Chin. Phys. B
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CN 11-5639/O4
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  • WEAK QUANTUM FLUX CREEP AND STRONG PINNING IN THE NEW SUPERCONDUCTOR MgB2

    Zhao Zhi-wen, Wen Hai-hu, Li Shi-liang, Ni Yong-ming, Ren Zhi-an, Che Guang-can, Yang Hai-peng, Liu Zhi-yong, Zhao Zhong-xian
    Chin. Phys. B 2001, 10 (4): 340-342
    The newly discovered superconductor MgB2 has a transition temperature Tc of about 40 K, which is touching the upper line of that predicted by the phonon-mediated Bardeen--Cooper--Schrieffer (BCS) theory. It is interesting to investigate the flux creep in MgB2 and compare it with other superconductor...

     
Chin. Phys. B  
  Chin. Phys. B--2001, Vol.10, No.4
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GENERAL

BIRKHOFF'S EQUATIONS AND GEOMETRICAL THEORY OF ROTATIONAL RELATIVISTIC SYSTEM

Luo Shao-kai, Chen Xiang-wei, Fu Jing-li
Chin. Phys., 2001, 10 (4): 271-276 doi: 10.1088/1009-1963/10/4/001
Full Text: [PDF 247 KB] (Downloads:380)
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The Birkhoffian and Birkhoff's functions of a rotational relativistic system are constructed, the Pfaff action of rotational relativistic system is defined, the Pfaff-Birkhoff principle of a rotational relativistic system is given, and the Pfaff-Birkhoff-D'Alembert principles and Birkhoff's equations of rotational relativistic system are constructed. The geometrical description of a rotational relativistic system is studied, and the exact properties of Birkhoff's equations and their forms on {\vec R}×T*M for a rotational relativistic system are obtained. The global analysis of Birkhoff's equations for a rotational relativistic system is studied, the global properties of autonomous, semi-autonomous and non-autonomous rotational relativistic Birkhoff's equations, and the geometrical properties of energy change for rotational relativistic Birkhoff's equations are given.

A GENERATION OF EXACTLY SOLVABLE ANHARMONIC SYMMETRIC OSCILLATORS

Liu Ke-jia
Chin. Phys., 2001, 10 (4): 277-281 doi: 10.1088/1009-1963/10/4/002
Full Text: [PDF 167 KB] (Downloads:296)
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Using the ideas of supersymmetric quantum mechanics, we exactly solve a continuous family of anharmonic potentials, which are the supersymmetric partners of the linear harmonic oscillators. The family includes a series of potentials in which the excited-state energy is the same as that of the harmonic oscillators, but the ground-state energy can be any value lower than the excited states. The shape of the potential is variable, which includes the double-well and triple-well potentials. All the potentials obtained in this paper are free of singularities, and the supersymmetry of the solutions is unbroken.
NUCLEAR PHYSICS

THE NUCLEAR STRUCTURE AND BACKBENDING PHENOMENON FOR 114-130Xe ISOTOPES

Shi Zhu-yi, Liu Yong, Sang Jian-ping
Chin. Phys., 2001, 10 (4): 282-285 doi: 10.1088/1009-1963/10/4/003
Full Text: [PDF 265 KB] (Downloads:303)
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In view of interacting boson fermion formalism, a microscopic sdIBM-2 +2q.p. model is used to describe the ground-state band, β-band, γ-band and two-quasi-particle band for 114-130Xe isotopes. The theoretical investigations indicate that the backbending is caused by crossing of the two-quasi-proton band and the ground-state band. This result seems to provide a possible way for understanding the backbending phenomenon of 114-130Xe isotopes.
CLASSICAL AREAS OF PHENOMENOLOGY

ABSORPTION PROPERTIES OF A DRIVEN FOUR-LEVEL DOPPLER-BROADENED SYSTEM

Yuan Shi, Wu Jin-hui, Gao Jin-Yue
Chin. Phys., 2001, 10 (4): 300-306 doi: 10.1088/1009-1963/10/4/007
Full Text: [PDF 216 KB] (Downloads:365)
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This paper deals with the absorption spectra of a weak probe in a four-level Doppler-broadened system driven by three coherent fields. The main aim is to extend earlier studies of the spontaneous emission spectrum and to present a comprehensive survey of the spectral features of this system. In addition to a derivation of exact formulae for the spectra, we give an explanation with the help of an appropriate set of dressed atomic states. We also get a deeper insight into the physical origin of gain in view of the existence of a population inversion between the levels of the lasing transition. Finally, we explore the effect of Doppler broadening on the absorption profile of the weak probe.

STEADY SOLUTIONS OF THE OPTICAL SOLITON EQUATION WITH A NONLINEAR RESPONSE DELAY TERM

Lin Chang, Zhang Xiu-Lian
Chin. Phys., 2001, 10 (4): 307-309 doi: 10.1088/1009-1963/10/4/008
Full Text: [PDF 175 KB] (Downloads:396)
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The exact solution of the optical soliton equation with a nonlinear response delay term has been obtained by using the method of separating variables. The new type of optical solitary wave solution, which is quite different from the bright and dark soliton solutions, has been found for a special case.

INCOHERENTLY COUPLED SCREENING-PHOTOVOLTAIC SOLITON FAMILIES IN BIASED PHOTOVOLTAIC PHOTOREFRACTIVE CRYSTALS

Hou Chun-feng, Li Bin, Sun Xiu-dong, Jiang Yong-yuan, Xu Ke-bin
Chin. Phys., 2001, 10 (4): 310-313 doi: 10.1088/1009-1963/10/4/009
Full Text: [PDF 179 KB] (Downloads:453)
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It is shown that the existence of incoherently coupled screening-photovoltaic soliton families is possible in biased photovoltaic photorefractive crystals under steady-state conditions. These screening-photovoltaic soliton families can be established provided the multiple incident beams have the same polarization and wavelength, and are mutually incoherent. Such soliton families reduce to screening-photovoltaic soliton pairs when they contain only two components. Relevant examples are presented where the photovoltaic photorefractive crystal is of the lithium niobate type.
ATOMIC AND MOLECULAR PHYSICS

CALCULATIONS OF STRETCHING VIBRATIONAL ENERGY LEVELS OF THE CH3I MOLECULE BY A NONLINEAR MODEL

Zhu Jun, Gou Qing-quan
Chin. Phys., 2001, 10 (4): 286-289 doi: 10.1088/1009-1963/10/4/004
Full Text: [PDF 192 KB] (Downloads:466)
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A nonlinear model, i.e. the quantized discrete self-trapping equation, is applied to calculate the highly excited CH stretching vibrational energy levels of the CH3I molecule in the liquid phase at the electronic ground state up to n=8. The obtained results agree well with the experimental data and with those obtained from local mode model calculations. We note that the dominant feature of the methyl CH stretching vibrational energy levels of the CH3I molecule is a pattern of local mode pairs. When n≥7, all the vibrational energy of the CH3 group can nearly be localized on a single CH bond.

EXCHANGE AND FINAL CHANNEL SCREENING EFFECTS IN (e, 2e) PROCESSES

Chen Zhang-jin, Xu Ke-zun
Chin. Phys., 2001, 10 (4): 290-294 doi: 10.1088/1009-1963/10/4/005
Full Text: [PDF 208 KB] (Downloads:329)
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The DS3C model has been improved by taking into account the final channel screening effects. The triple differential cross sections for electron impact ionization of helium at an incident energy of 40 eV are considered. The results of the present DS3C model are compared with the absolute measurements and those of other theoretical models. It has also been shown in which situation the exchange effects are crucial.

FRACTAL PATTERN GROWTH OF METAL ATOM CLUSTERS IN ION IMPLANTED POLYMERS

Zhang Tong-he, Wu Yu-guang, Sang Hai-bo, Li Yong-liang, Zhou Gu
Chin. Phys., 2001, 10 (4): 295-299 doi: 10.1088/1009-1963/10/4/006
Full Text: [PDF 815 KB] (Downloads:310)
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The fractal and multi-fractal patterns of metal atoms are observed in the surface layer and cross section of a metal ion implanted polymer using TEM and SEM for the first time. The surface structure in the metal ion implanted polyethylene terephthalane (PET) is the random fractal. Certain average quantities of the random geometric patterns contain self-similarity. Some growth origins appeared in the fractal pattern which has a dimension of 1.67. The network structure of the fractal patterns is formed in cross section, having a fractal dimension of 1.87. So it can be seen that the fractal pattern is three-dimensional space fractal. We also find the collision cascade fractal in the cross section of implanted nylon, which is similar to the collision cascade pattern in transverse view calculated by the TRIM computer program. Finally, the mechanism for the formation and growth of the fractal patterns during ion implantation is discussed.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

PHOTON ACCELERATION DRIVEN BY AN INTENSE LASER PULSE

Ji Pei-yong, Bao Jia-shan
Chin. Phys., 2001, 10 (4): 314-319 doi: 10.1088/1009-1963/10/4/010
Full Text: [PDF 244 KB] (Downloads:634)
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Interaction of a laser field with a plasma wave is studied by metric optics. Analysis shows that the frequency upshifting of the laser pulse results from the plasma density gradient. A laser beam can be thought of as a packet of photons moving in a plasma and thus the laser frequency upshifting is equivalent to photon acceleration. Examination of the three-dimensional motion equations shows that a laser beam diffraction occurs in the presence of a radial variation of the plasma density. It is argued that the focusing mechanism originating from the plasma wave can curb laser diffraction so that photons may be trapped in the plasma wave and accelerated continuously.

THE INFLUENCE OF ELECTRON OSCILLATION ON PLASMA TRANSPORT THROUGH A MAGNETIC DUCT

Zhang Tao, T. K. Kwok, P. K. Chu, I. G. Brown
Chin. Phys., 2001, 10 (4): 320-323 doi: 10.1088/1009-1963/10/4/011
Full Text: [PDF 182 KB] (Downloads:296)
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A magnetic duct is inserted between the cathodic arc plasma source and the chamber to eliminate the macroparticles. In this paper, the plasma output of the magnetic duct is determined as a function of the magnetic field and the bias voltage under the Bilek biasing mode and entire duct biasing mode. The computer simulation and the experimental result indicate that the {\vec E}×{\vec B} drift results in an extra diffusion flux under the Bilek biasing mode. The test verifying the electron oscillation was conducted in the magnetic duct biased in the Bilek mode. The electron behaviour under Bilek biasing mode is different from that under entire duct biasing mode. The Bilek biasing mode has a lower plasma output than the entire duct biasing mode.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

ANALYSIS OF THE X-RAY PHOTOELECTRON SPECTRA OF a-SiOCF FILMS PREPARED BY PLASMA-ENHANCED CHEMICAL VAPOUR DEPOSITION

Ding Shi-jin, Wang Peng-fei, Zhang Wei, Wang Ji-tao, Wei William Lee
Chin. Phys., 2001, 10 (4): 324-328 doi: 10.1088/1009-1963/10/4/012
Full Text: [PDF 217 KB] (Downloads:385)
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The preparation of a-SiOCF films from Si(OC2H5)4, C4F8 and/or Ar using the plasma-enhanced chemical vapour deposition method is reported. The chemical bonding structures of the films are analysed by x-ray photoelectron spectroscopy (XPS). In the case of the films deposited from the mixture with and without Ar, the configurations of F-Si-O-Si, Si-OH, Si-O-Si, C-CF and C-F are contained. However, there is also the C-C configuration in the film prepared from the mixture with Ar. Moreover, it is found that the photoelectron peaks of Si 2p, O 1s and F 1s for the film deposited from the feeding gas with Ar show the same shift of about 1eV toward high binding energy in comparison with those for the film prepared from the feeding gas without Ar. No evidence reveals the presence of an Si-C bond in the films.

ADATOM, VACANCY AND SPUTTERING YIELDS OF ENERGETIC Pt ATOMS IMPACTING ON Pt(100) BY MOLECULAR DYNAMICS SIMULATION

Ye Zi-yan, Zhang Qing-yu
Chin. Phys., 2001, 10 (4): 329-334 doi: 10.1088/1009-1963/10/4/013
Full Text: [PDF 286 KB] (Downloads:393)
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We have studied the influence of incident atoms with low energy on the Pt(100) surface by molecular dynamics simulation. The interaction potential obtained by the embedded atom method (EAM) was used in the simulation. The incident energy changes from 0.1eV to 200eV, and the target temperature ranges from 100 to 500 K. The target scales are 6×6×4 and 8×8×4 fcc cells for lower and higher incident energies, respectively. The adatom, sputtering, vacancy and backscattering yields are calculated. It was found that there is a sputtering threshold for the incident energy. When the incident energy is higher than the sputtering threshold, the sputtering yield increases with the increase of incident energy, and the sputtering shows a symmetrical pattern. We found that the adatom and vacancy yields increase as the incident energy increases. The vacancy yields are much higher than those obtained by Monte Carlo simulation. The dependence of the adatom and sputtering yields on the incident energy and the relative atomistic mechanisms are discussed.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

STRUCTURE AND SUPERCONDUCTIVITY OF Mg(B1-xCx)2 COMPOUNDS

Zhang Shao-ying, Zhang Jian, Zhao Tong-yun, Rong Chuan-bing, Shen Bao-gen, Cheng Zhao-hua
Chin. Phys., 2001, 10 (4): 335-337 doi: 10.1088/1009-1963/10/4/014
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In this paper, we report on the structural properties and superconductivity of Mg(B1-xCx)2 compounds. Powder X-ray diffraction results indicate that the samples crystallize in a hexagonal AlB2-type structure. Due to the chemical activity of Mg powders, a small amount of MgO impurity phase is detected by X-ray diffraction. The lattice parameters decrease slightly with the increasing carbon content. Magnetization measurements indicate that the non-stoichiometry of MgB2 has no influence on the superconducting transition temperature and the transition temperature width. The addition of carbon results in a decrease of Tc and an increase of the superconducting transition width, implying the loss of superconductivity.

HIGH-PRESSURE SYNTHESIS OF MgB2 SUPER-CONDUCTOR WITH Tc ABOVE 39 K

Li Shao-chun, Zhu Jia-lin, Yu Ri-cheng, Li Feng-ying, Liu Zhen-xing, Jin Chang-qing
Chin. Phys., 2001, 10 (4): 338-339 doi: 10.1088/1009-1963/10/4/015
Full Text: [PDF 259 KB] (Downloads:381)
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We report on the high-pressure synthesis and superconductivity of MgB2 intermetallic compounds. The compounds have been obtained through high-pressure sintering of the mixtures of magnesium and boron fine powders under 5.0 GPa and at ~1000℃ for 30 min. Magnetic measurements using a SQUID magnetometer show the sharp bulk superconducting transition above 39 K; the four-probe dc resistivity measurements indicate the highly-conductive normal state and sharp superconducting transition. The results highlight that high-pressure synthesis would be a promising way to promote the studies of this new kind of intermetallic superconductors.

WEAK QUANTUM FLUX CREEP AND STRONG PINNING IN THE NEW SUPERCONDUCTOR MgB2 Hot!

Zhao Zhi-wen, Wen Hai-hu, Li Shi-liang, Ni Yong-ming, Ren Zhi-an, Che Guang-can, Yang Hai-peng, Liu Zhi-yong, Zhao Zhong-xian
Chin. Phys., 2001, 10 (4): 340-342 doi: 10.1088/1009-1963/10/4/016
Full Text: [PDF 173 KB] (Downloads:407)
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The newly discovered superconductor MgB2 has a transition temperature Tc of about 40 K, which is touching the upper line of that predicted by the phonon-mediated Bardeen--Cooper--Schrieffer (BCS) theory. It is interesting to investigate the flux creep in MgB2 and compare it with other superconductors. We have measured the magnetization relaxation of MgB2 sintered at high temperature and high pressure. It is found that the quantum tunnelling and the thermally activated flux creep are very weak, implying a strong pinning in this material.

STRUCTURE ANALYSIS OF NEW SUPERCONDUCTOR MgB2

He Lun-hua, Hu Gui-qing, Zhang Pan-lin, Yan Qi-wei
Chin. Phys., 2001, 10 (4): 343-344 doi: 10.1088/1009-1963/10/4/017
Full Text: [PDF 143 KB] (Downloads:913)
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The superconductivity of a sintered pellet of the newly discovered MgB2 superconductor has been studied with magnetic measurements and its crystal structure was analysed using the Rietveld method of powder X-ray patterns. It has hexagonal symmetry (S.G. P6/mmm) with unit cell lattice parameters a=0.308136(14)nm and c=0.351782(17)nm.

STRUCTURE, MAGNETIC PROPERTIES AND GIANT MAGNETORESISTANCE OF YMn6Sn6-xGax (x=0-0.6) COMPOUNDS

Zhang Shao-ying, Zhao Peng, Li Run-wei, Sun Ji-rong, Cheng Zhao-hua, Zhang Hong-wei, Shen Bao-gen
Chin. Phys., 2001, 10 (4): 345-348 doi: 10.1088/1009-1963/10/4/018
Full Text: [PDF 189 KB] (Downloads:411)
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Structure, magnetic and transport properties of YMn6Sn6-xGax (0≤x≤0.6) compounds with a HfFe6Ge6-type structure were investigated. It was found that the Ga substitution leads to a contraction of the unit-cell volume. A transition from an antiferromagnetic to a ferromagnetic (or ferrimagnetic) state can be observed for samples (0.1≤x≤0.2) with increasing temperature. The antiferro-ferromagnetic transition for samples with x≤0.2 can also be induced by an external field. The required field is very low, and decreases with increasing Ga concentration. More Ga concentration (x≥0.3) leads to the samples being ferromagnetic in the whole temperature range below the Curie temperature. The Ga substitution weakens the interlayer magnetic coupling between the Mn spins. Corresponding to the metamagnetic transition, a magnetoresistance as large as 32% under a field of 5 T was observed at 5 K for the sample with x=0.2.
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