Table of contents

15 January 2012, Volume 21 Issue 1 Previous issue    Next issue

GENERAL

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Prolongation structure for nonlinear integrable couplings of a KdV soliton hierarchy Yu Fa-Jun(于发军) Chin. Phys. B, 2012, 21 (1):  010201.  DOI: 10.1088/1674-1056/21/1/010201 Abstract ( 1317 )   PDF (102KB) ( 886 )   In this paper, a new nonlinear integrable coupling system of the soliton hierarchy is presented. From the Lax pairs, the coupled KdV equations are constructed successfully. Based on the prolongation method of Wahlquist and Estabrook, we study the prolongation structure of the nonlinear integrable couplings of the KdV equation.

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Existence of periodic solutions for the nonlinear functional differential equation in the lossless transmission line model Wang Na(汪娜) Chin. Phys. B, 2012, 21 (1):  010202.  DOI: 10.1088/1674-1056/21/1/010202 Abstract ( 1392 )   PDF (107KB) ( 700 )   We study a time delay equation for the lossless transmission line model. Under suitable conditions, by using the continuation theorem of the coincidence degree theory, the existence of the periodic solution for the nonlinear functional differential equation is obtained.

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Synchronization of the minimal models of bursting neurons coupled by delayed chemical or electrical synapses Nebojša Vasović, Nikola Burić, Kristina Todorović, and Ines Grozdanović Chin. Phys. B, 2012, 21 (1):  010203.  DOI: 10.1088/1674-1056/21/1/010203 Abstract ( 1171 )   PDF (418KB) ( 729 )   The minimal two-dimensional model of bursting neuronal dynamics is used to study the influence of time-delay on the properties of synchronization of bursting neurons. Generic properties of bursting and dependence of the stability of synchronization on the time-lag and the strength of coupling are described, and compared with the two common types of synaptical coupling, i.e., time-delayed chemical and electrical synapses.

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Asymptotic solving method for a sea–air oscillator model of atmospheric physics Lin Wan-Tao(林万涛), Lin Yi-Hua(林一骅), and Mo Jia-Qi(莫嘉琪) Chin. Phys. B, 2012, 21 (1):  010204.  DOI: 10.1088/1674-1056/21/1/010204 Abstract ( 1364 )   PDF (155KB) ( 570 )   In this paper, a class of coupled system for the El Ni?o/La Ni?a southern oscillation (ENSO) atmospheric physics oscillation model is considered. We propose an ENSO atmospheric physics model using a method from the asymptotic theory. It is indicated from the results that the asymptotic method can be used for analyzing the sea surface temperature anomaly and the thermocline depth anomaly of the atmosphere-ocean oscillation for the ENSO model in the equatorial Pacific.

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Epidemic spreading in scale-free networks including the effect of individual vigilance Gong Yong-Wang(巩永旺), Song Yu-Rong(宋玉蓉), and Jiang Guo-Ping(蒋国平) Chin. Phys. B, 2012, 21 (1):  010205.  DOI: 10.1088/1674-1056/21/1/010205 Abstract ( 1772 )   PDF (163KB) ( 860 )   In this paper, we study the epidemic spreading in scale-free networks and propose a new susceptible-infected- recovered (SIR) model that includes the effect of individual vigilance. In our model, the effective spreading rate is dynamically adjusted with the time evolution at the vigilance period. Using the mean-field theory, an analytical result is derived. It shows that individual vigilance has no effect on the epidemic threshold. The numerical simulations agree well with the analytical result. Furthermore, we investigate the effect of individual vigilance on the epidemic spreading speed. It is shown that individual vigilance can slow the epidemic spreading speed effectively and delay the arrival of peak epidemic infection.

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Element-free Galerkin (EFG) method for analysis of the time-fractional partial differential equations Ge Hong-Xia(葛红霞), Liu Yong-Qing(刘永庆), and Cheng Rong-Jun(程荣军) Chin. Phys. B, 2012, 21 (1):  010206.  DOI: 10.1088/1674-1056/21/1/010206 Abstract ( 1608 )   PDF (519KB) ( 1304 )   The present paper deals with the numerical solution of time-fractional partial differential equations using the element-free Galerkin (EFG) method, which is based on the moving least-square approximation. Compared with numerical methods based on meshes, the EFG method for time-fractional partial differential equations needs only scattered nodes instead of meshing the domain of the problem. It neither requires element connectivity nor suffers much degradation in accuracy when nodal arrangements are very irregular. In this method, the first-order time derivative is replaced by the Caputo fractional derivative of order $\alpha$ (0<$\alpha$ ≤1). The Galerkin weak form is used to obtain the discrete equations, and the essential boundary conditions are enforced by the penalty method. Several numerical examples are presented and the results we obtained are in good agreement with the exact solutions.

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Maximal and total skew information of three-qubit system obtained using nonlinear interaction models Sun Hong-Gui(孙红贵), Zhang Li-Hua(章礼华), Liu Wan-Fang(刘万芳), and Li Chun-Jie(李春杰) Chin. Phys. B, 2012, 21 (1):  010301.  DOI: 10.1088/1674-1056/21/1/010301 Abstract ( 1313 )   PDF (566KB) ( 603 )   Both the maximal and the total skew information have been studied. For a three-qubit system implemented in three nonlinear interaction models, we give the exact state vector at any time t. Based on this, we give the maximal and the total skew information. It is found that they have the same form and their evolution periods are dependent on the energy difference between the ground state and the second excited state in these models. The maximal skew information is always in the (Sx,Sy) plane. We give the condition for the occurrence of |GHZ$\rangle$Sy, in which they can reach the extreme values of 9/4 and 15/4, respectively. In three different decoherence channels, two kinds of information and the concurrence are calculated. We find that the phenomenon of the concurrence of sudden death occurs, but the above two kinds of information do not die suddenly. In the phase-damping channel, the two kinds of information will not be lost completely.

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New theorem relating two-mode entangled tomography to two-mode Fresnel operator Xie Chuan-Mei(谢传梅) and Fan Hong-Yi(范洪义) Chin. Phys. B, 2012, 21 (1):  010302.  DOI: 10.1088/1674-1056/21/1/010302 Abstract ( 1310 )   PDF (158KB) ( 686 )   Based on the Fan-Hu's formalism, i.e., the tomogram of two-mode quantum states can be considered as the module square of the states' wave function in the intermediate representation, which is just the eigenvector of the Fresnel quadrature phase, we derive a new theorem for calculating the quantum tomogram of two-mode density operators, i.e., the tomogram of a two-mode density operator is equal to the marginal integration of the classical Weyl correspondence function of F2+ρF2, where F2 is the two-mode Fresnel operator. An application of the theorem in evaluating the tomogram of an optical chaotic field is also presented.

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Asymptotic iteration approach to supersymmetric bistable potentials H. Ciftci, O. őzer, and P. Roy Chin. Phys. B, 2012, 21 (1):  010303.  DOI: 10.1088/1674-1056/21/1/010303 Abstract ( 1320 )   PDF (103KB) ( 640 )   We examine quasi exactly solvable bistable potentials and their supersymmetric partners within the framework of the asymptotic iteration method (AIM). It is shown that the AIM produces excellent approximate spectra and that some×it is found to be more useful to use the partner potential for computation. We also discuss the direct application of the AIM to the Fokker-Planck equation.

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Entanglement transfer via two arrays of coupled resonator waveguides Zhang Ye-Qi(张业奇) and Xu Jing-Bo(许晶波) Chin. Phys. B, 2012, 21 (1):  010304.  DOI: 10.1088/1674-1056/21/1/010304 Abstract ( 1250 )   PDF (231KB) ( 713 )   We propose a scheme for transferring entanglement through two independent arrays of coupled resonator waveguides, where a three-level atom is embedded in each resonator. We investigate the entanglement dynamics of the transferred state. The influence of initial states and applied lasers on the entanglement sudden death phenomenon is also discussed. Furthermore, we study the dynamics of pairwise quantum correlations measured by the quantum discord.

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Four-mode coherent-entangled state and its application Li Hong-Qi(李洪奇), Ren Ting-Qi(任廷琦), Zhang Yun-Hai(张运海), and Xu Xing-Lei(徐兴磊) Chin. Phys. B, 2012, 21 (1):  010305.  DOI: 10.1088/1674-1056/21/1/010305 Abstract ( 1250 )   PDF (130KB) ( 630 )   A new kind of four-mode continuous variable coherent-entangled state is proposed in the Fock space by using the technique of integration within an ordered product, which exhibits both the properties of a coherent state and an entangled state, and spans a complete and orthonormal representation. The conjugate state of the four-mode continuous variable coherent-entangled state is derived by using the Fourier transformation. Moreover, a simple experimental protocol of generating a four-mode continuous variable coherent-entangled state is proposed by using beam splitters. As applications of this four-mode continuous variable coherent-entangled state, a four-mode entangled state and a four-mode squeezing-Fresnel operator are constructed.

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Partial evolution based local adiabatic quantum search Sun Jie(孙杰), Lu Song-Feng(路松峰), Liu Fang(刘芳), and Yang Li-Ping(杨莉萍) Chin. Phys. B, 2012, 21 (1):  010306.  DOI: 10.1088/1674-1056/21/1/010306 Abstract ( 1347 )   PDF (102KB) ( 607 )   Recently, Zhang and Lu provided a quantum search algorithm based on partial adiabatic evolution, which beats the time bound of local adiabatic search when the number of marked items in the unsorted database is larger than one. Later, they found that the above two adiabatic search algorithms had the same time complexity when there is only one marked item in the database. In the present paper, following the idea of Roland and Cerf [Roland J and Cerf N J 2002 Phys. Rev. A 65 042308], if within the small symmetric evolution interval defined by Zhang et al., a local adiabatic evolution is performed instead of the original “global” one, this “new” algorithm exhibits slightly better performance, although they are progressively equivalent with M increasing. In addition, the proof of the optimality for this partial evolution based local adiabatic search when M=1 is also presented. Two other special cases of the adiabatic algorithm obtained by appropriately tuning the evolution interval of partial adiabatic evolution based quantum search, which are found to have the same phenomenon above, are also discussed.

RAPID COMMUNICATION

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Cryptanalysis and improvement of a quantum secret sharing scheme based on $\chi$-type entangled states Zhu Zhen-Chao(朱珍超), Zhang Yu-Qing(张玉清), and Fu An-Min(付安民) Chin. Phys. B, 2012, 21 (1):  010307.  DOI: 10.1088/1674-1056/21/1/010307 Abstract ( 1620 )   PDF (105KB) ( 795 )   In the paper [2010 Chin. Phys. B 19 050306], Yang et al. put forward a novel three-party quantum secret sharing protocol of secure direct communication based on $\chi$-type entangled states, they claimed that the scheme is secure. However, in this paper, we study the security of the protocol and find that it is insecure. Applying intercept and resend attack, the agent Bob can obtain Alice's secret without the help from the other agent Charlie. In the end, we give our effective modification for its improvement.

GENERAL

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High-fidelity quantum memory realized via Wigner crystals of polar molecules Xue Peng(薛鹏) and Wu Jian-Zhi(午剑智) Chin. Phys. B, 2012, 21 (1):  010308.  DOI: 10.1088/1674-1056/21/1/010308 Abstract ( 1382 )   PDF (387KB) ( 702 )   The collective excitations of spin states of an ensemble of polar molecules are studied as a candidate for high-fidelity quantum memory. To avoid the collisional properties of the molecules, they are arranged in dipolar crystals under one or two dimensional trapping conditions. We calculate the lifetime of the quantum memory by identifying the dominant decoherence mechanisms and estimating their effects on gate operations when a molecular ensemble qubit is transferred to a microwave cavity.

RAPID COMMUNICATION

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Spontaneous symmetry breaking of a Bose–Fermi mixture in a two-dimensional double-well potential Wang Yuan-Sheng(王元生), Yan Pei-Gen(颜培根), Li Bin(李彬), and Liu Xue-Shen(刘学深) Chin. Phys. B, 2012, 21 (1):  010309.  DOI: 10.1088/1674-1056/21/1/010309 Abstract ( 1279 )   PDF (780KB) ( 841 )   We study the spontaneous symmetry breaking of a superfluid Bose-Fermi mixture in a two-dimensional double-well potential. The mixture is described by a set of coupled Gross-Pitaevskii equations. The symmetry breaking phenomenon is demonstrated in the two-dimensional double-well potential in the mixture. The results are summarized in the phase diagrams of the mixture particle numbers, which are divided into symmetric and asymmetric regions by the asymmetry ratios. The dynamical pictures of the spontaneous symmetry breaking induced by a gradual transformation of the single-well potential into a double-well one are also illustrated. The properties of the quantum degenerate mixture are explored using the realistic parameters for a 40K-87Rb system.

GENERAL

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Energy and momentum of general spherically symmetric frames on the regularizing teleparallelism Gamal G.L. Nashed Chin. Phys. B, 2012, 21 (1):  010401.  DOI: 10.1088/1674-1056/21/1/010401 Abstract ( 1279 )   PDF (134KB) ( 522 )   In the context of the covariant teleparallel framework, we use the 2-form translational momentum to compute the total energy of two general spherically symmetric frames. The first one is characterized by an arbitrary function $H(r)$, which preserves the spherical symmetry and reproduces all the previous solutions, while the other one is characterized by a parameter $\xi$ which ensures  the vanishing of the axial of trace of the torsion. We calculate the total energy by using two procedures, i.e., when the Weitzenböck  connection ${\varGamma_\alpha}^\beta$ is trivial, and show how $H(r)$ and $\xi$ play the role of an inertia that leads the total energy  to be unphysical. Therefore, we take into account ${\varGamma_\alpha}^\beta$ and show that although the spacetimes we use contain an  arbitrary function and one parameter, they have no effect on the form of the total energy and momentum as it should be.

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Oscillating Casimir force between two slabs in a Fermi sea Chen Li-Wei(陈礼炜), Su Guo-Zhen(苏国珍), Chen Jin-Can(陈金灿), and Andresen Bjarne Chin. Phys. B, 2012, 21 (1):  010501.  DOI: 10.1088/1674-1056/21/1/010501 Abstract ( 1370 )   PDF (247KB) ( 489 )   The Casimir effect for two parallel slabs immersed in an ideal Fermi sea is investigated at both zero and nonzero temperatures. It is found that the Casimir effect in a Fermi gas is distinctly different from that in an electromagnetic field or a massive Bose gas. In contrast to the familiar result that the Casimir force decreases monotonically with the increase of the separation L between two slabs in an electromagnetic field and a massive Bose gas, the Casimir force in a Fermi gas oscillates as a function of L. The Casimir force can be either attractive or repulsive, depending sensitively on the magnitude of L. In addition, it is found that the amplitude of the Casimir force in a Fermi gas decreases with the increase of the temperature, which also is contrary to the case in a Bose gas, since the bosonic Casimir force increases linearly with the increase of the temperature in the region T < Tc, where Tc is the critical temperature of the Bose-Einstein condensation.

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Chaos-based encryption for fractal image coding Yuen Ching-Hung(袁正雄) and Wong Kwok-Wo(黄国和) Chin. Phys. B, 2012, 21 (1):  010502.  DOI: 10.1088/1674-1056/21/1/010502 Abstract ( 1457 )   PDF (708KB) ( 1480 )   A chaos-based cryptosystem for fractal image coding is proposed. The Rényi chaotic map is employed to determine the order of processing the range blocks and to generate the keystream for masking the encoded sequence. Compared with the standard approach of fractal image coding followed by the Advanced Encryption Standard, our scheme offers a higher sensitivity to both plaintext and ciphertext at a comparable operating efficiency. The keystream generated by the Rényi chaotic map passes the randomness tests set by the United States National Institute of Standards and Technology, and so the proposed scheme is sensitive to the key.

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Bifurcations and chaos control in discrete small-world networks Li Ning(李宁), Sun Hai-Yi(孙海义), and Zhang Qing-Ling(张庆灵) Chin. Phys. B, 2012, 21 (1):  010503.  DOI: 10.1088/1674-1056/21/1/010503 Abstract ( 1458 )   PDF (2342KB) ( 3246 )   An impulsive delayed feedback control strategy to control period-doubling bifurcations and chaos is proposed. The control method is then applied to a discrete small-world network model. Qualitative analyses and simulations show that under a generic condition, the bifurcations and the chaos can be delayed or eliminated completely. In addition, the periodic orbits embedded in the chaotic attractor can be stabilized.

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Impulsive synchronization of a nonlinear coupled complex network with a delay node Sun Wen (孙文), Chen Zhong(陈忠), and Kang Yu-Hong(康玉红) Chin. Phys. B, 2012, 21 (1):  010504.  DOI: 10.1088/1674-1056/21/1/010504 Abstract ( 1488 )   PDF (243KB) ( 669 )   We investigate the impulsive synchronization of a nonlinear coupled complex network with a delay node. Both delay coupling and non-delay coupling, as well as the symmetrical coupling matrix and the asymmetrical coupling matrix are considered. Based on the comparison theorem of an impulsive differential system, some novel synchronization criteria are derived. Finally, numerical simulations demonstrate the effectiveness of the proposed synchronization criteria.

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Optimization criteria of a Bose Brayton heat engine Wang Hao (汪浩) and Wu Guo-Xing(吴国兴) Chin. Phys. B, 2012, 21 (1):  010505.  DOI: 10.1088/1674-1056/21/1/010505 Abstract ( 1356 )   PDF (183KB) ( 544 )   An irreversible cycle model of the quantum Bose Brayton engine is established, in which finite-time processes and irreversibilities in two adiabatic processes are taken into account. Based on the model, expressions for the power output and the efficiency are derived. By using a numerical computation, the optimal relationship between the power output and the efficiency of an irreversible Bose Brayton engine is obtained. The optimal regions of the power output and the efficiency are determined. It is found that the influences of the irreversibility and the quantum degeneracy on the main performance parameters of the Bose Brayton engine are remarkable. The results obtained in the present paper can provide some new theoretical information for the optimal design and the performance improvement of a real Brayton engine.

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Mixed polarization in determining the film thickness of a silicon sphere by spectroscopic ellipsometry Zhang Ji-Tao(张继涛), Wu Xue-Jian(吴学健), and Li Yan(李岩) Chin. Phys. B, 2012, 21 (1):  010701.  DOI: 10.1088/1674-1056/21/1/010701 Abstract ( 1340 )   PDF (663KB) ( 635 )   The effect of a spherical shape on the measurement result of spectroscopic ellipsometry (SE) is analyzed, and a method to eliminate this effect is proposed. Based on the simulation result of the SE measurement on a silicon sphere by ray tracking, we find that the sphere makes the parallel incident beam of the SE be divergent after reflection, and the measurement error of the SE caused by this phenomenon is explained by the mixed polarization theory. By settling an aperture in front of the detector of the SE, we can almost eliminate the error. For the silicon sphere with a diameter of 94 mm used in the Avogadro project, the thickness error of the oxide layer caused by the spherical shape can be reduced from 0.73 nm to 0.04 nm by using the proposed method. The principle of the method and the results of the experimental verification are presented.

ATOMIC AND MOLECULAR PHYSICS

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Theoretical study on 2s2p6np Rydberg states of Cu19+ ion Zhang Zheng-Rong(张正荣), Cheng Xin-Lu(程新路), Liu Zi-Jiang(刘子江), Yang Jian-Hui(杨建会), and Li Hui-Fang(李慧芳) Chin. Phys. B, 2012, 21 (1):  013101.  DOI: 10.1088/1674-1056/21/1/013101 Abstract ( 1295 )   PDF (124KB) ( 600 )   We report on the calculations of transition wavelengths and weighted oscillator strengths for 2s22p6-2s2p6np (4 ≤ n ≤ 20) electric dipole (E1) transitions of Cu19+ ion. The flexible atomic code (FAC) has been adopted for the calculations. Comparisons are made with the experimental data available, showing that the present results for 4 ≤ n ≤ 6 are more accurate than the previous calculated values. Furthermore, combining the quantum defect theory (QDT) with the transition energies of 2s22p6-2s2p6np, the quantum defects for 2s2p6np Rydberg series of Cu19+ ion are determined. In addition, the energies of any highly excited states (n > 20) for this series can be reliably predicted using the QDT and the given quantum defects. The ionization energies for Cu19+ and Cu20+ ions are also calculated and they excellently accord with previous experimental and calculated values.

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Influence of reagent vibration on the stereodynamics of the Li + HF → LiF + H reaction Li Shu-Juan(李淑娟), Shi Ying(石英), Xie Ting-Xian(解廷献), and Jin Ming-Xing(金明星) Chin. Phys. B, 2012, 21 (1):  013401.  DOI: 10.1088/1674-1056/21/1/013401 Abstract ( 1403 )   PDF (434KB) ( 690 )   We investigate the influence of reagent vibration on the stereodynamics of the title reaction by the quasi-classical trajectory on the Aguado-Paniagua2-potential energy surface developed by Aguado et al. (J. Chem. Phys. 1997 106 1013). The cross sections and reaction probability as functions of the reagent vibration are calculated in the centre-of-mass frame. The product angular distributions of $p(\theta_{\rm r})$, $p(\phi_{\rm r})$, and $p(\theta_{\rm r}, \phi_{\rm r})$, which reflect the vector correlation, are also presented and discussed. The results indicate that the vector properties are sensitively affected by the vibrational excitation.

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KLL dielectronic recombination process of He-like to O-like xenon ions Zhang Deng-Hong(张登红), Shi Ying-Long(师应龙), Jiang Jun(蒋军), Dong Chen-Zhong(董晨钟), and Fumihiro Koike(小池文博) Chin. Phys. B, 2012, 21 (1):  013402.  DOI: 10.1088/1674-1056/21/1/013402 Abstract ( 1684 )   PDF (867KB) ( 834 )   In this work, the KLL dielectronic recombination (DR) processes of highly charged He-like to O-like xenon ions are studied systematically by using a DR program, which is based on the multi-configuration Dirac-Fock (MCDF) method. The KLL DR resonant energies and the corresponding resonant strengths are calculated, asizing especially the effect of the Breit interaction on the DR strengths. The theoretical KLL DR spectra are obtained and compared with the latest experimental results obtained in the Shanghai Electron Beam Ion Trap.

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Motion and acceleration of electrons in high-intensity laser standing waves Zhang Qiu-Ju(张秋菊), Yu Wei(余玮), Luan Shi-Xia(栾仕霞), and Ma Guang-Jin(马光金) Chin. Phys. B, 2012, 21 (1):  013403.  DOI: 10.1088/1674-1056/21/1/013403 Abstract ( 1409 )   PDF (491KB) ( 996 )   The motion and the energy of electrons driven by the ponderomotive force in linearly polarized high-intensity laser standing wave fields are considered. The results show that there exists a threshold laser intensity, above which the motion of electrons incident parallel to the electric field of the laser standing waves undergoes a transition from regulation to chaos. We propose that the huge energy exchange between the electrons and the strong laser standing waves is triggered by inelastic scattering, which is related to the chaos patterns. It is shown that an electron's energy gain of tens of MeV can be realized for a laser intensity of 1020 W/cm2.

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Coupled-channels optical calculation of positron–hydrogen resonances Yu Rong-Mei(于荣梅), Zhou Ya-Jun(周雅君), Jiao Li-Guang(焦利光), and Cheng Yong-Jun(程勇军) Chin. Phys. B, 2012, 21 (1):  013404.  DOI: 10.1088/1674-1056/21/1/013404 Abstract ( 1109 )   PDF (163KB) ( 501 )   An application of the coupled-channels optical method is given for the energy-dependent phenomena of positron-hydrogen resonances below the n=2 excitation threshold. The equivalent local optical potential is used to account for the target polarization and positronium formation. The calculation includes 9 explicitly physical coupled channels. The lowest S-wave resonance energy position and new resonances are found. Angular dependence of the cross section in the resonance region are investigated.

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Total cross sections of positron–sodium scattering at low energies Cheng Yong-Jun(程勇军), Zhou Ya-Jun(周雅君), and Jiao Li-Guang(焦利光) Chin. Phys. B, 2012, 21 (1):  013405.  DOI: 10.1088/1674-1056/21/1/013405 Abstract ( 1288 )   PDF (138KB) ( 686 )   A new calculation for the total cross section of positron-sodium scattering is performed in an energy range down to a few tenths of one electron volt using the coupled-channel optical method. The ionization continuum and the positronium formation channels are included via an equivalent-local complex potential. The role played by the break-up and rearrangement processes in the low energy positron-sodium scattering is also investigated. The total scattering cross section is reported and compared with the available theoretical and experimental data.

CLASSICAL AREAS OF PHENOMENOLOGY

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Energy unidirectional transmission in an asymmetrically finite transmission line Tao Feng(陶锋), Chen Wei-Zhong(陈伟中), Xu Wen(许文), and Du Si-Dan(都思丹) Chin. Phys. B, 2012, 21 (1):  014101.  DOI: 10.1088/1674-1056/21/1/014101 Abstract ( 1339 )   PDF (456KB) ( 739 )   The phenomenon of energy unidirectional transmission is numerically investigated by using a system of two coupled discrete nonlinear electrical transmission lines, each line of the network contains a finite number of cells and has different pass band structures, respectively. Using numerical simulations, we examine the frequency multiplication of the driving frequency and the lattice filtering effect in the line. These lead to the generation of energy unidirectional transmission. In the present work, energy is carried by the second harmonic wave in the pass band. In addition, we also study the dependence of the energy efficiency on the driving amplitude and other parameters of the model, such as the system size and the nonlinear coefficient, by calculation. Furthermore, after detailed numerical simulation, an experimental demonstration is realized. The experimental results agree with those in simulation qualitatively.

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Wavefront correction of Ti:sapphire terawatt laser with varying precision of phase conjugation between deformable mirror and wavefront sensor Yu Liang-Hong(於亮红), Liang Xiao-Yan(梁晓燕), Ren Zhi-Jun(任志君), Wang Li(王利), Xu Yi(许毅), Lu Xiao-Ming(陆效明), and Yu Guo-Hao(于国浩) Chin. Phys. B, 2012, 21 (1):  014201.  DOI: 10.1088/1674-1056/21/1/014201 Abstract ( 1460 )   PDF (296KB) ( 11162 )   The phase conjugation between the deformable mirror and the wavefront sensor in the aberration correction of a terawatt Ti:sapphire laser is studied experimentally and theoretically in this paper. At varying values of phase-conjugation precision, we focus the corresponding beams into spots of the same size of 5.1 μm×5.3 μm with a f/4 parabola in the 32 TW/36 fs Ti:sapphire laser system. The results show that the precision of conjugation can induce an intensity modulation but does not significantly affect the wavefront correction.

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Design of wideband graded-index antireflection coatings at oblique light incidence Zhang Jun-Chao(张俊超), Fang Ming(方明), Jin Yun-Xia(晋云霞), and He Hong-Bo(贺洪波) Chin. Phys. B, 2012, 21 (1):  014202.  DOI: 10.1088/1674-1056/21/1/014202 Abstract ( 1279 )   PDF (243KB) ( 1183 )   We suggest a design method of graded-refractive-index (GRIN) antireflection (AR) coating for s-polarized or p-polarized light at off-normal incidence. The spectrum characteristic of the designed antireflection coating with a quintic effective refractive-index profile for a given state of polarization has been discussed. In addition, the genetic algorithm was used to optimize the refractive index profile of the GRIN antireflection for reducing the mean reflectance of s- and p-polarizations. The average reflectance loss was reduced to only 0.04% by applying optimized GRIN AR coatings onto BK7 glass over the wavelength range from 400 to 800 nm at the incident angle of θ0 =70°.

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Quantum correlations between two non-interacting atoms under the influence of a thermal environment Hu Yao-Hua(胡要花) and Wang Jun-Qiang(王军强) Chin. Phys. B, 2012, 21 (1):  014203.  DOI: 10.1088/1674-1056/21/1/014203 Abstract ( 1263 )   PDF (209KB) ( 878 )   By considering a double Jaynes-Cummings model, we investigate the dynamics of quantum correlations, such as the quantum discord and the entanglement, for two atoms in their respective noisy environments, and study the effect of the purity and the cavity temperature on the quantum correlations. The results show that the entanglement suffers sudden death and revival, however the quantum discord can still reveal the quantum correlations between the two atoms in the region where the entanglement is zero. Moreover, when the temperature of each cavity is high the entanglement dies out in a short time, but the quantum discord still survives for quite a long time. It means that the quantum discord is more resistant to environmental disturbance than the entanglement at higher temperatures.

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Role of phase fluctuation and dephasing in the enhancing continuous variable entanglement of a two-photon coherent beat laser Sintayehu Tesfa Chin. Phys. B, 2012, 21 (1):  014204.  DOI: 10.1088/1674-1056/21/1/014204 Abstract ( 1353 )   PDF (717KB) ( 695 )   A steady state analysis of the nonclassical features and statistical properties of the cavity radiation of a two-photon coherent beat laser is presented. Results show that the degree of two-mode squeezing, detectable entanglement and intensity of the cavity radiation can increase with the deviation of the phase fluctuations of the laser employed in preparing the atoms, but decrease with the increasing rate at which the induced coherence superposition decays. Although it is found that varying the phase fluctuations and dephasing can lead to modification in the quantum features and statistical properties of the radiation, it does not alter the similarity in the nature of the degree of entanglement detectable by the criteria following from Duan-Giedke-Cirac-Zoller and logarithmic negativity in a perceivable manner. Since the intensity and quantum features can be readily enhanced, this system is expected to be a viable source of a strong robust entangled (squeezed) light under various conditions. Moreover, comparison of the mean number of photon pairs with intensity difference shows that the chance of inciting a two-photon process can be enhanced by changing the rate of dephasing and phase fluctuations.

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The population and decay evolution of a qubit under the time-convolutionless master equation Huang Jiang(黄江), Fang Mao-Fa(方卯发), and Liu Xiang(刘翔) Chin. Phys. B, 2012, 21 (1):  014205.  DOI: 10.1088/1674-1056/21/1/014205 Abstract ( 1438 )   PDF (119KB) ( 729 )   We consider the population and decay of a qubit under the electromagnetic environment. Employing the time-convolutionless master equation, we investigate the Markovian and non-Markovian behaviour of the corresponding perturbation expansion. The Jaynes-Cummings model on resonance is investigated. Some figures clearly show the different evolution behaviours. The reasons are interpreted in the paper.

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Characteristics of xenon-lamp pumped pyrromethene 567-doped dye laser based on polymethylmethacrylater Wang Lei(王磊), Chen De-Ying(陈德应), Xia Yuan-Qin(夏元钦) Fan Rong-Wei(樊荣伟), and He Wei-Ming(何伟明) Chin. Phys. B, 2012, 21 (1):  014206.  DOI: 10.1088/1674-1056/21/1/014206 Abstract ( 1290 )   PDF (142KB) ( 714 )   The solid-state medium containing pyrromethene 567 (PM567) in a polymethylmethacrylate polymer host is shown to lase under the flash lamp excitation. The experimental setup is an ordinary industrial product without special design. The bulk transmission losses, the output energy, and the other lasing properties are compared. The medium with the lowest transmission loss, measured to be 0.392 %/cm at 633 nm, gives a laser output of 130 mJ with a slope efficiency of 0.082%.

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Efficient continuous-wave eye-safe region signal output from intra-cavity singly resonant optical parametric oscillator Li Bin(李斌), Ding Xin(丁欣), Sheng Quan(盛泉), Yin Su-Jia(殷苏嘉), Shi Chun-Peng(史春鹏), Li Xue(李雪), Yu Xuan-Yi(禹宣伊), Wen Wu-Qi(温午麒), and Yao Jian-Quan(姚建铨) Chin. Phys. B, 2012, 21 (1):  014207.  DOI: 10.1088/1674-1056/21/1/014207 Abstract ( 1404 )   PDF (1820KB) ( 686 )   We report an efficient continuous-wave (CW) tunable intra-cavity singly resonant optical parametric oscillator based on the multi-period periodically poled lithium niobate and using a laser diode (LD) end-pumped CW 1064 nm Nd:YVO4 laser as the pump source. A highly efficiency CW operation is realized through a careful cavity design for mode matching and thermal stability. The signal tuning range is 1401-1500 nm obtained by varying the domain period. The maximum output power of 2.2 W at 1500 nm is obtained with a 17.1 W 808 nm LD power and the corresponding conversion efficiency is 12.9%.

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Generalization and propagation of spiraling Bessel beams with a helical axicon Sun Qiong-Ge(孙琼阁), Zhou Ke-Ya (周可雅), Fang Guang-Yu (方光宇), Liu Zheng-Jun(刘正君), and Liu Shu-Tian (刘树田) Chin. Phys. B, 2012, 21 (1):  014208.  DOI: 10.1088/1674-1056/21/1/014208 Abstract ( 1720 )   PDF (354KB) ( 1803 )   A generalized type of spiral Bessel beam has been demonstrated by using a spatially displaced helical axicon (HA). The topological charge of the spiraling Bessel beams is determined by the order of the input Laguerre-Gaussian (LG) beam and the topological charge of the HA. The obtained spiraling Bessel beams have an LG type of modulation along their propagation direction and exhibit annihilation-reconstruction properties. Theoretical analysis is presented, including that of the stability, propagation distance, topological charge, and spiraling dynamic characteristics. The mathematical and numerical results show that the propagation distance and helical revolution of the spiraling Bessel beams can be controlled through choosing appropriate radius of the HA.

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Mode-I crack in a two-dimensional fibre-reinforced generalized thermoelastic problem Kh. Lotfy Chin. Phys. B, 2012, 21 (1):  014209.  DOI: 10.1088/1674-1056/21/1/014209 Abstract ( 1385 )   PDF (324KB) ( 1078 )   A general model of the equations of the Lord-Şulman theory including one relaxation time and the Green-Lindsay theory with two relaxation times, as well as the classical dynamical coupled theory, are applied to the study of the influence of reinforcement on the total deformation for an infinite space weakened by a finite linear opening mode-I crack. We study the influence of reinforcement on the total deformation of rotating thermoelastic half-space and their interaction with each other. The material is homogeneous isotropic elastic half space. The crack is subjected to prescribed temperature and stress distributions. The normal mode analysis is used to obtain the exact expressions for displacement components, force stresses, and temperature. The variations of the considered variables with the horizontal distance are illustrated graphically. Comparisons are made with the results obtained in the three theories with and without rotation. A comparison is also made between the two theories for different depths.

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Optical terminal analysis of a multigrating tiled compressor in a PW-class CPA-laser Yang Yu-Chuan(杨雨川), Luo Hui(罗晖), Wang Xiao(王逍), Li Fu-Quan(李富全), Huang Xiao-Jun(黄小军), and Jing Feng(景峰) Chin. Phys. B, 2012, 21 (1):  014210.  DOI: 10.1088/1674-1056/21/1/014210 Abstract ( 1281 )   PDF (634KB) ( 820 )   In the highest-power chirped-pulse amplification lasers, the pulse must be stretched in time, amplified, compressed in a grating compressor and subsequently focused by off-axis parabola to obtain a high peak power. In the optical terminal, the temporal and spatial effects of mismatched multigrating tiled compressor on the far-field pulse are critical factors to be analysed. In this paper, a k-space raytracing model is proposed for the temporal and spatial analyses of possible errors in a four-grating single-pass tiled compressor. The results show that the last grating affects mainly the partial focal spot, while the middle two gratings affect the temporal waveform, and the partial focal spot needs much higher error control than that in the temporal domain in a picosecond pulse compression.

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Low temperature laser absorption spectra of methane in the near-infrared at 1.65 μm for lower state energy determination Gao Wei(高伟), Chen Wei-Dong(陈卫东), Zhang Wei-Jun(张为俊), Yuan Yi-Qian(袁怿谦), and Gao Xiao-Ming(高晓明) Chin. Phys. B, 2012, 21 (1):  014211.  DOI: 10.1088/1674-1056/21/1/014211 Abstract ( 1511 )   PDF (525KB) ( 724 )   Direct absorption spectra of the 2v3 band of methane (CH4) from 6038 to 6050 cm-1 were studied at different low temperatures using a newly developed cryogenic cell in combination with a distributed feedback (DFB) diode laser. The cryogenic cell can operate at any stabilized temperature ranging from room temperature down to 100 K with temperature fluctuation less than ±1 K within 1 hour. In the present work, the CH4 spectra in the range of 6038-6050 cm-1 were recorded at 296, 266, 248, 223, 198, and 176 K. The lower state energy E″ and the rotational assignment of the angular momentum J were determined by a “2-low-temperature spectra method” using the spectra recorded at 198 and 176 K. The results were compared with the data from the GOSAT and the recently reported results from Campargue and co-workers using two spectra measured at room temperature and 81 K. We demonstrated that the use of a 2-low-temperature spectra method permits one to complete the E″ and J values missed in the previous studies.

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Electromagnetic scattering of the carbon nanotubes excited by an electric line source Wang Yue(王玥), Wu Qun(吴群), Wu Yu-Ming(吴昱明), He Xun-Jun(贺训军), and Li Le-Wei(李乐伟) Chin. Phys. B, 2012, 21 (1):  014212.  DOI: 10.1088/1674-1056/21/1/014212 Abstract ( 1413 )   PDF (1047KB) ( 1011 )   An analytical solution is presented for the electromagnetic scattering from an infinite-length metallic carbon nanotube and a carbon nanotube bundle. The scattering field and scattering cross section are predicted using a modal technique based on a Bessel and Hankel function for the electric line source and a quantum conductance function for the carbon nanotube. For the particular case of an isolated armchair (10, 10) carbon nanotube, the scattered field predicted from this technique is in excellent agreement with the measured result. Furthermore, the analysis indicates that the scattering pattern of an isolated carbon nanotube differs from that of the carbon nanotube bundle of identical index (m, n) metallic carbon nanotubes.

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Influence of limited-view scanning on depth imaging of photoacoustic tomography Hot! Wu Dan(吴丹), Tao Chao(陶超), Liu Xiao-Jun(刘晓峻), and Wang Xue-Ding(王学鼎) Chin. Phys. B, 2012, 21 (1):  014301.  DOI: 10.1088/1674-1056/21/1/014301 Abstract ( 1263 )   PDF (457KB) ( 703 )   We study the influence of limited-view scanning on the depth imaging of photoacoustic tomography. The situation, in which absorbers are located at different depths with respect to the limited-view scanning trajectory, is called depth imaging and is investigated in this paper. The results show that limited-view scanning causes the reconstructed intensity of deep absorbers to be weaker than that of shallow ones and that deep absorbers will be invisible if the scanning range is too small. The concept of effective scanning angle is proposed to analyse that phenomenon. We find that an effective scanning angle can well predict the relationship between scanning angle and the intensity ratio of absorbers. In addition, limited-view scanning is employed to improve image quality.

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Phonon relaxation and heat conduction in one-dimensional Fermi–Pasta–Ulam β lattices by molecular dynamics simulations Hot! Hou Quan-Wen(侯泉文) and Cao Bing-Yang(曹炳阳) Chin. Phys. B, 2012, 21 (1):  014401.  DOI: 10.1088/1674-1056/21/1/014401 Abstract ( 1378 )   PDF (195KB) ( 779 )   The phonon relaxation and heat conduction in one-dimensional Fermi-Pasta-Ulam (FPU) β lattices are studied by using molecular dynamics simulations. The phonon relaxation rate, which dominates the length dependence of the FPU β lattice, is first calculated from the energy autocorrelation function for different modes at various temperatures through equilibrium molecular dynamics simulations. We find that the relaxation rate as a function of wave number k is proportional to k1.688, which leads to a N0.41 divergence of the thermal conductivity in the framework of Green-Kubo relation. This is also in good agreement with the data obtained by non-equilibrium molecular dynamics simulations which estimate the length dependence exponent of the thermal conductivity as 0.415. Our results confirm the N2/5 divergence in one-dimensional FPU β lattices. The effects of the heat flux on the thermal conductivity are also studied by imposing different temperature differences on the two ends of the lattices. We find that the thermal conductivity is insensitive to the heat flux under our simulation conditions. It implies that the linear response theory is applicable towards the heat conduction in one-dimensional FPU β lattices.

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Directed segregation in compartmentalized bi-disperse granular gas Sajjad Hussain Shah, Li Yin-Chang(李寅阊), Cui Fei-Fei(崔非非), Zhang Qi(张祺), and Hou Mei-Ying(厚美瑛) Chin. Phys. B, 2012, 21 (1):  014501.  DOI: 10.1088/1674-1056/21/1/014501 Abstract ( 1469 )   PDF (533KB) ( 597 )   A bi-disperse granular gas in an asymmetrical two-compartment system is studied experimentally. The presence of asymmetry within the range of our experimental parameters results in a directed segregated state and a directed clustering state. This deterministic system does not depend on the initial conditions. A modified flux model based on Lohse's flux model for bi-disperse granular gases is derived. The modified flux model explains qualitatively the experimental results.

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Generalized thermoelsticity of the thermal shock problem in an isotropic hollow cylinder and temperature dependent elastic moduli Ibrahim A. Abbas and Mohamed I. A. Othman Chin. Phys. B, 2012, 21 (1):  014601.  DOI: 10.1088/1674-1056/21/1/014601 Abstract ( 1573 )   PDF (890KB) ( 1029 )   In this paper, we construct the equations of generalized thermoelasicity for a non-homogeneous isotropic hollow cylider with a variable modulus of elasticity and thermal conductivity based on the Lord and Shulman theory. The problem has been solved numerically using the finite element method. Numerical results for the displacement, the temperature, the radial stress, and the hoop stress distributions are illustrated graphically. Comparisons are made between the results predicted by the coupled theory and by the theory of generalized thermoelasticity with one relaxation time in the cases of temperature dependent and independent modulus of elasticity.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

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Analysis of the wave properties of a new two-lane continuum model with the coupling effect Arvind Kumar Gupta and Sapna Sharma Chin. Phys. B, 2012, 21 (1):  015201.  DOI: 10.1088/1674-1056/21/1/015201 Abstract ( 1486 )   PDF (654KB) ( 970 )   A multilane extension of the single-lane anisotropic continuum model (GK model) developed by Gupta and Katiyar for traffic flow is discussed with the consideration of the coupling effect between the vehicles of different lanes in the instantaneous traffic situation and the lane-changing effect. The conditions for securing the linear stability of the new model are presented. The shock and the rarefaction waves, the local cluster effect and the phase transition are investigated through simulation experiments with the new model and are found to be consistent with the diverse nonlinear dynamical phenomena observed in a real traffic flow. The analysis also focuses on empirically observed two-lane phenomena, such as lane usage inversion and the density dependence of the number of lane changes. It is shown that single-lane dynamics can be extended to multilane cases without changing the basic properties of the single-lane model. The results show that the new multilane model is capable of explaining some particular traffic phenomena and is in accordance with real traffic flow.

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Bursting behaviours in cascaded stimulated Brillouin scattering Liu Zhan-Jun(刘占军), He Xian-Tu(贺贤土), Zheng Chun-Yang(郑春阳), and Wang Yu-Gang(王宇钢) Chin. Phys. B, 2012, 21 (1):  015202.  DOI: 10.1088/1674-1056/21/1/015202 Abstract ( 1377 )   PDF (225KB) ( 748 )   Stimulated Brillouin scattering is studied by numerically solving the Vlasov-Maxwell system. A cascade of stimulated Brillouin scattering can occur when a linearly polarized laser pulse propagates in a plasma. It is found that a stimulated Brillouin scattering cascade can reduce the scattering and increase the transmission of light, as well as introduce a bursting behaviour in the evolution of the laser-plasma interaction. The bursting time in the reflectivity is found to be less than half the ion acoustic period. The ion temperature can affect the stimulated Brillouin scattering cascade, which can repeat several ×at low ion temperatures and can be completely eliminated at high ion temperatures. For stimulated Brillouin scattering saturation, higher-harmonic generation and wave-wave interaction of the excited ion acoustic waves can restrict the amplitude of the latter. In addition, stimulated Brillouin scattering cascade can restrict the amplitude of the scattered light.

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Influence of ignition condition on the growth of silicon thin films using plasma enhanced chemical vapour deposition Zhang Hai-Long(张海龙), Liu Feng-Zhen(刘丰珍), Zhu Mei-Fang(朱美芳), and Liu Jin-Long(刘金龙) Chin. Phys. B, 2012, 21 (1):  015203.  DOI: 10.1088/1674-1056/21/1/015203 Abstract ( 1209 )   PDF (181KB) ( 632 )   The influences of the plasma ignition condition in plasma enhanced chemical vapour deposition (PECVD) on the interfaces and  the microstructures of hydrogenated microcrystalline Si ($\mu $c-Si:H) thin films are investigated. The plasma ignition condition is  modified by varying the ratio of SiH$_{4}$ to H$_{2}$ ($R_{\rm H})$. For plasma ignited with a constant gas ratio, the time-resolved  optical emission spectroscopy presents a low value of the emission intensity ratio of H$\alpha $ to SiH$^*$ ($I_{\rm H\alpha }$/$I_{\rm  SiH^\ast })$ at the initial stage, which leads to a thick amorphous incubation layer. For the ignition condition with a profiling  $R_{\rm H}$, the higher $I_{\rm H\alpha }$/$I_{\rm SiH^\ast }$ values are realized. By optimizing the $R_{\rm H}$ modulation, a uniform  crystallinity along the growth direction and a denser $\mu $c-Si:H film can be obtained. However, an excessively high $I_{\rm H\alpha  }$/$I_{\rm SiH^\ast }$ may damage the interface properties, which is indicated by capacitance--voltage ($C$--$V)$ measurements. Well  controlling the ignition condition is critically important for the applications of Si thin films.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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Superior tribological properties of an amorphous carbon film with a graphite-like structure Wang Yong-Jun(王永军), Li Hong-Xuan(李红轩), Ji Li(吉利), Liu Xiao-Hong(刘晓红), Wu Yan-Xia(吴艳霞), Zhou Hui-Di(周惠娣), and Chen Jian-Min(陈建敏) Chin. Phys. B, 2012, 21 (1):  016101.  DOI: 10.1088/1674-1056/21/1/016101 Abstract ( 1546 )   PDF (11631KB) ( 933 )   Amorphous carbon films with high sp2 concentrations are deposited by unbalanced magnetron sputtering with a narrow range of substrate bias voltage. Field emission scanning electron microscopes (FESEMs), high resolution transmission electron microscopes (HRTEMs), atomic force microscopes (AFMs), the Raman spectrometers, nano-indentation, and tribometers are subsequently used to characterize the microstructures and the properties of the resulting films. It is found that the present films are dominated by the sp2 sites. However, the films demonstrate a moderate hardness together with a low internal stress. The high hardness of the deposited film originates from the crosslinking of the sp2 clusters by the sp3 sites. The presence of the graphite-like clusters in the film structure may be responsible for the low internal stress. What is more important is that the resulting films show excellent tribological properties with high load capacity and excellent wear resistance in humid atmospheres. The relationship between the microstructure determined by the deposition condition and the film characteristic is discussed in detail.

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Carbon nanotube–cuprous oxide composite based pressure sensors Kh. S. Karimov, Muhammad Tariq Saeed Chani, Fazal Ahmad Khalid, Adam Khan, and Rahim Khan Chin. Phys. B, 2012, 21 (1):  016102.  DOI: 10.1088/1674-1056/21/1/016102 Abstract ( 1272 )   PDF (134KB) ( 1332 )   In this paper, we present the design, the fabrication, and the experimental results of carbon nanotube (CNT) and Cu2O composite based pressure sensors. The pressed tablets of the CNT-Cu2O composite are fabricated at a pressure of 353 MPa. The diameters of the multiwalled nanotubes (MWNTs) are between 10 nm and 30 nm. The sizes of the Cu2O micro particles are in the range of 3-4 μm. The average diameter and the average thickness of the pressed tablets are 10 mm and 4.0 mm, respectively. In order to make low resistance electric contacts, the two sides of the pressed tablet are covered by silver pastes. The direct current resistance of the pressure sensor decreases by 3.3 ×as the pressure increases up to 37 kN/m2. The simulation result of the resistance-pressure relationship is in good agreement with the experimental result within a variation of ± 2%.

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New insight into the parasitic bipolar amplification effect in single event transient production Chen Jian-Jun(陈建军), Chen Shu-Ming(陈书明), Liang Bin(梁斌), and Deng Ke-Feng (邓科峰) Chin. Phys. B, 2012, 21 (1):  016103.  DOI: 10.1088/1674-1056/21/1/016103 Abstract ( 1350 )   PDF (702KB) ( 764 )   In this paper, a new method is proposed to study the mechanism of charge collection in single event transient (SET) production in 90 nm bulk complementary metal oxide semiconductor (CMOS) technology. We find that different from the case in the pMOSFET, the parasitic bipolar amplification effect (bipolar effect) in the balanced inverter does not exist in the nMOSFET after the ion striking. The influence of the substrate process on the bipolar effect is also studied in the pMOSFET. We find that the bipolar effect can be effectively mitigated by a buried deep P+-well layer and can be removed by a buried SO2 layer.

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Temperature dependence of the P-hit single event transient pulse width in a three-transistor inverter chain Chen Shu-Ming(陈书明) and Chen Jian-Jun(陈建军) Chin. Phys. B, 2012, 21 (1):  016104.  DOI: 10.1088/1674-1056/21/1/016104 Abstract ( 1259 )   PDF (351KB) ( 828 )   A comparison of the temperature dependence of the P-hit single event transient (SET) in a two-transistor (2T) inverter with that in a three-transistor (3T) inverter is carried out based on a three-dimensional numerical simulation. Due to the significantly distinct mechanisms of the single event change collection in the 2T and the 3T inverters, the temperature plays different roles in the SET production and propagation. The SET pulse will be significantly broadened in the 2T inverter chain while will be compressed in the 3T inverter chain as temperature increases. The investigation provides a new insight into the SET mitigation under the extreme environment, where both the high temperature and the single event effects should be considered. The 3T inverter layout structure (or similar layout structures) will be a better solution for spaceborne integrated circuit design for extreme environments.

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Interaction between impurity nitrogen and tungsten: a first-principles investigation Liu Yue-Lin(刘悦林), Jin Shuo(金硕), and Zhang Ying(张颖) Chin. Phys. B, 2012, 21 (1):  016105.  DOI: 10.1088/1674-1056/21/1/016105 Abstract ( 1438 )   PDF (942KB) ( 1369 )   We investigate the stability, diffusion, and impurity concentration of nitrogen in intrinsic tungsten single crystal employing a first-principles method, and find that a single nitrogen atom is energetically favourable for sitting at the octahedral interstitial site. A nitrogen atom prefers to diffuse between the two nearest neighboring octahedral interstitial sites with a diffusion barrier of 0.72 eV. The diffusion coefficient is determined as a function of temperature and expressed as D(N)=1.66×10-7exp (-0.72/kT). The solubility of nitrogen is estimated in intrinsic tungsten in terms of Sieverts' law. The concentration of the nitrogen impurity is found to be 4.82×10-16 Å-3 at a temperature of 600 K and a pressure of 1 Pa. A single nitrogen atom can easily sit in an off-vacancy-centre position close to the octahedral interstitial site. There exists a strong attraction between nitrogen and a vacancy with a large binding energy of 1.40 eV. We believe that these results can provide a good reference for the understanding of the behaviour of nitrogen in intrinsic tungsten.

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First-principles study of structural stability and elastic property of pre-perovskite PbTiO3 Liu Yong(刘涌), Ni Li-Hong(倪利红), Ren Zhao-Hui(任召辉), Xu Gang(徐刚), Li Xiang(李翔), Song Chen-Lu(宋晨路), and Han Gao-Rong(韩高荣) Chin. Phys. B, 2012, 21 (1):  016201.  DOI: 10.1088/1674-1056/21/1/016201 Abstract ( 1342 )   PDF (221KB) ( 1108 )   The structural stability and the elastic properties of a novel structure of lead titanate, which is named pre-perovskite PbTiO3 (PP-PTO) and is constructed with TiO6 octahedral columns arranged in a one-dimensional manner, are investigated by using first-principles calculations. PP-PTO is energetically unstable compared with conventional perovskite phases, however it is mechanically stable. The equilibrium transition pressures for changing from pre-perovskite to cubic and tetragonal phases are -0.5 GPa and -1.4 GPa, respectively, with first-order characteristics. Further, the differences in elastic properties between pre-perovskite and conventional perovskite phases are discussed for the covalent bonding network, which shows a highly anisotropic character in PP-PTO. This study provides a crucial insight into the structural stabilities of PP-PTO and conventional perovskite.

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Elastic properties of Nb-based alloys by using the density functional theory Liu Zeng-Hui(刘增辉) and Shang Jia-Xiang (尚家香) Chin. Phys. B, 2012, 21 (1):  016202.  DOI: 10.1088/1674-1056/21/1/016202 Abstract ( 1334 )   PDF (219KB) ( 2350 )   A first-principles density functional approach is used to study the electronic and the elastic properties of Nb15X(X = Ti, Zr, Hf, V, Ta, Cr, Mo, and W) alloys. The elastic constants c11 and c12, the shear modulus C', and the elastic modulus E〈100〉 are found to exhibit similar tendencies, each as a function of valence electron number per atom (EPA), while c44 seems unclear. Both c11 and c12 of Nb15X alloys increase monotonically with the increase of EPA. The C' and E〈100〉 also show similar tendencies. The elastic constants (except c44) increase slightly when alloying with neighbours of a higher d-transition series. Our results are supported by the bonding density distribution. When solute atoms change from Ti(Zr, Hf) to V(Ta) then to Cr(Mo, W), the bonding electron density between the central solute atom and its first neighbouring Nb atoms is increased and becomes more anisotropic, which indicates the strong interaction and thus enhances the elastic properties of Nb-Cr(Mo, W) alloys. Under uniaxial 〈100〉 tensile loading, alloyed elements with less (more) valence electrons decrease (increase) the ideal tensile strength.

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Influences of surface effects and large deformation on the resonant properties of ultrathin silicon nanocantilevers Zhang Jia-Hong(张加宏), Li Min(李敏), Gu Fang(顾芳), and Liu Qing-Quan(刘清惓) Chin. Phys. B, 2012, 21 (1):  016203.  DOI: 10.1088/1674-1056/21/1/016203 Abstract ( 1307 )   PDF (280KB) ( 690 )   The purpose of the present work is to quantify the influences of the discrete nature, the surface effects, and the large deformation on the bending resonant properties of long and ultrathin 〈100〉 silicon nanocantilevers. We accomplish this by using an analytical semi-continuum Keating model within the framework of nonlinear, finite deformation kinematics. The semi-continuum model shows that the elastic behaviors of the silicon nanocantilevers are size-dependent and surface-dependent, which agrees well with the molecular dynamics results. It also indicates that the dominant effect on the fundamental resonant frequency shift of the silicon nanocantilever is adsorption-induced surface stress, followed by the discrete nature and surface reconstruction, whereas surface relaxation has the least effect. In particular, it is found that a large deformation tends to increase the nonlinear fundamental frequency of the silicon nanocantilever, depending not only on its size but also on the surface effects. Finally, the resonant frequency shifts due to the adsorption-induced surface stress predicted by the current model are quantitatively compared with those obtained from the experimental measurement and the other existing approach. It is noticed that the length-to-thickness ratio is the key parameter that correlates the deviations in the resonant frequencies predicted from the current model and the empirical formula.

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Local thermal conductivity of polycrystalline AlN ceramics measured by scanning thermal microscopy and complementary scanning electron microscopy techniques Zhang Yue-Fei(张跃飞), Wang Li(王丽), R. Heiderhoff, A. K. Geinzer, Wei Bin(卫斌), Ji Yuan(吉元), Han Xiao-Dong(韩晓东), L.J. Balk, and Zhang Ze(张泽) Chin. Phys. B, 2012, 21 (1):  016501.  DOI: 10.1088/1674-1056/21/1/016501 Abstract ( 1413 )   PDF (892KB) ( 1094 )   The local thermal conductivity of polycrystalline aluminum nitride (AlN) ceramics is measured and imaged by using a scanning thermal microscope (SThM) and complementary scanning electron microscope (SEM) based techniques at room temperature. The quantitative thermal conductivity for the AlN sample is gained by using a SThM with a spatial resolution of sub-micrometer scale through using the 3ω method. A thermal conductivity of 308 W/m·K within grains corresponding to that of high-purity single crystal AlN is obtained. The slight differences in thermal conduction between the adjacent grains are found to result from crystallographic misorientations, as demonstrated in the electron backscattered diffraction. A much lower thermal conductivity at the grain boundary is due to impurities and defects enriched in these sites, as indicated by energy dispersive X-ray spectroscopy.

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Dissociations of O2 molecules on ultrathin Pb(111) films: first-principles plane wave calculations Hu Zi-Yu(胡自玉), Yang Yu(杨宇), Sun Bo(孙博), Zhang Ping(张平), Wang Wen-Chuan(汪文川), and Shao Xiao-Hong(邵晓红) Chin. Phys. B, 2012, 21 (1):  016801.  DOI: 10.1088/1674-1056/21/1/016801 Abstract ( 1373 )   PDF (1410KB) ( 772 )   Using first-principles calculations, we systematically study the dissociations of O2 molecules on different ultrathin Pb(111) films. According to our previous work revealing the molecular adsorption precursor states for O2, we further explore why there are two nearly degenerate adsorption states on Pb(111) ultrathin films, but no precursor adsorption states existing at all on Mg(0001) and Al(111) surfaces. The reason is concluded to be the different surface electronic structures. For the O2 dissociation, we consider both the reaction channels from gas-like and molecularly adsorbed O2 molecules. We find that the energy barrier for O2 dissociation from the molecular adsorption precursor states is always smaller than that from O2 gas. The most energetically favorable dissociation process is found to be the same on different Pb(111) films, and the energy barriers are found to be influenced by the quantum size effects of Pb(111) films.

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Water adsorption on the Be(0001) surface: from monomer to trimer adsorption Ning Hua(宁华), Tao Xiang-Ming(陶向明), and Tan Ming-Qiu(谭明秋) Chin. Phys. B, 2012, 21 (1):  016802.  DOI: 10.1088/1674-1056/21/1/016802 Abstract ( 1376 )   PDF (458KB) ( 1216 )   In this paper, the density functional theory has been used to perform a comparative theoretical study of water monomer, dimer, trimer, and bilayer adsorptions on the Be(0001) surface. In our calculations, the adsorbed water molecules are energetically favoured adsorbed on the atop sites, and the dimer adsorption is found to be the most stable with a peak adsorption energy of ～437 meV. Further analyses have revealed that the essential bonding interaction between the water monomer and the metal substrate is the hybridization of the water 3a1-like molecular orbital with the (s, pz) orbitals of the surface beryllium atoms. While in the case of the water dimer adsorption, the 1b1-like orbital of the H2O molecule plays a dominant role.

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Uniaxial stress influence on lattice, band gap and optical properties of n-type ZnO:first-principles calculations Yang Ping(杨平), Li Pei(李培), Zhang Li-Qiang(张立强), Wang Xiao-Liang(王晓亮), Wang Huan(王欢), Song Xi-Fu(宋喜福), and Xie Fang-Wei(谢方伟) Chin. Phys. B, 2012, 21 (1):  016803.  DOI: 10.1088/1674-1056/21/1/016803 Abstract ( 1445 )   PDF (180KB) ( 2150 )   The lattice, the band gap and the optical properties of n-type ZnO under uniaxial stress are investigated by first-principles calculations. The results show that the lattice constants change linearly with stress. Band gaps are broadened linearly as the uniaxial compressive stress increases. The change of band gap for n-type ZnO comes mainly from the contribution of stress in the c-axis direction, and the reason for band gap of n-type ZnO changing with stress is also explained. The calculated results of optical properties reveal that the imaginary part of the dielectric function decreases with the increase of uniaxial compressive stress at low energy. However, when the energy is higher than 4.0 eV, the imaginary part of the dielectric function increases with the increase of stress and a blueshift appears. There are two peaks in the absorption spectrum in an energy range of 4.0-13.0 eV. The stress coefficient of the band gap of n-type ZnO is larger than that of pure ZnO, which supplies the theoretical reference value for the modulation of the band gap of doped ZnO.

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

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Density-functional theory investigation of energy gaps and optical properties of Hg1-xCdxTe and In1-xGaxAs Guo San-Dong(郭三栋) and Liu Bang-Gui(刘邦贵) Chin. Phys. B, 2012, 21 (1):  017101.  DOI: 10.1088/1674-1056/21/1/017101 Abstract ( 1252 )   PDF (364KB) ( 889 )   We use a modified Becke-Johnson exchange plus a local density approximation correlation potential within the density functional theory to investigate the electronic structures of Hg1-xCdxTe and In1-xGaxAs with x being 0, 0.25, 0.5, 0.75, and 1. For both of the two series, our calculated energy gaps and dielectric functions (real part ε1 and imaginary part ε2) are in agreement with the corresponding experimental results with x being between 0 and 1. The calculated zero-frequency refractive index varies greatly with x for Hg1-xCdxTe, but changes little with x for In1-xGaxAs, which is consistent with the real parts of their dielectric functions. Therefore, this new approach is satisfactory to describe the electronic structures and the optical properties of the semiconductors.

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Electronic structure of PCBM Sheng Chun-Qi(盛春荠), Wang Peng(王鹏), Shen Ying(沈影), Li Yan-Jun(李艳君), Zhang Wen-Hua(张文华), Xu Fa-Qiang(徐法强), Zhu Jun-Fa(朱俊发), Lai Guo-Qiao(来国桥), and Li Hong-Nian(李宏年) Chin. Phys. B, 2012, 21 (1):  017102.  DOI: 10.1088/1674-1056/21/1/017102 Abstract ( 1589 )   PDF (984KB) ( 1621 )   We have studied the electronic structure of [6,6]-phenyl-C61-butyric-acid-methyl-ester (PCBM) using synchrotron radiation photoelectron spectroscopy (PES) measurements and first-principles calculations. The PES spectrum of the entire occupied valence band is reported, which exhibits abundant spectral features from the Fermi level to ～24 eV binding energy. All the spectral features are broadened as compared with the cases of C60. The reasons for the broadening are analysed by comparing the experimental data with the calculated energy levels and density of states. Special attention is paid to the analysis of the C60 highest occupied molecular orbital (HOMO)-1 derived states, which can play a crucial role in the bonding at the interfaces of PCBM/polymer blenders or PCBM/electrodes. Besides the well-known energy level splitting of the C60 backbone caused by the lowered symmetry, C 2p states from the side chain mix or hybridize with the molecular orbitals of parent C60. The contribution of the O 2p states can substantially modify the PES spectrum.

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Determination of the series resistance under the Schottky contacts of AlGaN/AlN/GaN Schottky barrier diodes Cao Zhi-Fang(曹芝芳), Lin Zhao-Jun(林兆军), LŰ Yuan-Jie(吕元杰), Luan Chong-Biao(栾崇彪), Yu Ying-Xia(于英霞), Chen Hong(陈弘), and Wang Zhan-Guo(王占国) Chin. Phys. B, 2012, 21 (1):  017103.  DOI: 10.1088/1674-1056/21/1/017103 Abstract ( 1468 )   PDF (247KB) ( 1201 )   Rectangular AlGaN/AlN/GaN heterostructure field-effect transistors (HFETs) were fabricated, and the gate and the source of the HFETs consisted of AlGaN/AlN/GaN Schottky barrier diodes (SBDs). Based on the measured forward current-voltage and the capacitance-voltage characteristics of the AlGaN/AlN/GaN SBDs, the series resistance under the Schottky contacts (RS) was calculated using the method of power consumption, which has been proved to be valid. Finally, the method of power consumption for calculating RS was successfully used to study the two-dimensional electron gas electron mobility for a series of circular AlGaN/AlN/GaN SBDs. It is shown that the series resistance under the Schottky contacts cannot be neglected and is important for analysing and characterizing the AlGaN/AlN/GaN SBDs and the AlGaN/AlN/GaN HFETs.

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New 4H silicon carbide metal semiconductor field-effect transistor with a buffer layer between the gate and the channel layer Zhang Xian-Jun(张现军), Yang Yin-Tang(杨银堂), Duan Bao-Xing(段宝兴), Chen Bin(陈斌), Chai Chang-Chun(柴常春), and Song Kun(宋坤) Chin. Phys. B, 2012, 21 (1):  017201.  DOI: 10.1088/1674-1056/21/1/017201 Abstract ( 1362 )   PDF (933KB) ( 764 )   A new 4H silicon carbide metal semiconductor field-effect transistor (4H-SiC MESFET) structure with a buffer layer between the gate and the channel layer is proposed in this paper for high power microwave applications. The physics-based analytical models for calculating the performance of the proposed device are obtained by solving one- and two-dimensional Poisson's equations. In the models, we take into account not only two regions under the gate but also a third high field region between the gate and the drain which is usually omitted. The direct-current and the alternating-current performances for the proposed 4H-SiC MESFET with a buffer layer of 0.2 μ m are calculated. The calculated results are in good agreement with the experimental data. The current is larger than that of the conventional structure. The cutoff frequency (fT) and the maximum oscillation frequency (fmax) are 20.4 GHz and 101.6 GHz, respectively, which are higher than 7.8 GHz and 45.3 GHz of the conventional structure. Therefore, the proposed 4H-SiC MESFET structure has better power and microwave performances than the conventional structure.

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Effects of gate-buffer combined with a p-type spacer structure on silicon carbide metal–semiconductor field-effect transistors Song Kun(宋坤), Chai Chang-Chun(柴常春), Yang Yin-Tang(杨银堂), Chen Bin(陈斌), Zhang Xian-Jun(张现军), and Ma Zhen-Yang(马振洋) Chin. Phys. B, 2012, 21 (1):  017202.  DOI: 10.1088/1674-1056/21/1/017202 Abstract ( 1118 )   PDF (454KB) ( 739 )   An improved structure of silicon carbide metal-semiconductor field-effect transistors (MESFET) is proposed for high power microwave applications. Numerical models for the physical and electrical mechanisms of the device are presented, and the static and dynamic electrical performances are analysed. By comparison with the conventional structure, the proposed structure exhibits a superior frequency response while possessing better DC characteristics. A p-type spacer layer, inserted between the oxide and the channel, is shown to suppress the surface trap effect and improve the distribution of the electric field at the gate edge. Meanwhile, a lightly doped n-type buffer layer under the gate reduces depletion in the channel, resulting in an increase in the output current and a reduction in the gate-capacitance. The structural parameter dependences of the device performance are discussed, and an optimized design is obtained. The results show that the maximum saturation current density of 325 mA/mm is yielded, compared with 182 mA/mm for conventional MESFETs under the condition that the breakdown voltage of the proposed MESFET is larger than that of the conventional MESFET, leading to an increase of 79% in the output power density. In addition, improvements of 27% cut-off frequency and 28% maximum oscillation frequency are achieved compared with a conventional MESFET, respectively.

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Spin-polarized transport in a normal/ferromagnetic/normal zigzag graphene nanoribbon junction Tian Hong-Yu(田宏玉) and Wang Jun(汪军) Chin. Phys. B, 2012, 21 (1):  017203.  DOI: 10.1088/1674-1056/21/1/017203 Abstract ( 1609 )   PDF (172KB) ( 1028 )   We investigate the spin-dependent electron transport in single and double normal/ferromagnetic/normal zigzag graphene nanoribbon (NG/FG/NG) junctions. The ferromagnetism in the FG region originates from the spontaneous magnetization of the zigzag graphene nanoribbon. It is shown that when the zigzag-chain number of the ribbon is even and only a single transverse mode is actived, the single NG/FG/NG junction can act as a spin polarizer and/or a spin analyzer because of the valley selection rule and the spin-exchange field in the FG, while the double NG/FG/NG/FG/NG junction exhibits a quantum switching effect, in which the on and the off states switch rapidly by varying the cross angle between two FG magnetizations. Our findings may shed light on the application of magnetized graphene nanoribbons to spintronics devices.

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Anomalous microwave reflection from a metal surface induced by spoof surface plasmon Wang Liang(王亮), Cao Jin-Xiang(曹金祥), LŰ You(吕铀), Liu Lei(刘磊), Du Yin-Chang(杜寅昌), and Wang Jian(汪建) Chin. Phys. B, 2012, 21 (1):  017301.  DOI: 10.1088/1674-1056/21/1/017301 Abstract ( 1503 )   PDF (179KB) ( 2129 )   The reflection of X-band microwaves (8-12 GHz) from a metallic aluminum (Al) surface with groove grating corrugations was investigated experimentally. It was shown that the reflection of p-polarization is much less than the microwave reflected from the corresponding area of an unruled Al surface, with selective wavelength. The experimental results demonstrated that the anomalous microwave reflection is strongly associated with the excitation of spoof surface plasmons at the Al-air interface by the surface grating coupler. This near-total absence of reflected microwaves is similar to the famous Wood's anomaly in the optical regime and is of fundamental importance to the applications of spoof surface plasmons in the microwave regime.

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Quantum computation with two-dimensional graphene quantum dots Li Jie-Sen(李杰森), Li Zhi-Bing (李志兵), and Yao Dao-Xin (姚道新) Chin. Phys. B, 2012, 21 (1):  017302.  DOI: 10.1088/1674-1056/21/1/017302 Abstract ( 1560 )   PDF (364KB) ( 854 )   We study an array of graphene nano sheets that form a two-dimensional S=1/2 Kagome spin lattice used for quantum computation. The edge states of the graphene nano sheets are used to form quantum dots to confine electrons and perform the computation. We propose two schemes of bang-bang control to combat decoherence and realize gate operations on this array of quantum dots. It is shown that both schemes contain a great amount of information for quantum computation. The corresponding gate operations are also proposed.

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Analysis and simulation of a 4H-SiC semi-superjunction Schottky barrier diode for softer reverse-recovery Cao Lin(曹琳), Pu Hong-Bin(蒲红斌), Chen Zhi-Ming(陈治明), and Zang Yuan(臧源) Chin. Phys. B, 2012, 21 (1):  017303.  DOI: 10.1088/1674-1056/21/1/017303 Abstract ( 1387 )   PDF (260KB) ( 943 )   In this paper, a 4H-SiC semi-superjunction (SJ) Schottky barrier diode is analysed and simulated. The semi-SJ structure has an optimized design and a specific on-resistance lower than that of conventional SJ structures, which can be achieved without increasing the process difficulty. The simulation results show that the specific on-resistance and the softness factor depend on the aspect and thickness ratios, and that by using the semi-SJ structure, specific on-resistance can be reduced without decreasing the softness factor. It is observed that a trade-off exists between the specific on-resistance and the softness of the diode.

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A study of GaN MOSFETs with atomic-layer-deposited Al2O3 as the gate dielectric Feng Qian(冯倩), Xing Tao(邢韬), Wang Qiang(王强), Feng Qing(冯庆), Li Qian(李倩), Bi Zhi-Wei(毕志伟), Zhang Jin-Cheng(张进成), and Hao Yue(郝跃) Chin. Phys. B, 2012, 21 (1):  017304.  DOI: 10.1088/1674-1056/21/1/017304 Abstract ( 1490 )   PDF (244KB) ( 1609 )   Accumulation-type GaN metal-oxide-semiconductor field-effect transistors (MOSFETs) with atomic-layer-deposited Al2O3 gate dielectrics are fabricated. The device, with atomic-layer-deposited Al2O3 as the gate dielectric, presents a drain current of 260 mA/mm and a broad maximum transconductance of 34 mS/mm, which are better than those reported previously with Al2O3 as the gate dielectric. Furthermore, the device shows negligible current collapse in a wide range of bias voltages, owing to the effective passivation of the GaN surface by the Al2O3 film. The gate drain breakdown voltage is found to be about 59.5 V, and in addition the channel mobility of the n-GaN layer is about 380 cm2/Vs, which is consistent with the Hall result, and it is not degraded by atomic-layer-deposition Al2O3 growth and device fabrication.

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Spin-dependent transport induced by magnetization in zigzag graphene nanoribbons coupled to one-dimensional leads Zhao Hua(赵华), Zhang Xiao-Wei(张小伟), Cai Tuo(蔡托) Sang Tian(桑田), Liu Xiao-Chun(刘晓春), and Liu Fang(刘芳) Chin. Phys. B, 2012, 21 (1):  017305.  DOI: 10.1088/1674-1056/21/1/017305 Abstract ( 1810 )   PDF (149KB) ( 1101 )   We study spin transport in a zigzag graphene nanoribbon sample with two ferromagnetic strips deposited on the two sides of the ribbon. A tight-binding Hamiltonian was adopted to describe the sample connected to two one-dimensional leads. Our theoretical study shows that the resonance peaks of conductance for the spin-up and spin-down electrons are separated for the parallel configuration of the ferromagnetic strips, while they are not separated for the case of antiparallel configuration. This means that giant magnetoresistance can be produced at particular energies by altering the configurations of the ferromagnetic strips, and the device can be designed as a spin filter.

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Sn-based type-VIII single-crystal clathrates with a large figure of merit Deng Shu-Kang(邓书康), Li De-Cong(李德聪), Shen Lan-Xian(申兰先), Hao Rui-Ting(郝瑞亭), and T. Takabatake Chin. Phys. B, 2012, 21 (1):  017401.  DOI: 10.1088/1674-1056/21/1/017401 Abstract ( 1308 )   PDF (232KB) ( 694 )   Single-crystal samples of type-VIII Ba8Ga16 - xCuxSn30 (x=0, 0.03, 0.06, 0.15) clathrates were prepared using the Sn-flux method. At room temperature the carrier density, n, is 3.5-5×1019 cm-3 for all the samples, the carrier mobility, μH, increases to more than twice that of Ba8Ga16Sn30 for all the Cu doping samples, and consequently the electrical conductivity is enhanced distinctly from 1.90×104 S/m to 4.40×104 S/m, with the Cu composition increasing from x=0 to x=0.15. The Seebeck coefficient, α , decreases slightly with the increases in Cu composition. The κ values are about 0.72 W/mK at 300 K and are almost invariant with temperature up to 500 K for the samples with x=0 and x=0.03. The lattice thermal conductivity, κL, decreases from 0.59 W/mK for x=0 to 0.50 W/mK for x=0.03 at 300 K. The figure of merit for x=0.03 reaches 1.35 at 540 K.

RAPID COMMUNICATION

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Magnetic phase transitions and large mass enhancement in single crystal CaFe4As3 Zhang Xiao-Dong(张晓冬), Wu Wei(吴伟), Zheng Ping(郑萍), Wang Nan-Lin(王楠林), and Luo Jian-Lin(雒建林) Chin. Phys. B, 2012, 21 (1):  017402.  DOI: 10.1088/1674-1056/21/1/017402 Abstract ( 1314 )   PDF (754KB) ( 689 )   High quality single crystal CaFe4As3 was grown by using the Sn flux method. Unlike layered CaFe2As2, CaFe4As3 crystallizes in an orthorhombic three-dimensional structure. Two magnetic ordering transitions are observed at ～90 K and ～27 K, respectively. The high temperature transition is an antiferromagnetic(AF) ordering transition. However, the low temperature transition shows complex properties. It shows a ferromagnetic-like transition when a field is applied along b-axis, while antiferromagnetism-like transition when a field is applied perpendicular to b-axis. These results suggest that the low temperature transition at 27 K is a first-order transition from an AF state to a canted AF state. In addition, the low temperature electron specific heat coefficient reaches as high as 143 mJ/mol·K2, showing a heavy fermion behavior.

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

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The structural and magnetic properties of barium ferrite powders prepared by the sol–gel method Li Jie(李颉), Zhang Huai-Wu(张怀武), Li Yuan-Xun(李元勋), Liu Ying-Li(刘颖力), and Ma Yan-Bing(马岩冰) Chin. Phys. B, 2012, 21 (1):  017501.  DOI: 10.1088/1674-1056/21/1/017501 Abstract ( 1316 )   PDF (535KB) ( 2153 )   In this paper, M-type hexagonal barium ferrite powders are synthesized using the sol-gel method. A dried precursor heated in air is analyzed in the temperature range from 50 to 1200 ℃ using thermo-gravimetric analysis and differential scanning calorimetry. The effects of the additives and the cacinating temperature on the magnetic properties are investigated, and the results show that single-phase barium ferrite powders can be formed. After heat-treating at 950 ℃ for 4h with 3 wt% additive, the coercivity and saturation magnetization are found to be 440 Oe and 57.9 emu/g, respectively.

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Simulation of the f–d transitions of lanthanide ions in YPO4 using quantum-chemical calculations Hu Liu-Sen(胡流森), Wen Jun(闻军), Yin Min(尹民), and Xia Shang-Da(夏上达) Chin. Phys. B, 2012, 21 (1):  017801.  DOI: 10.1088/1674-1056/21/1/017801 Abstract ( 1367 )   PDF (157KB) ( 671 )   We constructed an effective one-electron Hamiltonian by using the 4f/5d energies and eigenvectors obtained from the first-principles calculation with the relativistic self-consistent discrete variational Slater software package (DV-X$\alpha$). From the effective Hamiltonian, we obtained the crystal-field and spin-orbit interaction parameters for the 4f and 5d electrons of lanthanide ions (Ce3+, Pr3+, Nd3+ and Eu3+) doped in YPO4, and these parameters were used to calculate the 4fN-4fN-15d transition. Comparison with experiments shows that the obtained parameters are reasonable and the excitation spectra can be well predicted.

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The dielectric behaviour of doped near-stoichiometric lithium niobate in the terahertz range Wu Liang(吴亮), Ling Fu-Ri(凌福日), Zuo Zhi-Gao(左志高), Liu Jin-Song(刘劲松), and Yao Jian-Quan(姚建铨) Chin. Phys. B, 2012, 21 (1):  017802.  DOI: 10.1088/1674-1056/21/1/017802 Abstract ( 1485 )   PDF (209KB) ( 750 )   The dielectric properties of near-stoichiometric LiNbO3:Fe and LiNbO3:Ce single crystals have been investigated using terahertz time domain spectroscopy in a frequency range of 0.7-1.6 THz at room temperature. When coupled with an applied external optical field, obvious photorefractive effects were observed, resulting in a modulation of the complex dielectric constant for the crystals. The variation in refractive index, |Δn|, had a linear relationship with the applied light intensity, accompanied by a step-like decrease at high intensity. The findings were attributed to the internal space charge field of the photorefraction and the light-induced domain reversal in the crystals.

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A polarized micro-Raman study of a 0.65PbMg1/3Nb2/3O3–0.35PbTiO3 single crystal Zhang Li-Yan(张丽艳), Zhu Ke(朱恪), and Liu Yu-Long(刘玉龙) Chin. Phys. B, 2012, 21 (1):  017803.  DOI: 10.1088/1674-1056/21/1/017803 Abstract ( 1241 )   PDF (162KB) ( 552 )   Polarized micro-Raman spectra of a 0.65PbMg1/3Nb2/3O3-0.35PbTiO3 (0.65PMN-0.35PT) single crystal poled in the [001] direction are obtained in a wide frequency range (50-2000 cm-1) at different temperatures. The best fit to the Raman spectrum at 77 K is achieved using 17 Lorenzians to convolute into it, and this is proved to be a reasonable fit. According to the group theory and selection rules of overtone and combinational modes, apart from the seven Raman modes that are from first-order Raman scattering, the remaining ones are attributed to being from second-order Raman scattering. A comparison between the experimental results and theoretical predictions shows that they are in satisfactory agreement with each other. Our results indicate that at 77 K the sample belongs to the rhombohedral symmetry with the C3v5 (R3m) space group (Z=1). In our study, on heating, the 0.65PMN-0.35PT single crystal undergoes a rhombohedral to tetragonal to cubic phase transition sequence. The two phase transitions occur at 340 and 440 K, which correspond to the disappearance of the soft mode near 106 cm-1 recorded in VV polarization and the vanishing of the band around 780 cm-1 in VH polarization, respectively.

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The determination of the x value in doped Hg1-xCdxTe by transmission spectra Yue Fang-Yu(越方禹), Chen Lu(陈璐), Li Ya-Wei(李亚巍), Sun Lin(孙琳), Yang Ping-Xiong(杨平雄), and Chu Jun-Hao(褚君浩) Chin. Phys. B, 2012, 21 (1):  017804.  DOI: 10.1088/1674-1056/21/1/017804 Abstract ( 1386 )   PDF (377KB) ( 655 )   Variable-temperature transmission/absorption spectra are measured on As-doped Hg1-xCdxTe grown by molecular beam epitaxy. The nonlinear temperature-dependent shift of the absorption edge is also observed, which is similar to our previous report on V_textrmHg (unintentionally)-doped HgCdTe. By referring to the empirical formulas of Eg(x, T), the x value of the epilayer is calculated and its inconsistency between the extreme temperatures (e.g. 10 and 300 K) is discussed. The results confirm the assumption of the effect of shallow levels on the shift of the absorption edge, and suggest that the x value (or Eg) in intrinsic/extrinsic-doped HgCdTe should be determined by referring to as low a temperature as possible (e.g. 10 K), and not the commonly used temperatures of 77 or 300 K, when the transmission spectrum should be employed. This can give brief guidelines for fabricating HgCdTe-related devices.

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Room-temperature direct-bandgap photoluminescence from strain-compensated Ge/SiGe multiple quantum wells on silicon Hot! Hu Wei-Xuan(胡炜玄), Cheng Bu-Wen(成步文), Xue Chun-Lai(薛春来), Zhang Guang-Ze(张广泽), Su Shao-Jian(苏少坚), Zuo Yu-Hua(左玉华), and Wang Qi-Ming(王启明) Chin. Phys. B, 2012, 21 (1):  017805.  DOI: 10.1088/1674-1056/21/1/017805 Abstract ( 1418 )   PDF (358KB) ( 895 )   Strain-compensated Ge/Si0.15Ge0.85 multiple quantum wells were grown on an Si0.1Ge0.9 virtual substrate using ultrahigh vacuum chemical vapor deposition technology on an n+-Si(001) substrate. Photoluminescence measurements were performed at room temperature, and the quantum confinement effect of the direct-bandgap transitions of a Ge quantum well was observed, which is in good agreement with the calculated results. The luminescence mechanism was discussed by recombination rate analysis and the temperature dependence of the luminescence spectrum.

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The characteristics of sonoluminescence An Yu(安宇) and Zhang Wen-Juan(张文娟) Chin. Phys. B, 2012, 21 (1):  017806.  DOI: 10.1088/1674-1056/21/1/017806 Abstract ( 1287 )   PDF (299KB) ( 655 )   Cavitation luminescence is light emission from gases that are compressed to high temperature and high pressure inside a bubble or group of bubbles. The numerical simulation in this study indicates that if the temperature and pressure inside a bubble are not high enough, then dim and spectral line emission dominates. However, if the temperature and pressure inside the bubble are very high, then the light is bright and a continuum spectrum will be generated. Calculations of the spectrum using modified equations of bubble motion can simulate the spectral profile well. However, pulse width calculations using these equations only partly agree with the experimental results.

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Partial electrical potential distribution around nanospheres in metallic nanostructured films You Rong-Yi(游荣义) and Huang Xiao-Jing(黄晓菁) Chin. Phys. B, 2012, 21 (1):  017807.  DOI: 10.1088/1674-1056/21/1/017807 Abstract ( 1162 )   PDF (261KB) ( 1229 )   In light of the nanostructured surface model, where half-spherical nanoparticles grow out symmetrically from a plane metallic film, the mathematical model for the partial electrical potential around nanospheres is developed when a uniform external electric field is applied. On the basis of these models, the three-dimensional spatial distribution of the partial electrical potential is obtained and given in the form of a curved surface using a numerical computation method. Our results show that the electrical potential distribution around the nanospheres exhibits an obvious geometrical symmetry. These results could serve as a reference for investigating many abnormal phenomena such as abnormal infrared effects, which are found when CO molecules are adsorbed on the surface of nanostructured transition metals.

INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

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The luminescence enhancement of Eu3+ ion and SnO2 nanocrystal co-doped sol–gel SiO2 films Zhang Xiao-Wei(张晓伟), Lin Tao(林涛), Xu Jun(徐骏), Xu Ling(徐岭), and Chen Kun-Ji(陈坤基) Chin. Phys. B, 2012, 21 (1):  018101.  DOI: 10.1088/1674-1056/21/1/018101 Abstract ( 1379 )   PDF (524KB) ( 1167 )   SnO2 nanocrystal and rare-earth Eu3+ ion co-doped SiO2 thin films are prepared by sol-gel and spin coating methods. The formation of tetragonal rutile structure SnO2 nanocrystals with a uniform distribution is confirmed by X-ray diffraction and transmission electron microscopy. Fourier transform infrared spectroscopy is used to investigate the densities of the hydroxyl groups, and it is found that the emission intensity from the 5D0-7F2 transitions of the Eu3+ ions is enhanced by two orders of magnitude due to energy transfer from the oxygen-vacancy-related defects of the SnO2 nanocrystals to nearby Eu3+ ions. The influences of the amounts of Sn and the post-annealing temperatures are systematically evaluated to further understand the mechanism of energy transfer. The luminescence intensity ratio of Eu3+ ions from electric dipole transition and magnetic dipole transition indicate the different probable locations of Eu3+ ions in the sol-gel thin film, which are further discussed based on temperature-dependent photoluminescence measurements.

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Simulations of a two-stream backward-wave oscillator with a slot-hole structure Shi Zong-Jun(史宗君), Tang Xiao-Pin(唐效频), Yang Zi-Qiang(杨梓强), Lan Feng(兰峰), and Liang Zheng(梁正) Chin. Phys. B, 2012, 21 (1):  018401.  DOI: 10.1088/1674-1056/21/1/018401 Abstract ( 1562 )   PDF (306KB) ( 803 )   We study a two-stream backward-wave oscillator with a slot-hole structure at short millimeter waves with the help of a three-dimensional particle-in-cell simulation. In order to increase the interaction region of the electron beam, the efficiency and the output power, a slot-hole loaded rectangular waveguide structure used as the high-frequency system is proposed. Based on the mechanism of the backward-wave oscillator, a slow-wave oscillator with a frequency of 0.14 THz is designed. The simulations show that the output power and the efficiency of the oscillator can be enhanced due to the coupling between the two beams through the slot holes. The interaction efficiency is 5.18%, and the starting current density is below 5 A·cm-2 for the two beams. These attractive results indicate that, based on the two-stream backward-wave oscillator, we can get short millimeter wave sources with high power and low current density.

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The breakdown mechanism of a high-side pLDMOS based on a thin-layer silicon-on-insulator structure Zhao Yuan-Yuan(赵远远), Qiao Ming(乔明), Wang Wei-Bin(王伟宾), Wang Meng(王猛), and Zhang Bo(张波) Chin. Phys. B, 2012, 21 (1):  018501.  DOI: 10.1088/1674-1056/21/1/018501 Abstract ( 1246 )   PDF (410KB) ( 1040 )   A high-side thin-layer silicon-on-insulator (SOI) pLDMOS is proposed, adopting field implant (FI) and multiple field plate (MFP) technologies. The breakdown mechanisms of back gate (BG) turn-on, surface channel punch-through, and vertical and lateral avalanche breakdown are investigated by setting up analytical models, simulating related parameters and verifying experimentally. The device structure is optimized based on the above research. The shallow junction achieved through FI technology attenuates the BG effect, the optimized channel length eliminates the surface channel punch-through, the advised thickness of the buried oxide dispels the vertical avalanche breakdown, and the MFP technology avoids premature lateral avalanche breakdown by modulating the electric field distribution. Finally, for the first time, a 300 V high-side pLDMOS is experimentally realized on a 1.5 μ m thick thin-layer SOI.

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Integrating the environmental factor into the strategy updating rule to promote cooperation in evolutionary games Zhao Lin(赵琳), Zhou Xin(周鑫), Liang Zhi(梁治), and Wu Jia-Rui(吴家睿) Chin. Phys. B, 2012, 21 (1):  018701.  DOI: 10.1088/1674-1056/21/1/018701 Abstract ( 1202 )   PDF (397KB) ( 658 )   Many previous studies have shown that the environment plays an important role for social individuals. In this paper, we integrate the environmental factor, which is defined as the average payoff of all a player's neighbours, with the standard Fermi updating rule by introducing a tunable parameter, ω. It is found that the level of cooperation increases remarkably, and that the cooperators can better resist the invasion of defection with an increase in ω. This interesting phenomenon is then explained from a microscopic view. In addition, the universality of this mechanism is also proved with the help of the small-world network and the random regular graph. This work may be helpful in understanding cooperation behaviour in species from unicellular organisms up to human beings.

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Symbolic transfer entropy-based premature signal analysis Wang Jun(王俊) and Yu Zheng-Feng(余正锋) Chin. Phys. B, 2012, 21 (1):  018702.  DOI: 10.1088/1674-1056/21/1/018702 Abstract ( 1498 )   PDF (106KB) ( 952 )   In this paper, we use symbolic transfer entropy to study the coupling strength between premature signals. Numerical experiments show that three types of signal couplings are in the same direction. Among them, normal signal coupling is the strongest, followed by that of premature ventricular contractions, and that of atrial premature beats is the weakest. The T test shows that the entropies of the three signals are distinct. Symbolic transfer entropy requires less data, can distinguish the three types of signals and has very good computational efficiency.

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The excluded-volume effect in microscopic pedestrian simulations Guo Ren-Yong(郭仁拥) and Guo Xi(郭喜) Chin. Phys. B, 2012, 21 (1):  018901.  DOI: 10.1088/1674-1056/21/1/018901 Abstract ( 1175 )   PDF (389KB) ( 631 )   We propose a pedestrian position update rule, which is added to a microscopic pedestrian model to avoid pedestrian overlap. In the rule, the step size of a pedestrian moving in a selected direction at each update is in inverse proportion to the repulsive actions imposed by other pedestrians moving in a direction with an exponential rate. The positions of the pedestrians are then updated in each small time interval. In this way, a barrier between the pedestrians can be generated, and after updating their positions the pedestrians do not overlap with each other. The modified model is compared to the original model through a simulation of the evacuation process of pedestrians in a closed area. The simulation results indicate that the modified model is superior to the original model in several aspects.

GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS

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The characteristics of clusters of weather and extreme climate events in China during the past 50 years Yang Ping (杨萍), Hou Wei(侯威), and Feng Guo-Lin(封国林) Chin. Phys. B, 2012, 21 (1):  019201.  DOI: 10.1088/1674-1056/21/1/019201 Abstract ( 1212 )   PDF (2205KB) ( 864 )   The pick-up algorithm by the k-th order cluster for the closest distance is used in the fields of weather and climactic events, and the technical terms clustered index and high clustered region are defined to investigate their temporal and spatial distribution characteristics in China during the past 50 years. The results show that the contribution of extreme high-temperature event clusters changed in the period from the 1960s to the 1970s, and its strength was enhanced. On the other hand, the decreasing trend in the clusters of low-temperature extremes can be taken as a signal for warmer winters to follow in the decadal time scale. Torrential rain and heavy rainfall clusters have both been lessened in the past 50 years, and have different cluster characteristics because of their definitions. Regions with high clustered indexes are concentrated in southern China. The spatial evolution of the heavy rainfall clusters reveals that clustered heavy rainfall has played an important role in the rain-belt pattern over China during the last 50 years.

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Multi-user cognitive radio network resource allocation based on the adaptive niche immune genetic algorithm Zu Yun-Xiao(俎云霄) and Zhou Jie(周杰) Chin. Phys. B, 2012, 21 (1):  019501.  DOI: 10.1088/1674-1056/21/1/019501 Abstract ( 1233 )   PDF (287KB) ( 957 )   Multi-user cognitive radio network resource allocation based on the adaptive niche immune genetic algorithm is proposed, and a fitness function is provided. Simulations are conducted using the adaptive niche immune genetic algorithm, the simulated annealing algorithm, the quantum genetic algorithm and the simple genetic algorithm, respectively. The results show that the adaptive niche immune genetic algorithm performs better than the other three algorithms in terms of the multi-user cognitive radio network resource allocation, and has quick convergence speed and strong global searching capability, which effectively reduces the system power consumption and bit error rate.