Search results for "Polar"
showing 10 items of 3817 documents
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.
Dynamic N14 nuclear spin polarization in nitrogen-vacancy centers in diamond
2020
We studied the dynamic nuclear spin polarization of nitrogen in negatively charged nitrogen-vacancy (NV) centers in diamond both experimentally and theoretically over a wide range of magnetic fields from 0--1100 G covering both the excited-state level anticrossing and the ground-state level anticrossing magnetic field regions. Special attention was paid to the less studied ground-state level anticrossing region. The nuclear spin polarization was inferred from measurements of the optically detected magnetic resonance signal. These measurements show that a very large (up to $96\ifmmode\pm\else\textpm\fi{}2%$) nuclear spin polarization of nitrogen can be achieved over a very broad range of mag…
Spin pumping in noncollinear antiferromagnets
2021
The ac spin pumping of noncollinear antiferromagnets is theoretically investigated. Starting from an effective action description of the spin system, we derive the Onsager coefficients connecting the spin pumping and spin-transfer torque associated with the dynamics of the SO(3)-valued antiferromagnetic order parameter. Our theory is applied to a kagome antiferromagnet resonantly driven by a uniform external magnetic field. We demonstrate that the reactive (dissipative) spin-transfer torque parameter can be extracted from the pumped ac spin current in-phase (in quadrature) with the driving field. Furthermore, we find that the three spin-wave bands of the kagome AF generate spin currents wit…
Minimal Model of Spin-Transfer Torque and Spin Pumping Caused by the Spin Hall Effect
2015
In the normal metal/ferromagnetic insulator bilayer (such as Pt/Y$_{3}$Fe$_{5}$O$_{12}$) and the normal metal/ferromagnetic metal/oxide trilayer (such as Pt/Co/AlO$_{x}$) where spin injection and ejection are achieved by the spin Hall effect in the normal metal, we propose a minimal model based on quantum tunneling of spins to explain the spin-transfer torque and spin pumping caused by the spin Hall effect. The ratio of their damping-like to field-like component depends on the tunneling wave function that is strongly influenced by generic material properties such as interface $s-d$ coupling, insulating gap, and layer thickness, yet the spin relaxation plays a minor role. The quantified resu…
The magnetic moment anomaly of the electron bound in hydrogen-like oxygen16O7
2003
The measurement of the g-factor of the electron bound in a hydrogen-like ion is a high-accuracy test of the theory of quantum electrodynamics (QED) in strong fields. Here we report on the measurement of the g-factor of the bound electron in hydrogen-like oxygen (16O7+). In our experiment a single highly charged ion is stored in a Penning trap. The electronic spin state of the ion is monitored via the continuous Stern?Gerlach effect in a quantum non-demolition measurement. Quantum jumps between the two spin states (spin up and spin down) are induced by a microwave field at the spin precession frequency of the bound electron. The g-factor of the bound electron is obtained by varying the micro…
Nuclear-spin comagnetometer based on a liquid of identical molecules
2018
Atomic comagnetometers are used in searches for anomalous spin-dependent interactions. Magnetic field gradients are one of the major sources of systematic errors in such experiments. Here we describe a comagnetometer based on the nuclear spins within an ensemble of identical molecules. The dependence of the measured spin-precession frequency ratio on the first-order magnetic field gradient is suppressed by over an order of magnitude compared to a comagnetometer based on overlapping ensembles of different molecules. Our single-species comagnetometer is shown to be capable of measuring the hypothetical spin-dependent gravitational energy of nuclei at the $10^{-17}$ eV level, comparable to the…