Spin-orbit Term Research Articles

Spin-orbit coupling effects in the quantum Hall regime probed by electron spin resonance

The spin resonance of two-dimensional (2D) electrons confined in a high-quality 4.5-nm AlAs quantum well was studied in the regime of the integer quantum Hall effect. The electron $g$-factor extracted from the magnetic field position of the spin resonance at a fixed microwave frequency demonstrated a strong nonlinear dependence on the magnetic field with discontinuities around even filling factors. The value of the $g$-factor tended to increase with a decrease of the magnetic field around each odd filling. Furthermore, the $g$-factor at the exactly odd filling factor $\ensuremath{\nu}$ turned out to be dependent on $\ensuremath{\nu}$, suggesting the entanglement between the spin degree of freedom and the orbital motion of the electrons in the regime of the integer quantum Hall effect. This suggestion is further supported, as all the experimental data are well described, when a Dresselhaus-type spin-orbit interaction is introduced into the Hamiltonian of a single electron in the quantizing magnetic field. Surprisingly, such excellent agreement was observed even in the case of tilted magnetic fields. The fitting procedure allowed us to determine the strength of the Dresselhaus spin-orbit term in a 2D electron system and to extract the fundamentally important Dresselhaus constant for bulk AlAs. Unexpectedly, not only was single spin resonance observed around even fillings, it tended to split into two well-resolved lines. Yet this finding remains a mystery and highlights the need for further experimental and theoretical efforts.

Electron-Spin Structure and Metal-Ligand Bonding in Open-Shell Systems from Relativistic EPR and NMR: A Case Study of Square-Planar Iridium Catalysts.

Electron and nuclear magnetic resonance spectroscopies are indispensable and powerful methods for investigating the molecular and electronic structures of open-shell systems. We demonstrate that the NMR and EPR parameters are extremely sensitive quantitative probes for the electronic spin density around heavy-metal atoms and the metal-ligand bonding. Using relativistic density-functional theory, we have analyzed the relation between the spin density and the EPR and NMR parameters in paramagnetic iridium(II/IV) complexes with a PNP pincer ligand. As the magnetic-response parameters for compounds containing 5d transition metal(s) are heavily affected by spin-orbit coupling, relativistic effects must be included in the calculations. We have used a recent implementation of the fully relativistic Dirac-Kohn-Sham (DKS) method employing the hybrid PBE0 functional and an implicit solvent model to calculate EPR parameters and hyperfine NMR shifts. The modulation of the metal-ligand bond by the trans substituent (-Cl or ≡N) and the electronic spin structure around the central metal atom and ligands are shown to be reflected in the "long-range" through-bond Fermi-contact (FC) contributions to the ligand 13C and 1H hyperfine couplings. Interestingly, the hyperfine coupling constant of the ligand atom L ( AL) bonded directly to the iridium center changes its sign because of the dominating role of the paramagnetic spin-orbit (PSO) term. Furthermore, the electronic g-shift and the PSO contribution to the ligand AL are shown to invert their signs when nitrogen is substituted for chlorine, reflecting the different formal metal oxidation states and the change in metal-ligand bond character. A full understanding of the substituent effects is provided by using chemical bond concepts in combination with a molecular-orbital (MO) theory analysis of the second-order perturbation theory expression for the EPR parameters. Our findings are easily transferable to other systems containing d-block elements and beyond. Relativistic DFT calculations of magnetic-resonance parameters are expected to frequently assist in future experimental observations and the characterization of hitherto unknown unstable or exotic species.

G -factor of electrons in gate-defined quantum dots in a strong in-plane magnetic field

We analyze orbital effects of an in-plane magnetic field on the spin structure of states of a gated quantum dot based in a two-dimensional electron gas. Starting with a $k \cdot p$ Hamiltonian, we perturbatively calculate these effects for the conduction band of GaAs, up to the third power of the magnetic field. We quantify several corrections to the g-tensor and reveal their relative importance. We find that for typical parameters, the Rashba spin-orbit term and the isotropic term, $H_{43} \propto {\bf P}^2 {\bf B} \cdot \boldsymbol{\sigma}$, give the largest contributions in magnitude. The in-plane anisotropy of the g-factor is, on the other hand, dominated by the Dresselhaus spin-orbit term. At zero magnetic field, the total correction to the g-factor is typically 5-10% of its bulk value. In strong in-plane magnetic fields, the corrections are modified appreciably.

Ab initio surface hopping excited-state molecular dynamics approach on the basis of spin-orbit coupled states: An application to the A-band photodissociation of CH3 I.

Ab initio molecular dynamics approach has been extended to multi-state dynamics on the basis of the spin-orbit coupled electronic states that are obtained through diagonalization of the spin-orbit coupling matrix with the multi-state second-order multireference perturbation theory energies in diagonal elements and the spin-orbit coupling terms at the state-averaged complete active space self-consistent field level in off-diagonal elements. Nonadiabatic transitions over the spin-orbit coupled states were taken into account explicitly by a surface hopping scheme with utilizing the nonadiabatic coupling terms calculated by numerical differentiation of the spin-orbit coupled wavefunctions and analytical nonadiabatic coupling terms. The present method was applied to the A-band photodissociation of methyl iodide, CH3 I + hv → CH3 + I (2 P3/2 )/I* (2 P1/2 ), for which a pioneering theoretical work was reported by Amatatsu, Yabushita, and Morokuma. The present results reproduced well the experimental branching ratio and energy distributions in the dissociative products. © 2018 Wiley Periodicals, Inc.

Flat bands and dynamical localization of spin-orbit-coupled Bose-Einstein condensates

Flat bands and dynamical localization of binary mixtures of Bose-Einstein condensates, with spin-orbit coupling subjected to a deep optical lattice which is shaking in time and to a periodic time modulation of the Zeeman field, are investigated. In contrast with usual dynamical localization in the absence of spin-orbit coupling, we find that to fully suppress the tunneling in the system the optical lattice shaking is not enough, and a proper tuning of the spin-orbit term, achievable via the Zeeman field modulation, is also required. This leads to a sequence of Zeeman parameter values where energy bands become flat, the tunneling in the system is suppressed, and the dynamical localization phenomenon occurs. Exact wave functions at the dynamical localization points show that the binary mixture localizes on a dimer with the two components occupying different sites. This type of localization occurs in exact form also for the ground state of the system at the dynamical localization points in the presence of nonlinearity and remains valid, although in approximate form, for a wide range of the Zeeman parameter around these points. The possibility of observing the above phenomena in real experiments is also briefly discussed.

An efficient method for obtaining the ground and excited states mass spectrum of doubly heavy $ \Omega$ Ω baryons

In this paper, we obtained the ground state masses and the positive and negative parity excited state masses of doubly heavy $ \Omega$ baryons. For this goal we have analytically solved the radial Schrodinger equation for three identical particles with the hypercentral potential by using the ansatz method. In this study the hypercentral potential is regarded as a combination of the color Coulomb plus linear confining term and the six-dimensional harmonic oscillator potential which has a two-body character and turns out to be exactly hypercentral. We also added the first-order correction and the spin-dependent part contains three types of interaction terms (the spin-spin term, spin-orbit term and tensor term) to the hypercentral potential. Our calculations have been performed for the radial excited states as well as orbital excited states for $ \Omega_{cc}$ , $ \Omega_{bb}$ and $ \Omega_{bc}$ systems. The masses obtained are compared with other theoretical reports, which could be a benefit tool for the interpretation of experimentally unknown doubly heavy baryons spectrum. The doubly heavy baryons masses are experimentally unknown so that the Regge trajectories are plotted using calculated masses to assign the quantum numbers of baryons unknown states.

Using a quadrupole deformed generalized Woods–Saxon plus spin-orbit potential to describe the polarized interaction 7Li→ +12C at 34MeV

An overall description of the cross-sections and tensor analyzing powers corresponding to the elastic interaction [Formula: see text] at [Formula: see text] has been obtained with a coupled channel analysis using the rotational model. Based on the high electric quadrupole moment of the [Formula: see text] projectile, an optical model potential equal to the sum of a quadrupole deformed generalized Woods–Saxon potential and a standard Spin-Orbit term has been used. The deformed part of the potential induces reorientations and transitions that involve the first four energy states of the [Formula: see text] nucleus. These states are supposed to belong to an inverted [Formula: see text][Formula: see text][Formula: see text] rotational band proposed in the literature. Partial reproductions of the inelastic interaction [Formula: see text] have also been achieved by using the same deformed potential with the same parameter values that describe the elastic interaction. Comparisons are made with previous results obtained from optical model potential and continuum-discretized coupled-channel calculations using the cluster-folding model. The use of a deformed scattering potential introduces a tensor term that allows the reproduction of the tensor analyzing powers.

Weak field limit of infinite derivative gravity

A form of infinite derivative gravity is free from ghostlike instabilities with improved small scale behavior. In this theory, we calculate the tree-level scattering amplitude and the corresponding weak field potential energy between two localized covariantly conserved spinning pointlike sources that also have velocities and orbital motion. We show that the spin-spin and spin-orbit interactions take the same form as in Einstein's gravity at large separations, whereas at small separations, the results are different. We find that not only the usual Newtonian potential energy but also the spin-spin and spin-orbit interaction terms in the potential energy are nonsingular as one approaches $r\ensuremath{\rightarrow}0$.

K -matrix formulation of two-particle scattering in a waveguide in the presence of one-dimensional spin-orbit coupling

The creation of artificial gauge fields in neutral ultracold atom systems has opened the possibility to study the effects of spin-orbit coupling terms in clean environments. This work considers the multi-channel scattering properties of two atoms confined by a wave guide in the presence of spin-orbit coupling terms within a K-matrix scattering framework. The tunability of resonances, induced by the interplay of the external wave guide geometry, the interactions, and the spin-orbit coupling terms, is demonstrated. Our results for the K-matrix elements as well as partial and total reflection coefficients for two identical fermions interacting through a finite-range interaction potential in the singlet channel only are compared with those obtained for a strictly one-dimensional effective low- energy Hamiltonian, which uses the effective coupling constant derived in Zhang et al. [Scientific Reports 4, 1 (2014)] and Zhang et al. [Phys. Rev. A 88, 053605 (2013)] as input. In the regime where the effective Hamiltonian is applicable, good agreement is obtained, provided the energy- dependence of the coupling constant is accounted for. Our approach naturally describes the energy regime in which the bands associated with excited transverse modes lie below a subset of the bands associated with the lowest transverse modes. The threshold behavior is discussed and scattering observables are linked to bound state properties.

A New Model for Calculating the Ground and Excited States Masses Spectra of Doubly Heavy Ξ Baryons

Since the doubly heavy baryons masses are experimentally unknown (except Ξcc+ and Ξcc++), we present the ground state masses and the positive and negative parity excited state masses of doubly heavy Ξ baryons. For this purpose, we have solved the six-dimensional hyperradial Schrödinger equation analytically for three particles under the hypercentral potential by using the ansatz approach. In this paper, the hypercentral potential is regarded as a combination of the color Coulomb plus linear confining term and the six-dimensional harmonic oscillator potential. We also added the first-order correction and the spin-dependent part contains three types of interaction terms (the spin-spin term, spin-orbit term, and tensor term) to the hypercentral potential. Our obtained masses for the radial excited states and orbital excited states of Ξccd, Ξccu, Ξbbd, Ξbbu, Ξbcd, and Ξbcu systems are compared with other theoretical reports, which could be a beneficial tool for the interpretation of experimentally unknown doubly heavy baryons spectrum.

Electron-impact excitation of forbidden and allowed transitions in Fe ii

Extensive calculations are reported for electron collision strengths, rate coefficients, and transitions probabilities for a wide range of transitions in Fe ii. The collision strengths were calculated in the close-coupling approximation using the B-spline Breit-Pauli R-matrix method. The multiconfiguration Hartree-Fock method in connection with adjustable configuration expansions and a semiempirical fine-tuning procedure is employed for an accurate representation of the target wave functions. The energy correction was also used in the scattering calculations by adding to Hamiltonian matrices prior to transformation to intermediate coupling. The spin-orbit interaction term was added to the final Hamiltonian matrices in scattering calculations. The close-coupling expansion contains 340 fine-structure levels of Fe ii and includes all levels of the $3{d}^{6}4s$, $3{d}^{5}4{s}^{2}$, $3{d}^{7}$, and $3{d}^{6}4p$ configurations, plus a few lowest levels of the $3{d}^{5}4s4p$ configuration. The effective collision strengths are obtained by averaging the electron collision strengths over a Maxwellian distribution of velocities at electron temperatures in the range from ${10}^{2}$ to ${10}^{5}$ K and are reported for all possible inelastic transitions between the 340 fine-structure levels. The present results are more extensive than the previous calculations and considerably expand the existing data sets for Fe ii, allowing a more detailed treatment of the available measured spectra from different space observatories. Comparison with other calculations for collision rates and available experimental radiative rates is used to place uncertainty bounds on our collision strengths and to assess the likely uncertainties in the existing data sets.

Relativistic Jahn-Teller effect in triplet electronic states of tetrahedral molecules

We consider the relativistic multi-mode 3E×(t2+e) Jahn-Teller effect for tetrahedral atomic complexes in a triplet electronic state. Our analysis is based on the symmetry properties of the electronic Hamiltonian and includes spin-orbit coupling terms. The Taylor series expansion of the electronic Hamiltonian in terms of normal modes is restricted to second order in the electrostatic contributions and to first order in the spin-orbitspin-orbit contributions. The main result of this work is a 6×6 vibronic matrix which depends on the t2 and e vibrational normal modes and is specified by six electrostatic and three spin-orbit coupling constants.

Spin relaxation in wurtzite nanowires

We theoretically investigate the D'yakonov-Perel' spin-relaxation properties in diffusive wurtzite semiconductor nanowires and their impact on the quantum correction to the conductivity. Although the lifetime of the long-lived spin states is limited by the dominant $k$-linear spin-orbit contributions in the bulk, these terms show almost no effect in the finite-size nanowires. Here, the spin lifetime is essentially determined by the small $k$-cubic spin-orbit terms and nearly independent of the wire radius. At the same time, these states possess in general a complex helical structure in real space that is modulated by the spin-precession length induced by the $k$-linear terms. For this reason, the experimentally detected spin relaxation largely depends on the ratio between the nanowire radius and the spin-precession length as well as the type of measurement. In particular, it is shown that while a variation of the radius hardly affects the magnetoconductance correction, which is governed by the long-lived spin states, the change in the spin lifetime observed in optical experiments can be dramatic. We compare our results with recent experimental studies on wurtzite InAs nanowires.

Three-Boson Spectrum in the Presence of 1D Spin-Orbit Coupling: Efimov’s Generalized Radial Scaling Law

Spin-orbit coupled cold atom systems, governed by Hamiltonians that contain quadratic kinetic energy terms typical for a particle's motion in the usual Schr\"odinger equation and linear kinetic energy terms typical for a particle's motion in the usual Dirac equation, have attracted a great deal of attention recently since they provide an alternative route for realizing fractional quantum Hall physics, topological insulators, and spintronics physics. The present work focuses on the three-boson system in the presence of 1D spin-orbit coupling, which is most relevant to ongoing cold atom experiments. In the absence of spin-orbit coupling terms, the three-boson system exibits the Efimov effect: the entire energy spectrum is uniquely determined by the $s$-wave scattering length and a single three-body parameter, i.e., using one of the energy levels as input, the other energy levels can be obtained via Efimov's radial scaling law, which is intimately tied to a discrete scaling symmetry. It is demonstrated that the discrete scaling symmetry persists in the presence of 1D spin-orbit coupling, implying the validity of a generalized radial scaling law in five-dimensional space. The dependence of the energy levels on the scattering length, spin-orbit coupling parameters, and center-of-mass momentum is discussed. It is conjectured that three-body systems with other types of spin-orbit coupling terms are also governed by generalized radial scaling laws, provided the system exhibits the Efimov effect in the absence of spin-orbit coupling.

Erratum: Parametrized-4.5PN TaylorF2 approximants and tail effects to quartic nonlinear order from the effective one body formalism [Phys. Rev. D 95 , 124001 (2017)

By post-Newtonian (PN) expanding the well-known, factorized and resummed, effective-one-body energy flux for circularized binaries we show that: (i) because of the presence of the resummed tail factor, the 4.5PN-accurate tails-of-tails-of-tails contribution to the energy flux recently computed by Marchand et al. [Class. Q. Grav. 33 (2016) 244003] is actually contained in the resummed expression; this is also the case of the the next-to-leading-order tail-induced spin-orbit term of Marsat et al. [Class. Q. Grav. 31 (2014) 025023]; (ii) in performing this expansion, we also obtain, for the first time, the explicit 3.5PN leading-order tail-induced spin-spin flux term; (iii) pushing the PN expansion of the (nonspinning) EOB flux up to 5.5PN order, we compute 4PN, 5PN and 5.5PN contributions to the energy flux, though in a form that explicitly depends on, currently unknown, 4PN and 5PN non-test-mass corrections to the factorized waveform amplitudes. Within this (parametrized) 4.5PN accuracy, we calculate the TaylorF2 approximant. Focusing for simplicity on the nonspinning case and using the numerical-relativity calibrated IMRPhenomD waveform model as benchmark, we demonstrate that it is possible to reproduce the derivative of the IMRPhenomD phase (say up to the frequency of the Schwarzschild last-stable-orbit) by flexing only a 4PN "effective" waveform amplitude parameter. A preliminary analysis also illustrates that similar results can be obtained for the spin-aligned case provided only the leading-order spin-orbit and spin-spin terms are kept. Our findings suggest that this kind of, EOB-derived, (parametrized), higher-order, PN approximants may serve as promising tools to construct Inspiral-Merger-Ringdown phenomenological models or even to replace the standardly used 3.5PN-accurate TaylorF2 approximant in searches of small-mass binaries.

Second harmonic generation in a disk shaped quantum dot in the presence of spin-orbit interaction

The second harmonic generation (SHG) coefficients for a disk shaped quantum dot (DSQD) in the magnetic field are studied in the presence of spin-orbit interactions (SOI). The spin-orbit terms we have used in our calculations are both Rashba and Dresselhaus. We have shown that the presence of SOI modifies the SHG terms. In addition, it has been shown that SOI coupling terms influence the spectrum of DSQD resulting in defined changes in the harmonic generation.

Dirac Equation with Unequal Scalar and Vector Potentials under Spin and Pseudospin Symmetry

An approximate solution of the Dirac equation in the D-dimensional space is obtained under spin and pseudospin symmetry limits for the scalar and vector inversely quadratic Yukawa potential within the framework of parametric Nikiforov-Uvarov method using a suitable approximation scheme to the spin-orbit centrifugal term. The two components spinor of the wave function and their energy equations are fully obtained. Some numerical results are obtained for the energy level with various dimensions (D), quantum number (n), vector potential V0 and scalar potential S0 . The results obtained under spin symmetry using either V0 or S0 are equal to the results obtained usingV S 0 0  . But under the pseudospin symmetry, the results obtained using V0 or S0 are not equal to the results obtained usingV S 0 0  .

The resonant state at filling factor ν = 1/2 in chiral fermionic ladders

Helical liquids have been experimentally realized in both nanowires and ultracold atomic chains as the result of strong spin–orbit interactions. In both cases the inner degrees of freedom can be considered as an additional space dimension, providing an interpretation of these systems as chiral synthetic ladders, with artificial magnetic fluxes determined by the spin–orbit terms. In this work, we characterize the helical state which appears at filling ν = 1/2: this state is generated by a gap arising in the spin sector of the corresponding Luttinger liquid and it can be interpreted as the one-dimensional (1D) limit of a fractional quantum Hall state of bosonic pairs of fermions. We study its main features, focusing on entanglement properties and correlation functions. The techniques developed here provide a key example for the study of similar quasi-1D systems beyond the semiclassical approximation commonly adopted in the description of the Laughlin-like states.

Factorization and resummation: A new paradigm to improve gravitational wave amplitudes. II. The higher multipolar modes

The factorization and resummation approach of Nagar and Shah~[Phys.~Rev.~D~94 (2016), 104017], designed to improve the strong-field behavior of the post-Newtonian (PN) residual waveform amplitudes $f_{\ell m}$'s entering the effective-one-body, circularized, gravitational waveform for spinning coalescing binaries, is here improved and generalized to all multipoles up to $\ell=6$. For a test-particle orbiting a Kerr black hole, each multipolar amplitude is truncated at relative 6~post Newtonian (PN) order, both for the orbital (nonspinning) and spin factors. By taking a certain Pad\'e approximant (typically the $P^4_2$ one) of the orbital factor in conjuction with the inverse Taylor (iResum) representation of the spin factor, it is possible to push the analytical/numerical agreement of the energy fluxe at the level of $5\%$ at the last-stable-orbit for a quasi-maximally spinning black hole with dimensionless spin parameter $+0.99$. When the procedure is generalized to comparable-mass binaries, each orbital factor is kept at relative $3^{+3}$PN order, i.e. the 3PN comparable-mass terms are hybridized with higher PN test-particle terms up to 6PN relative order. The same Pad\'e resummation is used for continuity. By contrast, the spin factor is only kept at the highest comparable-mass PN-order currently available. We illustrate that the consistency between different truncations in the spin content of the waveform amplitudes is stronger in the resummed case than when using the standard Taylor-expanded form of Pan et al.~[Phys.~Rev.~D~83 (2011) 064003]. We finally introduce a method to consistently hybridize comparable-mass and test-particle information {\it also} in the presence of spin (including the spin of the particle), discussing it explicitly for the $\ell=m=2$ spin-orbit and spin-square terms.

Extended Creutz ladder with spin-orbit coupling: A one-dimensional analog of the Kane-Mele model

We construct a topological one-dimensional ladder model following the steps which lead to the Kane-Mele model in two dimensions. Starting with a Creutz ladder we modify it so that the gap closure points can occur at either or . We then couple two such models, one for each spin channel, in such a way that time-reversal invariance is restored. We also add a Rashba spin-orbit coupling term. The model falls in the CII symmetry class. We derive the relevant topological index, calculate the phase diagram and demonstrate the existence of edge states. We also give the thermodynamic derivation (Středa-Widom) of the quantum spin Hall conductance. Approximate implementation of this result indicates that this quantity is sensitive to the topological behavior of the model.