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Results for “L-S COUPLING”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

L-S coupling interpretation of high-resolution LMM Auger spectra of Cu and Zn.

High-resolution LMM Auger spectra of Cu and Zn obtained by X-ray excitation are shown to contain fine structures which have not been reported previously. An attempt has been made to classify these fine structures in terms of pure L-S coupling of the final vacancies of the atom. The agreement between the calculated and the observed energy separations of the fine-structure lines is good within the accuracy of the Hartree-Fock approximation.

Yin, L.↗
NASA NTRS1994

On the polarization of resonantly scattered emission lines - 1. Emission and absorption coefficients in an anisotropic radiation field

Source functions and absorptions coefficients for polarized radiation in a given ansiotropic radiation field are calculated for a variety of permitted electric dipole transitions in the L-S coupling limit. Collisional, radiative and magnetic mixing of the ground sublevels are all considered. The polarization of the self-consistent, emergent radiation field is computed, using an anisotropic escape probability formalism to treat the radiative transfer. It is found that the radiative mixing can enhance the polarization for transitions with large angular momentum, and degrees of polarization less than or approximately 10 per cent are obtained for transitions with small angular momentum.

Lee, H. -W.↗
DOE OSTI2019

Phase-Slip Lines in Wide Superconducting Strips: Charge and Spin Relaxation Lengths

Penetration of spin-polarized charges from a nearby ferromagnetic metallic layer into 100-μm-wide superconducting films of Pb and Mo–Re alloy with similar critical parameters but quite different spin-orbit coupling strengths is studied. It is shown that the diffusion of magnetic properties into a nearby superconductor can be employed as an electrically tunable source of phase-slip events manifesting itself by a staircase response in current-voltage characteristics of the superconductor with discrete metastable resistivity states. Unlike for normal metals, the spin injection into an adjoining quasi-two-dimensional superconducting strip creates not only spin but also charge imbalance in the quasiparticle population which are not necessarily relaxing over the same time scale. Interplay of the two intrinsic length scales sets the width of a phase-slip line in superconducting strips under the injection which may change from nano- to micro-scales. Its experimental determination can be used for estimating the longest relaxation length in a superconductor. Our observations show that spin-orbit coupling in superconductors may lead to novel non-trivial effects linking spin and charge degrees of freedom.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Skyrmions and composite vortex states in three-component Bose–Einstein condensates with spin–orbit coupling

Stable and metastable vortex states in two-dimensional three-component Bose–Einstein condensates are studied in the presence of spin–orbit coupling. The ground states exhibit two skyrmion structures which respectively correspond to the d-skyrmion in antiferromagnetic or the F-skyrmion in ferromagnetic condensates. The half skyrmion and full skyrmion can be controlled by changing the strength of the spin–orbit coupling. We also find a stable composite vortex state which is associated to mixing of the ferromagnetic and antiferromagnetic manifolds.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

On the pseudospin description of the electron Bloch bands

We study the transformation properties of the electron states in crystals with spin–orbit coupling, focusing primarily on the limitations of the frequently used pseudospin-1∕2 description of twofold degenerate Bloch bands. Using the language of corepresentations of magnetic point groups, we construct the Bloch bases across the Brillouin zone in a way which is consistent with all symmetry requirements. This construction is applied to derive the effective spin–orbit Hamiltonians in noncentrosymmetric crystals, known as the generalized Rashba models, in both single-band and multiband cases.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Anharmonicity of Lattice Vibrations in Bi{sub 2}Se{sub 3} Single Crystals

The temperature dependences of the Raman-active frequencies E{sub g}{sup 2}, A{sub 1g}{sup 2} in layered Bi{sub 2}Se{sub 3} single crystals are studied. The contribution of the thermal expansion to a temperature variation in the frequencies is determined. The decay of the anisotropy of the elastic properties in layered Bi{sub 2}Se{sub 3} single crystals due to strong spin–orbit coupling is shown. The Gruneisen-mode parameters for phonons E{sub g}{sup 2} and A{sub 1g}{sup 2} are calculated. Systematic features in the dependences of vibrational frequencies on the atomic masses in layered Bi{sub 2}Te{sub 3}, Bi{sub 2}Se{sub 3}, and Sb{sub 2}Te{sub 3} single crystals are determined.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Gauge-potential-induced vortices in spin-1 Bose–Einstein condensates with spin–orbit coupling

Highlights: •Effectively rotate the so-coupled condensate by an external magnetic field. •New effects of the Aharonov–Bohm geometric phase in ultracold atomic gases. •Many novel vortex structures have been studied. •A new stabilization mechanism for multiquantum vortices in spinor BECs. -- Abstract: We investigate the vortex states generated by the gauge-potential-induced rotation in spin-1 Bose–Einstein condensates with spin–orbit coupling. An external magnetic field coupling with spin equivalently imprints a non-zero gauge angular momentum, which induces an equivalent canonical angular momentum in the opposite direction, accompanied by the generation of quantized vortices. The competition between interatomic interactions, spin–orbit coupling and magnetic field leads to a variety of vortex structures. In the weakly interatomic interacting regime, as the increase of SO coupling strength, the condensate with a weak magnetic field gradient experiences the transition from polar-core vortex to Mermin–Ho vortex then to vortex cluster , and the three-vortex structures are found in the vortex cluster. As the SO coupling increases further, the condensate presents symmetrical density domains separated by radial vortex arrays. With the increase of magnetic field gradient, the number of density domains increases, and the condensate eventually turns into a giant vortex. In the relatively strong interatomic interacting regime, vortex sheets are formed when the magnetic field gradient is weak, and the increasing of magnetic field gradient makes the vortex arrangement orderly. Compared with the cases of weak interatomic interacting regime, density domain structures are broken because of the strong interatomic interactions, and the vortices are arranged in coaxial annular arrays.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Magnetic Behavior of Superconductor 2H-NbSe{sub 2} Intercalated with Iron: First Principle Study

We investigated the structural, electronic and magnetic properties of iron-intercalated niobium selinium, Fe{sub x}NbSe{sub 2} for x=0 and 0.25, from first principle calculations. The tendency towards the localization in superconductors criterion which has been extracted from our results placed the NbSe{sub 2} compound in vicinity of Fe-based superconductors. The DFT plus on-site coulomb repulsion U (DFT+U) and the exact exchange for correlated electrons (DFT+EECE)-based hybrid functional were used including the spin-orbit coupling (SOC) to understand the role of correlation and SOC effects in this type of systems. The calculation predicts the correct antiferromagnetic (AF) ground state, from both the generalized gradient approximation (GGA) and GGA+U. A shift up in the Fermi energy was observed after the intercalation of 2H-NbSe{sub 2} with iron, indicating a charge transfer from Fe to the host compound. The obtained magnetic moment of Fe is enhanced by a correlation effect in both DFT+U and DFT+EECE over the small value from GGA-only. Moreover, a large unquenched orbital magnetic moment is saturated to m{sub orb}∼0.6μ{sub B} under a moderate correlation effect of U{sub eff}∼2.0eV. We also show that the correlation effect is important along side with SOC in order to get a true picture for the band filling consistent with that of the crystal field splitting and a large unquenched m{sub orb} which has been found experimentally in such systems. Therefore, the combination of correlation and SOC effects is a decisive choice for further studies of such systems.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Supercurrent Generation by Spin-Twisting Itinerant Motion of Electrons

Superconductivity is a phenomenon where an external feeding current flows through the system without voltage drop. This is explained if an energy minimum exists under the current feeding boundary condition. We have found such minima in the system exhibiting spin-twisting itinerant motion of electrons with the Rashba spin–orbit interaction due to constraints of the charge conservation and single-valued requirement of the wave function. The supercurrent is shown to have the London equation form that exhibits the flux quantum h/2e.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Ground-State Fermion Parity and Caloric Properties of a Superconducting Nanowire

The ground-state structure and fermion parity have been determined for a semiconductor nano-wire with a strong Rashba spin–orbit interaction and proximity-induced superconductivity placed in an external magnetic field under periodic boundary conditions. Allowance for the open boundaries is shown to cause the topologically nontrivial parameter region to be partitioned into a set of subregions with a different ground-state fermionic parity. This peculiarity is related to the emergence of edge modes with nonmonotonically changing excitation energies in the system as its parameters change. At the quantum transition point, at which the ground-state fermionic parity changes, the edge-mode energy is zero. The magneto- and electrocaloric effects are shown to be effective characteristics that allow the series of quantum transitions in an open nanowire to be identified experimentally. These effects at low temperatures exhibit an anomalous behavior in the parameter region for which topologically stable Majorana modes are realized in long nanowires.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Carrier Lifetime in Semiconductors with Band-Gap Widths Close to the Spin-Orbit Splitting Energies

Expressions for the Auger- and radiative-recombination rates are derived in terms of Kane’s model for materials with a band-gap width close to the spin-orbit splitting energy, which is the case for InAs, InAsSb solid solutions, etc. Our results are compared with simplified expressions for recombination rates, frequently used in publications. It is shown that the nonparabolicity of the electronic structure should be taken into account in calculations of the recombination rates. As an example, the temperature dependences of the charge-carrier lifetimes governed by radiative and non-radiative processes are calculated for InAsSb solid solutions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Spin–Orbit Interaction and Carrier Mobility in a Longitudinal InSb Autosoliton under a Magnetic Field

A version of the spin–orbit interaction of orbitally moving and spin-oriented electrons in a longitudinal autosoliton in indium antimonide under a longitudinal magnetic field is proposed and considered. The additional energy gained by spin–orbit electrons due to this interaction is determined. Expressions for the change in the mobility during the orbital motion of electrons under a magnetic field and the additive mobility of spin-oriented electrons are derived and calculated. The coefficients of the mutual influence of changing electron mobility in the case of orbital motion and the additive mobility of spin-oriented electrons are calculated.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

On the Spin States of Electrons in a Double Quantum Dot in a Two-Dimensional Topological Insulator with Spin-Orbit Interaction

The spectra and spin structure of the states of two interacting electrons localized in a double quantum dot in a two-dimensional topological insulator with spin-orbit interaction are investigated. It is found that, in such a system, a singlet-triplet transition in the ground state without a magnetic field can be implemented. Spin-orbit interaction leads to the splitting of polarized triplet levels and to anticrossing, when one of them crosses the singlet.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Intraband Radiation Absorption by Free Holes in GaAs/InGaAs Quantum Wells with Allowance for Nonsphericity of the kP Hamiltonian

A system of Kane’s equations has been derived and solved with allowance for elastic stresses and nonsphericity of the kP Hamiltonian. On this basis, analytic expressions for the energy spectra of charge carriers have been obtained and calculations of the optical absorption coefficient for heavy holes with transition to a spin-orbit-split hole band in GaAs/InGaAs quantum wells (QWs) have been performed for various polarization directions of the incident radiation. It is established that the maximum absorption in GaAs/InGaAs heterostructure takes place at a QW width of 4–6 nm.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

The Misaligned Orbit of the Earth-sized Planet Kepler-408b

Kepler-408 is one of the 33 planet-hosting Kepler stars for which asteroseismology has been used to investigate the orientation of the stellar rotation axis relative to the planetary orbital plane. The transiting hot Earth, Kepler-408b, has an orbital period of 2.5 days and a radius of 0.86 R {sub ⊕}, making it much smaller than the planets for which spin–orbit alignment has been studied using the Rossiter–McLaughlin effect. Because conflicting asteroseismic results have been reported in the literature, we undertake a thorough re-appraisal of this system and perform numerous checks for consistency and robustness. We find that the conflicting results are due to the different models for the low-frequency noise in the power spectrum. A careful treatment of the background noise resolves these conflicts, and shows that the stellar inclination is i{sub ⋆}=42{sub −4}{sup +5} degrees. Kepler-408b is, by far, the smallest planet known to have a significantly misaligned orbit.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Asteroseismic Determination of the Stellar Rotation Period of the Kepler Transiting Planetary Systems and its Implications for the Spin–Orbit Architecture

We measure the rotation periods of 19 stars in the Kepler transiting planetary systems, P {sub rot,astero} from asteroseismology and P {sub rot,phot} from the photometric variation of their light curves. Two stars exhibit two clear peaks in the Lomb–Scargle periodogram, neither of which agrees with the seismic rotation period. Other four systems do not show any clear peak, whose stellar rotation period is impossible to estimate reliably from the photometric variation; their stellar equators may be significantly inclined with respect to the planetary orbital plane. For the remaining 13 systems, P {sub rot,astero} and P{sub rot,phot} agree within 30%. Interestingly, 3 out of the 13 systems are in the spin–orbit resonant state in which P{sub orb,b}/P{sub rot,astero}≈1 with P {sub orb,b} being the orbital period of the innermost planet of each system. The corresponding chance probability is (0.2–4.7)% based on the photometric rotation period data for 464 Kepler transiting planetary systems. While further analysis of stars with reliable rotation periods is required to examine the statistical significance, the spin–orbit resonance between the star and planets, if confirmed, has important implications for the star–planet tidal interaction, in addition to the origin of the spin–orbit (mis-)alignment of transiting planetary systems.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

KELT-9 b’s Asymmetric TESS Transit Caused by Rapid Stellar Rotation and Spin–Orbit Misalignment

KELT-9 b is an ultra-hot Jupiter transiting a rapidly rotating, oblate early-A-type star in a polar orbit. We model the effect of rapid stellar rotation on KELT-9 b’s transit light curve using photometry from the Transiting Exoplanet Survey Satellite to constrain the planet’s true spin–orbit angle and to explore how KELT-9 b may be influenced by stellar gravity darkening. We constrain the host star’s equatorial radius to be 1.089 ± 0.017 times as large as its polar radius and its local surface brightness to vary by ∼38% between its hot poles and cooler equator. We model the stellar oblateness and surface brightness gradient and find that it causes the transit light curve to lack the usual symmetry around the time of minimum light. We take advantage of the light-curve asymmetry to constrain KELT-9 b’s true spin–orbit angle (87{sup ∘}{sub −11{sup ∘+10{sup {sup ∘}}}}), agreeing with Gaudi et al. that KELT-9 b is in a nearly polar orbit. We also apply a gravity-darkening correction to the spectral energy distribution model from Gaudi et al. and find that accounting for rapid rotation gives a better fit to available spectroscopy and yields a more reliable estimate for the star’s polar effective temperature.

79 ASTRONOMY AND ASTROPHYSICS↗