Study of the electron momentum distribution in vanadium by positron annihilation

The angular correlation of the positron annihilation radiation has been measured with a bidimensional apparatus in four planes of V single crystals. The results are compared with calculations of the electron- positron momentum distribution and with theoretical Fermi surface.     

Models and approximations for the momentum distribution in nuclear matter

As a step toward development of a framework for phenomenological analysis of nuclear momentum distributions in terms of dynamical interparticle correlations, the momentum distribution n(k) of symmetrical nuclear matter described by a Jastrow wave function is studied within a variety of approximation schemes. In particular, two simple low-cluster-order approximations are proposed, one of which may be readily adapted to finite nuclei. For two choices of pair correlations tailored respectively to soft and moderately stiff repulsive cores, the results based on these approximations compare favorably with the standards set by Fermi-hypernetted-chain evaluation and (for the kinetic energy) by Monte Carlo integration — even at densities somewhat beyond the empirical equilibrium density of nuclear matter. The crucial role played by the Jastrow wound parameter, as a determinant of the overall behavior of n(k), emerges clearly from these calculations.     

Hartree-Fock investigation of the electron momentum distribution in metallic beryllium

The wave function resulting from an accurate Hartree-Fock computation has been used to describe the electron momentum distribution in beryllium metal. Appreciable discrepancies are found with respect to a simple model that amounts to filling with plane waves the first plus second Brillouin zone. In comparing the calculated with the experimental directional Compton profiles, very close agreement is found in particular with a recent set of accurate -ray profiles. The differential Compton profiles are also semiquantitatively reproduced, better on average than with all previous calculations. Concerning the Fourier transforms of the Compton profiles, all the features of the experimental curves are accurately reproduced, in particular the position of the zero passages, which is a powerful test of the adequacy of a theoretical model to account for the metallic nature of the solid. The possible influence of the correlation correction is discussed, and it is shown that such a correction would substantially improve the overall agreement with the experiment.     

Size dependent electron momentum density distribution in ZnS

In this paper, we present size dependent electron momentum density distribution in ZnS. ZnS nanoparticles of size 3.8 nm and 2.4 nm are synthesized using the chemical route and characterized by X-ray diffraction (XRD). The Compton profile measurements are performed on both the nano-sized as well as bulk ZnS samples employing 59.54 keV gamma-rays from ²⁴¹Am source. The results reveal that the valence electron density in momentum space becomes narrower with reduction of particle size. To evaluate the charge transfer on compound formation, the ionic model based calculations for a number of configurations of Zn^+xS^−x (0.0≤x≤2) are also performed utilizing free atom Compton profiles. These results suggest different amounts of charge transfer in these materials varying from 1.2 to 2.0 electron from Zn to S atom.     

Compton profiles of electron momentum distribution inβ-Ga

We report for the first time the Compton profiles of electron momentum distribution inβ-gallium calculated along the crystallographic directions (100), (110) and (111). The conduction electron states for this purpose are determined in the energy band calculations using model potential. The core states, on the other hand, are represented each by a single tight-binding function. The results show that the Compton profiles are nearly isotropic with very little directional dependence, which is suggestive of a free-electron-like distribution of the conduction electrons in this system. The latter conclusion is in close confirmity with similar conclusions drawn in augmented plane wave (APW) calculation of energy bands and the derived Knight-shift results inβ-Ga.     

Determination of the electron density distribution function in a plasma by a polarization spectroscopy method

The application of the method of polarization spectroscopy of Stark states to calculating the electron distribution function in a plasma is considered. A formula is obtained which relates the polarization tensors to the parameters of a model distribution function describing a group of fast electrons with beam properties. It is suggested that the polarization tensor can be found by using radiation from resonance levels displaying a marked Stark effect. State University, Tomsk. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 73–77, August, 1997.     

Renormalised-free-atom model and electron momentum distribution in magnesium metal

We have computed the Compton profile for magnesium metal using the renormalised-free-atom (RFA) model. It is shown that compared to the earlier LCAO and pseudopotential calculations, the RFA results are in better agreement with the experiment.     

A note on the momentum distribution function for an electron gas

The one-electron momentum distribution function $\text{〈a}{}_{\mathrm{k\sigma }}{}^2\text{a}{}_{\mathrm{k\sigma }}\text{〉}$ for an electron gas is investigated by a diagrammatic analysis of perturbation theory. It is shown that $\text{〈a}{}_{\mathrm{k\sigma }}{}^2\text{a}{}_{\mathrm{k\sigma }}\text{〉}$ has the following exact asymptotic form for large k (k ? p_F; p_F, the Fermi momentum): $\text{〈a}{}_{\mathrm{k\sigma }}{}^2\text{a}{}_{\mathrm{k\sigma }}\text{〉 =}\text{4}\text{9}\text{(}\text{αr}{}_{\mathrm{s}}\text{π}\text{)}{}^2\text{×(}\text{p}{}_{\mathrm{<mtext>F</mtext>}}{}^8\text{k}{}^8\text{) g?(0) + ?}$, where g?(0) is the zero-distance value of the spin-up-spin-down pair correlation function. The physical implications of the above asymptotic form are discussed.     

Calculation of valence electron momentum densities using the projector augmented-wave method

We present valence electron Compton profiles calculated within the density-functional theory using the all-electron full-potential projector augmented-wave method (PAW). Our results for covalent (Si), metallic (Li, Al) and hydrogen-bonded ((H₂O)₂) systems agree well with experiments and computational results obtained with other band-structure and basis-set schemes. The PAW basis set describes the high-momentum Fourier components of the valence wave functions accurately when compared with other basis set schemes and previous all-electron calculations.     

Two-dimensional electron momentum distribution in graphite revealed by means of angular correlation of positron annihilation

Two-dimensional angular correlation measurements with positron annihilation radiation (2D-ACAR) on a single crystal of Kish graphite reveal that the motion of the annihilating electrons is nearly free along the graphite layers and restricted within some distance shorter than the lattice constant in the direction perpendicular to the layers. The hollows appearing on the 2D-ACAR surfaces are explained in terms of preferential annihilation of positrons with π-electrons in graphite.     

Study on distribution of electron momentum density and Fermi surface in lead by positron annihilation

The momentum density of electrons and the Fermi surface are measured in metal lead by the technique of positron annihilation. The three-dimensional electron-positron momentum distribution is reconstructed from measurements of the two-dimensional angular correlation of positron annihilation radiation (2D-ACAR), followed by the image reconstruction technique based on a direct Fourier transformation. On the basis of the obtained experimental spectrum, the Fermi surface topology, the high momentum components (HMC), the enhancement effect, and the autocorrelation function are discussed. The obtained experimental results are in good agreement with theoretical calculations.     

The Migdal jump in the nucleon momentum distribution in nuclear matter is determined by the spin-isospin response function

The renormalization factor Z of the single-particle Green’s function in nuclear matter, equal to the jump in the nucleon momentum distribution (“Migdal jump”), is expressed in terms of the nuclear response function, using approximations that are realistic for nuclear physics. It is shown that the spin-isospin channel makes the dominant contribution to Z. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 7, 529–534 (10 October 1998)     

New reconstruction method of electron momentum densities from Compton profiles

Recent advances in Compton scattering experiments have led to renewed interest in reconstructing three-dimensional electron momentum densities from Compton profiles. We present a new reconstruction method based on the inversion of the Radon transform in terms of spherical harmonics and Jacobi polynomials. This technique is demonstrated on model projections having the hexagonal symmetry. Reconstructed densities, being in very good agreement with the model ones, are a very good performance of this new algorithm.     

Determination of the potential distribution of electron optical systems by agent-based simulation

We demonstrate that the potential distribution of electron optical systems can be quickly determined by agent-based simulation with relatively high accuracy. There is no need for the solution of large systems of algebraic equations. This method is especially useful for quick analysis of potential distributions and demonstration purposes.     

Quantized orbital angular momentum transfer and magnetic dichroism in the interaction of electron vortices with matter

Following the very recent experimental realization of electron vortices, we consider their interaction with matter, in particular, the transfer of orbital angular momentum in the context of electron energy-loss spectroscopy, and the recently observed dichroism in thin film magnetized iron samples. We show here that orbital angular momentum exchange does indeed occur between electron vortices and the internal electronic-type motion, as well as center-of-mass motion of atoms in the electric dipole approximation. This contrasts with the case of optical vortices where such transfer only occurs in transitions involving multipoles higher than the dipole. The physical basis of the observed dichroism is explained.     

The self-energy of the electron in the Coulomb field (momentum space method)

A new method for calculating the self-energy of an electron in a central Coulomb field is presented. It is a pure momentum space procedure. Singularities of the Coulomb t-matrix are avoided by suitable contour deformations. In this procedure renormalization is standard.     

Calculation of the dissipated-energy distribution in the theory of electron transport in matter

A method is proposed for calculating the spatial distribution of the dissipated energy from a unidirectional point source of monoenergetic electrons in an infinite homogeneous medium. The distribution is found by a moment-method solution of the corresponding kinetic equations, formulated in the approximation of continuous electron deceleration; the distribution function from the calculated moment system is subsequently reconstructed along the spatial coordinates.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, Vol. 12, No. 3, pp. 13–19, March, 1969.