Spin-orbit Coupling Interaction Research Articles

Approaching Phosphorescence Lifetimes in Solution: The Two-Component Polarizable-Embedding Approximate Coupled-Cluster Method.

Theoretical description of phosphorescence lifetimes in the condensed phase requires a method that takes into account both spin-orbit coupling and solvent-solute interactions. To obtain such a method, we have coupled our recently developed two-component coupled-cluster method with singles and approximated doubles to a polarizable environment. With this new method, we investigate how different solvents effect the electronic phosphorescence energies and lifetimes of 4H-pyran-4-thione.

Possible half-metallic antiferromagnetism in an iridium double-perovskite material

Using the first-principles density functional approach, we investigate a material Pr$_2$MgIrO$_6$ (PMIO) of double perovskite structure synthesized recently. According to the calculations, PMIO is a magnetic Mott-Hubbard insulator influenced by the cooperative effect of spin-orbit coupling (SOC) and Coulomb interactions of Ir-5$d$ and Pr-4$f$ electrons, as well as the crystal field. When Pr is replaced with Sr gradually, the system exhibits half metallic (HM) states desirable for spintronics applications. In [Pr$_{2-x}$Sr$_x$MgIrO$_6$]$_2$, HM antiferromagnetism (HMAFM) with zero spin magnetization in the unit cell is obtained for $x=1$, whereas for $x=0.5$ and 1.5 HM ferrimagnetism (HMFiM) is observed with $\mu_{\rm tot}=3\mu_{\rm B}$ and $\mu_{\rm tot}=-3\mu_{\rm B}$ per unit cell respectively. It is emphasized that the large exchange splitting between spin-up and spin-down bands at the Fermi level makes the half metallicity possible even with strong SOC.

Effective spin dephasing mechanism in confined two-dimensional topological insulators

A Kramers pair of helical edge states in quantum spin Hall effect (QSHE) is robust against normal dephasing but not robust to spin dephasing. In our work, we provide an effective spin dephasing mechanism in the puddles of two-dimensional (2D) QSHE, which is simulated as quantum dots modeled by 2D massive Dirac Hamiltonian. We demonstrate that the spin dephasing effect can originate from the combination of the Rashba spin-orbit coupling and electron-phonon interaction, which gives rise to inelastic backscattering in edge states within the topological insulator quantum dots, although the time-reversal symmetry is preserved throughout. Finally, we discuss the tunneling between extended helical edge states and local edge states in the QSH quantum dots, which leads to backscattering in the extended edge states. These results can explain the more robust edge transport in InAs/GaSb QSH systems.

Periodicity Dependence of Magnetic Anisotropy and Magnetization of FeCo Heterostructure

The magnetic anisotropy energy (MAE) and the saturation magnetization Bs of (110) FenCon heterostructures with n = 1, 2, and 3 are investigated in first-principles within the density functional theory by using the precise full-potential linearized augmented plane wave (FLAPW) method. We compare the results employing two different exchange correlation potentials, that is, the local density approximation (LDA) and the generalized gradient approximation (GGA), and include the spin-orbit coupling interaction of the valence states in the second variational way. The MAE is found to be enhanced significantly compared to those of bulk Fe and Co and the magnetic easy axis is in-plane in agreement with experiment. Also the MAE exhibits the in-plane angle dependence with a two-fold anisotropy showing that the [1Ī0] direction is the most favored spin direction. We found that as the periodicity increases, (ⅰ) the saturation magnetization Bs decreases due to the reduced magnetic moment of Fe far from the interface, (ⅱ) the strength of in-plane preference of spin direction increases yielding enhancement of MAE, and (ⅲ) the volume anisotropy coefficient decreases because the volume increase outdo the MAE enhancement.

Carrier-dependent magnetic anisotropy of Gd-adsorbed graphene

Using first-principles calculation based on density functional theory, we study the magnetic anisotropy of Gd-adsorbed graphene and its dependence on carrier accumulation. We show that carrier accumulation not only impacts the magnitude of magnetic anisotropy but also switches its sign. Hole accumulation enhances the perpendicular anisotropy up to ∼16 meV per Gd atom, while electron accumulation switches the anisotropy from perpendicular to in-plane direction. Moreover, we find that the first order perturbation of spin-orbit coupling interaction induces a pseudo-gap at Γ for the perpendicular magnetization, which leads to the the anomalous magnetic anisotropy for the neutral composite. Our findings pave the way for magneto-electric materials based on rare-earth-decorated graphene for voltage-controlled spintronics.

Extensive ab initio study of the electronic states of BSe radical including spin–orbit coupling

The internally contracted multi-reference configuration interaction method (MRCI) with Davidson modification and the Douglas–Kroll scalar relativistic correction has been used to calculate the BSe molecule at the level of aug-cc-pV5Z basis set. The calculated electronic states, including 9 doublet and 6 quartet Λ-S states, are correlated to the dissociation limit of B(2Pu)+Se(3Pg) and B(2Pu)+Se(1Dg). The Spin-orbit coupling (SOC) interaction is taken into account via the state interaction approach with the full Breit-Pauli Hamiltonian operator, which causes the entire 15 Λ-S states to split into 32Ω states. This is the first time that the spin-orbit coupling calculation has been carried out on BSe. The potential energy curves of the Λ-S and Ω electronic states are depicted with the aid of the avoided crossing rule between electronic states of the same symmetry. The spectroscopic constants of the bound Λ-S and Ω states were determined, which are in good agreement with the experimental data. The transition dipole moments (TDMs) and the Franck-Condon factors (FCs) of the transitions from the low-lying bound Ω states A2Π(I)3/2, B2Π(I)1/2 and C2Δ(I)3/2 to the ground state X2Σ+1/2 have also been presented. Based on the previous calculations, the radiative lifetimes of the A2Π(I)3/2, B2Π(I)1/2 and C2Δ(I)3/2 were evaluated.

Investigation of Spin Hamiltonian Parameters and Defect Structure of Cu2+ In Srcl2 Crystals

The spin Hamiltonian parameters (g-factors and hyperfine structure constants) and defect structure of tetragonal Cu2+ ion in SrCl2 are theoretically investigated, using the high-order perturbation formulas for 3d 9 ions in tetragonally elongated octahedra. In these formulas, the contributions to the spin Hamiltonian from the ligand orbital and spin-orbit coupling interactions are considered with respect to strong covalency. Based on the studies, the impurity Cu2+ is found to be located at a distance of about 0.42 A from the nearest chlorine plane. The signs of the hyperfine structure constants A|| and A⊥ are suggested. The theoretical spin Hamiltonian parameters show good agreement with the experimental values. The results are discussed.

Spin-orbit excitations and electronic structure of the putative Kitaev magnetα−RuCl3

Mott insulators with strong spin-orbit coupling have been proposed to host unconventional magnetic states, including the Kitaev quantum spin liquid. The 4$d$ system $\alpha$-RuCl$_3$ has recently come into view as a candidate Kitaev system, with evidence for unusual spin excitations in magnetic scattering experiments. We apply a combination of optical spectroscopy and Raman scattering to study the electronic structure of this material. Our measurements reveal a series of orbital excitations involving localized total angular momentum states of the Ru ion, implying that strong spin-orbit coupling and electron-electron interactions coexist in this material. Analysis of these features allows us to estimate the spin-orbit coupling strength, as well as other parameters describing the local electronic structure, revealing a well-defined hierarchy of energy scales within the Ru $d$ states. By comparing our experimental results with density functional theory calculations, we also clarify the overall features of the optical response. Our results demonstrate that $\alpha$-RuCl$_3$ is an ideal material system to study spin-orbit coupled magnetism on the honeycomb lattice.

Collective dynamics of a spin-orbit-coupled Bose-Einstein condensate.

We study the collective dynamics of the spin-orbit coupled two pseudospin components of a Bose-Einstein condensate trapped in a quasi-one-dimensional harmonic potential, by using variational and directly numerical approach of binary mean-field Gross-Pitaevskii equations. The results show that, because of strong coupling of spin-orbit coupling (SOC), Rabi coupling, and atomic interaction, the collective dynamics of the system behave as complex characters. When the Rabi coupling is absent, the density profiles of the system preserve the Gauss type and the wave packets do harmonic oscillations. The amplitude of the collective oscillations increases with SOC. Furthermore, when the SOC strength increases, the dipole oscillations of the two pseudospin components undergo a transition from in-phase to out-of-phase oscillations. When the Rabi coupling present, there will exist a critical value of SOC strength (which depends on the Rabi coupling and atomic interaction). If the SOC strength is less than this critical value, the density profiles of the system can preserve the Gauss type and the wave packets do anharmonic (the frequency of dipole oscillations depends on SOC) oscillations synchronously (i.e., in-phase oscillations). However, if the SOC strength is larger than this critical value, the wave packets are dynamically fragmented and the stable dipole oscillations of the system can not exist. The collective dynamics of the system can be controlled by adjusting the atomic interaction, SOC, and Rabi-coupling strength.

Electric Control of the Hall effect in Pt/Bi0.9La0.1FeO3 bilayers.

Platinum metal, being nonmagnetic and with a strong spin-orbit coupling interaction, has been deposited on weak ferromagnetic Bi0.9La0.1FeO3 thin films. The Hall effect is studied as a function of the polarization direction of multiferroic Bi0.9La0.1FeO3 thin films, as well as magnetic field (H) and temperature (T). For the two polarization directions, besides the obvious difference of the anomalous Hall resistance RAH, it increases sharply with decreasing temperature, and even changes sign, thus violating the conventional expression. This observations indicate local magnetic moments in Pt caused by the local electric fields at the interface of Bi0.9La0.1FeO3 films. Also, possible proximity effects and induced magnetic ordering in Pt on weak ferromagnetic Bi0.9La0.1FeO3 thin films of both upward and downward polarization states may exist and their contribution to the spin-related measurements should not be neglected.

Investigations of the EPR Parameters and Local Lattice Structure for the Rhombic Cu2+ Centre in TZSH Crystal

Abstract The electron paramagnetic resonance (EPR) parameters [i.e. g factors g i (i=x, y, z) and hyperfine structure constants A i ] and the local lattice structure for the Cu2+ centre in Tl2Zn(SO4)2·6H2O (TZSH) crystal were theoretically investigated by utilising the perturbation formulae of these parameters for a 3d9 ion under rhombically elongated octahedra. In the calculations, the admixture of d orbitals in the ground state and the ligand orbital and spin-orbit coupling interactions are taken into account based on the cluster approach. The theoretical EPR parameters show good agreement with the observed values, and the Cu2+–H2O bond lengths are obtained as follows: R x ≈1.98 Å, R y ≈2.09 Å, R z ≈2.32 Å. The results are discussed.

First examples of carbacylamidophosphate pentanuclear hydroxo-complexes: Synthesis, structure, luminescence and magnetic properties

The first representatives of pentanuclear carbacylamidophosphate complexes of composition Ln5L6(μ-L)4(μ3-OH)4(μ4-OH) (LnIII=Eu (1), Gd (2), Tb (3), L−=dimethylbenzoylamidophosphate ion [C6H5C(O)–N–P(O)(OCH3)2]−) were obtained. The single crystal X-ray analysis revealed that polynuclear core of 1 contains five europium ions, connected by the μ3- and μ4-hydroxo groups and carbacylamidophosphate ligands. Compounds 1–3 were found to be isostructural. Temperature dependencies of magnetic susceptibility (χM) of the compounds 1 and 2 could be explained by spin-orbit coupling of EuIII ions or antiferromagnetic exchange interactions of four GdIII ions located in the base of Gd5 pyramid, respectively. In the case of 3, the value of χM increases with temperature decreasing from 300K to 50K, and then falls down during temperature decrease till 2K. Such behavior can be explained by comparable contribution of spin-orbit coupling and exchange interactions. No signs of single-molecule magnet behavior for 3 were found at 2K. Phosphorescence, emission and excitation spectra at 298K and 77K for the complexes were measured, as well as luminescence decay times were determined. The compounds 1 and 3 showed intense luminescence with decay time at 298K equal to 0.66 and 1.44ms respectively. Intrinsic quantum yield for 1 determined from its emission spectrum was found to be 25%.

Nonequilibrium dynamics of spin-orbit-coupled lattice bosons

We study the nonequilibrium dynamics of two-component bosonic atoms in a one-dimensional optical lattice in the presence of spin-orbit coupling. In the Mott-insulating regime, the two-component bosonic system at unity filling can be described by the quantum spin $XXZ$ model. The atoms are initially prepared in their lower spin states. The system becomes out of equilibrium by suddenly introducing spin-orbit coupling to the atoms. The system shows the relaxation and nonstationary dynamics, respectively, in the different interaction regimes. We find that the time average of magnetization is useful to characterize the many-body dynamics. The effects of even and odd numbers of sites are discussed. Our result sheds light on nonequilibrium dynamics due to the interplay between spin-orbit coupling and atomic interactions.

Coulomb-exchange effects in nanowires with spin splitting due to a radial electric field

We present a theoretical study of Coulomb exchange interaction for electrons confined in a cylindrical quantum wire and subject to a Rashba-type spin-orbit coupling with radial electric field. The effect of spin splitting on the single-particle band dispersions, the quasiparticle effective mass, and the system's total exchange energy per particle are discussed. Exchange interaction generally suppresses the quasiparticle effective mass in the lowest nanowire subband, and a finite spin splitting is found to significantly increase the magnitude of the quasiparticle-mass suppression (by upto 15\% in the experimentally relevant parameter regime). In contrast, spin-orbit coupling causes a modest (1\%-level) reduction of the magnitude of the exchange energy per particle. Our results shed new light on the interplay of spin-orbit coupling and Coulomb interaction in quantum-confined systems, including those that are expected to host exotic quasiparticle excitations.

Giant spin-orbit-induced spin splitting in Bi zigzag chains on GaAs(110)

The search for one-dimensional electron systems with a giant Rashba-type spin splitting is of importance for the application of spin transport. Here we report, based on a first-principles density-functional-theory calculation, that Bi zigzag chains formed on a heterogeneous GaAs(110) surface have a giant spin splitting of surface states. This giant spin splitting is revealed to originate from spin-orbit coupling (SOC) and electric dipole interaction that are significantly enhanced by (i) the asymmetric surface charge distribution due to the strong SOC-induced hybridization of the Bi px , py , and pz orbitals and (ii) the large out-of-plane and in-plane potential gradients generated by two geometrically and electronically inequivalent Bi atoms bonding to Ga and As atoms. The results demonstrate an important implication of the in-plane and out-of-plane asymmetry of the Bi/GaAs(110) interface system in producing the giant spin splitting with the in-plane and out-of-plane spin components.

EPR investigation of local structure for the [Mn(H2O)6]2+cluster in M(ClO4)2· 6H2O:Mn2+(M = Cd, Hg) systems at different temperatures

Local lattice structure distortion studies of the octahedral Mn 2+ center in M(ClO 4 ) 2 · 6H 2 O:Mn 2+ (M = Cd, Hg) systems have been performed systematically based on the diagonalization of the complete energy matrices of electron-electron repulsion, spin-orbit coupling and trigonal ligand-field interaction for a d 5 configuration ion in a trigonal ligand field. From the EPR calculation, the local structure distortion parameters R and θ are determined, respectively. Results show that the local lattice structure around a trigonal Mn 2+ center has a compressed distortion along the crystalline C 3 axis. The compression distortion may be ascribed to the fact that the radius of the Mn 2+ ion is smaller than that of the Hg 2+ ion and the Cd 2+ ion. The local lattice structure parameters for Mn 2+ in M(ClO 4 ) 2 · 6H 2 O:Mn 2+ (M = Cd, Hg) systems are determined at liquid-nitrogen temperature and room temperature.

Finite temperature orbital and spin magnetism of small Fe linear chains

The finite temperature spin and orbital magnetism of FeN linear chains is theoretically studied in the framework of a spin fluctuation theory based on a realistic d-band model Hamiltonian, which includes the spin–orbit coupling interaction in a non-perturbative way. Spin and orbital magnetic moments are calculated as a function of the temperature by using an exchange Monte Carlo method that takes into account in a full way the short-range magnetic order. The finite temperature anisotropy effects on the spin and orbital cluster moment values are analysed by considering magnetization directions perpendicular to and along the chain axis. The temperature dependence of the orbital cluster moment follows a general trend similar to that of the spin one and shows clear anisotropy effects at low and intermediate temperatures, before total thermal disorder appears. Interesting anisotropy effects driven by thermal spin fluctuations are also observed for the spin results in most of the systems.

Control of the spin to charge conversion using the inverse Rashba-Edelstein effect

We show here that using spin orbit coupling interactions at a metallic interface it is possible to control the sign of the spin to charge conversion in a spin pumping experiment. Using the intrinsic symmetry of the “Inverse Rashba Edelstein Effect” (IREE) in a Bi/Ag interface, the charge current changes sign when reversing the order of the Ag and Bi stacking. This confirms the IREE nature of the conversion of spin into charge in these interfaces and opens the way to tailoring the spin sensing voltage by an appropriate trilayer sequence.

Theoretical investigations of the spin Hamiltonian parameters for the CoCl(PPh3)3 molecules

The perturbation formulas of the spin Hamiltonian parameters (zero-field splitting and g factor g// and g⊥) are established for a 3d8 ion in trigonally distorted tetrahedra for the first time. In the theoretical treatments, the contributions from the Jahn–Teller effect, the ligand orbital and spin–orbit coupling interactions and configuration interactions are taken into account from the cluster approach in a uniform way. The above formulas are applied to the studies of the spin Hamiltonian parameters for the three CoCl(PPh3)3 molecules, and the experimental electron paramagnetic resonance spectra of all the molecules are satisfactorily explained. The significant compressions of the ligand tetrahedra with mixed chlorine and PPh3 groups around Co+ are analysed for three distinct CoCl(PPh3)3 compounds, characterised by the Cl–Co–P bond angles θ larger than the tetrahedral angle of 109.47°. The local trigonal distortions are discussed in view of the Jahn–Teller effect.

Interaction-induced quantum anomalous Hall phase in (111) bilayer ofLaCoO3

In the present paper, the Gutzwiller density functional theory (LDA+G) has been applied to study the bilayer system of ${\mathrm{LaCoO}}_{3}$ grown along the $(111)$ direction on ${\mathrm{SrTiO}}_{3}$. The LDA calculations show that there are two nearly flat bands located at the top and bottom of ${e}_{g}$ bands of Co atoms with the Fermi level crossing the lower one. After including both the spin-orbit coupling and the Coulomb interaction in the LDA+G method, we find that the interplay between spin-orbit coupling and Coulomb interaction stabilizes a very robust ferromagnetic insulator phase with the nonzero Chern number indicating the possibility of realizing the quantum anomalous Hall effect in this system.