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CN 11-5639/O4
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  • The double Lagrangian with U(1, J) symmetry and its applications to the cosmology

    Wu Ya-Bo, Lü Jian-Bo, He Jing, Fu Ming-Hui
    Chin. Phys. B 2007, 16 (12): 3560-3565
    By introducing the double complex scalar field, this paper constructs the double Lagrangian with the potential $V({\it\Phi}(J), {\it\Phi}^{*}(J))=V(|{\it\Phi}(J)|)$, which not only can describe the evolution of quintom Universe, but also can naturally give the spintessence and hessence Universe. Fur...

     
  • Magnetic properties and magnetocaloric effects in Tb6Co1.67Si3 compound

    Shen Jun, Wang Fang, Li Yang-Xian, Sun Ji-Rong, Shen Bao-Gen
    Chin. Phys. B 2007, 16 (12): 3853-3857
    Magnetic properties and magnetocaloric effects of Tb6Co1.67Si3 have been investigated by magnetization measurement. This compound is of a hexagonal Ce6Ni2Si3-type structure with a saturation magnetization of 187emu/g at 5K and a reversible second-order magnetic transition at Curie temperature TC= 18...

     
Chin. Phys. B  
  Chin. Phys. B--2007, Vol.16, No.12
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GENERAL

Economical quantum secure direct communication network with single photons

Deng Fu-Guo, Li Xi-Han, Li Chun-Yan, Zhou Ping, Zhou Hong-Yu
Chin. Phys., 2007, 16 (12): 3553-3559 doi: 10.1088/1009-1963/16/12/001
Full Text: [PDF 259 KB] (Downloads:840)
Show Abstract
In this paper a scheme for quantum secure direct communication (QSDC) network is proposed with a sequence of polarized single photons. The single photons are prepared originally in the same state $\vert 0\rangle$ by the servers on the network, which will reduce the difficulty for the legitimate users to check eavesdropping largely. The users code the information on the single photons with two unitary operations which do not change their measuring bases. Some decoy photons, which are produced by operating the sample photons with a Hadamard, are used for preventing a potentially dishonest server from eavesdropping the quantum lines freely. This scheme is an economical one as it is the easiest way for QSDC network communication securely.

The double Lagrangian with U(1, J) symmetry and its applications to the cosmology Hot!

Wu Ya-Bo, Lü Jian-Bo, He Jing, Fu Ming-Hui
Chin. Phys., 2007, 16 (12): 3560-3565 doi: 10.1088/1009-1963/16/12/002
Full Text: [PDF 131 KB] (Downloads:433)
Show Abstract
By introducing the double complex scalar field, this paper constructs the double Lagrangian with the potential $V({\it\Phi}(J), {\it\Phi}^{*}(J))=V(|{\it\Phi}(J)|)$, which not only can describe the evolution of quintom Universe, but also can naturally give the spintessence and hessence Universe. Furthermore, the $U(1,J)$ symmetry of the double complex Lagrangian is verified, and the total conserved charge within the physical volume is derived by means of the No\"{e}ther theorem. Moreover, it can point out that the `imaginary motion' of the angular parameter in Ref.[14], in fact, is only a real phase displacement in our model.

Evolutionary snowdrift game with disordered environments in mobile societies

Guan Jian-Yue, Wu Zhi-Xi, Wang Ying-Hai
Chin. Phys., 2007, 16 (12): 3566-3570 doi: 10.1088/1009-1963/16/12/003
Full Text: [PDF 328 KB] (Downloads:724)
Show Abstract
We investigate an evolutionary snowdrift game on a square $N=L\times L$ lattice with periodic boundary conditions, where a population of $n_{0}$ ($n_{0}\leq N$) players located on the sites of this lattice can either cooperate with or defect from their nearest neighbours. After each generation, every player moves with a certain probability $p$ to one of the player's nearest empty sites. It is shown that, when $p=0$, the cooperative behaviour can be enhanced in disordered structures. When $p>0$, the effect of mobility on cooperation remarkably depends on the payoff parameter $r$ and the density of individuals $\rho$ ($\rho=n_{0}/N$). Compared with the results of $p=0$, for small $r$, the persistence of cooperation is enhanced at not too small values of $\rho$; whereas for large $r$, the introduction of mobility inhibits the emergence of cooperation at any $\rho<1$; for the intermediate value of $r$, the cooperative behaviour is sometimes enhanced and sometimes inhibited, depending on the values of $p$ and $\rho$. In particular, the cooperator density can reach its maximum when the values of $p$ and $\rho$ reach their respective optimal values. In addition, two absorbing states of all cooperators and all defectors can emerge respectively for small and large $r$ in the case of $p>0$.

The effects of degree correlations on network topologies and robustness

Zhao Jing, Tao Lin, Yu Hong, Luo Jian-Hua, Cao Zhi-Wei, Li Yi-Xue
Chin. Phys., 2007, 16 (12): 3571-3580 doi: 10.1088/1009-1963/16/12/004
Full Text: [PDF 1331 KB] (Downloads:1751)
Show Abstract
Complex networks have been applied to model numerous interactive nonlinear systems in the real world. Knowledge about network topology is crucial to an understanding of the function, performance and evolution of complex systems. In the last few years, many network metrics and models have been proposed to investigate the network topology, dynamics and evolution. Since these network metrics and models are derived from a wide range of studies, a systematic study is required to investigate the correlations among them. The present paper explores the effect of degree correlation on the other network metrics through studying an ensemble of graphs where the degree sequence (set of degrees) is fixed. We show that to some extent, the characteristic path length, clustering coefficient, modular extent and robustness of networks are directly influenced by the degree correlation.

New algorithms for constrained dynamics based on Faddeev--Jackiw approach

Jia Yi-Feng, Wu Ke, Xu Zhi-Qiang
Chin. Phys., 2007, 16 (12): 3581-3588 doi: 10.1088/1009-1963/16/12/005
Full Text: [PDF 147 KB] (Downloads:425)
Show Abstract
In this paper, the Faddeev--Jackiw approach is improved by the Wu elimination method, so a great many complicated computations in solving constraints for the finite-dimensional polynomial-type constrained dynamics can be executed easily by using computers. Moreover, based on the Faddeev--Jackiw approach, a new algorithm of solving the constrained dynamics is presented. The new algorithm is simpler and stricter than the Faddeev--Jackiw approach. Using the new algorithm, the second Cawley counterexample is solved.

A kind of extended Korteweg--de Vries equation and solitary wave solutions for interfacial waves in a two-fluid system

Yang Hong-Li, Song Jin-Bao, Yang Lian-Gui, Liu Yong-Jun
Chin. Phys., 2007, 16 (12): 3589-3594 doi: 10.1088/1009-1963/16/12/006
Full Text: [PDF 136 KB] (Downloads:446)
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This paper considers interfacial waves propagating along the interface between a two-dimensional two-fluid with a flat bottom and a rigid upper boundary. There is a light fluid layer overlying a heavier one in the system, and a small density difference exists between the two layers. It just focuses on the weakly non-linear small amplitude waves by introducing two small independent parameters: the nonlinearity ratio $\varepsilon $, represented by the ratio of amplitude to depth, and the dispersion ratio $\mu $, represented by the square of the ratio of depth to wave length, which quantify the relative importance of nonlinearity and dispersion. It derives an extended KdV equation of the interfacial waves using the method adopted by Dullin {\it et al} in the study of the surface waves when considering the order up to $O(\mu ^2)$. As expected, the equation derived from the present work includes, as special cases, those obtained by Dullin {\it et al} for surface waves when the surface tension is neglected. The equation derived using an alternative method here is the same as the equation presented by Choi and Camassa. Also it solves the equation by borrowing the method presented by Marchant used for surface waves, and obtains its asymptotic solitary wave solutions when the weakly nonlinear and weakly dispersive terms are balanced in the extended KdV equation.

Entanglement in a generalized Jaynes--Cummings model

Zhang Guo-Feng, Liu Jia
Chin. Phys., 2007, 16 (12): 3595-3600 doi: 10.1088/1009-1963/16/12/007
Full Text: [PDF 1366 KB] (Downloads:550)
Show Abstract
We investigate the pairwise entanglement and global entanglement in a generalized Jaynes--Cummings model, which can be used to realize Greenberger--Horne--Zeilinger (GHZ) entangled state (Zheng S B 2001 {\it Phys. Rev. Lett.} {\bf 87} 230404). Our results show that the W-type entangled states cannot be generated based on the model. The dependences of entanglement on Rabi frequency $\lambda$ and dipole--dipole coupling strength ${\it \Omega}$ are given. It is found that there exists the quantum phase transition when $\lambda={\it \Omega}$. For typical experimental data, the critical temperature for pairwise entanglement is on the order of $10^{-6}$\,K. Based on these results, two strategies that overcome decoherence are proposed.

Quantum search via superconducting quantum interference devices in a cavity

Lu Yan, Dong Ping, Xue Zheng-Yuan, Cao Zhuo-Liang
Chin. Phys., 2007, 16 (12): 3601-3604 doi: 10.1088/1009-1963/16/12/008
Full Text: [PDF 152 KB] (Downloads:443)
Show Abstract
We propose a scheme for implementing the Grover search algorithm with two superconducting quantum interference devices (SQUIDs) in a cavity. Our scheme only requires single resonant interaction of the SQUID-cavity system and the required interaction time is very short. The simplicity of the process and the reduction of the interaction time are important for restraining decoherence.

Supplement to the previous application of the first junction condition to a highly symmetric spacetime

Qin Yi-Ping
Chin. Phys., 2007, 16 (12): 3605-3609 doi: 10.1088/1009-1963/16/12/009
Full Text: [PDF 96 KB] (Downloads:373)
Show Abstract
Application of the first junction condition to a highly symmetric spacetime was investigated recently in {\it Chin. Phys. Lett.} B {\bf 546} 189 2006, where a partial differential equation arising from the connection of the Robertson--Walker and the Schwarzschild--de Sitter metrics was presented, but no solutions of the equation were provided. Here we provide a proof to the statement that there exist solutions of the equation. In addition, an example of the solution and some analyses associated with this issue are presented. We find that in connecting the two metrics, there are three conditions which should be satisfied. Of these conditions, one condition constrains the place where the two metrics can take the same value for a local system whose mass is provided which marks the boundary of the system, and the other two constrain the transformation form. In realizing the connection of the two metrics, the latter two conditions are required to be satisfied only at the boundary defined by the former condition.

Finite entropy of Schwarzschild anti-de sitter black hole in different coordinates

Ding Chi-Kun, Jing Ji-Liang
Chin. Phys., 2007, 16 (12): 3610-3615 doi: 10.1088/1009-1963/16/12/010
Full Text: [PDF 120 KB] (Downloads:413)
Show Abstract
This paper studies the finite statistical-mechanical entropy of the Schwarzschild anti-de Sitter (AdS) spacetime arising from quantum massless scalar field by using the `brick wall' approach in the Painlev\'e and Lemaitre coordinates. At first glance, it seems that the results would be different from that in the Schwarzschild-like coordinate since both the Painlev\'e and the Lemaitre spacetimes do not possess the event horizon obviously. However, this paper proves that the entropies in these coordinates are exactly equivalent to that in the Schwarzschild-like coordinate.

Image encryption using high-dimension chaotic system

Sun Fu-Yan, Liu Shu-Tang, Lü Zong-Wang
Chin. Phys., 2007, 16 (12): 3616-3623 doi: 10.1088/1009-1963/16/12/011
Full Text: [PDF 3399 KB] (Downloads:2128)
Show Abstract
In recent years, the chaos based cryptographic algorithms have suggested some new and efficient ways to develop secure image encryption techniques. This paper proposes a new approach for image encryption based on a high-dimensional chaotic map. The new scheme employs the Cat map to shuffle the positions, then to confuse the relationship between the cipher-image and the plain-image using the high-dimensional Lorenz chaotic map preprocessed. The results of experimental, statistical analysis and key space analysis show that the proposed image encryption scheme provides an efficient and secure way for real-time image encryption and transmission.
CLASSICAL AREAS OF PHENOMENOLOGY

PM567-Doped solid dye lasers based on PMMA

Li Xiao-Hui, Fan Rong-Wei, Xia Yuan-Qin, Liu Wei, Chen De-Ying
Chin. Phys., 2007, 16 (12): 3681-3684 doi: 10.1088/1009-1963/16/12/021
Full Text: [PDF 402 KB] (Downloads:787)
Show Abstract
Polymers are a kind of attractive hosts for laser dyes due to their high transparency in both pumping and lasing ranges and superior optical homogeneity. In this paper solid dye samples based on polymethyl methacrylate (PMMA) doped with different concentrations of 1, 3, 5, 7, 8 -pentamethyl-2, 6-diethylpyrromethene-BF$_{2 }$ (PM567) are prepared. The absorption, fluorescence and lasing spectra of the samples are obtained. Wide absorption and fluorescence bands are obtained and a red shift of the maxima of the lasing emission spectra is observed. With the second-harmonic generation of Q-switched Nd:YAG laser (532\,nm, $\sim $20\,ns) pumping the samples longitudinally, the slope efficiencies of the samples are obtained. There is an optimal dye concentration for the highest slope efficiency when the pumping energy is lower than some typical value ($\sim $250\,mJ), and the highest slope efficiency 35.6{\%} is obtained in the sample with a dye concentration of $2\times10^{ - 4}$\,mol/L. Pumping the samples at a rate of 10Hz with a pulse energy as high as 200\,mJ (the fluence is 0.2\,J/cm$^{2})$, the output energy drops to one-half of its initial value after approximate 15500 pulses and the normalized photostability is 5.17\,GJ/mol. A kind of solid dye laser which could have some applications is built.

Preparation and control of entangled states in the two-mode coherent fields interacting with a moving atom via two-photon process

Liu Xiao-Juan, Zhou Bing-Ju, Liu Ming-Wei, Li Shou-Cun
Chin. Phys., 2007, 16 (12): 3685-3691 doi: 10.1088/1009-1963/16/12/022
Full Text: [PDF 266 KB] (Downloads:513)
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We investigate the preparation and the control of entangled states in a system with the two-mode coherent fields interacting with a moving two-level atom via the two-photon transition. We discuss entanglement properties between the two-mode coherent fields and a moving two-level atom by using the quantum reduced entropy, and those between the two-mode coherent fields by using the quantum relative entropy. In addition, we examine the influences of the atomic motion and field-mode structure parameter $p$ on the quantum entanglement of the system. Our results show that the period and the duration of the prepared maximal atom-field entangled states and the frequency of maximal two-mode field entangled states can be controlled, and that a sustained entangled state of the two-mode field, which is independent of atomic motion and the evolution time, can be obtained, by choosing appropriately the parameters of atomic motion, field-mode structure, initial state and interaction time of the system.

Teleportation of a bipartite entangled coherent state via cavity QED

Zhou Yan-Li, Dai Hong-Yi, Yang Li-Jia
Chin. Phys., 2007, 16 (12): 3692-3696 doi: 10.1088/1009-1963/16/12/023
Full Text: [PDF 746 KB] (Downloads:564)
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Based on the atom--cavity--field interaction, this paper proposes a scheme for the teleportation of a bipartite entangled coherent state (ECS) with high fidelity as long as $\left| \alpha \right|$ is not too small. In this proposal, only four cavities and a three-level cascade atom are needed. The fidelity of the ECS is calculated and analysed in detail.

Entanglement properties in a system of a pairwise entangled state

Liu Tang-Kun, Cheng Wei-Wen, Shan Chuan-Jia, Gao Yun-Feng, Wang Ji-Suo
Chin. Phys., 2007, 16 (12): 3697-3703 doi: 10.1088/1009-1963/16/12/024
Full Text: [PDF 1091 KB] (Downloads:571)
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Based on the quantum information theory, this paper has investigated the entanglement properties of a system which is composed of the two entangled two-level atoms interacting with the two-mode entangled coherent fields. The influences of the strength of light field and the two parameters of entanglement between the two-mode fields on the field entropy and on the negative eigenvalues of partial transposition of density matrix are discussed by using numerical calculations. The result shows that the entanglement properties in a system of a pairwise entangled states can be controlled by appropriately choosing the two parameters of entanglement between the two-mode entangled coherent fields and the strength of two light fields respectively.

Properties of field quantum entropy evolution in the Jaynes--Cummings model with initial squeezed coherent states field

Liu Wang-Yun, An Yu-Ying, Yang Zhi-Yong
Chin. Phys., 2007, 16 (12): 3704-3709 doi: 10.1088/1009-1963/16/12/025
Full Text: [PDF 572 KB] (Downloads:552)
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The properties of the field quantum entropy evolution in a system of a single-mode squeezed coherent state field interacting with a two-level atom is studied by utilizing the complete quantum theory, and we focus our attention on the discussion of the influences of field squeezing parameter $\gamma $, atomic distribution angle $\theta $ and coupling strength $g$ between the field and the atom on the properties of the evolution of field quantum entropy. The results obtained from numerical calculation indicate that the amplitude of oscillation of field quantum entropy evolution decreases with the increasing of squeezing parameter $\gamma $, and that both atomic distribution angle $\theta $ and coupling strength $g$ between the field and the atom can influence the periodicity of field quantum entropy evolution.

Intracavity power addition with a close-ended composite four-mirror cavity

Lei Ming, Gong Ma-Li, Liu Qiang, Zhang Hai-Tao, Wang Yun-Xiang
Chin. Phys., 2007, 16 (12): 3710-3718 doi: 10.1088/1009-1963/16/12/026
Full Text: [PDF 588 KB] (Downloads:366)
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We present a novel four-mirror cavity with two active gains to combine power intracavity and also give a detailed theoretical analysis of the combined gain. By using the effective field method, the four-mirror cavity with two gain media can be regarded as a linear resonator with one effective combined gain (ECG), and we procure a theoretical model of the ECG and deduce its exact analytical expression. When the two branch gains are close to each other, the combined gain can be reduced to their product, and the simplified presentation of ECG has been demonstrated. The combined output power which directly reflects the small signal ECG of the four-mirror cavity is studied experimentally, and the results are in good agreement with the theoretical ones.

All-optical XNOR and AND gates simultaneously realized in a single semiconductor optical amplifier with improved dynamics

Li Pei-Li, Huang De-Xiu, Zhang Xin-Liang, Zhu Guang-Xi
Chin. Phys., 2007, 16 (12): 3719-3727 doi: 10.1088/1009-1963/16/12/027
Full Text: [PDF 2055 KB] (Downloads:1135)
Show Abstract
All-optical XNOR and AND logic gates using four-wave mixing (FWM) and cross-gain modulation (XGM) in a single semiconductor optical amplifier (SOA) with improved dynamics are simultaneously realized. By numerical simulation, the effects of the input optical wave powers and injection current on the critical factors of the logic gate performances, such as the ON--OFF contrast ratio, the power-output level of the logic `1', and the difference between power outputs of the logic `1', are investigated in detail. In addition, the effect of the counter-propagating CW pump on the gain recovery is analysed.
ATOMIC AND MOLECULAR PHYSICS

Introduction of the Coulomb dressed potential into atomic scattering

Hu Xian-Quan, Xu Jie, Luo Guang, Ma Yan
Chin. Phys., 2007, 16 (12): 3631-3636 doi: 10.1088/1009-1963/16/12/013
Full Text: [PDF 119 KB] (Downloads:355)
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The model of the Coulomb dressed potential is applied to solving the problem of electron scattering for simplifying the calculation in the electrostatic field and the excimer laser field. The introduction and the application of the model are based on the electric dipole approximation, so the contribution of the electric multipole is neglected. In this paper, rigorous analysis and deduction are carried out for the introduction of the dressed Coulomb potential into the laser field. It is found that the introduction of the dressed potential in the fractional form is feasible only when the laser field (not including far ultraviolet field and x-ray) is a weak field, i.e. the quiver radius of the free electron is smaller than the atomic scale. In addition, the necessary analysis is also conducted of the limitation of the application of the Coulomb dressed potential.

Effects of charge on the structures and spin moments of Ni13 cluster

Xie Zun, Ma Qing-Min, Wang Jing, Liu Ying, Li You-Cheng
Chin. Phys., 2007, 16 (12): 3637-3641 doi: 10.1088/1009-1963/16/12/014
Full Text: [PDF 305 KB] (Downloads:602)
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The structural stability and magnetic properties of the icosahedral Ni$_{13}$, Ni$_{13}^{ + 1}$ and Ni$_{13}^{ - 1}$ clusters have been obtained by utilizing all-electron density functional theory with the generalized gradient approximations for the exchange-correlation energy. The calculated results show that the ground states of neutral and charged clusters all favour a $D_{3d}$ structure, a distorted icosahedron, due to the Jahn--Teller effect. The radial distortions caused by doping one electron and by doping one hole are opposite to each other. Doping one electron will result in a 1/2 decrease and doping one hole will result in a 1/2 increase of the total spin. Both increasing interatomic spacing and decreasing coordination will lead to an enhancement of the spin magnetic moments for Ni$_{13}$ clusters.

Experimental investigation of barium spectra in crossed electric and magnetic fields

Quan Wei, Liu Hong-Ping, Shen Li, Zhan Ming-Sheng
Chin. Phys., 2007, 16 (12): 3642-3646 doi: 10.1088/1009-1963/16/12/015
Full Text: [PDF 522 KB] (Downloads:2804)
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This paper has studied the barium spectra in external magnetic and electric fields on the recently-built system based on a super-conducting solenoid with high stability of better than 1 Gauss. Firstly, we compared the spectra in a high pure magnetic field of $B=4.00000$\,T for different polarized laser, $\sigma^{+}$ and $\sigma^-$. We prove that after a proper shift, the $\sigma^+$ and $\sigma^-$ spectra are completely identical. We also investigated the dependence of the spectral feature in the high magnetic field on an additionally applied crossing electric field. Along with the increase of the electric field, there is an energy shift for every spectral line. Based on a transformative Hamiltonian, we explained this energy shift well.

Novel electrostatic trap for cold polar molecules

Xu Xue-Yan, Ma Hui, Yin Jian-Ping
Chin. Phys., 2007, 16 (12): 3647-3654 doi: 10.1088/1009-1963/16/12/016
Full Text: [PDF 967 KB] (Downloads:607)
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We propose a novel scheme in which cold polar molecules are trapped by an electrostatic field generated by the combination of a pair of parallel transparent electrodes (i.e., two infinite transparent plates) and a ring electrode (i.e., a ring wire). The spatial distributions of the electrostatic fields from the above charged wire and the charged plates and the corresponding Stark potentials for cold CO molecules are calculated; the dependences of the trap centre position on the geometric parameters of the electrode are analysed. We also discuss the loading process of cold molecules from a cold molecular beam into our trap. This study shows that the proposed scheme is not only simple and convenient to trap, manipulate and control cold polar molecules in weak-field-seeking states, but also provides an opportunity to study cold collisions and collective quantum effects in a variety of cold molecular systems, etc.

Cluster-assisted generation of multicharged ions in nanosecond laser ionization of carbon bisulfide clusters at 1064nm

Xiao Xue, Li Hai-Yang, Niu Dong-Mei, Luo Xiao-Lin
Chin. Phys., 2007, 16 (12): 3655-3661 doi: 10.1088/1009-1963/16/12/017
Full Text: [PDF 1026 KB] (Downloads:439)
Show Abstract
The photoionization of seeded carbon bisulfide molecular beam by a 1064\,nm nanosecond Nd-YAG laser with intensities varying from $0.8\times10^{11}$ to $5.6\times10^{11}$\,W/cm$^{2}$ have been studied by time-of-flight mass spectrometry. Multiply charged ions of S$^{q + }$ ($q$ = 2--6) and C$^{q +}$ ($q$ = 2--4) with kinetic energy of hundreds of electron volts have been observed, and there are strong experimental evidences indicating that those multicharged ions originate from the ionization of CS$_{2}$ neat clusters in the beam. An electron recolliding ionization model is proposed to explain the appearance of those multiply charged atomic ions under such low laser intensities.

Laser-manipulated the multiphoton transitions of a harmonically trapped particle

Chen Qiong, Hai Kuo, Hai Wen-Hua
Chin. Phys., 2007, 16 (12): 3662-3667 doi: 10.1088/1009-1963/16/12/018
Full Text: [PDF 206 KB] (Downloads:443)
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A single particle magneto-confined in a one-dimensional (1D) quantum wire experiences a harmonic potential, and imposing a sharply focused laser beam on an appropriate site shapes a $\delta$ potential. The theoretical investigation has demonstrated that for a sufficiently strong $\delta$ pulse the quantum motional stationary state of the particle is one of the eigenstates of the free harmonic oscillator, and it is determined by the site of the laser beam uniquely, namely a quantum state is admissible if and only if the laser site is one of its nodes. The numerical computation shows that all the nodes of the lower energy states with quantum numbers $n \le 20$, except the coordinate origin, are mutually different. So we can manipulate the multiphoton transitions between the quantum states by adjusting the position of the laser $\delta$ pulse and realize the transition from an unknown higher excitation state to a required lower energy state.

Multireference configuration interaction potential curve and analytical potential energy function of the ground and low-lying excited states of CdSe

Gao Feng, Yang Chuan-Lu, Hu Zhen-Yan, Wang Mei-Shan
Chin. Phys., 2007, 16 (12): 3668-3674 doi: 10.1088/1009-1963/16/12/019
Full Text: [PDF 339 KB] (Downloads:709)
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The potential energy curves (PECs) of the ground state ($^{3}\Pi )$ and three low-lying excited states ($^{1}\Sigma $, $^{3}\Sigma $,$^{ 1}\Pi )$ of CdSe dimer have been studied by employing quasirelativistic effective core potentials on the basis of the complete active space self-consistent field method followed by multireference configuration interaction calculation. The four PECs are fitted to analytical potential energy functions using the Murrel--Sorbie potential function. Based on the PECs, the vibrational levels of the four states are determined by solving the Schr\"{o}dinger equation of nuclear motion, and corresponding spectroscopic constants are accurately calculated. The equilibrium positions as well as the spectroscopic constants and the vibrational levels are reported. By our analysis, the $^{3}\Pi $ state, of which the dissociation asymptote is Cd($^{1}$S) + Se($^{3}$P), is identified as a ground state of CdSe dimer, and the corresponding dissociation energy is estimated to be 0.39\,eV. However, the first excited state is only 1132.49\,cm$^{ - 1}$ above the ground state and the $^{3}\Sigma $ state is the highest in the four calculated states.

Spin polarization effect for Co2 molecule

Yan Shi-Ying, Bao Wen-Sheng
Chin. Phys., 2007, 16 (12): 3675-3680 doi: 10.1088/1009-1963/16/12/020
Full Text: [PDF 139 KB] (Downloads:496)
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The density functional theory (DFT)(b3p86) of Gaussian 03 has been used to optimize the structure of the Co$_{2}$ molecule, a transition metal element molecule. The result shows that the ground state for the Co$_{2}$ molecule is a 7-multiple state, indicating a spin polarization effect in the Co$_{2}$ molecule. Meanwhile, we have not found any spin pollution because the wavefunction of the ground state is not mingled with wavefunctions of higher-energy states. So for the ground state of Co$_{2}$ molecule to be a 7-multiple state is the indicative of spin polarization effect of the Co$_{2}$ molecule, that is, there exist 6 parallel spin electrons in a Co$_{2}$ molecule. The number of non-conjugated electrons is the greatest. These electrons occupy different spacial orbitals so that the energy of the Co$_{2}$ molecule is minimized. It can be concluded that the effect of parallel spin in the Co$_{2}$ molecule is larger than the effect of the conjugated molecule, which is obviously related to the effect of electron d delocalization. In addition, the Murrell--Sorbie potential functions with the parameters for the ground state and the other states of the Co$_{2}$ molecule are derived. The dissociation energy $De$ for the ground state of Co$_{2}$ molecule is 4.0489eV, equilibrium bond length $R_{\rm e}$ is 0.2061~nm, and vibration frequency $\omega _\e $ is 378.13~cm$^{ - 1}$. Its diatomic molecule force constants $f_2$, $f_3$, and $f_4$ are 2.4824~aJ$\cdot$nm$^{ - 2}$, -7.3451~aJ$\cdot$nm$^{ - 3}$, and 11.2222~aJ$\cdot$nm$^{ - 4 }$respectively(1~aJ=$10^{-18}$~J). The other spectroscopic data for the ground state of Co$_{2}$ molecule $\omega_{\e}\chi _{\e}$, $B_{\e}$, and $\alpha_{\e}$ are 0.7202~cm$^{-1}$, 0.1347~cm$^{-1 }$, and 2.9120$\times $ 10$^{-1}$~cm$^{-1}$ respectively. And $\omega_{\e}\chi _{\e}$ is the non-syntonic part of frequency, $B_{\e}$ is the rotational constant, $\alpha_{\e}$ is revised constant of rotational constant for non-rigid part of Co$_2$ molecule.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS

Neutrino energy loss by electron capture on strongly screened iron group nuclei

Liu Jing-Jing, Luo Zhi-Quan
Chin. Phys., 2007, 16 (12): 3624-3630 doi: 10.1088/1009-1963/16/12/012
Full Text: [PDF 868 KB] (Downloads:434)
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The influences on the neutrino energy loss rates in iron group nuclei at the same density are investigated in the presence of strong electron screening and in the absence of electron screening. The results show that at a temperature of $15\ti10^9$\,K, the neutrino energy loss rates which come from the electron capture process for most iron group nuclei decrease no more than 2 orders of magnitude but for the others (such as $^{53,55,56,57,58,59,60}$Co, $^{56,59}$Ni) they can decrease about 3 orders of magnitude due to strong electron screening (SES), whereas, at a temperature of $10^9K$ the neutrino energy loss rates of the most iron group nuclei can be diminished greatly due to the SES. For example, $^{61}$Fe, $^{60}$Fe, and $^{62}$Ni the neutrino energy loss rates decrease about 4, 15 and 16 orders of magnitude and for $^{57}$Cr, $^{58}$Cr, and $^{60}$Cr decrease about 18, 12, and 10 orders of magnitude respectively. According to our calculations the neutrino energy loss rates of nuclei $^{58}$Mn, $^{59}$Mn, $^{60}$Mn, and $^{62}$Mn may decrease about 13 orders of magnitude at a temperature of $10^9$\,K due to the SES.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

Evolution of shock waves formed by laser-induced breakdown in air

Zhang Yi, Li Yu-Tong, Zheng Zhi-Yuan, Liu Feng, Zhong Jia-Yong, Lin Xiao Xuan, Liu Feng, Lu Xin, Zhang Jie
Chin. Phys., 2007, 16 (12): 3728-3731 doi: 10.1088/1009-1963/16/12/028
Full Text: [PDF 967 KB] (Downloads:1598)
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The evolution of shock waves produced by 7 ns laser pulses in air is investigated by time-resolved shadowgraph. A nodular structure of the shock wave is observed. It is found that the origin of the structure is the multi-longitudinal-microfocus caused by the astigmatism of the laser beam. The spherical shock waves formed by each microfocus expand gradually and collide with each other, resulting in the nodular structure of the shock wave.

Large area planar plasma sustained by surface microwave

Liang Bo, Ou Qiong-Rong, Liang Yi-Zi, Liang Rong-Qing
Chin. Phys., 2007, 16 (12): 3732-3737 doi: 10.1088/1009-1963/16/12/029
Full Text: [PDF 971 KB] (Downloads:593)
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In this paper, we show theoretically and experimentally that the large-area planar plasma with high density and good uniformity can be sustained by a surface microwave when the electron density is over-dense. From the experimental results we find that the nonuniformities in azimuthal plasma density and electron temperature have been greatly improved and in particular the nonuniformity is less than 10{\%} when the gas pressure is 30 Pa. By improving the antenna shape, enhancing the microwave power and choosing the appropriate gas pressure, the large area planar plasma with high density can be produced.

HL-2A tokamak disruption forecasting based on an artificial neural network

Wang Hao, Wang Ai-Ke, Yang Qing-Wei, Ding Xuan-Tong, Dong Jia-Qi, Sanuki H, Itoh K
Chin. Phys., 2007, 16 (12): 3738-3741 doi: 10.1088/1009-1963/16/12/030
Full Text: [PDF 229 KB] (Downloads:531)
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Artificial neural networks are trained to forecast the plasma disruption in HL-2A tokamak. Optimized network architecture is obtained. Saliency analysis is made to assess the relative importance of different diagnostic signals as network input. The trained networks can successfully detect the disruptive pulses of HL-2A tokamak. The results obtained show the possibility of developing a neural network predictor that intervenes well in advance for avoiding plasma disruption or mitigating its effects.

Numerical investigation of non-local electron transport in laser-produced plasmas

Dong Ya-Lin, Zhao Bin, Zheng Jian
Chin. Phys., 2007, 16 (12): 3742-3746 doi: 10.1088/1009-1963/16/12/031
Full Text: [PDF 324 KB] (Downloads:498)
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Non-local electron transport in laser-produced plasmas under inertial confinement fusion (ICF) conditions is studied based on Fokker-Planck (FP) and hydrodynamic simulations. A comparison between the classical Spitzer--H\"arm (SH) transport model and non-local transport models has been made. The result shows that among those non-local models the Epperlein and Short (ES) model of heat flux is in reasonable agreement with the FP simulation in overdense region. However, the non-local models are invalid in the hot underdense plasmas. Hydrodynamic simulation is performed with the flux limiting model and the non-local model, separately. The simulation results show that in the underdense region of the laser-produced plasmas the temperature given by the flux limiting model is significantly higher than that given with the non-local model.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

A simulation study of microstructure evolution during solidification process of liquid metal Ni

Liu Hai-Rong, Liu Rang-Su, Zhang Ai-Long, Hou Zhao-Yang, Wang Xin, Tian Ze-An
Chin. Phys., 2007, 16 (12): 3747-3753 doi: 10.1088/1009-1963/16/12/032
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A molecular dynamics simulation study has been performed for the microstructure evolution in a liquid metal Ni system during crystallization process at two cooling rates by adopting the embedded atom method (EAM) model potential. The bond-type index method of Honeycutt--Andersen (HA) and a new cluster-type index method (CTIM-2) have been used to detect and analyse the microstructures in this system. It is demonstrated that the cooling rate plays a critical role in the microstructure evolution: below the crystallization temperature $T_{\rm c}$, the effects of cooling rate are very remarkable and can be fully displayed. At different cooling rates of $2.0\times10^{13}$\,K\,$\cdot$\,s$^{-1}$ and $1.0\times10^{12}$\,K\,$\cdot$\,s$^{-1}$, two different kinds of crystal structures are obtained in the system. The first one is the coexistence of the hcp (expressed by (12 0 0 0 6 6) in CTIM-2) and the fcc (12 0 0 0 12 0) basic clusters consisting of 1421 and 1422 bond-types, and the hcp basic cluster becomes the dominant one with decreasing temperature, the second one is mainly the fcc (12 0 0 0 12 0) basic clusters consisting of 1421 bond-type, and their crystallization temperatures $T_{\rm c}$ would be 1073 and 1173\,K, respectively.

New CMOS compatible super junction LDMOST with n-type buried layer

Duan Bao-Xing, Zhang Bo, Li Zhao-Ji
Chin. Phys., 2007, 16 (12): 3754-3759 doi: 10.1088/1009-1963/16/12/033
Full Text: [PDF 778 KB] (Downloads:632)
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A new super-junction lateral double diffused MOSFET (LDMOST) structure is designed with n-type charge compensation layer embedded in the p$^{ - }$-substrate near the drain to suppress substrate-assisted depletion effect that results from the compensating charges imbalance between the pillars in the n-type buried layer. A high electric field peak is introduced in the surface by the pn junction between the p$^{ - }$-substrate and n-type buried layer, which given rise to a more uniform surface electric field distribution by modulation effect. The effect of reduced bulk field (REBULF) is introduced to improve the vertical breakdown voltage by reducing the high bulk electric field around the drain. The new structure features high breakdown voltage, low on-resistance and charges balance in the drift region due to n-type buried layer.

Study of total ionizing dose radiation effects on enclosed gate transistors in a commercial CMOS technology

Li Dong-Mei, Wang Zhi-Hua, Huangfu Li-Ying, Gou Qiu-Jing
Chin. Phys., 2007, 16 (12): 3760-3765 doi: 10.1088/1009-1963/16/12/034
Full Text: [PDF 991 KB] (Downloads:1501)
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This paper studies the total ionizing dose radiation effects on MOS (metal-oxide-semiconductor) transistors with normal and enclosed gate layout in a standard commercial CMOS (compensate MOS) bulk process. The leakage current, threshold voltage shift, and transconductance of the devices were monitored before and after $\gamma $-ray irradiation. The parameters of the devices with different layout under different bias condition during irradiation at different total dose are investigated. The results show that the enclosed layout not only effectively eliminates the leakage but also improves the performance of threshold voltage and transconductance for NMOS (n-type channel MOS) transistors. The experimental results also indicate that analogue bias during irradiation is the worst case for enclosed gate NMOS. There is no evident different behaviour observed between normal PMOS (p-type channel MOS) transistors and enclosed gate PMOS transistors.

Pressure effect on the electron mobility in AlAs/GaAs quantum wells

Hao Guo-Dong, Ban Shi-Liang, Jia Xiu-Min
Chin. Phys., 2007, 16 (12): 3766-3771 doi: 10.1088/1009-1963/16/12/035
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By taking the influence of optical phonon modes into account, this paper adopts the dielectric continuum phonon model and force balance equation to investigate the electronic mobility parallel to the interfaces for AlAs/GaAs semiconductor quantum wells (QWs) under hydrostatic pressure. The scattering from confined phonon modes, interface phonon modes and half-space phonon modes are analysed and the dominant scattering mechanisms in wide and narrow QWs are presented. The temperature dependence of the electronic mobility is also studied in the temperature range of optical phonon scattering being available. It is shown that the electronic mobility reduces obviously as pressure increases from 0 to 4GPa, the confined longitudinal optical (LO) phonon modes play an important role in wide QWs, whereas the interface optical phonon modes are dominant in narrow QWs, the half-space LO phonon modes hardly influence the electronic mobility expect for very narrow QWs.

First-principles calculations of structure and high pressure phase transition in gallium nitride

Tan Li-Na, Hu Cui-E, Yu Bai-Ru, Chen Xiang-Rong
Chin. Phys., 2007, 16 (12): 3772-3776 doi: 10.1088/1009-1963/16/12/036
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The phase transitions of semiconductor GaN from the Wurtzite (WZ) structure and the zinc-blende (ZB) structure to the rocksalt (RS) structure are investigated by using the first-principles plane-wave pseudopotential density functional method combined with the ultrasoft pseudopotential scheme in the generalized gradient approximation (GGA) correction. It is found that the phase transitions from the WZ structure and the ZB structure to the RS structure occur at pressures of 46.1 GPa and 45.2 GPa, respectively. The lattice parameters, bulk moduli and their pressure derivatives of these structures of GaN are also calculated. Our results are consistent with available experimental and other theoretical results. The dependence of the normalized formula-unit volume $V/V_{0 }$ on pressure $P$ is also successfully obtained.

Thermal conductivity of dielectric nanowires with different cross-section shapes

Gu Xiao-Kun, Cao Bing-Yang
Chin. Phys., 2007, 16 (12): 3777-3782 doi: 10.1088/1009-1963/16/12/037
Full Text: [PDF 821 KB] (Downloads:1450)
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Non-equilibrium molecular dynamics simulations have been performed to investigate the effect of the cross-section shape on the thermal conductivity of argon nanowires. Some typical cross-section shapes, such as triangle, square, pentagon, hexagon and circle, are carefully explored. The simulation results show that with the same cross-sectional area of the regular polygons, the thermal conductivities decrease with the reduction of the sides of the polygons, and the thermal conductivity of the circular nanowire is larger than those of the other polygonal ones. Phonon gas kinetic theory is used to analyse the phonon transport in nanowires, and the concept of equivalent diameter is proposed to illustrate the characteristic dimension of the none-circular cross-section.

Structural and thermodynamic properties of wurtzite-type aluminium nitride from first-principles calculations

Wang Yong-Liang, Ai Qiong, Chen Xiang-Rong, Cai Ling-Cang
Chin. Phys., 2007, 16 (12): 3783-3789 doi: 10.1088/1009-1963/16/12/038
Full Text: [PDF 382 KB] (Downloads:774)
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The lattice parameter, bulk modulus and its pressure derivative of the wurtzite-type aluminium nitride (w-AlN) are investigated by using the Cambridge Serial Total Energy Package (CASTEP) program in the framework of Density Functional Theory (DFT). The calculated results are in good agreement with the available experimental data and other theoretical results. Through the quasi-harmonic Debye model, the dependences of the normalized lattice parameters $a/a_{0}$ and $ c/c_{0}$, axial ratio $c/a$, normalized primitive-cell volume $V/V_{0}$, Debye temperature ${\it\Theta} _{\rm D} $ and heat capacity $C_{\rm V}$ on pressure $P $ and temperature $ T$ are obtained. It is found that the interlayer covalent interactions (Al-N bonds) are more (even a little) sensitive to temperature and pressure than intralayer ones (N--N bonds), which gives rise to a little lattice anisotropy in the w-AlN.

Tribological properties of diamond-like carbon films deposited by pulsed laser arc deposition

Zhang Zhen-Yu, Lu Xin-Chun, Luo Jian-Bin
Chin. Phys., 2007, 16 (12): 3790-3797 doi: 10.1088/1009-1963/16/12/039
Full Text: [PDF 2008 KB] (Downloads:576)
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A novel method, pulsed laser arc deposition combining the advantages of pulsed laser deposition and cathode vacuum arc techniques, was used to deposit the diamond-like carbon (DLC) nanofilms with different thicknesses. Spectroscopic ellipsometer, Auger electron spectroscopy, x-ray photoelectron spectroscopy, Raman spectroscopy, atomic force microscopy, scanning electron microscopy and multi-functional friction and wear tester were employed to investigate the physical and tribological properties of the deposited films. The results show that the deposited films are amorphous and the sp$^{2}$, sp$^{3}$ and C--O bonds at the top surface of the films are identified. The Raman peak intensity and surface roughness increase with increasing film thickness. Friction coefficients are about 0.1, 0.15, 0.18, when the film thicknesses are in the range of 17--21~nm, 30--57~nm, 67--123~nm, respectively. This is attributed to the united effects of substrate and surface roughness. The wear mechanism of DLC films is mainly abrasive wear when film thickness is in the range of 17--41~nm, while it transforms to abrasive and adhesive wear, when the film thickness lies between 72 and 123~nm.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

First-principles study on the electronic structure and optical properties of Tl2Cd2(SO4)3 and Rb2Cd2(SO4)4

Xu Bin, Cheng Zheng--Ze, Yi Lin, Cheng Ze
Chin. Phys., 2007, 16 (12): 3798-3802 doi: 10.1088/1009-1963/16/12/040
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With the help of ab initio full-potential linearized augmented plane wave (FPLAPW) method, calculating the electronic structure and linear optical properties is carried out for $X$Cd$_{2}$(SO$_4$)$_{3}$ ($X=$Tl, Rb). The results show that Tl$_{2}$Cd$_{2}$(SO$_4$)$_{3}$ (TlCdS) has a larger band gap than Rb$_{2}$Cd$_{2}$(SO$_4$)$_{3}$ (RbCdS) and the energy bands for RbCdS are more dispersive than those of TlCdS. From their partial densities of states (PDOS), we have observed that the hybridization between S ionic 2p and O atomic 2p orbitals forms SO$_{4}$ ionic groups. The remarkable difference between RbCdS and TlCdS is, however, the degree of hybridization between cation (Tl and Rb) and its surrounding oxygen atoms. In the view of quantum chemistry, the strong p-d hybridization indicates the existence of their cation ionic bonds (Cd-O, Rb-O, and Tl-O). The calculations of TlCdS and RbCdS show their optical properties to be less anisotropic. Their anisotropies in the optical properties mainly occur in a low photon energy region of 5--16 eV.

First principle study of nitrogen vacancy in aluminium nitride

Ye Hong-Gang, Chen Guang-De, Zhu You-Zhang, Lü Hui-Min
Chin. Phys., 2007, 16 (12): 3803-3908 doi: 10.1088/1009-1963/16/12/041
Full Text: [PDF 512 KB] (Downloads:821)
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In the framework of density functional theory, using the plane-wave pseudopotential method, the nitrogen vacancy ($V_{\rm N})$ in both wurtzite and zinc-blende AlN is studied by the supercell approach. The atom configuration, density of states, and formation energies of various charge states are calculated. Two defect states are introduced by the defect, which are a doubly occupied single state above the valance band maximum (VBM) and a singly occupied triple state below the conduction band minimum (CBM) for wurtzite AlN and above the CBM for zinc-blende AlN. So $V_{\rm N}$ acts as a deep donor in wurtzite AlN and a shallow donor in zinc-blende AlN. A thermodynamic transition level $E({3 + } \mathord{\left/ {\vphantom {{3 + } + }} \right. \kern-\nulldelimiterspace} + )$ with very low formation energy appears at 0.7 and 0.6eV above the VBM in wurtzite and zinc-blende structure respectively, which may have a wide shift to the low energy side if atoms surrounding the defect are not fully relaxed. Several other transition levels appear in the upper part of the bandgap. The number of these levels decreases with the structure relaxation. However, these levels are unimportant to AlN properties because of their high formation energy.

Anisotropic properties of TaS2

Qiao Yan-Bin, Li Yan-Ling, Zhong Guo-Hua, Zeng Zhi, Qin Xiao-Ying
Chin. Phys., 2007, 16 (12): 3809-3814 doi: 10.1088/1009-1963/16/12/042
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The anisotropic properties of 1{T}- and 2{H}-TaS$_{2}$ are investigated by the density functional theory within the framework of full-potential linearized augmented plane wave method. The band structures of 1{T}- and 2{H}-TaS$_{2}$ exhibit anisotropic properties and the calculated electronic specific-heat coefficient $\gamma$ of 2{H}-TaS$_{2}$ accords well with the existing experimental value. The anisotropic frequency-dependent dielectric functions including the effect of the Drude term are analysed, where the $\varepsilon^{xx}(\omega)$ spectra corresponding to the electric field ${\bm E}$ perpendicular to the ${z}$ axis show excellent agreement with the measured results except for the $\varepsilon_{1}^{xx}(\omega)$ of 1{T}-TaS$_{2}$ below the energy level of 2.6 eV which is due to the lack of the enough CDW information for reference in our calculation. Furthermore, based on the values of optical effective mass ratio \emph{P} of 1{T} and 2{H} phases it is found that the anisotropy in 2{H}-TaS$_{2}$ is stronger than that in 1{T}-TaS$_{2}$.

The effect of electronic orbital interactions on p-type doping tendency in ZnO series: First-principles calculations

Zhang Fang-Ying, You Jian-Qiang, Zeng Zhi, Zhong Guo-Hua
Chin. Phys., 2007, 16 (12): 3815-3819 doi: 10.1088/1009-1963/16/12/043
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The electronic structures and optical properties of B3 ZnO series of Zn$_{4}$$X_{4-y}M_{y}$($X=$O, S, Se or Te; $M=N$, Sb, Cl or I; $y=0$ or 1) are studied by first-principles calculations using a pseudopotential plane-wave method. The results show that Zn d-$X$ p orbital interactions play an important role in the p-type doping tendency in zinc-based II-VI semiconductors. In Zn$X$, with increasing atomic number of $X$, Zn d-$X$ p orbital interactions decrease and Zn s-$X$ p orbital interactions increase. Additionally, substituting group-V elements for $X$ will reduce the Zn d-$X$ p orbital interactions while substituting group-VII elements for $X$ will increase the Zn d-$X$ p orbital interactions. The results also show that group-V-doped Zn$X$ and group-VII-doped Zn$X$ exhibit different optical behaviours due to their different orbital interaction effects.

Effect of interface-roughness scattering on mobility degradation in SiGe p-MOSFETs with a high-k dielectric/SiO2 gate stack

Zhang Xue-Feng, Xu Jing-Ping, Lai Pui-To, Li Chun-Xia, Guan Jian-Guo
Chin. Phys., 2007, 16 (12): 3820-3826 doi: 10.1088/1009-1963/16/12/044
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A physical model for mobility degradation by interface-roughness scattering and Coulomb scattering is proposed for SiGe p-MOSFET with a high-$k$ dielectric/SiO$_{2}$ gate stack. Impacts of the two kinds of scatterings on mobility degradation are investigated. Effects of interlayer (SiO$_{2})$ thickness and permittivities of the high-$k$ dielectric and interlayer on carrier mobility are also discussed. It is shown that a smooth interface between high-$k$ dielectric and interlayer, as well as moderate permittivities of high-$k$ dielectrics, is highly desired to improve carriers mobility while keeping a low equivalent oxide thickness. Simulated results agree reasonably with experimental data.

Determination of conduction band edge characteristics of strained Si/Si1-xGex

Song Jian-Jun, Zhang He-Ming, Hu Hui-Yong, Dai Xian-Ying, Xuan Rong-Xi
Chin. Phys., 2007, 16 (12): 3827-3831 doi: 10.1088/1009-1963/16/12/045
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The feature of conduction band (CB) of Tensile-Strained Si(TS-Si) on a relaxed Si$_{1 - x}$Ge$_{x}$ substrate is systematically investigated, including the number of equivalent CB edge energy extrema, CB energy minima, the position of the extremal point, and effective mass. Based on an analysis of symmetry under strain, the number of equivalent CB edge energy extrema is presented; Using the K$\cdot$P method with the help of perturbation theory, dispersion relation near minima of CB bottom energy, derived from the linear deformation potential theory, is determined, from which the parameters, namely, the position of the extremal point, and the longitudinal and transverse masses ($m_{\rm l}^{\ast }$ and $m_{\rm t}^{\ast })$ are obtained.

Internal energy and specific heat in a ferromagnetic- antiferromagnetic double layers

Jiang Wei, Guo An-Bang
Chin. Phys., 2007, 16 (12): 3832-3836 doi: 10.1088/1009-1963/16/12/046
Full Text: [PDF 319 KB] (Downloads:441)
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The internal energy and specific heat of a Heisenberg ferro- antiferromagnetic double-layer system are studied by using spin-wave theory and the retarded Green function method at low temperatures. Numerical results show that the antiferromagnetic intralayer coupling $J_2 $ has an important influence on internal energy and specific heat for a four-sublattice system with antiferromagnetic (or ferrimagnetic) interlayer couplings.

Microstructure and magnetic characteristics of nanocrystalline Ni0.5Zn0.5 ferrite synthesized by a spraying--coprecipitation method

Liu Yin, Qiu Tai
Chin. Phys., 2007, 16 (12): 3837-3842 doi: 10.1088/1009-1963/16/12/047
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Nanocrystalline Ni$_{0.5}$Zn$_{0.5}$ ferrite with average grain sizes ranging from 10 to 100~nm is prepared by using a spraying--coprecipitation method. The results indicate that the nanocrystalline Ni$_{0.5}$Zn$_{0.5}$ ferrite is ferromagnetic without the superparamagnetic phenomenon observed at room temperature. Specific saturation magnetization of nanocrystalline Ni$_{0.5}$Zn$_{0.5}$ ferrite increases from 40.2 to 75.6 emu/g as grain size increases from 11 to 94nm. Coercivity of nanocrystalline Ni$_{0.5}$Zn$_{0.5}$ ferrite increases monotonically when $d < 62$~nm.The relationship between the coercivity and the mean grain size is well fitted into a relation $H_{\rm c }\sim d^{3}$. A theoretically evaluated value of the critical grain size is 141nm larger than the experimental value 62nm for nanocrystalline Ni$_{0.5}$Zn$_{0.5}$ ferrite. The magnetic behaviour of nanocrystalline Ni$_{0.5}$Zn$_{0.5}$ ferrite may be explained by using the random anisotropy theory.

Magnetic properties and magnetocaloric effect in TbCo2-xFex compounds

Zou Jun-Ding, Shen Bao-Gen, Sun Ji-Rong
Chin. Phys., 2007, 16 (12): 3843-3847 doi: 10.1088/1009-1963/16/12/048
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Magnetic properties and magnetocaloric effect in TbCo$_{2 - x}$Fe$_{x}$ compounds are studied by DC magnetic measurement. With increasing content of Fe, the entropy changes decrease slightly, though the Curie temperature is tuned from 231 K ($x=0$) to 303 K ($x=0.1$). Magnetic entropies of TbCo$_{2}$ compound are calculated by using mean field approximation (MFA). Results estimated by using Maxwell relation are consistent with that of MFA calculation. It is shown that the entropy changes are mainly derived from the magnetic entropy changes. The lattice has almost no contribution to the entropy change in the vicinity of phase transition.

Magnetic properties and magnetic entropy changes of La1-xPrxFe11.5Si1.5 compounds with 0≤x≤ 0.5

Shen Jun, Gao Bo, Yan Li-Qin, Li Yang-Xian, Zhang Hong-Wei, Hu Feng-Xia, Sun Ji-Rong
Chin. Phys., 2007, 16 (12): 3848-3852 doi: 10.1088/1009-1963/16/12/049
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Magnetic properties and magnetic entropy changes in LaFe$_{11.5}$Si$_{1.5}$ have been investigated by partially substituting Pr by La. It is found that La$_{1 - x}$Pr$_{x}$Fe$_{11.5}$Si$_{1.5}$ compounds remain cubic NaZn$_{13}$-type structures even when the Pr content is increased to 0.5, i.e. $x = 0.5$. Substitution of Pr for La leads to a reduction in both the crystal constant and the Curie temperature. A stepwise magnetic behaviour in the isothermal magnetization curves is observed, indicating that the characteristic of the itinerant electron metamagnetic (IEM) transition above TC becomes more prominent with the Pr content increasing. As a result, the magnetic entropy change is remarkably enhanced from 23.0 to 29.4\,J/kg$\cdot$K as the field changes from 0 to 5\,T, with the value of $x$ increasing from 0 to 0.5. It is more attractive that the magnetic entropy changes for all samples are shaped into high plateaus in a wide range of temperature, which is highly favourable for Ericsson-type magnetic refrigeration.

Magnetic properties and magnetocaloric effects in Tb6Co1.67Si3 compound Hot!

Shen Jun, Wang Fang, Li Yang-Xian, Sun Ji-Rong, Shen Bao-Gen
Chin. Phys., 2007, 16 (12): 3853-3857 doi: 10.1088/1009-1963/16/12/050
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Magnetic properties and magnetocaloric effects of Tb6Co1.67Si3 have been investigated by magnetization measurement. This compound is of a hexagonal Ce6Ni2Si3-type structure with a saturation magnetization of 187emu/g at 5K and a reversible second-order magnetic transition at Curie temperature TC= 186K. A magnetic entropy change \Delta S = 7J.kg-1.K-1 is observed for a magnetic field change from 0 to 5. A large value of refrigerant capacity (RC) is found to be 330J/kg for fields ranging from 0 to 5T. The large RC, the reversible magnetization around TC and the easy fabrication make the Tb6Co1.67Si3 compound a suitable candidate for magnetic refrigerants in a corresponding temperature range.

The symmetric and antisymmetric superexchange interactions in spin-Peierls system

Liu Hai-Lian, Wang Zhi-Guo, Yang Cheng-Quan, Huang Xian-Shan, Shi Yun-Long
Chin. Phys., 2007, 16 (12): 3858-3862 doi: 10.1088/1009-1963/16/12/051
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The influences of Dzyaloshinskii--Moriya (DM) interaction and Kaplan--Shekhtman--Entinwohlman--Aharony (KSEA) interaction on the dimerization of a spin-Peierls system are investigated theoretically by using the Lanczos numerical method. The ground state of the spin-Peierls system is still dimerized phase when both of the DM and the KSEA interactions have the same value with Heisenberg interaction. It is found that the KSEA interaction and uniform DM interaction are always against systemic dimerization, but the staggered DM interaction acts in favour of dimerization. Furthermore, the influences of the DM and the KSEA interactions are also studied in terms of the ground state index rate and the energy gap index rate of the dimerized Heisenberg system. The results show that the DM interaction makes the index rates larger, while the KSEA interaction makes them smaller.

First principles study on the electronic structure and magnetism of Fe1-xCoxSi alloys

Hu Zhi-Hui, He Wei, Sun Young, Cheng Zhao-Hua
Chin. Phys., 2007, 16 (12): 3863-3867 doi: 10.1088/1009-1963/16/12/052
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Electronic and magnetic properties of Fe1 - x CoxSi alloys were investigated by using a full-potential linear augmented-plane-wave method based on density functional theory. Electronic structure calculation demonstrates that half-metallic property appears in the Fe-rich region of 0 < x \le 0.25, while the alloys turn out to be a magnetic metal for x > 0.25. The concentration dependence of the magnetic moment of the alloys can be understood by the fixed Fermi level at minority band in Fe-rich region, as well as at the majority band in Co-rich region. In Fe-rich alloys, the electronic structure and the magnetic properties at Fe site depend mainly on the spin-polarization of nearest neighbouring Co atoms, while in Co-rich alloys, these features at Co site arise mainly from the neighbours of Fe atoms.

Growth parameter dependence of magnetic property of CrAs thin film

Bi Jing-Feng, Zhao Jian-Hua, Deng Jia-Jun, Zheng Yu-Hong, Wang Wei-Zhu, Lu Jun, Ji Yang, Li Shu-Shen
Chin. Phys., 2007, 16 (12): 3868-3872 doi: 10.1088/1009-1963/16/12/053
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This paper has systematically investigated the substrate temperature and thickness dependence of surface morphology and magnetic property of CrAs compound films grown on GaAs by molecular-beam epitaxy. It finds that the substrate temperature affects the surface morphology and magnetic property of CrAs thin film more potently than the thickness.

Two-photon absorption coefficient dichroism in II--VI semiconductor crystals

Ma Hong, Ma Guo-Hong, Ma Hong-Liang, Tang Sing-Hai
Chin. Phys., 2007, 16 (12): 3873-3878 doi: 10.1088/1009-1963/16/12/054
Full Text: [PDF 377 KB] (Downloads:531)
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Considering two beams propagate in semiconductor crystal, this paper discusses the polarization dependence of pump beam-induced intensity attenuation of probe beam due to two-photon absorption (TPA). Numerical calculation and experimental measurement demonstrate that TPA coefficient is polarization dependent. For homogeneous materials, probe beam attenuation arises from the imaginary part of diagonal and off-diagonal components of third-order nonlinear susceptibilities.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS

Hawking radiation via tunnelling from general stationary axisymmetric black holes

Zhang Jing-Yi, Fan Jun-Hui
Chin. Phys., 2007, 16 (12): 3879-3884 doi: 10.1088/1009-1963/16/12/055
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Hawking radiation is viewed as a tunnelling process. In this way the emission rates of massless particles and massive particles tunnelling across the event horizon of general stationary axisymmetric black holes are calculated, separately. The emission spectra of these two different kinds of outgoing particles have the same functional form and both are consistent with an underlying unitary theory.
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