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

Positron Annihilation Characteristics in Zn1−x\text{}_{1-x}Mgx\text{}_{x}Se Mixed Crystals

Positron annihilation characteristics as a function of composition and annealing in zinc vapour were measured and compared with photoluminescence spectra for Zn$\text{}_{1-x}$Mg$\text{}_{x}$Se mixed crystals with 0 ≤ x ≤ 0.6. The positron annihilation data show that there is a substantial number of divacancies present in the system under study. The concentration of such defects is reduced at least by the factor of two upon annealing in zinc vapour

Investigation of Electronic Structure of Zn1−x\text{}_{1-x}Mgx\text{}_{x} Mixed Crystals by Compton Spectroscopy Method

The first experimental study of the Compton profiles of Zn$\text{}_{1-x}$Mg$\text{}_{x}$Se for x=0.25, 0.47, 0.56 mixed crystals is presented. The Compton profiles were measured with the use of the $\text{}^{241}$Am radioactive source with a resolution of 0.57 a.u. The experimentally obtained Compton profiles were compared with the theoretical ones based on the free-atom model. The results are interpreted in terms of outermost electrons of Zn and Mg being promoted to the higher momentum states, and 4p-electrons of Se becoming more delocalised in a solid, being thus promoted to the lower momentum states