Different ways of dealing with Compton scattering and positron annihilation experimental data

Different ways of dealing with one-dimensional (1D) spectra, measured e.g. in the Compton scattering or angular correlation of positron annihilation radiation (ACAR) experiments are presented. On the example of divalent hexagonal close packed metals it is shown what kind of information on the electronic structure one can get from 1D profiles, interpreted in terms of either 2D or 3D momentum densities. 2D and 3D densities are reconstructed from merely two and seven 1D profiles, respectively. Applied reconstruction techniques are particular solutions of the Radon transform in terms of orthogonal Gegenabauer polynomials. We propose their modification connected with so-called two-step reconstruction. The analysis is performed both in the extended p and reduced k zone schemes. It is demonstrated that if positron wave function or many-body effects are strongly momentum dependent, analysis of 2D densities folded into k space may lead to wrong conclusions concerning the Fermi surface. In the case of 2D ACAR data in Mg we found very strong many-body effects. PACS numbers: 71.18.+y, 13.60.Fz, 87.59.FmComment: 17 pages, 9 figure

Many-body effects observed in the positron annihilation experiment

This paper is devoted to study many-body effects in the positron annihilation experiment, both electron-positron (e-p) and electron-electron (e-e) correlations. Various theories of the e-p interaction in real solids were used to verify them by comparing theoretical and experimental e-p momentum densities in Cu and Y. We show that the lattice potential has an essential influence on the e-p correlation effects, i.e. their proper description must be done via periodic lattice potential as e.g. in the Bloch Modified Ladder (BML) theory. Moreover, it is not true that that the dynamic parts of the direct e-p and e-e interactions cancel each other because e-e correlations are observed not only in the Compton scattering but also in the positron annihilation experiments. Keywords: positron annihilation, Compton scattering, momentum densities, many-body effectsComment: 9 pages, 3 figure

Fermiology via the electron momentum distribution (Review Article)

Investigations of the Fermi surface via the electron momentum distribution reconstructed from either angular correlation of annihilation radiation or Compton scattering experimental spectra are presented. The basis of these experiments and mathematical methods applied in reconstructing three-dimensional electron momentum densities from line or plane projections measured in these experiments are described. Finally, papers where such techniques have been applied to study the Fermi surface of metallic materials are reviewed

Fermi-Surface Mapping from 2D Positron Annihilation Data

We demonstrate which kind of information on the electronic structure one can get from one-dimensional profiles, interpreted in terms of two--dimensional reconstructed densities. The conversion from one-dimensional to two-dimensional is applied to one-dimensional angular correlation of annihilation radiation profiles of divalent hexagonal close packed metals Mg and Cd. On the example of Mg we show that one should be very careful while studying the Fermi surface from electron-positron (e-p) densities folded into the first Brillouin zone