Search results for " Polarization"
showing 10 items of 668 documents
Kinetics of Ordered Phases in Finite Spin Systems
1989
We study the growth of the ordered phase in a spin system of finite size suddenly brought below the transition temperature. Such a growth is driven by the instability of the mode corresponding to the largest eigenvalue of the interaction matrix. The relaxation occurs through different regimes according to whether the unstable mode has a negligible or macroscopic amplitude. One regime is characterised by dynamical scaling properties whereas in the other we can distinguish the growth to a macroscopic amplitude followed by rare transitions from one equilibrium amplitude to another. The analysis is carried out in the framework of a dynamical generalisation of the spherical model assuming non-ra…
Σ+ and Σ¯− Polarization in the J/ψ and ψ(3686) Decays
2020
From 1310.6 x 10(6) J/psi and 448.1 x 10(6) psi (3686) events collected with the BESIII experiment, we report the first observation of Sigma(+) and (Sigma) over bar (-) spin polarization in e(+)e(- ...
Electronic, magnetic, and structural properties of the ferrimagnet Mn2CoSn
2011
The magnetic ground state of the Heusler compound Mn${}_{2}$CoSn was predicted to be nearly half-metallic ferrimagnetic with a high spin polarization by ab initio electronic structure calculations. Mn${}_{2}$CoSn was synthesized, and the magnetic behavior of the compound was studied using a superconducting quantum interference device and x-ray magnetic circular dichroism. The experimental values were found to be in fair accordance with the theoretical predictions. The electronic structure and the crystal structure of Mn${}_{2}$CoSn were characterized comprehensively using x-ray powder diffraction, $^{119}\mathrm{Sn}$ M\"ossbauer spectroscopy, nuclear magnetic resonance, and hard x-ray photo…
Test of band structure calculations for Heusler compounds by spin-resolved photoemission spectroscopy
2012
The electronic density of states of epitaxial thin films of the Heusler compound Co${}_{2}$MnGa is probed in situ by spin-resolved ultraviolet photoemission spectroscopy. The experiments reveal several characteristic features in the intensity spectrum and a clear Fermi edge signature. A high spin polarization of $\ensuremath{\simeq}\phantom{\rule{-0.16em}{0ex}}55%$ at the Fermi edge is followed by a sign change at the binding energy of $\ensuremath{\simeq}$0.8 eV. Corresponding calculations of the band structure and the photoemission spectrum were performed employing a spin-polarized relativistic Korringa-Kohn-Rostoker code. Good agreement between the experimental data and calculations was …
Hund's Rules and Spin Density Waves in Quantum Dots
1997
Spin density functional theory is used to calculate the ground state electronic structures of circular parabolic quantum dots. We find that such dots either have a spin configuration determined by Hund's rule or make a spin-density-wave-like state with zero total spin. The dependence of the spin-density-wave amplitudes on the density of the two-dimensional electron gas is studied.
Polarization in mott scattering of multi-MeV electrons from heavy nuclei
1999
To aid fundamental studies on the polarization of electrons in beta decay, measurements were made of the spin dependence in the scattering of 14 MeV electrons from Pb as a function of scattering angle and foil thickness. The experiment made use of a beam of polarized electrons from a strained GaAsP cathode. A simple theoretical model based on plural scattering explains the observed dependence of the analyzing power on foil thickness. The results extrapolated to infinitely thin targets are in excellent agreement with theory if the finite nuclear size is taken into account.
3He neutron spin filter at ILL
1997
Abstract The strongly spin-dependent absorption of neutrons in nuclear spin polarized 3He opens the possibility to polarize neutrons over the full-spectrum of cold, thermal and epithermal neutrons. At ILL a neutron spin filter (NSF) development started which uses the direct optical pumping of metastable 3He atoms in a 3He plasma at 1 mbar. At present 0.5 bar 1 of gaseous 3He can be polarized within 1 h. Subsequent polarization-preserving compression by a two-stage compressor system enables one to prepare NSF cells of about 300 cm3 volume in the required pressure range of several bars. A remote type of operation based on relaxation times of up to 100 h has been demonstrated in a first survey…
Exchange and correlation energy functionals for two-dimensional open-shell systems
2009
We consider density functionals for exchange and correlation energies in two-dimensional systems. The functionals are constructed by making use of exact constraints for the angular averages of the corresponding exchange and correlation holes, respectively, and assuming proportionality between their characteristic sizes. The electron current and spin are explicitly taken into account, so that the resulting functionals are suitable to deal with systems exhibiting orbital currents and/or spin polarization. Our numerical results show that in finite systems the proposed functionals outperform the standard two-dimensional local spin-density approximation, still performing well also in the importa…
Realization of a broad-band neutron spin filter with compressed, polarized 3He gas
1997
The strongly spin-dependent absorption of neutrons in nuclear spin polarized 3He opens the possibility to polarize beams of thermal and epithermal neutrons. An effective 3He neutron spin filter (NSF) requires high 3He nuclear polarization as well as a filter thickness corresponding to amount of gas in the order of 1 bar 1. We realized such a filter using direct optical pumping of metastable 3He∗ atoms in a 3He plasma at 1 mb. Metastable exchange scattering transfers the angular momentum to the whole ensemble of 3He atoms. At present 3.6 × 1018 3He-atoms s−1 are polarized up to 68%. Subsequent polarization preserving compression by a two-stage compressor system enables to prepare NSF cells o…
Neutron optics P-violation effects near p-wave resonance
1999
Abstract The observations of large enhancement of parity-violation at p-wave compound resonance encourage prompt active discussion of TRI test in neutron optics. One of the most attractive objects for investigation is the p-wave resonance of 139 La at energy 0.734 eV for which the strongest P-odd effect of spin dichroism has been observed. A new technique of neutron spin analysis based on optically pumped 3 He spin filter has been applied successfully to measure the complementary effect of P-odd spin rotation near the same p-wave resonance of 139 La . The results obtained are consistent with theory predictions.