The NMR indirect nuclear spin–spin coupling constant of the HD molecule

We present new calculated and experimental values of the NMR indirect nuclear spin–spin coupling constant in HD. In the quantum-chemical ab initio calculations, the full configuration-interaction (FCI) method is used, yielding an equilibrium value of 41.22?Hz in the basis-set limit. Adding a calculated zero-point vibrational correction of 1.89?Hz and a temperature correction of 0.20?Hz at 300?K, we obtain a total calculated spin–spin coupling constant of J _FCI(HD)?=?43.31(5)?Hz at 300?K. This result is within the error bars of the experimental gas-phase NMR value, J _exp(HD)?=?43.26(6)?Hz, obtained by extrapolating values measured in HD–He mixtures to zero density.     

Density-functional theory calculation of the nuclear magnetic resonance indirect nuclear spin—spin coupling constants in C60

Density-functional theory is used to study the nuclear magnetic resonance (NMR) indirect nuclear spin-spin coupling constants in C₆₀. Knowledge of these coupling constants may help in the analysis of future experimental NMR studies of ¹³C-enriched C₆₀. At the Becke 3-parameter Lee-Yang-Parr (B3LYP) Kohn-Sham level, the one-bond couplings within pentagons and between pentagons are 62 Hz and 77 Hz, respectively; the corresponding geminal couplings are 7 Hz and 1 Hz, respectively. Except for the vicinal couplings (about 4 Hz), the long-range couplings are all 1 Hz or smaller. This is the largest theoretical calculation to date of the complete set of indirect nuclear spin-spin coupling constants of a molecular system; it has been made possible by solving the response equations only for the perturbing operators related to one nuclear magnetic moment, making the calculation feasible.     

Snowballs of radioactive ions — nuclear spin polarization of core ions

Short-lived ions¹²B (beta-radioactive, T_1/2=20.3 ms) sustaining nuclear spin polarization were introduced into superfluid helium at 1.7 K. It was found that the¹²B ions were transported as charged entities under a static electric field and that the nuclear polarization was maintained throughout the lifetime of¹²B nuclei. Polarization of¹²B was determined through beta-NMR method. Snowball, a singly charged microcluster of helium atoms formed around an impurity ion, is responsible for the behaviour and thus constitutes a suitable environment for preserving nuclear polarization of the core ions¹²B. In a separate experiment snowballs were produced by implanting⁸Li (T_1/2=830 ms) into liquid helium and detected by means of alpha particles from the core ions to guarantee that the snowballs survive longer than the lifetime of¹²B.     

Manifestation of nuclear spin dependent P odd electron–nucleon interaction in atomic ytterbium

P odd effects caused by the nuclear spin dependent electron-nucleon interaction are considered. P-odd amplitudes are calculated for ¹S₀ → ³D_1,2 transitions in atomic ytterbium. This revised version was published online in August 2006 with corrections to the Cover Date.     

Molecular properties in the Tamm–Dancoff approximation: indirect nuclear spin–spin coupling constants

The Tamm–Dancoff approximation (TDA) can be applied to the computation of excitation energies using time-dependent Hartree–Fock (TD-HF) and time-dependent density-functional theory (TD-DFT). In addition to simplifying the resulting response equations, the TDA has been shown to significantly improve the calculation of triplet excitation energies in these theories, largely overcoming issues associated with triplet instabilities of the underlying reference wave functions. Here, we examine the application of the TDA to the calculation of another response property involving triplet perturbations, namely the indirect nuclear spin–spin coupling constant. Particular attention is paid to the accuracy of the triplet spin–dipole and Fermi-contact components. The application of the TDA in HF calculations leads to vastly improved results. For DFT calculations, the TDA delivers improved stability with respect to geometrical variations but does not deliver higher accuracy close to equilibrium geometries. These observations are rationalised in terms of the ground- and excited-state potential energy surfaces and, in particular, the severity of the triplet instabilities associated with each method. A notable feature of the DFT results within the TDA is their similarity across a wide range of different functionals. The uniformity of the TDA results suggests that some conventional evaluations may exploit error cancellations between approximations in the functional forms and those arising from triplet instabilities. The importance of an accurate treatment of correlation for evaluating spin–spin coupling constants is highlighted by this comparison.     

β-NMR and nuclear spin diffusion in a spatially disordered subsystem

The results of theoretical and experimental investigations of delocalization of nuclear polarization in spatially disordered media are presented. The experiment is based on the measurement of a depolarization of β-active ⁸Li impurity nuclei (β-nuclei) in the spatially disordered subsystem of ⁸Li-⁶Li nuclei in LiF single crystals. The process is determined by the dipole-dipole interaction in this subsystem and by its dipole interactions with nuclei of the ⁷Li¹⁹F matrix. It is effective in a wide range of external magnetic fields H ₀ = 200–3000 G owing to proximity of g-factors. The kinetics of a depolarization of β-nuclei at the ⁶Li concentration c = 0.15–10.06% in fields H ₀ = 200 and 1210 G is investigated. A satisfactory explanation of the results is based on the numerical-analytical simulation of the process.     

Theory of spin polarization in mesoscopic spin–orbit coupling systems

We establish a general formalism of the bulk spin polarization (BSP) and the current-based spin polarization (CSP) for mesoscopic ferromagnetic and spin–orbit interaction (SOI) semiconducting systems. Based on this formalism, we reveal the basic properties of BSP and CSP and their relationships. The BSP describes the intrinsic spin polarized properties of devices. The CSP depends on both intrinsic parameters of device and the incident current. For the non-spin-polarized incident current with the in-phase spin-phase coherence, CSP equals to BSP. We give analytically the BSP and CSP of several typical nanodevice models, ferromagnetic nanowire, Rashba nanowire and rings. These results provide basic physical behaviors of BSP and CSP and their relationships.     

Effects of vibrational averaging on coupled cluster calculations of spin–spin coupling constants for hydrocarbons

We present vibrationally corrected nuclear spin–spin coupling constants for four hydrocarbons with different types of carbon–carbon bonds calculated with coupled cluster (CC) theory. First, we perform a systematic basis set investigation on acetylene for all of the four contributions (Fermi-contact, spin-dipole, para- and diamagnetic spin–orbit) to the spin–spin coupling constants and subsequently choose basis sets of sufficient flexibility to describe converged electronic properties. Then, in order to describe the effects of vibrational motion for the studied molecules we perform a Taylor expansion in the normal coordinates up to second order – a method that is well known for both its quality and efficiency – and rigorously estimate the resulting contribution for all types of spin–spin coupling constants. Combined, this allows us to obtain highly accurate benchmark estimates of the spin–spin coupling constants for acetylene, ethylene, ethane, and cyclopropane. This work provides one of the first systematic benchmarks of zero-point vibrational contributions to spin–spin coupling constants in poly-atomic molecules using the reliable CC theory and it is thus an important reference for further research within in-silico spin–spin coupling constant determination. We note that earlier computational estimates of zero-point vibrational effects agree well with those presented here (for acetylene, ethylene, and cyclopropane) while vibrational corrections for ethane are reported for the first time.     

A review of current research on spin currents and spin–orbit torques

Spintronics is a new discipline focusing on the research and application of electronic spin properties. After the discovery of the giant magnetoresistance effect in 1988, spintronics has had a huge impact on scientific progress and related applications in the development of information technology. In recent decades, the main motivation in spintronics has been efficiently controlling local magnetization using electron flow or voltage rather than controlling the electron flow using magnetization. Using spin–orbit coupling in a material can convert a charge current into a pure spin current(a flow of spin momenta without a charge flow) and generate a spin–orbit torque on the adjacent ferromagnets. The ability of spintronic devices to utilize spin-orbit torques to manipulate the magnetization has resulted in large-scale developments such as magnetic random-access memories and has boosted the spintronic research area. Here in, we review the theoretical and experimental results that have established this subfield of spintronics. We introduce the concept of a pure spin current and spin-orbit torques within the experimental framework, and we review transport-, magnetization-dynamics-, and opticalbased measurements and link then to both phenomenological and microscopic theories of the effect. The focus is on the related progress reported from Chinese universities and institutes, and we specifically highlight the contributions made by Chinese researchers.     

Saturation of nuclear partons: Fermi statistics or nuclear opacity?

We derive the two-plateau momentum distribution of final state (FS) quarks produced in deep inelastic scattering (DIS) off nuclei in the saturation regime. The diffractive plateau, which dominates for small p, measures precisely the momentum distribution of quarks in the beam photon; the role of the nucleus is simply to provide an opacity. The plateau for truly inelastic DIS exhibits a substantial nuclear broadening of the FS momentum distribution. We discuss the relationship between the FS quark densities and the properly defined initial state (IS) nuclear quark densities. The Weizsäcker-Williams glue of a nucleus exhibits a substantial nuclear dilution, still soft IS nuclear sea saturates because of the anti-collinear splitting of gluons into sea quarks.     

Semi-gross theory of nuclear β-decay

The gross theory of β-decay is refined to take into account shell effects of the parent nuclei, and the resulting theory is named semi-gross theory. In this theory, the one-particle energy distribution in the parent nucleus is taken to have structures, and the one-particle strength function is assumed to depend on the quantum numbers of the initial state of the decaying nucleon. β-decay (partial) half-lives are calculated for 1659 nuclides, and the results are compared with experimental data as well as with those calculated by the gross theory. The β-decay strength functions are shown for two selected nuclides, and briefly discussed. These numerical studies confirm that the semi-gross theory includes some part of the shell effects correctly, although there still remain deviations of the theoretical results from experimental data, which should, at least partly, be due to shell effects of the daughter nuclei. Comparison of the present results with microscopic theories shows that the overall accuracy of the semi-gross theory is comparable with those of the microscopic theories.     

Thermoelectric transport and spin density of graphene nanoribbons with Rashba spin–orbit interaction

In the present paper, we have theoretically investigated thermoelectric transport properties of armchair and zigzag graphene nanoribbons with Rashba spin–orbit interaction, as well as dephasing scattering processes by applying the nonequilibrium Green function method. Behaviors of electronic and thermal currents, as well as thermoelectric coefficients are studied. It is found that both electronic and thermal currents decrease, and thermoelectric properties been suppressed, with increasing strength of Rashba spin–orbit interaction. We have also studied spin split and spin density induced by Rashba spin–orbit interaction in the graphene nanoribbons.     

Nuclear spin–spin constants,rotational g factor and susceptibility of sulphur hexafluoride

Following our previous study on spin–rotation and shielding constants of the SF₆ molecule, the rotational g factor and the magnetic susceptibility are calculated here, using ab initio methods to evaluate the electronic contribution to the nuclear hyperfine constants, and compared with experimental results. It is shown, for the first time, that the electronic component of the rotational g factor is proportional to a constant, which is given by a sum over electronic states. We also evaluate for the SF₆ molecule the indirect, or electron-coupled spin–spin interaction, theoretically described by Ramsey, and show that it gives non-negligible corrections to direct coupling constants d ₁ and d ₂. The contributions of the terms included in this interaction (DSO, PSO, SD and FC) are also analysed.     

Effect of in-plane magnetic field on spin polarization in the presence of the Dresselhaus spin–orbit effect

In this paper, we theoretically study the effect of the in-plane magnetic field on spin polarization in the presence of the Dresselhaus spin–orbit effect. It is shown that the large spin polarization can be achieved in such a nanostructure due to the effects of both the Dresselhaus spin–orbit term and the in-plane magnetic field, but the latter plays a main role in the tunneling process. It is also shown that with the increase of in-plane magnetic field, the degree of spin splitting obviously becomes larger.     

Characteristics of persistent spin current components in a quasi-periodic Fibonacci ring with spin–orbit interactions: Prediction of spin–orbit coupling and on-site energy

In the present work we investigate the behavior of all three components of persistent spin current in a quasi-periodic Fibonacci ring subjected to Rashba and Dresselhaus spin–orbit interactions. Analogous to persistent charge current in a conducting ring where electrons gain a Berry phase in presence of magnetic flux, spin Berry phase is associated during the motion of electrons in presence of a spin–orbit field which is responsible for the generation of spin current. The interplay between two spin–orbit fields along with quasi-periodic Fibonacci sequence on persistent spin current is described elaborately, and from our analysis, we can estimate the strength of any one of two spin–orbit couplings together with on-site energy, provided the other is known.     

Influences of spin–orbit interaction on quantum speed limit and entanglement of spin qubits in coupled quantum dots

Quantum speed limit and entanglement of a two-spin Heisenberg XYZ system in an inhomogeneous external magnetic field are investigated. The physical system studied is the excess electron spin in two adjacent quantum dots. The influences of magnetic field inhomogeneity as well as spin–orbit coupling are studied. Moreover, the spin interaction with surrounding magnetic environment is investigated as a non-Markovian process. The spin–orbit interaction provides two important features: the formation of entanglement when two qubits are initially in a separated state and the degradation and rebirth of the entanglement.     

Dynamics of semi-infinite quantum spin chains atT=∞

Time-dependent spin autocorrelation functions and their spectral densities for the semi-infinite one-dimensionals=1/2 XY and XXZ models atT= are determined in part by rigorous calculations in the fermion representation and in part by the recursion method in the spin representation. Boundary effects yield valuable new insight into the different dynamical processes which govern the transport of spin fluctuations in the two models. The results obtained for theXXX model bear the unmistakable signature of spin diffusion in the form of a squareroot infrared divergence in the spectral density.From April 1 to September 30, 1992 also at Institut für Physik Universität Augsburg, W-8900 Augsburg, Federal Republic of Germany