Effect of ellipsodial fermi surfaces and relaxation processes on the indirect exchange in the Bloembergen-Rowland approximation

We investigate the effect of relaxation processes (mean free path) and ellipsodial Fermi surfaces on the indirect exchange interaction in the Bloembergen-Rowland approximation and obtain a simple analytic expression which oscillates with mean free path and emphasizes the relative importance of this parameter on the oscillatory behaviour of the indirect exchange.     

Short time corrections to random phase approximation in thermal conduction

Conduction of heat is often described in the random phase approximation (RPA), referring to phonon number but neglecting phases. At is found in several solvable one-dimensional models that there are corrections to RPA at short times t, including a quantum correction which may be irregular as t→0⁺.     

Effects of finite temperatures,valence bands and energy gaps on the indirect exchange interaction in intrinsic semiconductors

The indirect exchange interaction between localized magnetic moments via virtual excitations from the valence band in intrinsic semiconductors is calculated taking into account the temperature, energy gaps, finite valence bands and effective masses. The inclusion of finite temperature effects changes significantly the phase and magnitude of the oscillations. For small gap semiconductors the oscillatory character and the possibility of ferro-magnetic as well as anti-ferromagnetic coupling are obtained. The exchange interaction oscillates with temperature suggesting interesting applications of this model.     

Numerical results on the indirect exchange interaction in crystalline and amorphous metals

Computer simulation of the indirect exchange interaction is carried out for a single tight-binding s-band in ordered (simple cubic, body-centered cubic, face-centered cubic) and amorphous (relaxed dense-random-packed) structures. All cases show very similar features in the spatial dependence of the interaction, with no attenuation being observed in the amorphous structure. The structural dependence of the phase coherence of the electron wavefunctions is analysed. Effects due to alloying are briefly discussed.     

High order corrections to the time-dependent Born-Oppenheimer approximation. II: Coulomb systems

We study the dynamics of molecular systems with Coulomb forces. We prove that if the nuclear masses are proportional to ^–4, then certain solutions to the time dependent Schrödinger equation have asymptotic expansions to arbitrarily high order in powers of , as 0.Supported in part by the National Science Foundation under grant number DMS-8601536     

High order corrections to the time-independent Born-Oppenheimer approximation II: Diatomic Coulomb systems

We study the bound states of diatomic molecular systems. We prove that if the nuclear masses are proportional to ε^?4 then certain eigenvalues and eigenvectors of the Hamiltonian have asymptotic expansions to arbitrarily high order in powers of ε, as ε→0. The zeroth through fourth order terms in the expansions for the eigenvalues are those of the well-known Born-Oppenheimer approximation. The fifth order term is zero.     

Influence of s-f exchange interaction on electrical conduction in rare-earth dialuminides

The electrical resistivity has been measured between 4.2 and 300°K for RA1₂ compounds, where R denotes the rare-earth elements La, Ce, Pr, Nd, Gd, Tb, Dy, Ho, Er, Yb and Y. From an analysis of the resistivity behaviour of the ferromagnetic compounds values are deduced for the effective s-f exchange coupling constants. These values agree reasonably well with data given in literature for the Knight shift of the A1 nuclear magnetic resonance. For CeA1₂ a resistivity minimum has been observed at 13°K.     

Non-linear effects in the spin-wave conduction electron interaction

The effect of non-linear terms on the interaction of spin-waves with conduction electrons has been studied. For small spin-wave amplitudes, the non-linear terms introduce only small corrections to the linear approximation.     

磁性夹层交换耦合中传导电子的间接交换作用分析

应用量子干涉理论和第一性原理研究了Co/Cu/Co夹层结构在[100]和[110]取向上振荡交换耦合及对磁层厚度的依赖,对夹层交换耦合振荡的计算结果表明：当相应的周期不变时,磁性层（Co）厚度的变化将导致在不同的RKKY振荡特征中势的再分配,磁层厚度发生变化时,磁性层上电子结构也发生变化,当磁性层较厚时,交换耦合仅在某一渐近值附近有一小的振荡。耦合振荡的周期、振幅和相位的测量与实验相一致,也与Barnas和Bruno 理论吻合。     

磁性夹层交换耦合中传导电子的间接交换作用分析

应用量子干涉理论和第一性原理研究了Co/Cu/Co夹层结构在[100]和[110]取向上振荡交换耦合及对磁层厚度的依赖,对夹层交换耦合振荡的计算结果表明:当相应的周期不变时,磁性层(Co)厚度的变化将导致在不同的RKKY振荡特征中势的再分配,磁层厚度发生变化时,磁性层上电子结构也发生变化,当磁性层较厚时,交换耦合仅在某一渐近值附近有一小的振荡.耦合振荡的周期、振幅和相位的测量与实验相一致,也与Barnas和Bruno理论吻合.     

Anderson impurity model: Vertex corrections within the finite U non-crossing approximation

We revise the simplest possible approximations to solve numerically the vertex equations for the single impurity Anderson model (SIAM) within the finite U non-crossing approximation (UNCA), considering the self-energies at lowest order in the 1/N diagrammatic expansion. We introduce an approximation to the vertex corrections that includes the double energy dependence and compare it with an approximation (NCAf²v) that neglects a second energy argument. Finally, we analyse the influence of the different approximations on the estimated Kondo scale for simple electronic models.     

On the role of exchange interaction in magnetic ordering and conduction of manganates

A model of chemical bonds in manganates that allows for one-electron covalent σ bonding between manganese and oxygen ions is suggested. One-electron covalent bonding results in the strongly correlated state of electrons due to exchange interaction between the electrons when they are shared by the cation and anion orbitals. The correlated state shows up as the spatial ordering of electrons and the ordering of their spins, causing the spin-ordered electron lattice to form. In this model, electrical conduction in manganates takes place when the electron lattice (more precisely, its part) shifts from one site of localization to another. The conductivity of the material depends on the type of the spin order of electrons in the electron lattice and on the energy of localization, which is defined by the energy of one-electron σ bonding. The model also implies the strong cationic polarization of anions, which facilitates the 3s2p hybridization of anions and the transition of one of the pairs of 2p electrons from the singlet state to the triplet one. The 3s2p hybridization of anions favors the formation of the spin-polarized electron lattice (the electron spins are parallel) and the ferromagnetic ordering of manganese ions. Under these assumptions, the effect of giant magnetoresistance is explained by a change in the conduction mechanism when an external voltage is applied. In this case, the conduction mechanism typical of ionic crystals changes to that specified by the spin-polarized electron lattice.     

On correlation effects in the indirect interaction between adatoms

Starting from a nonorthogonal basis set a model Hamiltonian for the chemisorption of two adsorbates is derived. The nonorthogonality is converted into a renormalization of the matrix elements. A solution is presented which becomes exact in two limiting cases. The indirect interaction energy of two hydrogen atoms is calculated for adsorption on a semi infinite simple cubic solid described by ans-band. For the band nearly filled (parameters of Ni) a 2 × 2 structure seems to be energetically favourable.     

On the antiferromagnetic resonance in superconductors: Influence of indirect exchange interaction

The special features of the antiferromagnetic resonance in metals in presence of a superconducting ordering are analyzed on the basis of the surface impedance. The indirect exchange interaction determines the shift of the resonace frequency and the spectrum of a new undamped mode near ω_r. A parallel is drawn bettween the antiferromagnetic resonances in normal and superconducting states.     

The quantum theory of nucleon correlation in finite nuclei. II. Higher order correlation effects and additive pair approximation

In the first part of this article it was shown that the variational solution of the Schroedinger equation of a finite Fermion system can be written as a finite sum of A terms (for A particles) the first of which is the Hartree-Fock energy, while the rest represent the correlation effects. In the first part explicit formulas for the 2-particle correlation energy were given. In this paper explicit formulas are given for the higher order correlation energies. It is shown that two different models can be developed depending on the orthogonality condition used. Beginning with the 4th order effects the “linked” and “unlinked” correlation terms are separated. An exact formula is given for the case in which only the 2-particle effects, linked and unlinked are taken into account. The “additive pair approximation” in which the correlation energy is given as the sum of 2-particle energies is investigated and it is shown to be related to the exact formula by a clearly defined set of approximations. Various possible applications of the model are discussed.     

Higher order corrections and the scale parameter in QCD

I estimate the influence of the higher order corrections on the determination of the scale parameter Λ². I find a sizeable effect (a reduction of Λ² by a factor 3 to 4). This factor can be relevant in the comparison of Λ² with the characteristic confinement parameters.     

On the exchange and overlap corrections in electron capture

The approximations made in the calculations of the exchange and overlap correction coefficients were investigated. It is shown that the one-electron wave functions of the final state cannot be replaced by those of the unexcited daughter atom, and that the overlap of all inner s, p and d electrons is to be taken into consideration. The new approximation gives a better agreement with the experimental K/β⁺, L/K and M/L capture ratios than the old approximation.