1993年, 第20卷, 第4期　
刊出日期：1993-12-15

  

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  Scaling Variat ion-Truncat ion Approximation in an Operator Form

  Fan-Mei KONG, Yi-Wen WANG

  理论物理通讯. 1993, 20(4): 385-392.

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  An operator form of scaling variational method combining truncation approximation is propoied to solve the energy eigenvalue problem of the onedimensional polynomial potential, in which the scaling parameters of the Hamiltonian are determined by variational principle, followed by a truncation approximation. As examples, the energy values of onedimensional anharnionic and pure quartic oscillators are calculated. The results axsimple in form and have high accuracy. Moreover, the operator method and two-step approximation are combined in a unified treatment on the ground of scaling variational method in an operator form.
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  Spin Waves in a Surface-Diluted Quant um Spin system

  Song-Tao DAI, Zhen-Ya LI, Chuan-Zhang YANG

  理论物理通讯. 1993, 20(4): 393-400.

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  A theoretical investigation of the effects of surface dilution on spin waves in a semi-infinite transverse Ising model (TIM) is presented. Within the framework of the double-time Green's function theory, the loctl density of spin-wave states is obtained by the application of the cluster-Bethe-lattice (CBL) method. Numerical calculations of paramagnetic phases reveal that surface dilution will lead to appearance of the localized spin-wave states whose frequencies are bulk independent while the corresponding density of states is a function of the exchange interactions. Increase of the bulk exchange interactions between the surface and the bulk spins tends to diminish the localized spin-wave states. Dependence of the local density of states on the concentration p of the magnetic atoms is similar with that in a three-dimensional infinite TIM which has been discussed in our previous paper.
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  Shallow Donor Impurities in Quantum Well WiresIEffects of Image potential

  Zhen-Yan DENG, Shi-Wei GU

  理论物理通讯. 1993, 20(4): 401-407.

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  We calculate the shallow donor impurity binding.energies including image potential in quasione- dimensional GaAs/AIAs quantum well wires with rectangular cross section using the variational approach. The results we have obtained show that when impurity ion image potential is considered the variations of binding energy are remarkable, and when the image potentials of impurity ion and electron are considered simultaneously the corresponding variations of binding energy are small. The results also show that the image potential is important, especially when the cross section dimensions of quantum wires become small.
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  Rigorous Study of Charged Carriers in Electric Fields with Alternating Site Energies and Intersite Interactions

  Xian-Geng ZHAO

  理论物理通讯. 1993, 20(4): 409-414.

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  The problem of charged carriers moving in a one-dimensional infinite system subject to a uniform electric field is studied by taking into account the presence of alternating site energies and intersite interactions. Exact results for the energy spectrum and the eigenvectors are obtained by using the perturbation theory. It is shown that the energy spectrum is that of two interspaced Stark ladders. The role of both alternating site energies and intersite interactions is also discussed. It is found that the enhancement of the alternating site energies and intersite interactions will give rise to an increase in the energy gap between two coupled Stark ladders.
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  Spin Wave Theory for Magnetic Field-Induced Transition in La₂Cu0₄

  Ming-Wei WU, Hang-Sheng WU

  理论物理通讯. 1993, 20(4): 415-420.

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  We develop a spin wave theory for the canting antisymmetrism bj using Holstein-Primakoff transformation, and study the field-induced transition in La₂Cu0₄ when the magnetic field is applied perpendicular to the CuO₂ plane. The temperature dependence of the critical magnetic field predicted by our theory agrees fairly well with the experiment at low temperature.
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  Magneto-Polarons in a Harmonic Quant um Dot

  Ka-Di ZHU, Shi-Wei GU

  理论物理通讯. 1993, 20(4): 421-426.

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  We study cyclotron resonance of magnetopolarons in a harmonic quantum dot. The results show that for weak magnetic field (ω_c< ω_LO), the cyclotron mass in a harmonic quantum dot is split into two cyclotron masses (m₊^* and m_-^*). One (m₊^*) is larger than the bare band mass for large quantum dots but is lower than the bare band mass for small quantum dots, and with decreasing the effective confinement length of the quantum dot, the negative mass renormalization for the small quantum dots is important. The other (m_-^*) is greater than the bare band mass and might be a measurable effect fbr the small quantum dots.
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  The Two-Soliton Bound-State Solution in an Order-Parameter-Preserving Ant iferromagnet

  Wu-Ming LIU, Ben-Lian ZHOU, Jing-Dong GUO, Xuan-Rong MA

  理论物理通讯. 1993, 20(4): 427-432.

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  Employing the Dyson-Maleev transformation and the coherent state ansatz, the two-soliton bound-state solution in an order-parameter-preserving antiferromagnet is investigated by using the method of multiple scales and long-wavelength approximation.
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  Surface Spin Waves in Anisotropic Heisenberg Magnet with a Single-Ion Uniaxial Anisotropy

  Ming-Rong SHEN, Zhen-Ya LI

  理论物理通讯. 1993, 20(4): 433-438.

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  The technique of Green's function is used to investigate the surface spin waves in semiinfinite anisotropic Heisenberg magnet with a single-ion uniaxial anisotropy. The dispersion relations of surface excitations are obtained for the ferromagnetic, antiferromagnetic and ferrimagnetic systems, respectively. Results in some particular cases are discussed.
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  A Simple Model fop the First-Order Phase Transition and Met astability

  Wei-Mou ZHENG

  理论物理通讯. 1993, 20(4): 439-444.

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  An extremely simplified dynamical model is proposed to consistently explain the first-order phase transition and metastability.
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  Nucleon Form Factors in an Extended Nambu-Jona-Lasinio Model with the Relativistic Mean Field Approximation

  J.W. ZHANG, L.M. YANG, W.Z. DENG

  理论物理通讯. 1993, 20(4): 445-452.

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  An extended Nambu-Jona-Lasinio model is proposed and solved in relativistic Hartree approximation. An effective confining potential for individual quarks is obtained in a self-consistent way through an ansatz on the form of the interaction kernel. Various nucleon form factors and static properties are evaluated comparably with the empirical measurement.
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  New Theoretical Results of 2νββ Decay with the Operator Expansion Method

  X.R. WU, M. Hirsch, A. Staudt, H.V. Klapdor-Kleingrothaus, Cheng-Rui CHING, Tso-Hsiu HO

  理论物理通讯. 1993, 20(4): 453-460.

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  The half-lives for 2νββ decay for all the potential Pp-emitters with A≥70 are calculated by the operator expansion method. Compared with the directly measured half-lives of ⁷⁶Ge, ⁸²Se, ¹⁰⁰Mo and ²³⁸U the theoretical values are in excellent agreement with experimental ones.
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  A New Method of the Functional Integral Constructed Directly from Hamiltonian

  Zhong-Can ZHANG, Chong-Sheng LI, an-Sheng Wel

  理论物理通讯. 1993, 20(4): 461-470.

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  We establish a new method of constructing the functional integral for the matrix elements of the time evolution operator of quantum system directly from the Ifamiltonian. In this first paper, we present the general principles and methods, and realize the construction of the functional integral for a two-dimensional Hamiltonian. In the second paper, the method is extended to arbitrary N-dimensional state space.
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  Some q-Deformed Combinat orial Identities and Their Applications

  Si-Cong JING, Hong-Yi FAN

  理论物理通讯. 1993, 20(4): 471-476.

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  A q-deformed binomial theorem is firstly presented in this work. Some operator identities in q-deformed two-mode Fock space are derived by virtue of the q-binomial theorem. As an application of these identities, we prove a new completeness relation for the q-analogue of the singlecomplex-variablestate in the two-mode Fock space.
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  Dynamic Critical Behavior of 2D X-Y Model on a Random Lattice from Cluster Update Monte Carlo

  Da-Ren JI, Jian-Bo ZHANG, He-Ping YING

  理论物理通讯. 1993, 20(4): 477-480.

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  We performed a numerical simulation of X-Y model on the two-dimensional random lattice using cluster update algorithm. The critical region was found around β≈1.0 by the peaks in the specific heat and the susceptibility. The autocorrelation in energy and the square of magnetization was also calculated. The results show that the critical slowing down was greatly reduced.
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  The Energy Mode of Multi-Frequency Phonon in the Nonradiative Transition

  Rong-Yi JIA, He-Feng LEE, Li-Gen YAN

  理论物理通讯. 1993, 20(4): 481-484.

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  On the basis of Huang Kun's statistical distribution theory of multiphonon, the probability factors of nonradiative transitions and the average numbers of phonon have been calculated at 100 K for various energy modes of phonon frequency groups. The results show that the probability of nonradiative transitions for the finite temperature will increase obviously if the energy mode contains more than one phonon frequency groups of high energy. Moreover, with the increasing of transition energy the average phonon number at high energy is also tending to increase. In addition, for the lattice relaxations of moderate strength the transitions are less influenced by the choice of minimal phonon energy hω₀.
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  Quantum Ashkin-Teller Model and Conformal Theory

  Hai-Yan ZHANG, Bo-Wei XU

  理论物理通讯. 1993, 20(4): 485-488.

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  A simple derivation of the field theory of quantum Ashkin-Teller (AT) model shows that the AT model is equivalent to a complex fermion field. -At the critical t, the field equation is conformally covariant. Thus the critical point condition and the normalizing factor ξ are given.
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  The IWOP Method of Normally Ordering Multimode Exponential Operators

  Luo-Yu FENG

  理论物理通讯. 1993, 20(4): 489-492.

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  This paper states that the technique of integration within ordered product (IWOP) provides us with a generally effective approach to normally ordering multimode exponential operators. In fact, all the operators listed in Ref. [5] can be normally ordered by virtue of IWOP, in contrast to the comment of Ref. [5].
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  New Dark Soliton Solutions of the KdV Equation

  Zong-Yun CHEN, Nian-Ning HUANG

  理论物理通讯. 1993, 20(4): 493-493.

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  By using the Miura transformation, from the dark soliton solutions of the mKdV equdation which are found recently by Darboux transformations, a series of new dark soliton solutions of the KdV equation is obtained.
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  Successively Squeezed States Studied by Virtue of the IWOP Technique

  Hong-Yi FAN, Jia-Fan FAN

  理论物理通讯. 1993, 20(4): 495-498.

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  Two kinds of successively squeezed states which are generated by re-squeezing two single mode squeezed states by the two-mode squeezing operator, or by re-squeezing a two-mode squeezed state by two single-mode squeezing operators, are studied in terms of the newly developed technique of integration within an ordered product (IWOP) of operators. The fluctuations in quadrature phases for the resqueezed states are analyzed.