079401 doi: 10.1088/1674-1056/23/7/079401
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The contribution of parasitic bipolar amplification to SETs is experimentally verified using two P-hit target chains in the normal layout and in the special layout. For PMOSs in the normal layout, the single-event charge collection is composed of diffusion, drift, and the parasitic bipolar effect, while for PMOSs in the special layout, the parasitic bipolar junction transistor cannot turn on. Heavy ion experimental results show that PMOSs without parasitic bipolar amplification have a 21.4% decrease in the average SET pulse width and roughly a 40.2% reduction in the SET cross-section.