Free energy of semiflexible polymers and structure of interfaces

The free energy of semiflexible polymers is calculated as a functional of the compositional scalar order parameter and the orientational order parameter of second-rank tensor S_ij on the basis of a microscopic model of wormlike chains with variable segment lengths. We use a density functional theory and a gradient expansion to evaluate the entropic part of the free energy, which is given in a power series of .The interaction term of the free energy is derived with a random phase approximation. For the rigid rod limit, the nematic-isotropic transition point is given by , N and w being the degree of polymerization and the anisotropic interaction parameter, respectively, and the degree of ordering at the transition point is 0.33448. We also find that the contour length of polymer chains becomes larger in a nematic phase than in an isotropic phase. Interface profiles are obtained numerically for some typical cases. In the neighborhood of isotropic-isotropic interfaces, polymer chains tend to align parallel to the interface on the polymer-rich side and perpendicular on the poor side. When an isotropic region and a nematic region coexist, orientational order parallel to the interface is preferred in the nematic region. Received: 28 May 1998 / Revised: 12 August 1998 / Accepted: 8 September 1998     

On the theory of second harmonic generation

It is shown how the theory of non-linear interaction between the modes of the open resonator, developed previously [1] and used to study resonant second harmonic generation [2], can be applied to second harmonic generation in the absence of a resonator. The conditions under which the second harmonic output, in the small conversion approximation, can be approximated by a Gaussian beam are derived.The optimum value of the focusing parameter I/z₀ (hereI is the length of the crystal, andz ₀ is one-half the confocal parameter of the fundamental beam) for the total output is shown to be 5.68 agreeing precisely with the value given by Boyd and Kleinman [3].     

Interaction of vortices in type II superconductors and the behavior nearH c1 at arbitrary temperature

The interaction between well-separated Abrikosov vortices is calculated using Eilenberger's version of the Gorkov theory. Let λ and ξ be the decay lengths determining the asymptotic behavior of the magnetic field and the order parameter for an isolated vortex. Then the onset of attraction in the limit of large vortex separation is either given by λ=ξ or by λ becoming complex, whichever occurs first. It is shown that in general a first order transition atH _c1 takes place already in the region of asymptotic repulsion because of the appearance of a minimum in the interaction energy at finite vortex separation.     

Competition mechanism between singlet and triplet superconductivity in the tight-binding model with anisotropic attractive potential

Based upon the tight-binding formalism a model of a high-T_c superconductor with isotropic and anisotropic attractive interactions is considered analytically. Symmetry facets of the group C_4v are included within a method of successive transformations of the reciprocal space. Complete sets of basis functions of C_4v irreducible representations are given. Plausible spin-singlet and spin-triplet superconducting states are classified with regard to the chosen basis functions. It is displayed that pairing interaction coefficients and the dispersion relation, which can be characterized by the parameter η= 2t₁/t₀, have a diverse and mutually competing influence on the value of the transition temperature. It is also shown that in the case of a nearly half-filled conduction band and an anisotropic pairing interaction the spin-singlet d-wave symmetry superconducting state is realized for small values of the parameter η, whereas in the opposite limit, for sufficiently large values, the spin-triplet p-wave symmetry superconducting state has to be formed. This result cannot be obtained within the Van Hove scenario or BCS-type approaches, where the p-wave symmetry superconducting state absolutely dominates. The specific heat jump and the isotope shift as functions of the parameter η are assessed and discussed for the d-wave symmetry singlet and the p-wave symmetry triplet states.     

Thermal entanglement in the anisotropic Heisenberg model with Dzyaloshinskii-Moriya interaction in an inhomogeneous magnetic field

The thermal entanglement of a two-qubit anisotropic Heisenberg XXZ chain with Dzyaloshinskii-Moriya (DM) interaction in an inhomogeneous magnetic field was studied in detail. The effects of the DM parameter, external magnetic field (B), a parameter b which controls the inhomogeneity of B and the bilinear interaction parameters J_x = J_y ≠ J_z (the anisotropic case) on the concurrence (C) was formulated and studied in detail. The behaviors of the concurrences for the cases between (J = J_z = 1) and (J = -1,J_z = 1) and, (J = J_z = -1) and (J = 1,J_z = -1) at the ground state and at the thermal equilibrium are exactly the same. It was found that for the antiferromagnetic (AFM) case the entanglements persist to higher temperatures in comparison with the ferromagnetic (FM) case. In addition, the AFM case presents a special point at which the nonzero concurrences are all equal at some special temperatures. The further properties will be given in the text.     

The calculation of the superexchange interaction parameters in Europium chalcogenides

The superexchange interaction parameters have been calculated for a series of Eu-chalcogenides EuX (X = O, S, Se, Te). The calculation has been made in a many-electron model for the chosen complex Eu₁-X-Eu₂ with the account of the non-orthogonality of the wave functions at different centers. The influence of the remaining crystal ions has been taken into account in the model of point charges creating a non-homogeneous potential in the region of the chosen complex. The results obtained are compared with the experimental values of the I₂ parameter for the given compounds.     

Zero-sound condensate in a Fermi liquid

We consider a normal Fermi liquid with a local scalar interaction given by the Landau parameter f₀. The system becomes unstable for f₀ < ?1 against a growth of scalar-mode excitations (Pomeranchuk instability). We show that the instability may be tamed by the formation of a static Bose condensate of the scalar modes. We study a possible reconstruction of the isospin-symmetric nuclear matter owing to the appearance of the condensate. Possibility of a novel metastable state at subnuclear densities is demonstrated.     

The theoretical calculation of collision-induced predissociation

A theoretical treatment of the collision-induced predissociation of a diatomic molecule caused by collisions with an atom is given in terms of the impact parameter method. Numerical calculations of the collision-induced predissociation of the D ¹Π _u state of the hydrogen molecule due to collisions with helium atoms have been performed using an ab initio calculation of the electronic interaction of the helium atom and the hydrogen molecule. The results show good agreement with the available experimental evidence. The continuum energy of the predissociation fragments is shown to have an energy spread determined by the range of the interaction potential.     

Thermal entanglement in the XYZ model for a two-qutrit system

The negativity as a measure of thermal entanglement was studied for a two-qutrit spin-1 anisotropic Heisenberg XYZ chain with Dzyaloshinskii-Moriya (DM) interaction in a homogeneous magnetic field in detail. An analytical expression was found for the negativity and then the thermal variations of negativity were investigated in full detail for given values of the DM interaction parameter D_z, the external magnetic field B, the measure of the anisotropy on the xy-plane γ = (J_x − J_y)/(J_x + J_y), a parameter J = (J_x + J_y)/2 and the bilinear interaction parameter J_z along the z-axis.     

Quadrupole interaction in the solid halogens—a new (not final) look

The nuclear quadrupole interaction in the molecular solids Cl₂, Br₂ and I₂ is reanalyzed with the help of density functional calculations. Though the present formalism overestimates the intermolecular interaction responsible for the solid–gas frequency shift and the asymmetry parameter η, a consistent picture is derived by appropriate corrections. The published experimental values of η for Cl₂ and Br₂ are found to be in error.     

On the cation distribution in the spinel systemyMg2TiO4−(1−y)MgFe2O4

The cation distribution and the oxygen parameter for the system Mg_1+y Fe₂(1?y) Ti _y O₄ have been determined using the intensities of X-ray reflections. Results are given for slowly cooled and quanched samples. An explanation is proposed to account for the behaviour of the lattice parameter and the oxygen parameter.     

What does NMR tell us about the electronic state of high-T c superconductors?

An introduction to the models which are usually applied, when interpreting the NMR (nuclear magnetic resonance) parameter Knight shift (K _s) and spin-lattice relaxation rate 1/T ₁ in the normal and the superconducting state of high-temperature superconductors, is given. The different hyperfine interaction parameters involved, as well as the static and dynamic susceptibility χ(q,ω) will be discussed. I will point at those highlights as antiferromagnetic correlations, spin gap and vortex lattice dynamics which have emerged from the analysis of the NMR data.     

Accurate description of ultra-short tightly focused Gaussian laser pulses and vacuum laser acceleration

High-order correction terms to the expression of the field of ultra-short tightly focused Gaussian laser pulses are derived. Terms up to seventh order in the small dimensionless spatial parameter s=1/(k₀w₀₀) and first order in the small dimensionless temporal parameter ε=1/(ω₀t₀) are explicitly presented (ω₀=ck₀ the central oscillatory frequency, 2t₀ the pulse duration, w₀₀ the beam waist radius at the central frequency ω₀). To evaluate the correction efficacy, both the corrected and the paraxial field equations are used in detailed simulation studies of laser/electron interaction dynamics. Special attention is given to the vacuum laser acceleration scheme. The influence on the electron dynamics due to the diffraction edge field of a tightly focused laser beam is also investigated. PACS  42.25.Bs; 42.60.Jf; 41.75.Jv     

A Mössbauer study on the interaction of active component and support

In order to directly determine and compare the interaction strength between one active component (Fe₂O₃) and six different supports, Mössbauer spectra of the six catalysts under room temperatures 373K, 473K and 573K were recorded. From the temperature dependence of area under the resonance curve and isomer shift (IS) parameter which could be extracted from the resonance spectrum, a lattice vibration related parameter θ_M was calculated._M values can characterize the strength of interaction forces between Mössbauer Fe atoms and its neighbour atoms of supports, hence the order of interaction strength between Fe₂O₃ and various supports is obtained.     

Substrate strain induced interaction of adatoms on W (110)

The interaction of adatoms due to elastic strains created in an elastically isotropic substrate is investigated. For cases where the adatoms occupy sites with low symmetry, an angular dependent interaction results which falls off as s^–3 at large distances. An exact expression is given for the long range interaction in terms of an anisotropy parameter of the force dipole tensor. The short range interaction is calculated by introducing a smooth cutoff. Interactions of adatoms on near neighbour sites on W (110) are given.     

Acoustic NMR in spin-1 systems

Acoustic magnetic resonance, both pulsed and continuous has been discussed in terms of the Bloch-Wangsness-Redfield formulation of the magnetic resonance phenomenon. The quadrupolar mechanism has been taken for the spin-phonon coupling and the mutual interaction has been treated in the ‘effective field approximation’. The expressions for the power absorbed both for Δm=±1 and Δm=±2 have been obtained. It is found that from the measurements of the relaxation parameters for Δm=±1 and Δm=±2 it is possible to estimate the non-secular contributions to the line-width. The power absorbed in pulse excitation comes out to be small for short pulse (short compared to the relaxation parameter) and it reduces to the value obtained in continuous excitation for a long pulse. It is seen that for a given pulse-width the signal decreases with the increase of the relaxation parameter and this happens as temperature is lowered. The saturation of electromagnetic signal in presence of the acoustic excitation has also been studied. The analysis indicates that the relaxation parameter obtained from the plot of the relative signal (〈〉_ω/〈〉₀) vs the acoustic frequency ω, is always less than its true value which can be determined by observing the frequency dependence of the relative fractional signal defined as [(〈〉₀?〈〉_ω)/〈〉_ω]/[(〈〉₀?〈〉_2ω0)/〈〉_2ω0].     

High order Coriolis interactions in NO2

A small widespread Coriolis perturbation in the infrared bands of NO₂ has been quantitatively analyzed. The resonance which affects all levels which differ by two quanta in the bending vibration and one in the antisymmetric stretch has been included explicitly in the reanalysis of five infrared bands. This reanalysis has led to improved constants for the bands analyzed and five consistent values for the interaction parameter. Two theoretical estimates of this interaction parameter are also presented.     

CeCu2Si2和UBe13的超导理论(Ⅰ) ——模型,Tc及序参量

本文从周期性的Anderson晶格模型出发,考虑到局域电子与局域晶格形变的作用,对CeCu₂Si₂和UBe₁₃的重费密子超导现象进行了理论研究。通过计算,得到了合理的超导转变温度T_c;给出了描述同位素效应大小的参数α<1/2,甚至等于零(在BCS理论中α=1/2),说明现在的理论给出的同位素效应比BCS理论小,甚至可以不存在同位素效应,这与重费密子超导的实验相符合;此外还给出了序参量随温度及态密度变化的关系曲线,由此可 关键词：     

Ni2+掺杂到氟化物钙钛矿中的局域结构畸变和基态分裂的理论研究

基于双自旋轨道耦合系数模型并结合完全能量矩阵的方法,研究了AMF₃(A=K, Rb; M=Zn, Cd, Ca):Ni²⁺和K₂ZnF₄:Ni²⁺体系中Ni²⁺的基态分裂和局域结构． 通过模拟光谱和电子顺磁共振(EPR)谱,结果显示在研究氟化物络合分子的能级精细结构和局域结构畸变时,配体F^-对体系的自旋轨道耦合机理的影响不可忽略,同时讨论了EPR参量随夹角、自选轨道耦合、平均参量以及偏离参量的变化规律.     

‘Hot phonon’ contribution to Urbach's tails in semiconductors

We consider electron-hole recombination in semiconductors under high injection levels of electrons and holes interacting with ‘hot LO-phonons’. It is shown that the increasing value of E₀, an energy parameter which characterizes the exponential low energy edge in the luminescence spectra, with laser light intensity is the result of the increasing concentration of phonons in excess of equilibrium. Dependence of E₀ with the effective temperature T¹ of the phonons is given. Furthermore, it is shown that the electron-phonon interaction also contributes to the shift of the spectra towards lower energies.