Theory of electronic light scattering in lateral superlattices with Rashba spin–orbit coupling under quantizing electric and magnetic fields

The influence of an in-plane electric and out-of-plane magnetic field on the electronic light scattering is calculated for a lateral semiconductor superlattice within Rashba spin–orbit interaction. Sharp resonances are predicted to appear when the Raman shift matches one frequency of the Wannier–Stark ladder. The spin–orbit interaction gives rise to a dispersion of the exact one-particle eigenstates and an associated finite width of the Raman line, which can be tuned by the electric and magnetic field. When the Bloch frequency is located in this Raman line, a Fano resonance is observed.     

Determination of the Rashba and Dresselhaus coupling constants using the conductance of a ballistic nanowire

We study the conductance steps of a ballistic nanowire in the presence of a harmonic potential, an in-plane magnetic field, and spin–orbit interactions induced by Rashba and Dresselhaus effects. Calculations of the conductance, at low temperature, using the Landauer–Büttiker formalism, reveal different patterns of steps that are strongly dependent on the magnetic field. Such dependence provides a powerful tool for determining the strengths of the spin–orbit interaction independently, especially in nanowires with low carrier density.     

Effects of interaction of nanoparticles in a highly anisotropic ferrimagnet

This paper reports on a study of the field and temperature dependences of the parameters of the particle magnetic interaction in a densely packed system of nanocrystals of the highly anisotropic hexagonal ferrite BaFe₁₂O₁₉ with the particles distributed in diameter within the range 10—100 nm and having volumes satisfying the criterion of “small Stoner—Wohlfarth particles.” It is shown that the resultant particle interaction in the temperature range 300 K≤T≤640 K has a negative sign, whereas for T>640 K, it is positive. The maximum values of the parameter Δm allow classification of the interaction as moderate in strength. The temperature dependences of the interaction parameters are found to correlate with manifestation of the size and surface effects in the system, which are characteristic of small particles (transition to the superparamagnetic state, “surface” anisotropy, and reduced exchange interaction in a structurally defective near-surface layer of particles).     

Symmetry and optical transition rule for low-dimensional semiconductor system with spin–orbit interaction and magnetic field

Starting from effective mass Hamiltonian, we systematically investigate the symmetry of low-dimensional structures with spin–orbit interaction and transverse magnetic field. The position-dependent potentials are assumed to be space symmetric, which is ever-present in theory and experiment research. By group theory, we analyze degeneracy in different cases. Spin–orbit interaction makes the transition between Zeeman sub-levels possible, which is originally forbidden within dipole approximation. However, a transition rule given in this paper for the first time shows that the transition between some levels is forbidden for space symmetric potentials.     

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.     

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.     

Theoretical investigation of magnetic property in paramagnetic neodymium gallium garnet under high magnetic field

The magnetic property in neodymium gallium garnet (NdGaG) is studied by the quantum theory. The ground configuration split states are calculated taking into account the spin–orbit interaction and crystal field effect. Taking account of the Nd–Nd exchange interaction, a good agreement between experimental and theoretical values can be obtained for the variation of the magnetic moment with the external magnetic field under “extreme” conditions (low temperature and high magnetic field). Moreover, the temperature dependence of magnetic moment and the magnetic susceptibility χ is also discussed. Above 30 K, the magnetization (M) shows a linear field (H_e) dependence.     

Quasilocal density functional theory in nuclei and its extension to include pairing correlations

We propose first a generalization of the Density Functional Theory. This theory leads to single-particle equations of motion with a quasilocal mean-field operator, which contains a quasiparticle position-dependent effective mass and a spin—orbit potential. The energy density functional is constructed using the extended Thomas—Fermi approximation. Some ground-state properties of doubly magic nuclei are considered within the framework of this approach. Calculations are performed using the finite-range Gogny D1S forces, and the results are compared with the exact Hartree—Fock calculations. Next, we present an extension of the density functional theory to include pairing correlations without formal violation of the particle-number condition. This problem, which is nonlocal, can be simplified by a suitable quasilocal reduction, which is also briefly discussed in this paper. The text was submitted by the authors in English.     

Some consequences of relativistic effects upon optical spectra

Large spin–orbit interaction produces large orbital magnetic moments in narrow energy bands. Since the orbital character of the wave functions is more important in orbital than in spin magnetism, the limitations of the local spin density approximation become evident. It is possible to keep the orbital dependence of the exchange interactions by using an orbital polarization scheme or by using Hartree–Fock theory with screened Slater integrals for exchange. This leads to an enhancement of the calculated orbital moment when the magnetism is strong. Recently calculated magnetic moments and calculated sum rules for X-ray magnetic circular dichroism in US are described. Received: 23 May 2001 / Accepted: 4 July 2001 / Published online: 5 October 2001     

Spin–orbit coupling and semiclassical electron dynamics in noncentrosymmetric metals

Spin–orbit coupling of electrons with the crystal lattice plays a crucial role in materials without inversion symmetry, lifting spin degeneracy of the Bloch states and endowing the resulting nondegenerate bands with complex spin textures and topologically nontrivial wavefunctions. We present a detailed symmetry-based analysis of the spin–orbit coupling and the band degeneracies in noncentrosymmetric metals. We systematically derive the semiclassical equations of motion for fermionic quasiparticles near the Fermi surface, taking into account both the spin–orbit coupling and the Zeeman interaction with an applied magnetic field. Some of the lowest-order quantum corrections to the equations of motions can be expressed in terms of a fictitious “magnetic field” in the momentum space, which is related to the Berry curvature of the band wavefunctions. The band degeneracy points or lines serve as sources of a topologically nontrivial Berry curvature. We discuss the observable effects of the wavefunction topology, focusing, in particular, on the modifications to the Lifshitz–Onsager semiclassical quantization condition and the de Haas-van Alphen effect in noncentrosymmetric metals.     

Influence of the magnetic field on the angular power spectrum of an electromagnetic wave multiply scattered in a turbulent collisional magnetized plasma

We consider a small-amplitude plane electromagnetic wave incident on a semi-infinite layer of a collisional turbulent magnetized plasma. The system of differential equations for the statistical moments of the angular power spectrum of the normal wave is derived in the narrow-angle approximation of radiation transfer theory. The dependence of the center of mass, variance, and asymmetry of the normal-wave spectrum on the distance from the plasma boundary is studied numerically. The results for different refraction angles of the illuminating wave and magnitudes and directions of the external magnetic field are presented. The nonmonotonic dependences of the variance and the third central moment on the distance from the plasma boundary are revealed. These dependences are shown to become more nonmonotonic if the absorption of the scattered waves becomes more isotropic, in particular, if the strength of the external magnetic field increases. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 42, No. 12, pp. 1165–1171. December 1999.     

Equal coupling strength approach to spin precession effects concerning Rashba and Dresselhaus spin–orbit interactions in the presence of in-plane magnetic fields

The influence of Rashba and Dresselhaus spin–orbit interactions on the electronic properties of quasi one-dimensional systems like InAs quantum wires is discussed in the presence of in-plane magnetic fields. One shows that equal coupling strength conditions are provided specifically by the commutativity of two-dimensional constituents of velocity and current operators. The interesting point is that equal strength spin–orbit couplings one deals with proceed in conjunction with related spin conservations, which amounts to account for selected orientations of the magnetic field. Accordingly, the in-plane magnetic fields should be directed solely along the bisectrices. Other angles may be conceivable, but in this case spin conservations alluded to above are lost. Such results open the way to a consistent derivation of the equal coupling strength limit of the energy, which leads in turn to the derivation of novel spin-precession effects. A related effective gyromagnetic factor has also been established.     

Magnetic interactions in strongly correlated systems: Spin and orbital contributions

We present a technique to map an electronic model with local interactions (a generalized multi-orbital Hubbard model) onto an effective model of interacting classical spins, by requiring that the thermodynamic potentials associated to spin rotations in the two systems are equivalent up to second order in the rotation angles, when the electronic system is in a symmetry-broken phase. This allows to determine the parameters of relativistic and non-relativistic magnetic interactions in the effective spin model in terms of equilibrium Green’s functions of the electronic model. The Hamiltonian of the electronic system includes, in addition to the non-relativistic part, relativistic single-particle terms such as the Zeeman coupling to an external magnetic field, spin–orbit coupling, and arbitrary magnetic anisotropies; the orbital degrees of freedom of the electrons are explicitly taken into account. We determine the complete relativistic exchange tensors, accounting for anisotropic exchange, Dzyaloshinskii–Moriya interactions, as well as additional non-diagonal symmetric terms (which may include dipole–dipole interaction). The expressions of all these magnetic interactions are determined in a unified framework, including previously disregarded features such as the vertices of two-particle Green’s functions and non-local self-energies. We do not assume any smallness in spin–orbit coupling, so our treatment is in this sense exact. Finally, we show how to distinguish and address separately the spin, orbital and spin–orbital contributions to magnetism, providing expressions that can be computed within a tight-binding Dynamical Mean Field Theory.     

A spin field effect transistor for low leakage current

In a spin field effect transistor, a magnetic field is inevitably present in the channel because of the ferromagnetic source and drain contacts. This field causes random unwanted spin precession when carriers interact with non-magnetic impurities. The randomized spins lead to a large leakage current when the transistor is in the “off”-state, resulting in significant standby power dissipation. We can counter this effect of the magnetic field by engineering the Dresselhaus spin–orbit interaction in the channel with a backgate. For realistic device parameters, a nearly perfect cancellation is possible, which should result in a low leakage current.     

Magnetic properties of Co clusters deposited on Pt(111)

Using the fully relativistic version of the Korringa–Kohn–Rostoker method for electronic structure calculations within local spin density functional theory, the magnetic and spectroscopic properties of Co clusters deposited on Pt(111) have been investigated. Of central interest was the role of spin–orbit coupling, since it influences the spontaneous formation and orientation of magnetic moments and gives rise among other things to the occurrence of orbital magnetic moments, magnetic anisotropy energy and magnetic circular dichroism in X-ray absorption. The results have been complemented by calculations of the exchange coupling parameters J_ij used within Monte Carlo simulations on the basis of the extended classical Heisenberg Hamiltonian. This allowed us to simulate the magnetic properties at finite temperatures, which are of central importance for applications. PACS 73.20.-r; 71.15.Rf; 73.22.-f; 87.64.Ni     

Mesoscopic Fano effect modulated by Rashba spin–orbit coupling and external magnetic field

By employing non-equilibrium Green's function method, the mesoscopic Fano effect modulated by Rashba spin–orbit (SO) coupling and external magnetic field has been elucidated for electron transport through a hybrid system composed of a quantum dot (QD) and an Aharonov–Bohm (AB) ring. The results show that the orientation of the Fano line shape is modulated by the Rashba spin–orbit interaction kRL$k_{R}L$ variation, which reveals that the Fano parameter q will be extended to a complex number, although the system maintains time-reversal symmetry (TRS) under the Rashba SO interaction. Furthermore, it is shown that the modulation of the external magnetic field, which is applied not only inside the frame, but also on the QD, leads to the Fano resonance split due to Zeeman effect, which indicates that the hybrid is an ideal candidate for the spin readout device.     

Effect of non-uniform exchange field in ferromagnetic graphene

We have presented here the consequences of the non-uniform exchange field on the spin transport issues in spin chiral configuration of ferromagnetic graphene. Taking resort to the spin–orbit coupling (SOC) term and non-uniform exchange coupling term we are successful to express the expression of Hall conductivity in terms of the exchange field and SOC parameters through the Kubo formula approach. However, for a specific configuration of the exchange parameter we have evaluated the Berry curvature of the system. We also have paid attention to the study of SU(2) gauge theory of ferromagnetic graphene. The generation of anti damping spin–orbit torque in spin chiral magnetic graphene is also briefly discussed.     

Electron–phonon-induced spin relaxation in InAs quantum dots

We have calculated spin-relaxation rates in parabolic quantum dots due to the phonon modulation of the spin–orbit interaction in the presence of an external magnetic field. Both deformation potential and piezoelectric electron–phonon coupling mechanisms are included within the Pavlov–Firsov spin–phonon Hamiltonian. Our results have demonstrated that, in narrow gap materials, the electron–phonon deformation potential and piezoelectric coupling give comparable contributions to spin-relaxation processes. For large dots, the deformation potential interaction becomes dominant. This behavior is not observed in wide or intermediate gap semiconductors, where the piezoelectric coupling, in general, governs the spin-relaxation processes. We have also demonstrated that spin-relaxation rates are particularly sensitive to the Landé g-factor.     

Electronic structures of ternary iron arsenides A Fe 2 As 2 ( A = Ba,Ca, or Sr)

We have studied the electronic and magnetic structures of the ternary iron arsenides AFe₂As₂ (A = Ba, Ca, or Sr) using the first-principles density functional theory. The ground states of these compounds are in a collinear antiferromagnetic order, resulting from the interplay between the nearest and the next-nearest neighbor superexchange antiferromagnetic interactions bridged by As 4p orbitals. The correction from the spin–orbit interaction to the electronic band structure is given. The pressure can reduce dramatically the magnetic moment and diminish the collinear antiferromagnetic order. Based on the calculations, we propose that the low energy dynamics of these materials can be described effectively by a t−J_H−J₁−J₂-type model [arXiv: 0806.3526v2, 2008].     

Magneto-absorption in cylindrical quantum dots

The absorption of light in an ensemble of non-interacting cylindrical quantum dots in the presence of a magnetic field is discussed using a model consisting of dots with rectangular infinitely-high potential barriers. The ensemble’s absorption coefficient is calculated — as well as the threshold frequency of absorption — as a function of the applied magnetic field and the quantum dot size. Theoretical results are compared with experimental data on magneto-luminescence in an In_0.53Ga_0.47As/InP cylindrical quantum dot system. In addition, using a perturbation theory framework, the influence of excitonic effects on the behaviour of the electron-hole energetic spectrum of said system is discussed.