Search results for " magnitude"
showing 10 items of 407 documents
Néel Spin-Orbit Torque Driven Antiferromagnetic Resonance in Mn2Au Probed by Time-Domain THz Spectroscopy
2018
We observe the excitation of collective modes in the terahertz (THz) range driven by the recently discovered Neel spin-orbit torques (NSOTs) in the metallic antiferromagnet Mn_{2}Au. Temperature-dependent THz spectroscopy reveals a strong absorption mode centered near 1 THz, which upon heating from 4 to 450 K softens and loses intensity. A comparison with the estimated eigenmode frequencies implies that the observed mode is an in-plane antiferromagnetic resonance (AFMR). The AFMR absorption strength exceeds those found in antiferromagnetic insulators, driven by the magnetic field of the THz radiation, by 3 orders of magnitude. Based on this and the agreement with our theory modeling, we inf…
Spin-lattice relaxation via quantum tunneling in anEr3+-polyoxometalate molecular magnet
2010
We investigate the mechanism of spin-lattice relaxation of Er ions encapsulated in polyoxometalate clusters, which below 4 K can only reverse its spin via quantum tunneling processes. The temperature-independent rate −1 is, at zero field, ten orders of magnitude larger than the rates predicted for direct phonon-induced processes. In addition, we observe that −1 is suppressed by external magnetic bias and hyperfine interactions but enhanced by increasing the concentration of Er ions. The observed relaxation agrees with predictions for pure quantum tunneling, showing that this phenomenon drives the thermalization of electronic spins. A possible link between these two phenomena is discussed, i…
Identification of Néel Vector Orientation in Antiferromagnetic Domains Switched by Currents in NiO/Pt Thin Films
2021
Understanding the electrical manipulation of the antiferromagnetic order is a crucial aspect to enable the design of antiferromagnetic devices working at THz frequencies. Focusing on collinear insulating antiferromagnetic $\mathrm{Ni}\mathrm{O}/\mathrm{Pt}$ thin films as a materials platform, we identify the crystallographic orientation of the domains that can be switched by currents and quantify the N\'eel-vector direction changes. We demonstrate electrical switching between different T domains by current pulses, finding that the N\'eel-vector orientation in these domains is along [$\ifmmode\pm\else\textpm\fi{}5$ $\ifmmode\pm\else\textpm\fi{}5$ 19], different compared to the bulk $⟨112⟩$ d…
Optimization of multilayered nanotubes for maximal scattering cancellation
2016
An optimization for multilayered nanotubes that minimizes the scattering efficiency for a given polarization is derived. The cylindrical nanocavities have a radially periodic distribution, and the marginal layers that play a crucial role particularly in the presence of nonlocalities are disposed to reduce the scattering efficiency up to two orders of magnitude in comparison with previous proposals. The predominant causes leading to such invisibility effect are critically discussed. A transfer-matrix formalism is additionally developed for the fast estimation of the scattering efficiency of the nanostructures.
Sub-MeV dark matter and the Goldstone modes of superfluid helium
2019
We show how the relativistic effective field theory for the superfluid phase of helium-4 can replace the standard methods used to compute the production rates of low momentum excitations due to the interaction with an external probe. This is done by studying the scattering problem of a light dark matter particle in the superfluid, and comparing to some existing results. We show that the rate of emission of two phonons, the Goldstone modes of the effective theory, gets strongly suppressed for sub-MeV dark matter particles due to a fine cancellation between two different tree-level diagrams in the limit of small exchanged momenta. This phenomenon is found to be a consequence of the particular…
Self-diffusion coefficients in plastic crystals by multiple-pulse NMR in large static field gradients.
1996
Measurements of self-diffusion coefficients in solids with the gradient spin echo technique have until now been limited due to short spin-spin relaxation times. Here we make use of multiple-pulse sequences, which average out the nuclear dipole interaction, to expand the measurable range for macroscopic self-diffusion coefficients by 2 orders of magnitude. By combining multiple-pulse NMR, in our case using the MREV-8 sequence, with a high static gradient we measured the self-diffusion coefficient in a molecular crystal of camphene down to a value of $D\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}16}{\mathrm{m}}^{2}{\mathrm{s}}^{\en…
Amplitude Analysis of Ds+→π+π0η and First Observation of the W -Annihilation Dominant Decays Ds+→a0(980)+π0 and Ds+→a0(980)0π+
2019
We present the first amplitude analysis of the decay D_{s}^{+}→π^{+}π^{0}η. We use an e^{+}e^{-} collision data sample corresponding to an integrated luminosity of 3.19 fb^{-1} collected with the BESIII detector at a center-of-mass energy of 4.178 GeV. We observe for the first time the W-annihilation dominant decays D_{s}^{+}→a_{0}(980)^{+}π^{0} and D_{s}^{+}→a_{0}(980)^{0}π^{+}. We measure the absolute branching fraction B(D_{s}^{+}→a_{0}(980)^{+(0)}π^{0^{(}+)},a_{0}(980)^{+(0)}→π^{+(0)}η)=(1.46±0.15_{stat}±0.23_{sys})%, which is larger than the branching fractions of other measured pure W-annihilation decays by at least one order of magnitude. In addition, we measure the branching fracti…
Quasi-resonant energy transfer in collisions: Na2(A1? u + )+K(4S)
1994
Cross sections for electron energy transfer from the initial rotational stateJ′of the two lowest vibrational levelsv′=0 andv′=1 of excited dimers Na2(A) to potassium atoms as described by Na2(A1Σu+,v′J′)+K(4S)→Na2 (X1Σg+,v″J″)+K(4P)+ΔE have been examined by laser-induced fluorescence. A strong increase of the cross section by as much as an order of magnitude has been observed for those dimerv′J′-levels for which the dipole transitions are close to resonance of the 4S-4P transitions in the atom (ΔE<4 cm−1). The absolute cross sections for energy transfer have been calculated by the Rabitz approximation of first-order perturbation theory. In the case of closest energy resonance (ΔE=0.9 cm−1) …
Evidence for Three Microscopically Different Kinds of E1 Transitions in Lead-Region Nuclei
1986
One outstanding feature of the shell model in heavy nuclei is that within a main shell the single-particle transitions of electric dipole (E1) character are forbidden. This leads to the experimentally observed fact that the E1 transitions are usually hindered by a factor of about 10 with respect to the Weisskopf estimate. But since there is a dispersion of about two or three orders of magnitude among these hindrance factors, the isomeric E1 transitions have not been used to elucidate the mocroscopic properties of the involved states, as has been done for the E3 transitions of this nuclear region [1]. The E3 transitions often proceed via admixtures of the low-lying collective octupole state,…
Extremely slow Drude relaxation of correlated electrons
2005
The electrical conduction of metals is governed by how freely mobile electrons can move throughout the material. This movement is hampered by scattering with other electrons, as well as with impurities or thermal excitations (phonons). Experimentally, the scattering processes of single electrons are not observed, but rather the overall response of all mobile charge carriers within a sample. The ensemble dynamics can be described by the relaxation rates, which express how fast the system approaches equilibrium after an external perturbation1,2,3. Here we measure the frequency-dependent microwave conductivity of the heavy-fermion metal UPd2Al3 (ref. 4), finding that it is accurately described…