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Momentum Density (momentum + density)

Distribution by Scientific Domains
Physics and Astronomy50%

Selected Abstracts

Spectral momentum densities in matter determined by electron scattering,

ACTA CRYSTALLOGRAPHICA SECTION A, Issue 2 2004
Erich Weigold
In electron momentum spectroscopy (EMS), an incoming energetic electron (50,keV in this work) ionizes the target and the scattered and ejected electrons are detected in coincidence (at energies near 25,keV). From the energy and momentum of the detected particles, the energy and momentum transferred to the target can be inferred. The observed intensity distribution is proportional to the spectral momentum density of the target and hence provides a direct challenge to many-body theoretical descriptions of condensed matter. This is illustrated by comparing some many-body calculations with EMS measurements on graphite and polycrystalline aluminium. [source]

Many body effects seen in the positron annihilation experiment

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2007
G. Kontrym-Sznajd
Abstract The electron-positron (e-p) momentum density in p -space for copper, magnesium, cadmium and yttrium, calculated by using various theoretical approaches, are compared with corresponding densities reconstructed from two-dimensional angular correlation of annihilation radiation (2D ACAR) experimental spectra. We demonstrate that (at least for positrons in metals) strong electron-electron (e-e) correlations are clearly visible not only in the Compton scattering but also in positron annihilation experiments. Moreover, a proper description of e-p correlations needs to include the lattice-periodical crystal potential. In case of strong lattice effects, the increase of the e-p enhancement with increasing momentum - the so-called Kahana-like enhancement, is vanishing. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Spectral momentum densities in matter determined by electron scattering,

ACTA CRYSTALLOGRAPHICA SECTION A, Issue 2 2004
Erich Weigold
In electron momentum spectroscopy (EMS), an incoming energetic electron (50,keV in this work) ionizes the target and the scattered and ejected electrons are detected in coincidence (at energies near 25,keV). From the energy and momentum of the detected particles, the energy and momentum transferred to the target can be inferred. The observed intensity distribution is proportional to the spectral momentum density of the target and hence provides a direct challenge to many-body theoretical descriptions of condensed matter. This is illustrated by comparing some many-body calculations with EMS measurements on graphite and polycrystalline aluminium. [source]

Anisotropic distribution of quantum-vacuum momentum density in a moving electromagnetic medium

ANNALEN DER PHYSIK, Issue 7 2010
J.Q. Shen
Abstract An isotropic electromagnetic medium becomes gyrotropically anisotropic when it moves, and an anisotropic electromagnetic environment can then be created in this motion-induced anisotropic medium. One of the most remarkable features is that the quantum vacuum in the anisotropic electromagnetic environment exhibits a nonzero electromagnetic momentum density, since the universal symmetry of the vacuum fluctuation field is broken, and the anisotropic quantum vacuum mode structure is produced because of the symmetry breaking. This would give rise to a noncompensation effect among the four vacuum eigenmodes (i.e., the forward and backward propagating modes as well as their respective mutually perpendicular polarized components), and leads to an anisotropic correction to the vacuum momentum in the moving medium. The physical significance and the potential applications of the anisotropic quantum vacuum are discussed. This quantum-vacuum effect may be used to develop sensitive sensor techniques and to design new quantum optical and photonic devices. [source]