72 research outputs found
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
Influence of experimental noise on densities reconstructed from line projections
The influence of experimental noise on densities rho(p) reconstructed by the
Cormack method from their line projections, e.g. 2D ACAR spectra, is
investigated. Simulations of statistical noise are performed for various sets
of 2D spectra for two model rho(p) having the cubic symmetry. For the
reconstructed densities propagation of the statistical error in terms of
standard deviations, sigma[rho(p)], is estimated. We observe that the
distribution of sigma[rho(p)] has its extremes along the main symmetry
directions and also a tendency to accumulate for small p. Moreover, the more
density components, rho_n(p), have to be taken to description of rho(p) the
less anisotropic is the distribution of sigma[rho(p)]. Additionally, the error
generated by the reconstruction method itself is discussed.Comment: 6 pages, 8 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
On the reliability of linear band structure methods
We discuss an efficiency of various band structure algorithms in determining
the Fermi surface (FS) of the paramagnetic ErGa3. The linear muffin-tin orbital
(LMTO) in the atomic sphere approximation (ASA) method and three full potential
(FP) codes: FP-LMTO, FP linear augmented plane wave (FLAPW), and FP local
orbitals (FPLO) methods are employed. Results are compared with
electron-positron (e-p) momentum densities reconstructed from two dimensional
angular correlation of annihilation radiation (2D ACAR). Unexpectedly, none of
used modern FP codes is able to give satisfying description of the experimental
data that are in perfect agreement with LMTO-ASA results. We suspect that it
can be connected with a different choice of the linearization energy.Comment: 6 pages, 2 figure
Comment on “Magnetic Compton scattering study of Laves phase ZrFe<sub>2</sub> and Sc doped ZrFe<sub>2</sub>:Experiment and Green function based relativistic calculations” by Bhatt et al.
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