Electron momentum density in yttrium

Sormann

2005

Acta Phys. Pol. A

Self Cite

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 theory. Moreover, it is not true 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.

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 95%

See 1 more Smart Citation

Many-Body Effects Observed in the Positron Annihilation Experiment

Sormann

2005

Acta Phys. Pol. A

Self Cite

“…[26]. The fact that they are greater than those of lower degree (with l = 2 and 4) is not unusual -it depends on a particular lattice potential: either anisotropy dominates on the planes perpendicular to the main rotation axis (as in Gd or Y [27]) or along the main rotation axis (as, e.g., in Cd [28], where the largest is f 2 (p)). Because harmonics f l,0 along the [0001] direction have very high values, growing with l, anisotropy of 1D profi les could be very high compared to absolute values of particular anisotropic components f l, (p).…”

Section: Original Papermentioning

confidence: 99%

“…Thus, in order to visualize the importance of a proper determining of f 0 (p), fi rst of all when one performs theoretical calculations, in Fig. 4, we show the anisotropy of theoretical spectra in Y [27] compared with Lam-Platzman correction (LPC), which describes electron-electron correlation effects [30].…”

Section: Original Papermentioning

confidence: 99%

Isotropic distributions in hcp crystals

2015

Nukleonika

This paper is devoted to the studies of the isotropic average of quantities in the momentum space having the full symmetry of the Brillouin zone. Such quantities, denoted here as f(p), can be expressed as a series of lattice harmonics F l, (,) of an appropriate symmetry [1,2] (1) where  distinguishes harmonics of the same order and (,) are the azimuthal and polar angles of the direction p with respect to the reciprocal lattice coordinate system. Isotropic distributions f 0 (p) (f(p) averaged over angles (,)) are used in calculating many physical properties, e.g. the specifi c heat and Debye temperature [1,[3][4][5][6][7] and density of states in disorder systems [8,9], or (in some particular cases) in probing electron momentum densities via angular correlation of annihilation radiation (ACAR) [10,11], Compton scattering [12][13][14][15][16][17][18][19][20][21][22], and Doppler broadening spectra [23].In the previous paper, devoted to the cubic structures [24], we showed that for calculating the isotropic component, the common procedure of applying high symmetry directions (HSD) is the worst choice (the same occurs for the anisotropic components). In this paper, similar considerations are performed for the hcp structure, although obtained results may be generalized on all structures with the unique R-fold axes. For such structures with R = 6, 4, and 3 (hcp, tetragonal, and trigonal symmetry, respectively), the lattice harmonics having the full symmetry of the Brillouin zone have a very simple form: Isotropic distributions in hcp crystalsGrażyna Kontrym-Sznajd Abstract. Some anisotropic quantities in crystalline solids can be determined from their knowledge along a limited number of sampling directions. The importance of the choice of such directions is illustrated on the example of estimating, from angular correlation of annihilation radiation data, the isotropic electron momentum density in Gd.

Electron–positron momentum densities in crystalline solids

Physica Status Solidi (b)

Sormann

2013

The uniqueness of information contained in electron densities r(p) in the extended momentum space is pointed out, showing that certain electronic properties can be derived only from r(p), directly related to the electron Bloch wave functions. The influence of many-body effects on the electron-positron (e-p) momentum density and of the crystal lattice periodicity on scattering effects is discussed. On the example of Mg it is illustrated that for simple metals there is a unique opportunity to estimate, for e-p densities, electron-electron correlation effects quantitatively.1 Introduction The knowledge of the Fermi surface (FS) topology is crucial to understand the electron properties of quantum systems [1][2][3][4]. The FS can be determined experimentally with various methods. The most common quantum oscillatory techniques [5][6][7] allow estimation of only some quantities related to FS without a visualization of its shape. Other techniques such as Compton scattering [8,9], angular correlation of annihilation radiation (ACAR) [10,11], and angle-resolved photoemission spectroscopy (ARPES) [12] yield information on the shape of FS in the whole reciprocal space [13]. The most direct method of probing electronic structure is ARPES, also known as ARUPS (angleresolved ultraviolet photoemission spectroscopy) [14,15]. As for each method, it has also some limitations [16], such as, e.g., those appearing in studies of small elliptical FS hole pockets in hydrated sodium cobalt oxides. These pockets were seen in Shubnikov-de Haas oscillations [17], phonon softening [18] and Compton scattering experiments [19] but not in ARPES measurements [20].ACAR experiments probe the momentum density of electron-positron (e-p) pairs in the extended momentum (p) space [11,13]