Vol. 43, No. 12 (1994)
1994-06-20
GENERAL
1994, 43 (12): 1913-1918.
doi: 10.7498/aps.43.1913
Abstract +
Under Landau gauge center coherent states of charged particles in a uniform magnetic field are derived. It is convenient by use of these coherent states to describe the circular motion of charged particles in the field. The comparison between the circular motion and the result of classical mechanics shows that a center coherent state describes the averaged motion of an ensemble.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
BENDING STRENGTH OF MOLECULE AND THE STERIC REPULSIVE POTENTIAL BETWEEN MOLECULES OF LIQUID CRYSTALS
1994, 43 (12): 1919-1931.
doi: 10.7498/aps.43.1919
Abstract +
A new concept called the bending strength K of molecule is introduced, which can be calculated from the concret structure of molecular chemical bonds and the force constants of th: bonds, and the method of calculation is given. For example for PAA, anisaldehyde azine and BA, K is ３．１７×１０4，２．９３×１０4，４．１７×１０4ｎｍｋBＫ， respectively, from calculations. The elastic repulsive potential between two molecules is deduced and the statistical method for the system of elastic rod-like molecules is presented by means of cell model. A detailed calculation is made for PAA. The microscopic mechanism for forming nematic order is discussed and it is concluded that the attractive potential is aomininant, but the effect of steric repulsive potential is also important.
NUCLEAR PHYSICS
EFFECT OF THE BOTTOM ELECTRODES ON THE STRUCTURE AND ELECTRIC PROPERTIES OF FERROELECTRIC THIN FILMS
1994, 43 (12): 1932-1937.
doi: 10.7498/aps.43.1932
Abstract +
The effect of electrode materials on the structure and electric properties of ferroelectric PLZT(7.5/65/35) ceramic thin films has been investigated. It has been shown that, for a certain thickness of the Pt layer, the thickness of the Ti layer has a dominant effect on the structure and electric properties of the ferroele-ctric thin films. When the Ti layer was too thick or too thin, PUT thin films had undesireable crystalline structure. However, with appropriate thickness of the Ti layer, ferroelectric thin films of good microstructure and electric properties be obtained, with typical remanent polarization 27.8μ Ｃ·ｃｍ-2，and coercive field 65.1kV·ｃｍ-1，respectively.
ATOMIC AND MOLECULAR PHYSICS
1994, 43 (12): 1938-1942.
doi: 10.7498/aps.43.1938
Abstract +
Based on a two-level model, the two-photon absorption cross Sections of 1s5-4d1″ transition in Ne are calculated and experimentally determined. These results are in good agreement.
1994, 43 (12): 1943-1949.
doi: 10.7498/aps.43.1943
Abstract +
Theory of pulse rotation and time evolution of Hamiltonian in I≥1 spins weakly coupled system is derived by means of the so called semi-rotation with the projection operators of Liouville space as basis. Time evolution formula of Hemiltonian and the analytic decomposition forms of pulse rotation are obtained.
1994, 43 (12): 1950-1956.
doi: 10.7498/aps.43.1950
Abstract +
The charge states of Cs ions/atoms scattered from Cs/W(110) surfaces have been calculated as a function of the work function and temperature of surfaces with the aid of the time-dependent News-Anderson quantum model. The calculated results are in good agreement with the experimental data. Furthermore, the variations of charge states of the moving Cs ions/atoms approaching and leaving the surface are demonstrated and compared.
1994, 43 (12): 1957-1965.
doi: 10.7498/aps.43.1957
Abstract +
In this work, molecular dynamics (MD) method is applied to study the mechanical properties of Ag/Ni and Cu/Ni interface in two-dimensional models with atomic interactions represented by Lennard-Jones pair potentials. Because the investigated properties depend on the number of atoms in simulaton, and the run time and other resources are limited, we find the proper atom number of MD cell should be between 500-1000. Here, two types of boundary condition are used, one is rigid boundary, corresponding to three-point-bended inferface, the other is circular periodic condition, corresponding to circular-bended inferface. By using these boundary conditions, our MD calculations provide us a useful and consistent picture of the atomic scale processes which occur at Ag/Ni and Cu/Ni interfaces with different MD cell sizes, especially during bending interface processes. The results of our simulation are in good agreement with the macroscopic mechanical behavior, which verifies that the results of our work are correct to a large degree. We find that the properties of the interface are very different from that of single crystal, while the misfit of both lattices plays an important role in the interface properties of epitaxy bicrystal, and the interface structure greatly affects the properties of materials
CLASSICAL AREA OF PHENOMENOLOGY
1994, 43 (12): 1966-1972.
doi: 10.7498/aps.43.1966
Abstract +
Emission spectra of two atoms coupled by dipoie-dipole force in two-mode cavity fields are studied. It is found that emission spectra manifest the following new properties when two-mode cavity fields are initially in various-number states. When two fields are all in vacuum states, the spectrum shows six peaks and five peaks alternately, with the increase of δ＝ｇa／ｇ. Furthermore, the non-symmetric five peaks appear in the spectrum when δ is very small, which reflects the atomic dipole-dipole interaction more sensitively compared with the spectrum of two atoms in a single-cavity. The spectrum consists of symmetric six peaks and distance between each two symmetric peaks is proportional to (2ｎ2)１／２ｇ when one of the fields is in the vacuum states and the other is a strong field. However when one of the fields is in the vacuum state and the other in number state and δ＝2１／２，the spectrum will generally show non-symmetric six peaks structure, but when ｎ2＝５, it becomes non-symmetric five peaks structure.
1994, 43 (12): 1973-1978.
doi: 10.7498/aps.43.1973
Abstract +
Based on the previous four-wave interaction model, it is expected the pump power transfer is possible in a crystal (LiNbO3:Fe) with a local nonlinear response. The experimental results, i.e., the signal beam amplification and the emergence of a higher diffraction order, are analyzed.
1994, 43 (12): 1979-1986.
doi: 10.7498/aps.43.1979
Abstract +
The optical bistability in a dye ring cavity has been investigated. It is shown that the bistability can be realized in a much wider frequency range, and that the bistable regions are functions of the band structures (the bandwidth and the distri-bution of dipole moments).
1994, 43 (12): 1987-1996.
doi: 10.7498/aps.43.1987
Abstract +
In this paper, the quantum energy levels and the level's splitlings of the first exciting state and the second exciting states generated by OH and HOH stretching vibrations of water molecules and vapour and liquid water have been studied by a new self-trapping dynamical theory and the quantized perturbation theory in weak disperse limit. The results obtained are consistent with experimental data, and are better as compared with that of normal model and the localized model. Thus, this method of self-trapping theory is found to be a good method for calculating quanturn vibrational levels of molecules.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
1994, 43 (12): 1997-2002.
doi: 10.7498/aps.43.1997
Abstract +
The photorefractive Fe-dopoed KTa1-xNbxO3(KTN) with a Curie point near room temperature has been topographically studied by Beijing synchrotron radiation white-beam X-ray source. Besides inclusions and the [010] oriented growth bands present in KTN, a set of domains perpendicular to the growth bands is shown, the latter is found to disobey the vanishing rule of planar defects, and to be revealed only by X-ray anomalous scattering. A striking wavelength dependence of the domain contrast is shown by tuning the synchrotron radiation, and the contrast reversal of the domains is demonstrated in antiparallel reflections. The domains are ascertained to be 1800 ones. The origins of formation of the domains and the growth features in KTN are outlined.
1994, 43 (12): 2003-2008.
doi: 10.7498/aps.43.2003
Abstract +
Two-dimensional spin 1/2 Ising model and the "inequality method" are used to determine the planar ground-state structures and ground-state phase diagram of ternary III-V semiconductor alloys. Long-range ordered structures in epitaxial growth are deduced according to layer-by-layer stacking. Some experimental long-range ordered features on (001)substrate growth are explained.
1994, 43 (12): 2009-2015.
doi: 10.7498/aps.43.2009
Abstract +
The preferential sputtering of the ternary alloy system Cu76Ni15Sn9 has been studied under 27keV argon ion bombardment at normal incidence using collection film technique combined with Auger electron spectroscopy analysis. After sputtering target surface was examined in a scanning electron microscope, and the surface composition was measured with electron probe microanalyser for topographical features of different micro-region surface. The experimental results showed that the preferred ejection of Cu atoms compared with Ni atoms and of Ni atoms compared with Sri atoms take place over the whole range of the measured ejection angle (0-600). The influence of the topographical features and "locally rich element" phenomenon on the ejection atoms are discussed.
1994, 43 (12): 2015-2022.
doi: 10.7498/aps.43.2015
Abstract +
W/C multilayer mirror for 4.47nm had been fabricated by planar magnetron sputtering. Using small angle X-ray, transmission electon microscopy cross-section analysis and 4.47nm absolute reflectivity measurement techniques, the structrure and optical properties of this multilayer had been characterized.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
1994, 43 (12): 2023-2030.
doi: 10.7498/aps.43.2023
Abstract +
The electronic structures of the three lattice-orientation (i.e.,(110),(100) and (111))superlattices (AlAs)1(GaAs)1, (AlAs)3(GaAs)3 are studied with the linearized-muffin-Tin-orbitals band-structure method. The frozen shape approach is adopted to investigate the charge transfer across the interfaces, the alignment of age-bond-energy(ABE) and the valence-band offsets (VBO) under the conditions of different latticeorientations and different thickness of superlattice slab. The ABE method for determining the VBO's, in which the ABE is regarded as a energy reference, is further comprehensively tested numerically.
1994, 43 (12): 2031-2037.
doi: 10.7498/aps.43.2031
Abstract +
Transverse magnet ores istance, electronic mobility and Hall coefficient of low compensated (K《1)n-Hg1-xCdxTe(x=0.214) have been measured at low temperatures from 0.3K to 30K and high magnetic field up to 7T. Magnetic-field-induced metal-insulator transition (MIT) has been found in our sample. According to the experimental data, we suggest that the mechanism of the magnetic induced MIT in low copmensated n-Hg1-xCdxTe (x is around 0.2) is magnetic freeze-out of carriers to shallow impurity states. Prerequisite condition of the magnetic freeze-out is thermal freeze-out which forces the carriers from conduction band to shallow impurity state at very low temperature. Thermally activated conduction of electrons can be described by the expression ＲH（Ｔ）＝ＲH0exp[a/kT]. It represents the thermally activated process of electrons bound in impurity state. From activation energy of the conductivity in nonmetallic region, we infer that there are two shallow impurity states in the sample.
1994, 43 (12): 2038-2044.
doi: 10.7498/aps.43.2038
Abstract +
A class of ceramic composite prepared with two kinds of oxide ceramics of ferroelectric BaTiO3 and superconducting YBa2Cu3O6+δ is reported, and the phase structure and electrical transport properties of the samples are investigated. The results show that the main phases varied in different composition regions. For low nominal YBa2Cu3O6+δ content, the conductive characteristics of the two-phase (BaTiO3 and YBa3Ti2O8.5) composite follow the three-dimensional percolation model; while for high nominal YBa2Cu3O6+δ contents, superconductivity is observed.
1994, 43 (12): 2045-2051.
doi: 10.7498/aps.43.2045
Abstract +
The properties of two variational states, the displaced state and the displaced-squeezed state, are compared for a two-state system with superohmic dissipation by a variational approach. We find that, in strong coupling region, the displaced-squeezed state is the more stable and the ground-state properties depend not only on the spectral density but also on the index λ of the coupling strength ｇ1～ω1λ(ω1 is phonon frequenceis). Moreover, we obtain that the stable area of the displaced-squeezed state increases as λ reduces. Similar properties have been obtained for ohmic dissipation and it is shown that the delocalization area of the displaced-squeezed state increases as λ reduces.
1994, 43 (12): 2052-2058.
doi: 10.7498/aps.43.2052
Abstract +
With the help of the static replica symmetric spin glass theory, thermodynamic properties of the Sherrington-Kirkpatrick (SK) spin glass model with the random Dzyaloshinskii-Moriya (DM) interaction in external magnetic fields are investigated. The dependences of entropy, specific heat, susceptibility and the corresponding order parameters on temperature are studied numerically for different magnetic fields and spin numbers 1/2 and 1. It is found that the local susceptibility is in good agreemeat with that given by the thermo-field dynamic theory. Especially, the crossover behavior of the specific heat-temperature curves for different magnetic fields observed by Brodale et al. can be explained very excellently.
1994, 43 (12): 2059-2064.
doi: 10.7498/aps.43.2059
Abstract +
A new kind of anisotropic photorefractive light-induced diffracted ring pattern——ovallike pattern in c-cut LiNbO3:Fe crystal sheet is observed and a mechanism of four-wave mixing induced by the incident light and its strong backward scattered light is proposed to explain the experimental results.
