Elusive <Emphasis Type="Italic">s-f</Emphasis> intrasite interactions and double exchange in solids: Ferromagnetic versus nonmagnetic ground state

From the theory of many-electron states in atoms, we know that there exists a strong Coulomb repulsion, which results in the electronic term structure of atoms and is responsible for Hund’s rules. By expanding the Coulomb on-site repulsion into a multipolar series, we derive this interaction and show that it is also present in solids as a correlation effect, which means that the interaction requires a multideterminant version of the Hartree-Fock method. Of particular interest is the case where this interaction couples states of localized (f) and delocalized (s) electrons. We show that the interaction is bilinear in the creation/annihilation operators for localized electrons and bilinear in the operators for conduction electrons. To study the coupling, we consider a simple model in the framework of an effective limited configuration interaction method with one localized f-electron and one itinerant s-electron per crystal site. The on-site multipole interaction between the f- and s-electrons is explicitly taken into account. It is shown that depending on the low-lying excitation spectrum imposed by the crystal electric field, the model can lead not only to ferromagnetism but also to a nonmagnetic state. The model is relevant for solids with localized and itinerant electron states.     

QED Derived from the Two-Body Interaction

We have shown in a previous paper that the Dirac bispinor can vary like a four-vector and that Quantum Electrodynamics (QED) can be reproduced with this form of behaviour.⁽¹⁾ In Part I of this paper, we show that QED with the same transformational behaviour also holds in an alternative space we call M-space. We use the four-vector behaviour to model the two-body interaction in M and show that this has similar physical properties to the usual model in L which it predicts. In Part II of this paper we use M-space to show that QED can be reduced to two simple rules for a two-body interaction.     

Critical Stability in Nuclei – An Old Problem Revisited

In this paper we will focus on the nucleon-nucleon interaction in relative S-states. The ¹S₀ interaction is known to be close to that for critical two-body binding. We will discuss two approaches to the NN interaction, which are equivalent on-shell but not off-shell. There is a well-defined transformation between these approaches [1]. One (my preferred approach) is to minimize the tensor forces far off-shell, which leads to more rapid convergence, but at the price of significant non-locality. This approach is used in a model of relativistic tensor quenching of OPEP [2]. With non-local NN interactions it is possible to fit not only NN observables, but also the NNN ground-state energies [3]. The other approach is to maximize the role of the and keep the interaction as local as possible [4]. This approach is also internally consistent, but requires additional NNN interactions to fit nuclear data. Also, we discuss briefly a so-called low momentum interaction [5, 6], which fits S-wave phase shifts quite well. This interaction is strongly non-local, and it can be approximated by a schematic separable interaction. Finally, we mention the Nambu–Jona-Lasinio model [7] and a good approximation, the Hulthen potential, which provides some insight into the near critical two-body binding.     

Quantization of gauge fields through fibre bundle multiconnectivity

A geometric model for the quantum nature of interaction fields is proposed. We utilize a trivial fibre bundle whose typical fibre has a multiconnectivity characterized by a discrete group Γ. By seeing Γ as a gauge group with global action on each fibre, we show that the corresponding field strength is non-zero only on the future part of the light cone whose vertex is at the interaction point. When the interaction is submitted to the symmetries of a Lie group G, we consider the gauge group G x Γ. The field strength of the gauge having this group includes a term expressing the quantization of the interaction field described by G. This geometric interpretation of quantization makes use of topological arguments similar to those applied to explain the Aharonov-Bohm effect. Two examples show how this interpretation applies to the cases of electromagnetic and gravitational fields.      

X-rays and matter – the basic interactions

In this introductory article we attempt to provide the theoretical basis for developing the interaction between X-rays and matter, so that one can unravel properties of matter by interpretation of X-ray experiments on samples. We emphasize that we are dealing with the basics, which means that we shall limit ourselves to a discussion of the interaction of an X-ray photon with an isolated atom, or rather with a single electron in a Hartree–Fock atom. Subsequent articles in this issue deal with more complicated – and interesting – forms of matter encompassing many atoms or molecules. To cite this article: J. Als-Nielsen, C. R. Physique 9 (2008).     

Triangle anomaly free weak interaction with two neutral currents

Considering that the neutral interaction is free of triangle anomalies we derive an expression for the most general neutral interaction with two neutral currents. We show that the Bargers version is a special case. We also determine the interaction wheneverZ, D are mass eigen states and show that this differs from the Barger’s version in an essential way.     

Studies of chemical diffusion in La1-X SrXCoO3-δ

Recent investigations of superconductivity in carbon nanotubes have shown that a single-wall zig-zag nanotube can become superconducting at around 15?K. Theoretical studies of superconductivity in nanotubes using the traditional phonon exchange model, however, give a superconducting transition temperature T _c less than 1?K. To explain the observed higher critical temperature we explore the possibility of the plasmon exchange mechanism for superconductivity in nanotubes. We first calculate the effective interaction between electrons in a nanotube mediated by plasmon exchange and show that this interaction can become attractive. Using this attractive interaction in the modified Eliashberg theory for strong coupling superconductors, we then calculate the critical temperature T _c in a single-wall nanotube. Our theoretical results can explain the observed T _c in a single-wall nanotube. In particular, we find that T _c is sensitively dependent on the dielectric constant of the medium, the effective mass of the electrons and the radius of the nanotube. We then consider superconductivity in a bundle of single-wall nanotubes and find that bundling of nanotubes does not change the critical temperature significantly. Going beyond carbon nanotubes we show that in a metallic hollow nanowire T _c has some sort of oscillatory behaviour as a function of the surface number density of electrons.     

Possibility of T-violating P-conserving magnetism and its contribution to the T-odd P-even neutron–nucleus forward elastic scattering amplitude

T-violating P-even magnetism is considered. The magnetism arises from the T-violating P-conserving vertex of a spin 1/2 particle interaction with the electromagnetic field. The vertex vanishes for a particle on the mass shell. Considering the particle interaction with a point electric charge we have obtained the T-violating P-even spin dependent potential, which is inversely proportional to the cubed distance from the charge. The matrix element of this potential is zero for particle states on the mass shell; nevertheless, the potential contributes to the T-odd P-even neutron forward elastic scattering amplitude by a deformed nucleus with spin . The contribution arises if we take into account incident neutron plane wave distortion by the strong neutron interaction with the nucleus. Received: 29 August 2000 / Revised version: 22 January 2001 / Published online: 23 March 2001     

A reaction-diffusion model for moderately interacting particles

We consider a nonlinear reaction-diffusion model:n Brownian particles move independently inR ^d and eventually die. The interaction, of binary type, affects only the death rate. The radius of interaction goes to zero as the number of particles increases and we characterize a wide range of speeds at which the radius goes to zero. Within this range we show a law of large numbers for the empirical distributions of the alive particles. The limit is independent of the choice of the speed and it is characterized as the solution of a nonlinear reaction-diffusion equation.     

Localization of a pair of bound particles in a random potential

We study the localization length l_c of a pair of two attractively bound particles moving in a one-dimensional random potential. We show in which way it depends on the interaction potential between the constituents of this composite particle. For a pair with many bound states N the localization length is proportional to N, independently of the form of the two particle interaction. For the case of two bound states, we present an exact solution for the corresponding Fokker–Planck equation and demonstrate that l_c depends sensitively on the shape of the interaction potential and the symmetry of the bound state wave functions.     

极性晶体界面附近激子的性质

本文利用么正变换方法计算了极性晶体界面附近激子的基态能量,得到了激子基态能量及倒半径随激子质心距界面距离变化的曲线。发现当晶体在真空中时,表面会出现死层,晶体与金属相接触时,界面附近会出现相变。     

The Ground State Energy of Dilute Bose Gas in Potentials with Positive Scattering Length

The leading term of the ground state energy/particle of a dilute gas of bosons with mass m in the thermodynamic limit is 2p(^h/_2p)² a r/m{2\pi \hbar^2 a \varrho/m} when the density of the gas is r{\varrho}, the interaction potential is non-negative and the scattering length a is positive. In this paper, we generalize the upper bound part of this result to any interaction potential with positive scattering length, i.e, a > 0 and the lower bound part to some interaction potentials with shallow and/or narrow negative parts.     

Interacting entropy-corrected holographic dark energy with apparent horizon as an infrared cutoff

In this work we consider the entropy-corrected version of interacting holographic dark energy (HDE), in the non-flat universe enclosed by apparent horizon. Two corrections of entropy so-called logarithmic ‘LEC’ and power-law ‘PLEC’ in HDE model with apparent horizon as an IR-cutoff are studied. The ratio of dark matter to dark energy densities u, equation of state parameter w _D and deceleration parameter q are obtained. We show that the cosmic coincidence problem is solved for interacting models. By studying the effect of interaction in EoS parameter of both models, we see that the phantom divide may be crossed and also understand that the interacting models can drive an acceleration expansion at the present and future, while in non-interacting case, this expansion can happen only at the early time. The graphs of deceleration parameter for interacting models, show that the present acceleration expansion is preceded by a sufficiently long period deceleration at past. Moreover, the thermodynamical interpretation of interaction between LECHDE and dark matter is described. We obtain a relation between the interaction term of dark components and thermal fluctuation in a non-flat universe, bounded by the apparent horizon. In limiting case, for ordinary HDE, the relation of interaction term versus thermal fluctuation is also calculated.     

Heavy Meson Spectroscopy

In this article we give a review of certain aspects of the present understanding of spectroscopy of heavy mesons and constituent quark masses in the light of non-relativistic potential model approach motivated by quantum chromodynamics. We find that the one gluon exchange at short distance and colour-confining interaction at large distance which is pure scalar (or scalarvector admixture with dominant scalar interaction) under the Lorentz transformation, can explain only partially the present data on 1 P states of bb and bb states. The S-wave data, that are available at present, however can be understood with both scalar confinement or scalar-vector admixture with scalar-dominant interaction.     

Thermal Fields as Causal Fluids

In a previous paper we investigated a divergence-type theory (DDT) describing the dissipative interaction between a field and a fluid. In this paper we compare the macroscopic view of DDT with a microscopic special case, an O(N) scalar field to leading order in the large N approximation and its thermal fluctuations. Our aim is to compare within a simple model the two approaches.     

Mode coupling theory for the description of two particle-two hole states of208Pb

It is shown that for²⁰⁸Pb the 1p-1h space decouples from the 2p-2h space to a very high degree at least for the more collective states. We then calculate the low-lying 2p-2h spectrum of²⁰⁸Pb in a mode-coupling approach that seems to be very well justified in this case. For the particle-particle interaction we use theG-matrix of Herling and Kuo and for the particle-hole force we take the effective density-dependent interaction of Ring and Speth.     

Stochastic fluctuations of persistent currents in mesoscopic rings

We investigate systematically the effect of the electronic Coulomb interaction on the stochastic fluctuations (from sample to sample) in the persistent currents I(Φ) of mesoscopic rings threaded by a magnetic flux Φ. In contrast to our recent publication [Europhys. Lett. 18 (1992) 457], we avoid separation of impurity and interaction scattering events and we present here a comprehensive view. By this alternative procedure, we are able to confirm our earlier result, namely that 〈I²〉^1/2 ～ ev_F/L, which is a much larger quantity than the average current 〈I〉 ～ ev_Fl/L².     

Removing the Forbidden States in a 4<Emphasis Type="Italic">α</Emphasis> System

In previous calculations we considered some α systems with local and non-local αα potentials, and we have shown that the nonlocality nature of the cluster–cluster interaction is indispensable. In those calculations we investigated systems in which we had a maximum of three αα pairs, and we succeeded, although it was not so easy, to remove the forbidden states with a satisfactory degree. In this paper we try to apply the same techniques and same potentials in describing ¹⁶O as a 4α system, where now we have a six αα pairs, but unfortunately we find out that it is difficult to remove the forbidden states in this system. We therefore devote this paper to show in some detail the difficulty we face.     

The importance of gravitational self-field effects in binary systems with compact objects. II. The “static two-body problem” and the attraction law in a post-post-Newtonian approximation of general relativity

The attraction force of two massive bodies connected by a rod is calculated in a post-post-Newtonian approximation. As far as we know this is the first calculation in such an order of approximation. Although the result already shows a complicated field-field interaction, we reproduce Newton's attraction forceM ₁ M ₂/R ² as the leading term in powers of 1/R.