scholarly journals Force-Mediating Particle of Coupling of Spin Angular Momenta

2021 ◽  
pp. 49-65
Author(s):  
ShaoXu Ren
Keyword(s):  
Angular Momentum ◽  
Topological Space ◽  
Spin Coupling ◽  
Spin Angular Momentum ◽  
Spin Particle ◽  
Angular Momenta

In this paper, a hypothesis is proposed, that something similar to what happen to the puzzle of the energy losing in decay of neutron may also occur to the puzzle of the sum losing of the z-components of spin angular momenta in the synthetic course of spin coupling in Spin Topological Space. The former puzzle is related to hidden neutrial antineutrino that carries a small amount of energy away, the latter puzzle is related to hidden "constructive" zero-spin particle playing the role of a force-mediator that carries some amount of spin angular momentum, which just offsets the same amount of angular momentum losing in the formation of spin coupling.

scholarly journals The angular momentum of vectorial non-paraxial fields and the role of radial charges in orbit-spin coupling

2020 ◽  
Vol 238 ◽  
pp. 12017
Author(s):  
Omar El Gawhary ◽  
Paul Urbach
Keyword(s):  
Angular Momentum ◽  
Electromagnetic Fields ◽  
Orbital Angular Momentum ◽  
Total Angular Momentum ◽  
Polarization State ◽  
Spin Coupling ◽  
Spin Orbit Coupling ◽  
Spin Angular Momentum ◽  
Phase Profile

Electromagnetic fields carry a linear and an angular momentum, the first being responsible for the existence of the radiation pressure and the second for the transfer of torque from electromagnetic radiation to matter. The angular momentum is considered to have two components, one due to the polarization state of the field, usually called Spin Angular Momentum (SAM), and one due to existence of topological azimuthal charges in the field phase profile, which leads to the Orbital Angular Momentum (OAM). For non-paraxial fields these two contributions are not independent of each other, something which is described as spin-orbit coupling. It has been recently proved that electromagnetic fields necessarily carry also invariant radial charges that, as discussed in this work, play a key role in the angular momentum. Here we show that the total angular momentum consists in fact of three components: one component only dependent on the spin of the field, another dependent on the azimuthal charges carried by the field and a third component dependent on the spin and the radial charges contained in the field. By properly controlling the number and coupling among these radial charges it is possible to design electromagnetic fields with a desired total angular momentum. In this way it is also possible to discover fields with no orbital angular momentum and a spin angular momentum typical of spin-3/2 objects, irrespective of the fact that photons are spin-1 particles.

scholarly journals Revealing angular momentum transfer channels and timescales in the ultrafast demagnetization process of ferromagnetic semiconductors

2019 ◽  
Vol 116 (39) ◽  
pp. 19258-19263
Author(s):  
Zhanghui Chen ◽  
Jun-Wei Luo ◽  
Lin-Wang Wang
Keyword(s):  
Angular Momentum ◽  
Density Functional ◽  
Dominant Role ◽  
Spin Transfer ◽  
Theory Approach ◽  
Spin Angular Momentum ◽  
Spintronic Devices ◽  
Electron Phonon Coupling ◽  
Stage Process

Ultrafast control of magnetic order by light provides a promising realization for spintronic devices beyond Moore’s Law and has stimulated intense research interest in recent years. Yet, despite 2 decades of debates, the key question of how the spin angular momentum flows on the femtosecond timescale remains open. The lack of direct first-principle methods and pictures for such process exacerbates the issue. Here, we unravel the laser-induced demagnetization mechanism of ferromagnetic semiconductor GaMnAs, using an efficient time-dependent density functional theory approach that enables the direct real-time snapshot of the demagnetization process. Our results show a clear spin-transfer trajectory from the localized Mn-d electrons to itinerant carriers within 20 fs, illustrating the dominant role of sp−d interaction. We find that the total spin of localized electrons and itinerant carriers is not conserved in the presence of spin-orbit coupling (SOC). Immediately after laser excitation, a growing percentage of spin-angular momentum is quickly transferred to the electron orbital via SOC in about 1 ps, then slowly to the lattice via electron–phonon coupling in a few picoseconds, responsible for the 2-stage process observed experimentally. The spin-relaxation time via SOC is about 300 fs for itinerant carriers and about 700 fs for Mn-d electrons. These results provide a quantum-mechanical microscopic picture for the long-standing questions regarding the channels and timescales of spin transfer, as well as the roles of different interactions underlying the GaMnAs demagnetization process.

scholarly journals Angular momenta in fields from a rotational mechanical antenna

2021 ◽  
Author(s):  
Yu Mao ◽  
Y. Liu ◽  
Hai Lin
Keyword(s):  
Fourier Transform ◽  
Angular Momentum ◽  
Electric Dipole ◽  
Energy Flow ◽  
Flow Density ◽  
Spin Angular Momentum ◽  
Transform Method ◽  
Rotation Direction ◽  
Binding Force ◽  
Angular Momenta

Abstract Mechanic antennas provide opportunities for human portable, VLF communications, where a rotational dipole emits EM signals with angular momenta. In this paper we analytically derive the electromagnetic fields from a rotational electric dipole using Fourier transform method, and find that the radiated fields from the rotational electric dipole carries nonzero energy flow density in both orbital and spin angular momentum (AM) parts by AM flux tensors. Intuitively, a rotation of a dipole induces a longitudinal orbital angular momentum and a longitudinal spin angular momentum both circulating in the rotation direction. And the binding force for the rotational electric dipole is then shown to result mainly from the Coulomb fields. We believe that our work can provide novel communication designs for portable mechanic antennas.

scholarly journals Staggering of angular momentum distribution in fission

2018 ◽  
Vol 169 ◽  
pp. 00023
Author(s):  
Pierre Tamagno ◽  
Olivier Litaize
Keyword(s):  
Angular Momentum ◽  
Excitation Energy ◽  
Momentum Distribution ◽  
Ad Hoc ◽  
Rayleigh Distribution ◽  
Fission Process ◽  
Angular Momenta ◽  
Model Derivation ◽  
The Impact

We review here the role of angular momentum distributions in the fission process. To do so the algorithm implemented in the FIFRELIN code [?] is detailed with special emphasis on the place of fission fragment angular momenta. The usual Rayleigh distribution used for angular momentum distribution is presented and the related model derivation is recalled. Arguments are given to justify why this distribution should not hold for low excitation energy of the fission fragments. An alternative ad hoc expression taking into account low-lying collectiveness is presented as has been implemented in the FIFRELIN code. Yet on observables currently provided by the code, no dramatic impact has been found. To quantify the magnitude of the impact of the low-lying staggering in the angular momentum distribution, a textbook case is considered for the decay of the 144Ba nucleus with low excitation energy.

scholarly journals Role of guiding center in Landau level system and mechanical and pseudo orbital angular momenta

2020 ◽  
Vol 35 (19) ◽  
pp. 2050096
Author(s):  
Yoshio Kitadono ◽  
Masashi Wakamatsu ◽  
Liping Zou ◽  
Pengming Zhang
Keyword(s):  
Angular Momentum ◽  
Coordinate System ◽  
Landau Level ◽  
The Other ◽  
Level System ◽  
Cyclotron Motion ◽  
Gauge Invariant ◽  
Angular Momenta ◽  
Gauge Principle

There is an interesting but not-so-popular quantity called pseudo orbital angular momentum (OAM) in the Landau-level system, besides the well-known canonical and mechanical OAMs. The pseudo OAM can be regarded as a gauge-invariant extension of the canonical OAM, which is formally gauge invariant and reduces to the canonical OAM in a certain gauge. Since both of the pseudo OAM and the mechanical OAM are gauge invariant, it is impossible to judge which of those is superior to the other solely from the gauge principle. However, these two OAMs have totally different physical meanings. The mechanical OAM shows manifest observability and clear correspondence with the classical OAM of the cyclotron motion. On the other hand, we demonstrate that the standard canonical OAM as well as the pseudo OAM in the Landau problem is the concept which crucially depend on the choice of the origin of the coordinate system. We try to reveal the relation between the pseudo OAM and the mechanical OAM as well as their observability by paying special attention to the role of guiding-center operator in the Landau problem.

PHENOMENOLOGY OF NUCLEI AT VERY HIGH ANGULAR MOMENTA USING PARAMETRIZED TWO-CENTER NUCLEAR SHAPES

1995 ◽  
Vol 04 (04) ◽  
pp. 789-800
Author(s):  
RAJ K. GUPTA ◽  
SHAM S. MALIK ◽  
J.S. BATRA ◽  
PETER O. HESS ◽  
WERNER SCHEID
Keyword(s):  
Angular Momentum ◽  
Deformation Energy ◽  
Moment Of Inertia ◽  
Yrast Band ◽  
Spin States ◽  
High Spin States ◽  
Angular Momenta ◽  
Forward Bending ◽  
Very High

The nuclear shapes and variation of moment of inertia with angular momentum, as well as the limiting angular momentum carried by a nucleus at its fissioning stage, are derived from the observed data of the ground-state yrast band and quadrupole deformations of these states. The necking-in of the nuclear shapes are shown to start already at J*~14+−18+. The empirical variation of moment of inertia with angular momentum is found to include the back-bending and forward-bending effects and supports the nuclear softness model of the nucleus. The fission of nuclei is shown to occur at very high angular momenta, which is different for different nuclei. The role of deformation energy is analyzed and the possibility of predicting the quadrupole deformations, or B(E2) transitions, for very high spin states is discussed. The calculations are presented for 156Dy, 158Er, and 164Hf.

Exchange Spin Coupling from Gaussian Process Regression

2020 ◽  
Author(s):  
Marc Philipp Bahlke ◽  
Natnael Mogos ◽  
Jonny Proppe ◽  
Carmen Herrmann
Keyword(s):  
Machine Learning ◽  
Gaussian Process ◽  
Gaussian Process Regression ◽  
Molecular Magnets ◽  
Molecular Structures ◽  
Spin Coupling ◽  
Structure Property ◽  
Data Set ◽  
Uncertainty Estimates

Heisenberg exchange spin coupling between metal centers is essential for describing and understanding the electronic structure of many molecular catalysts, metalloenzymes, and molecular magnets for potential application in information technology. We explore the machine-learnability of exchange spin coupling, which has not been studied yet. We employ Gaussian process regression since it can potentially deal with small training sets (as likely associated with the rather complex molecular structures required for exploring spin coupling) and since it provides uncertainty estimates (“error bars”) along with predicted values. We compare a range of descriptors and kernels for 257 small dicopper complexes and find that a simple descriptor based on chemical intuition, consisting only of copper-bridge angles and copper-copper distances, clearly outperforms several more sophisticated descriptors when it comes to extrapolating towards larger experimentally relevant complexes. Exchange spin coupling is similarly easy to learn as the polarizability, while learning dipole moments is much harder. The strength of the sophisticated descriptors lies in their ability to linearize structure-property relationships, to the point that a simple linear ridge regression performs just as well as the kernel-based machine-learning model for our small dicopper data set. The superior extrapolation performance of the simple descriptor is unique to exchange spin coupling, reinforcing the crucial role of choosing a suitable descriptor, and highlighting the interesting question of the role of chemical intuition vs. systematic or automated selection of features for machine learning in chemistry and material science.

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