1990年, 第14卷, 第2期　
刊出日期：1990-09-15

  

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  Two-Band Model for High T_c Superconductivity

  YANG Zhen-qing, KONG Fan-mei

  理论物理通讯. 1990, 14(2): 129-138.

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  A two-band model is dealt with by the canonical perturbation theory of projection operators. An effective Hamiltonian with Cu-Cu, Cu-O and O-O couplings is obtained. A unified treatment for such a coupled system gives the variations of transition temperatures for Cu-Cu, Cu-O and O-O parings with the concentration of O-holes. A window of δ for superconductivity is obtaihed and compared with experimental data qualitatively and quantitatively.
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  Quantum Theory of Surface Polaritons in Semi-Infinite Dielectric Systems

  Zhang-long XU, Ka-di ZHU, Shi-wei GU

  理论物理通讯. 1990, 14(2): 139-158.

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  The interaction system of a semi-infinite diatomic dielectric and the electromagnetic field propagating parallelly to the surface is studied. The long-wave optical phonon modes of the semi-infinite dielectric are calculated including the electronic polarizability by a quantum-mechanical theory. Retardation effects are neglected. A quantum field theory method of surface polaritons is developed to calculate the operator describing the interaction between a photon and the phonon polarization fields of the semi-infinite crystal, with explicit inclusion of surface effects. The dispersion relations of the surface phonon-polaritons are derived and discussed. The results are in good agreement with those obtained by the conventional, macroscopic dielectric theory of surface polaritons and experimental ATR (attenuated total reflection) spectra. The dispersion cuwes of polariton leaking modes caused by the interaction between bulk TO mode with surface effect and photons are presented in a graphical form. The k_||-dependence of the electric field strength in each polariton branch is calculated and presented also in a graphical form. We also research the spatial dependence of the field strength in each polariton branch. It is found that these properties are influenced and modulated by the surface phonons because of the interaction between photons and the surface phonon modes of the semi-infinite dielectric system. Hence the divergent nature (diffraction effect) of light propagating along the fib& and waveguides is restrained. We present a method how to use the boundary conditions in the quantum theory, which will be discussed in detail.
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  Phonon Interaction Free Energy Between Adatom and Impurity

  J. Gryko, W. K. Liu, Y. Shen

  理论物理通讯. 1990, 14(2): 159-166.

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  The change of the phonon contribution to the free energy, ΔF, due to the interaction between an adatom and an impurity substrate atom is calculated by expressing ΔF as a contour integral in the complex-frequency plane and evaluating it directly along a suitably chosen contour numerically. Results are given as a function of the adatomsurface bond force constant, the mass defect of the impurity atom, and the adatomimpurity separation for both a one-dimensional and a three-dimensional simple cubic model substrate.
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  Displaced-Squeezed States in a Spin-Phonon Model

  Yun-long SHI, Hong CHEN, Xiang WU

  理论物理通讯. 1990, 14(2): 167-172.

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  The influence-of a tunneling system on phonons is studied in a spin-phonon model. We find the coupling may induce the transition of coherence from the tunneling system to phonons, and then the phonon state may be described by displaced-squeezed state. Comparing with displaced state, this new state has the properties that, its energy is renormalized, and its suppression effect on tunneling parameter is reduced. Moreover, the ground state of the whole system is investigated by a variational calculation and its dependence on tunneling parameter, phonon energy, and coupling strength is analyzed.
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  L^⊗N-Generalization of Partial Algebraization Method for spectral Problems and Heisenberg Model

  SONG Zhi, SHEN Hong, SUN Chang-pu

  理论物理通讯. 1990, 14(2): 173-180.

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  In terms of the N-multiple direct product of Lie algebra the method of partial algebraization for quantal spectrum problems is generalized to deal with the cases of many-mode coupling. Using this generalized method to the antiferromagnetic Heisenberg model, we explicitly obtain some analytic and numeral results for the eigenstates and eigenvalues.
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  A Compact Exponential Operator for Generating Rotating and Squeezing Transformations

  FAN Hong-yi

  理论物理通讯. 1990, 14(2): 181-188.

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  We point out that the compact exponential operator V≡exp[-i(λ₁Q²-λ₂P²)/2] (where λ₁, λ₂ are real;P and Q are momentum and coordinate operators, respectively;the units of h=m=ω=l is taken, m and ω are harmonic oscillator's mass and'frequency, respectively) is a generalized single-mode squeeze operator which can generate mixed squeezing and rotating transformations. The decomposition of V as a product of a squeeze operator and a rotating operator is derived through the technique of integration within an ordered product.The fluctuation in quadrature phases for the squeezed vacuum state generated by V is analyzed.
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  A KN Operator Formalism for a Bosonic System

  CHENG Qi-hua

  理论物理通讯. 1990, 14(2): 189-195.

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  We present a KN operator formalism for a non-chiral bosonic system on higher genus Riemann surfaces using the KN bases and construct a Fock space in terms of infinitely many conserved charges.
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  Characteristic Features of Microscopic Collision and Macroscopic Movement of the Brownian Motion

  BAO Jing-dong, ZHUO Yi-zhong, WU Xi-zheng

  理论物理通讯. 1990, 14(2): 197-202.

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  The Brownian motion with three kinds of force fields is simulated by making use of the Monte-Carlo method. It is shown from our studies that the time.step must be macroscopically small and microscopically large from both physical requirement and accurate numerical computation.
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  Eliashberg Equations and Coulomb Pseudopotential for Superconductivity via Sign-Opposite Interactions

  Shi-jie XIONG

  理论物理通讯. 1990, 14(2): 203-208.

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  A new type of attractive interactions, the second retarded ones, is investigated with the Eliaehberg treatment. Several mechanisms, leading to the pairing in the high frequency window, belong to this type. The equations for gap parameter are derived. From these a formula of the Coulomb pseudopotential is obtained. It is found that the Coulomb repulsion against the pairing is completely suppressed by the pseudopotential effect in the unscreened case. Its significance for the high T_c superconductivity is discussed.
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  Note on the Electron-Hole Symmetry Breaking of the Energy Band Structure of Polyacetylene

  XIAO Yi

  理论物理通讯. 1990, 14(2): 209-212.

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  SSH model is generalized to include the long-range hopping interactions to explain the electron-hole symmetry breaking of the energy band structure of polyacetylene.
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  Continuum Field Approximation for the η Pairing Mechanism of a Hubbard Model Within the Framework of a Mean-Field Theory

  SU Gang

  理论物理通讯. 1990, 14(2): 213-216.

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  A quantum field theory for the η pairing mechanism of a Hubbard model within the mean-field framework is presented in this letter. It is found that the energy spectrum has two separate branches, and the eigenfunction has a plane-wave type. This result differs from the discrete lattice case in momentum space.
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  A Hierarchy of Universal Quantities in RG Equations for the 2D Coulomb Gas

  Sen-yue LOU, Guang-jiong NI

  理论物理通讯. 1990, 14(2): 217-220.

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  A hierarchy of universal quantities in the double expansion RG equations for two dimensional (2D) Coulomb gas is found by using a length-dependent dielectric function ε(γ).
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  A Higher Order (2+1)-Dimensional Korteweg-de Vries Equation and Its Exact Solitary Wave Solutions

  Guo-xiang HUANG, Xian-xi DAI, Sen-yue LOU

  理论物理通讯. 1990, 14(2): 221-224.

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  The (2+l)-dimensional Korteweg-de Vries (KdV) equation proposed recently by Levi is extended to a higher order (2+1)-dimensional KdV equation from water wave dynamics when considering surface tension. Its exact and explicit solitary wave solutions can be obtained by relating it to the higher order KdV equation.
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  The Densities of Electronic States of Polyparaphenylene Upon Disorder Doping in Bipolaron Model

  XIAO Yi, LUO Xiao-ming

  理论物理通讯. 1990, 14(2): 225-226.

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  The densities of valence electronic states of polyparaphenylene upon disorder doping are calculated by using Dean's method. The results are compared with those of the periodic model and experiments.
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  Circular Polarized Soliton Propagating at a Small Angle to Strong Bias Magnetic Field in a Ferromagnetic System

  Ying WU

  理论物理通讯. 1990, 14(2): 227-230.

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  A variant of the derivative nonlinear Schrödinger equation for the low frequency circular polarized wave, propagating at a small angle to the bias magnetic field in a ferromagnetic system, is derived by the reductive perturbation expansion method. Bright and dark solitons are obtained.
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  Triton-Clustering in Light Nuclei Near the Neutron Drip Line

  REN Zhong-shou, XU Gong-ou

  理论物理通讯. 1990, 14(2): 231-234.

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  Triton-clustering in light nuclei near the neutron drip line is analyzed from their binding energies. Various properties of these exotic nuclei are explained.
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  Phase Transition in the Chiral Quark Soliton

  ZHANG Jian-wei, QIU Xi-jun

  理论物理通讯. 1990, 14(2): 235-240.

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  Chiral symmetry phase transition is studied by making use of the finite temperature Green's function and the path integral approach in the chiral soliton model. The temperature-dependent effective potential is obtained in the one-loop approximation, including quark and σ-, π-meson loop. The critical temperature-versus the nuclear density is calculated. At zero baryop density the critical temperature is 172 MeV. In nuclear medium it is found that the critical temperature decreases fast when the nuclear density is increasing.
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  The Phase Transition Generated by Radial Mode of the Higgs Field in Lattice Z(2) Gauge-Higgs Model

  JL-min YANG, Ling-de WAN, Chi-min WU

  理论物理通讯. 1990, 14(2): 241-246.

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  We study the 4-dimensional lattice Z(2) gauge-Higgs theory in the variational cumulant expansion approach. It is shown that the existence of the first drder phase transition between Higgs and confinement regions is fundamentally dependent on the fluctuation of the radial mode of the scalar (Higgs) field.
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  KM Matrix Parametrizatidn Convenient for Both B_d Study and Data Analysis

  Wei CHEN, Dan-di WU

  理论物理通讯. 1990, 14(2): 247-252.

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  The value of the ε parameter of a pseudoscalar mixing system is phase-conventiondependent. We prove that one can make two of the three ε parameters, ε_K, ε_Bd and ε_Bd, small but not all of them simultaneously by adjusting the phase convention of the Kobayashi-Maskawa (KM) matrix. We give corresponding KM matrices based on the Wolfenstein parametrization, which are also suitable for ahalyzing the values of KM parameters. The transformation from one matrix to the other is extremely simple.
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  Acoustic Gravity Vortices

  Ying WU, Kai-lun YAO

  理论物理通讯. 1990, 14(2): 253-256.

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  The solitary dipole vortex solution is shown. to exist for the nonlinear equation describing low frequency acoustic gravity waves.