Chin. Phys. B
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CN 11-5639/O4
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Chin. Phys. B  
  Chin. Phys. B--2001, Vol.10, No.9
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GENERAL

COHERENT INFORMATION ON THERMAL RADIATION NOISE CHANNEL: AN APPROACH OF INTEGRAL WITHIN ORDERED PRODUCT OF OPERATORS

Chen Xiao-yu, Qiu Pei-liang
Chin. Phys., 2001, 10 (9): 779-782 doi: 10.1088/1009-1963/10/9/001
Full Text: [PDF 207 KB] (Downloads:393)
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An analytical expression is given to the coherent information of the thermal radiation signal transmitted over the thermal radiation noise channel, one of the most essential quantum Gaussian channels. Focusing on the single normal mode of the thermal radiation signal and noise, we resolve the entangled state density operator, which characterizes quantum information transmission, into a direct product of two parts, with each part being a thermal radiation density operator. The calculation is aided by the technique known as "integral within ordered product of operators".

OPTICAL SPACE OF THE KERR SOLUTIONS

Lü Jun-li
Chin. Phys., 2001, 10 (9): 783-786 doi: 10.1088/1009-1963/10/9/002
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In this paper, we discuss the optical geometry of the Kerr solutions, and show the embedding diagram at the equator θ=π/2 for the optical space of the Kerr solution with a/M=1. It is noticed that at the equator θ=π/2, the Gaussian curvature K for the ordinary space is negative, and the \stackrel{\sim}{K} for the optical space is positive.

STATIC SPHERICALLY SYMMETRIC SOLUTION OF EINSTEIN GRAVITY COUPLED TO ELECTRO-MAGNETIC AND SCALAR FIELDS

Chen Guang
Chin. Phys., 2001, 10 (9): 787-789 doi: 10.1088/1009-1963/10/9/003
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The static spherically symmetric solution of Einstein gravity coupled to electromagnetic and scalar fields is obtained under the consideration of the self-gravitational interaction of the electromagnetic and scalar fields, which is singularity-free and stable.

NUMERICAL ANALYSIS OF A CHAOTIC SYSTEM

Ren Zhi-jian
Chin. Phys., 2001, 10 (9): 790-795 doi: 10.1088/1009-1963/10/9/004
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This paper further proves that a single spiral strange attractor can be observed in an extremely simple autonomous electrical circuit by computer simulation. It is of third order and has only one nonlinear element: a three-segment piece-wise linear resistor. The digital analyses show that the strange attractor has peculiar features compared with other third-order differential systems.

ON FEEDBACK CONTROL OF DELAYED CHAOTIC SYSTEM

Li Li-xiang, Peng Hai-peng, Lu Hui-bin, Guan Xin-ping
Chin. Phys., 2001, 10 (9): 796-804 doi: 10.1088/1009-1963/10/9/005
Full Text: [PDF 256 KB] (Downloads:437)
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In this paper two different types of feedback control technique are discussed: the standard feedback control and the time-delay feedback control which have been successfully used in many control systems. In order to understand to what extent the two different types of control technique are useful in delayed chaotic systems, some analytic stabilization conditions for chaos control from the two types of control technique are derived ased on Lyapunov stabilization arguments. Similarly, we discuss the tracking problem by applying the time-delay feedback control. Finally, numerical examples are provided.
NUCLEAR PHYSICS

MULTI-LAMBDA MATTER IN A CHIRAL HADRONIC MODEL

Guo Hua, Yang Shu, Hu Xiang, Liu Yu-xin
Chin. Phys., 2001, 10 (9): 805-808 doi: 10.1088/1009-1963/10/9/006
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Multi-lambda matter is investigated in the framework of a chiral hadronic model. It is shown that multi-lambda matter consisting of {N,Λ} is a metastable state as the strangeness per baryon and the density of hadronic matter are varied. The effective lambda mass decreases as the baryon density increases, and remains larger than that of the nucleon.
CLASSICAL AREAS OF PHENOMENOLOGY

UNCORRELATED TWO-MODE SU(1,1) COHERENT STATES

Hou Li-zhen, Zeng Gao-jian
Chin. Phys., 2001, 10 (9): 821-826 doi: 10.1088/1009-1963/10/9/009
Full Text: [PDF 243 KB] (Downloads:796)
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We have constructed a new kind of two-mode bosonic realization of SU(1,1) Lie algebra, on the basis of which the SU(1,1) generalized coherent states in the two-mode Fock space are derived. These two-mode SU(1,1) coherent states, which are called uncorrelated two-mode SU(1,1) coherent states, include three special cases. For these states, we study the mean photon number distribution and their non-classical properties, which are photon anti-bunching, violations of Cauchy-Schwarz inequality and two-mode squeezing.

ANALYSIS OF LASING PERFORMANCES OF Yb3+-DOPED YAG, FAP, KYW CRYSTALS

Huang Li-lei, Hong Zhi, Fang Da-wei
Chin. Phys., 2001, 10 (9): 827-831 doi: 10.1088/1009-1963/10/9/010
Full Text: [PDF 238 KB] (Downloads:328)
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The Yb3+ laser emitting at a 1.03μm wavelength has been evoking strong interest recently due to its advantages of long fluorescence lifetime, broad absorption band and the fact that it never shows concentration quenching. On the other hand, as a laser of three-level system it has, in general, a relatively high threshold power, which makes it important to seek some suitable host crystals to reduce this. Here, we present a comparison of the lasing performances of Yb3+-doped YAG [Y3Al5O12], FAP [Ca5(PO4)3F] and KYW [KY(WO4)2] crystals, including threshold power and slope efficiency, with those of the Nd:YAG laser based on the threshold formula of three-and four-level systems deduced by the authors. The results show that the Yb3+ laser can output a power larger than the Nd:YAG laser does in the case of comparably higher pumping power, if the length of the lasing rod and the concentration of the active ions satisfy some conditions. The theoretical results are also close to the experimental results reported.
ATOMIC AND MOLECULAR PHYSICS

THEORETICAL CALCULATION OF THE RELATIVISTIC SUBCONFIGURATION-AVERAGED TRANSITION ENERGIES

Zhang Ji-yan, Yang Xiang-dong, Yang Guo-hong, Zhang Bao-han, Lei An-le, Liu Hong-jie, Li Jun
Chin. Phys., 2001, 10 (9): 809-813 doi: 10.1088/1009-1963/10/9/007
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A method for calculating the average energies of relativistic subconfigurations in highly ionized heavy atoms has been developed in the framework of the multiconfigurational Dirac-Fock theory. The method is then used to calculate the average transition energies of the spin-orbit-split 3d-4p transition of Co-like tungsten, the 3d-5f transition of Cu-like tantalum, and the 3d-5f transitions of Cu-like and Zn-like gold samples. The calculated results are in good agreement with those calculated with the relativistic parametric potential method and also with the experimental results.

FIELD IONIZATION OF MOLECULES IN AN INTENSE LASER FIELD

Wu Cheng-yin, Gong Qi-huang
Chin. Phys., 2001, 10 (9): 814-820 doi: 10.1088/1009-1963/10/9/008
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In order to predict the field ionization probabilities, the accurate ab initio electrostatic potential of molecules has to be calculated. However, the calculation of the full ab initio electrostatic potential of molecules is complicated, even impossible for some larger molecules with low symmetry. Here, we present a semi-empirical model to treat the field ionization of molecules in an intense laser field. In this model, a modified Coulomb potential is used to take the place of the complicated ab initio electrostatic potential of molecules. The analytic equations of the Keldysh adiabatic parameter using the Coulomb potential and the modified Coulomb potential have first been given. Using our semi-empirical model, we have calculated the field ionization probabilities and the Keldysh adiabatic parameters of O2, N2, SO2, C2H4, CH3CN and C6H6 in an intense laser field. The results agree excellently with the calculations using the ab initio electrostatic potential of molecules. As the modified parameter for the Coulomb potential can be found from experimental measurements, the field ionization mechanism of molecules can be immediately predicted with our semi-empirical model.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

STUDY OF THE Al/GRAPHITE INTERFACE

Lu Hua, Shen Dian-hong, Deng Xin-fa, Xue Qi-kun, N. Froumin, M. Polak
Chin. Phys., 2001, 10 (9): 832-835 doi: 10.1088/1009-1963/10/9/011
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Thin Al films with a thickness of 20-30nm were prepared by ultra-high vacuum deposition of Al onto a graphite surface parallel to a (0001) basal plane. The samples were annealed up to 1070K. X-ray photoelectron spectroscopy analysis has shown that for temperatures just higher than 770K, a little carbide occurs in the Al film and only an Al-C phase is present at the Al/graphite interface. After annealing at 970K, the Al4C3 phase can be observed, and the binding energy of the Al2p electrons increases continuously from 72.7 to 74.2eV with increasing temperature up to 1070K. Auger electron spectroscopy depth profiles are measured to investigate the phases existing in the Al film as well as at the Al/graphite interface. It is found that the Al4C3 phase at the interface is the final product of a series of Al carbides from the interfacial reaction between Al and graphite.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

INFLUENCES OF NONLINEAR INTERACTIONS ON POLARITONS

Niu Jia-sheng, Luo Ying, Ma Ben-kun
Chin. Phys., 2001, 10 (9): 836-839 doi: 10.1088/1009-1963/10/9/012
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In this paper, we have analysed theoretically the polarization and dielectric constant generated by the nonlinear interactions between ions in ionic crystals. The spectrum of polaritons (coupling modes of photons and optical phonons) under nonlinear interactions has been developed. A new branch of dispersion relations has emerged in the original frequency gap between ωTO and ωLO.

TERAHERTZ SPECTRA EMITTED FROM HOT CARRIERS IN TWO-DIMENSIONAL SEMICONDUCTORS

Lei Xiao-lin, Liu Shi-yong
Chin. Phys., 2001, 10 (9): 840-843 doi: 10.1088/1009-1963/10/9/013
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We propose a simple method to calculate the spectrum of spontaneous terahertz (THz) emission from hot carriers in two-dimensional semiconductors by means of transport quantities, which are easily obtained during the process of solving the transport problem using the recently developed balance-equation approach for THz-driven transport. The method has been applied to examine the surface emission from a GaAs/AlGaAs heterojunction and the edge emission from a GaAs-based multiple quantum-well system subjected to strong dc biases. The theoretical results obtained are in reasonably good agreement with measurements.

COULOMB BLOCKADE OSCILLATIONS OF Si SINGLE-ELECTRON TRANSISTORS

Wang Tai-hong, Li Hong-wei, Zhou Jun-ming
Chin. Phys., 2001, 10 (9): 844-846 doi: 10.1088/1009-1963/10/9/014
Full Text: [PDF 171 KB] (Downloads:556)
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Coulomb blockade oscillations of Si single-electron transistors, which are fabricated completely by the conventional photolithography technique, have been investigated. Most of the single-electron transistors clearly show Coulomb blockade oscillations and these oscillations can be periodic by applying negative voltages to the in-plane gates. A shift of the peak positions is observed at high temperatures. It is also found that the fluctuation of the peak spacing cannot be neglected.

INVESTIGATION OF EMPIRICAL LAWS FOR SUPERCONDUCTIVITY OF ALLOY AND COMPOUND SUPERCONDUCTORS

Liu Long-jian, Zhang Zhuang-jian
Chin. Phys., 2001, 10 (9): 847-852 doi: 10.1088/1009-1963/10/9/015
Full Text: [PDF 237 KB] (Downloads:477)
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By studying the average effect of the electronegativity of alloy and compound superconductors, some empirical laws are found. The average value of the electronegativity of alloy superconductors \overlineχ is from 1.3 to 1.9, most of which is concentrated in the region 1.5<\overlineχ<1.8. The \overlineχ of many higher Tc superconductors is nearly 1.60. All these characteristics are similar to element superconductors. The average value of the electronegativity \overlineη of positive valence elements in oxide superconductors is from 1.3 to 1.6, and the average effect of an electronegativity of zero on every element \overlineζ is from 1.75 to 2.00. The mean of \overlineη and \overlineζ is from 1.5 to 1.8. When both \overlineη and \overlineζ are near the limit value (1.3 or 1.6 and 1.75 or 2.00), the material has a very low Tc, even is non-superconductive. The \overlineζ of other compound superconductors is either too high or too low, and the \overlineζ is too low so that the Tc of these superconductors is quite low. Studying the average effect of the electronegativity of non-superconducting compounds further confirms the laws.

CRYSTAL STRUCTURE AND MAGNETIC PROPERTIES OF La1.2Sr1.8-xCaxMn2O7

He Lun-hua, Zhang Pan-lin, Yan Qi-wei
Chin. Phys., 2001, 10 (9): 853-856 doi: 10.1088/1009-1963/10/9/016
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The effect of divalent cation substitution on the structure and magnetic properties of La1.2Sr1.8-xCaxMn2O7 (x = 0-0.900) is investigated in this paper. Partly replacing divalent cation Sr2+ by Ca2+ ions results in the weakening and then disappearance of long-range ferromagnetic ordering, and the formation of spin canting and low-temperature spin-glass. Based on structural analysis by Rietveld profile fitting, we suggest that this variation of magnetic property be related to a Jahn-Teller-type attice distortion of MnO6 octahedra due to the introduction of the smaller sized Ca2+ ions.

THE STRUCTURE AND MAGNETIC PROPERTIES OF La2-2xSr1Ca2xMn2O7 (x=0.25-1.00)

He Lun-hua, Zhang Pan-lin, Yan Qi-wei
Chin. Phys., 2001, 10 (9): 857-861 doi: 10.1088/1009-1963/10/9/017
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In this paper, the effect of divalent cation substitution on the structure and magnetic properties in La2-2xSr1Ca2xMn2O7 have been investigated systematically using bulk samples with a wide doping concentration range 0.25≤x≤1.00. Replacing trivalent La ions by divalent Ca ions results in the weakening and then disappearance of the long-range ferromagnetic (FM) ordering, the formation of spin canting, antiferromagnetic (AFM) ordering and low-temperature spin-glass. These results show that increasing the hole-doping concentration significantly suppresses the FM state. We suggest that this variation of magnetic properties is related to the competition of the FM and AFM interactions resulting from the change of Mn3+/Mn4+ ratio and Jahn-Teller-type lattice distortion of MnO6 octahedra due to the introduction of Ca2+ ions.

ANISOTROPIC CHARACTERISTICS OF DEMAGNETIZATION CURVE FOR NANOCRYSTALLINE Nd-Fe-B MAGNET CALCULATED BY MICROMAGNETICS

Jin Han-min, Wang Xue-feng, Zhao Su-fen, Yan Yu
Chin. Phys., 2001, 10 (9): 862-868 doi: 10.1088/1009-1963/10/9/018
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The demagnetization curves for nanocrystalline Nd-Fe-B magnets of a stoichiometric composition were calculated by making use of the finite element technique of micromagnetics. The curve, especially iHc, varies in a wide range with the direction of applied field if the grain number N is taken to be small. With the increase of N, the range becomes smaller and the average of iHc decreases and approaches a limit iHc(N=∞). iHc for finite N is larger than, or at least equal to, iHc(N=∞). Jr/Js is weakly affected by N and the field direction. Jr/Js(N=∞) decreases with the increase of grain size L. These are larger than the experimental values for the Nd-rich Nd2.33Fe14B1.06Si0.21 magnets by ~0.05. iHc(N=∞) increases with the increase of L, and is close to or somewhat smaller than the experimental values of the Nd-rich magnet, as would be expected. In contrast, the curve calculated for the non-interacting grain system (Stoner-Wohlfarth model) of N≥30 depends neither on the field direction nor on N.

REMARKABLE IMPROVEMENT OF THE COERCIVITY OF TbMn6Sn6 COMPOUND BY MELT-SPINNING PROCESS

Zhao Peng, Zhang Shao-ying, Zhang Hong-wei, Yan A-ru, Shen Bao-gen
Chin. Phys., 2001, 10 (9): 869-873 doi: 10.1088/1009-1963/10/9/019
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The melt-spinning process has been carried out to improve the hard-magnetic properties of the TbMn6Sn6 compound. For the TbMn6Sn6 ribbons quenched at a rate of 40m/s and annealed at 545K for 30min, the highest coercivity of about 0.6T is achieved at room temperature, which is much higher than that of the TbMn6Sn6 ingot. Both the ingot and the ribbon coercivities will increase with decreasing temperature. For ribbons, a greater improvement of coercivity has been made at lower temperatures. Microstructural studies show the uniform nanocrystalline distribution in the TbMn6Sn6 ribbons and a small amount of Tb-rich phase in grain boundaries. The observed remarkable improvement of magnetic hardening in ribbons is believed to arise from the uniform nanoscale microstructure and the domain-wall pinning at the grain boundaries.

TIME-RESOLVED PHOTOLUMINESCENCE OF SINTERED ZnO CERAMICS

Wen Xiao-ming, N. Ohno, Zhang Zhong-ming
Chin. Phys., 2001, 10 (9): 874-876 doi: 10.1088/1009-1963/10/9/020
Full Text: [PDF 198 KB] (Downloads:556)
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The time-resolved photoluminescence (TRPL) of sintered ZnO ceramics was measured at low temperatures. A broad luminescence band was observed in the visible region. The TRPL experiment shows that photoluminescence decay behaviour can be depicted as t-n(r). The decay rate n(r) and lifetime are wavelength dependent, and the former varies exponentially with wavelength. The power-lowering behaviour of the luminescence intensity indicates that the luminescence band originates from the recombination of donor-acceptor pairs.
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