Spin-orbit Parameters Research Articles

Dependence of Spin-orbit Parameters in AlxGa1−xN/GaN Quantum Wells on the Al Composition of the Barrier

In this paper, we obtain considerable spin-orbit (SO) parameters in AlxGa1−xN/GaN quantum wells (QWs) with sheet carrier concentration Ns = 120 × 1011/cm2. With increasing Al content (x) of the barrier, the SO parameters increase as a whole, and the two major contributions are found to be the decrease of the expansion region of the envelope functions and the increase of the polarized electric field in the well. Compared with the Rashba parameters for the first two subbands, the intersubband SO parameter is a bit smaller and varies more slowly with x. The results indicate the SO parameters, especially the Rashba parameters can be engineered by the Al composition of the barrier, which may be helpful to the spin manipulation of III-nitride low-dimensional heterostructures.

Research on the g factors and tetragonal distortion of the Cu2+ tetrahedral center in ZnS:Cu2+ nanocrystals

The EPR g factors g∥ and g⊥ for the tetragonal Cu2+ tetrahedral clusters in ZnS:Cu2+ nanocrystals are calculated from two theoretical methods, the complete diagonalization (of the energy matrix) method (CDM) and the perturbation theory method (PTM). Both methods are based on the cluster approach in which not only the contribution due to the spin–orbit parameter of the central metal (3dn) ion but also that of ligand ions via the covalence effect are considered. The calculated results from both methods are in reasonable agreement with the experimental values, suggesting that either CDM or PTM can be used to explain the g factors of d9 ions in tetrahedral clusters. The calculations indicate that the Cu2+ tetrahedra in ZnS:Cu2+ nanocrystals are tetragonally compressed (with the ground singlet 2B2 ()) rather than tetragonally elongated. This point is consistent with the expectation based on the Jahn–Teller effect.

Optical absorption and photoreflectance spectroscopy of the single-crystalline chalcopyrite semiconductor AgGaSe2

Optical absorption and photoreflectance (PR) spectra have been measured on the single-crystalline chalcopyrite semiconductor AgGaSe2 for light polarization perpendicular (E ⊥ c) and parallel to the c-axis (E ‖ c) at T = 15–300 K. Optical absorption measurements suggest that AgGaSe2 is a direct-gap semiconductor having an optical band gap of E0 ∼ 1.8 eV at T = 15–300 K. The temperature-dependent PR spectra are obtained at T = 20–300 K in the 1.8–2.5 eV spectral ranges. The lowest band-gap energy E0 of AgGaSe2 shows unusual temperature dependence at T ≤ 80 K. The resultant temperature coefficients dE0/dT are positive at T ≤ 70 K and negative above 70 K, and are explained by considering the effects of thermal expansion and electron-phonon interaction. The spin-orbit and crystal-field splitting parameters are also determined to be Δso = 327 meV and Δcr = −288 meV at T = 20 K, respectively.

Magnetoconduction in a two-dimensional system confined in wurtzite AlxGa1−xN/GaN heterostructure

The magnetoresistivity of a two dimensional electron system confined in a wurtzite Al0.22Ga0.78N/GaN heterostructure has been reproduced using a theoretical model based on a modified semiclassical theory. When an external magnetic field is applied, nodes appear on the beating pattern Subnikov-de Haas oscillations due to carriers with different spin orientations. The analysis of the magnetoresistivity experimental data with the model led us to know accurately the value of the spin-orbit coupling material parameters.

What Factors Affect the5D0Energy of Eu3+? An Investigation of Nephelauxetic Effects

Relationships involving the interelectronic repulsion parameters, F(k) (k = 2, 4, 6), the spin-orbit coupling constant, ζf, and J-mixing, with the (5)D0-(7)F0 energy, E, have been investigated for Eu(3+) using various approaches. First, the linear relationship between E and the (7)F1 splitting (or the second rank crystal field parameter) is shown to be applicable not only to glasses but also to solid-state crystalline systems with Eu(3+) site symmetry of C2, C2v, or lower. In these cases, the change in (5)D0-(7)F0 energy is mainly due to the J-mixing effect of (7)F(J) (J = 2, 4, 6: most notably J = 2) which depresses (7)F0, whereas the (5)D0 energy is relatively constant. The (5)D0-(7)F0 energy also depends upon certain energy parameters in the Hamiltonian, in particular, F(k) and ζf. Model calculations show that increase in F(4) or F(6) produces an increase in E, whereas increase in F(2) produces a decrease in E. An increase in ζf produces a decrease in E. These findings are rationalized. Most previous 4f(6) crystal field calculations have only considered the F and D terms of Eu(3+) so that the Slater parameters are not well-determined. More reliable energy level data sets and crystal field calculations for Eu(3+) with fluoride, oxide, or chloride ligands have been selected, and certain of these have been repeated since most previous calculations have errors in matrix elements. The fitted Slater parameters have been corrected for the effects of three-body Coulomb interactions. Some systems do not follow the ligand trend F ~ O > Cl for Slater and spin-orbit parameters. From the limited data available, the average values of the corrected Slater parameters are greater for fluoride compared with chloride ligands, but the differences are comparable with the standard deviations of the parameters. There is no clear nephelauxetic series for these three types of ligands, with respect to spin-orbit coupling. Previous correlations of E with various parameters are of limited value because the (5)D0-(7)F0 energy difference not only depends upon the F(k) and ζf parameters but in addition is sensitive to the importance of J-mixing for low symmetry systems.

Studies of the optical band positions, spin-Hamiltonian parameters and defect structure for Cr3+ in CdIn2S4 crystal

The calculations of optical band positions and spin-Hamiltonian parameters (g factors g//, g⊥ and zero-field splitting D) for Cr3+ ion at the trigonal octahedral In3+ site in semiconducting spinel CdIn2S4 have been carried out by using the complete diagonalization (of energy matrix) method based on the two-spin–orbit-parameter model. In the model, differing from the conversional one-spin–orbit-parameter in the widely-used crystal-field theory, both the contribution to spin-Hamiltonian parameters from the spin–orbit parameter of central dn ion and that of ligand are contained. The calculated results are in reasonable agreement with the experimental values. It is found from the calculations that the MO6 octahedral cluster in CdIn2S4:Cr3+ changes from the trigonal elongation in the host crystal to the trigonal compression in the Cr3+ impurity center owing to the impurity-induced local lattice relaxation. The results are discussed.

Ab-initio calculations of the crystal-field parameters and energy level structure for Yb3+ doped in tantalate

In this paper, the DV-X method of ab-initio calculations and the effective Hamiltonian model are introduced to calculate the crystal-field and spin-orbit parameters of rare earth ions doped in various crystals, especially for the crystal with low-symmetry. For the low-symmetry crystal, the number of parameters is more than that of energy levels, thus experimental energy levels fitting cannot determine all parameters, while ab-initio calculations can determine all crystal-field and spin-orbit parameters accurately. Firstly, the crystal-field and spin-orbit parameters of Yb3+ doped in GdTaO4 crystal are calculated by this model, and then the energy level structure of Yb3+:GdTaO4 is given and the continuous emission band of Yb3+:GdTaO4 emission spectrum is analyzed, which is conducive to the laser tunable and laser mode-locking output, so Yb3+:GdTaO4 is a potential laser medium for high efficiency laser operation and new ultrashort pulse output. Also, the crystal-field and spin-orbit parameters of Yb3+ doped in YTaO4 and ScTaO4 are calculated by this model, and the energy level structures of Yb3+:YTaO4 and Yb3+ :ScTaO4 are given, which leads to a conclusion similar to that drawn from the Yb3+:GdTaO4 crystal.

Research on the spin-Hamiltonian parameters and defect structure for Ni+ ion in CdS

The spin-Hamiltonian parameters (g factors g//, g⊥ and hyperfine structure constants A//, A⊥) for Ni+ in the trigonally-distorted tetrahedral Cd2+ site of CdS are calculated from the complete diagonalization (of energy matrix) method with the suitable parameters. In the method, the contributions to spin-Hamiltonian parameters from both the spin-orbit parameters of central dn ion and ligands are contained and the interactions among all the ground and excited states are considered. The calculated results show reasonable agreement with the experimental values. The defect structure of Ni+ center, which is similar to those of other 3dn centers in CdS, is obtained from the calculation.

Seasonal melting and the formation of sedimentary rocks on Mars, with predictions for the Gale Crater mound

A model for the formation and distribution of sedimentary rocks on Mars is proposed. In this model (ISEE-Mars), the rate-limiting step is supply of liquid water from seasonal melting of snow or ice. The model is run for a O(102) mbar pure CO2 atmosphere, dusty snow, and solar luminosity reduced by 23%. For these conditions snow melts only near the equator, when obliquity and eccentricity are high, and when perihelion occurs near equinox. These requirements for melting are satisfied by 0.01–20% of the probability distribution of Mars’ past spin–orbit parameters. This fraction is small, consistent with the geologic record of metastable surface liquid water acting as a “wet-pass filter” of Mars climate history, only recording orbital conditions that permitted surface liquid water. Total melt production is sufficient to account for observed aqueous alteration. The pattern of seasonal snowmelt is integrated over all spin–orbit parameters and compared to the observed distribution of sedimentary rocks. The global distribution of snowmelt has maxima in Valles Marineris, Meridiani Planum and Gale Crater. These correspond to maxima in the sedimentary-rock distribution. Higher pressures and especially higher temperatures lead to melting over a broader range of spin–orbit parameters. The pattern of sedimentary rocks on Mars is most consistent with a model Mars paleoclimate that only rarely produced enough meltwater to precipitate aqueous cements (sulfates, carbonates, phyllosilicates and silica) and indurate sediment. This is consistent with observations suggesting that surface aqueous alteration on Mars was brief and at low water/rock ratio. The results suggest intermittency of snowmelt and long globally-dry intervals, unfavorable for past life on Mars. This model makes testable predictions for the Mars Science Laboratory Curiosity rover at Gale Crater’s mound (Mount Sharp, Aeolis Mons). Gale Crater’s mound is predicted to be a hemispheric maximum for snowmelt on Mars.

Spin Hall and Spin Nernst Effects Due to Intrinsic Spin-Orbit Coupling in Monolayer and Bilayer Graphene

We consider intrinsic contributions to the spin Hall and spin Nernst effects in monolayer and bilayer graphene. The spin Hall (Nernst) effect consists in the generation of transverse spin current by longitudinal electric field (temperature gradient). The relevant electronic spectrum for monolayer and bilayer graphene has been obtained from the corresponding effective Hamiltonians. Both spin Hall and spin Nernst conductivities have been determined within the linear response theory and Green function formalism. The influence of an external vertical voltage between the two atomic sheets in the case of a bilayer graphene is also analyzed and discussed. This voltage can generally lead to a phase transition between the topological insulator phase and conventional insulator. In the case of bilayer graphene, the main focuss is on an asymmetrical case, with different spin-orbit parameters in the two atomic sheets. Such a difference may be generated by different atomic planes adjacent to bilayer graphene on its both sides.

Pseudogap phase in cuprates: Oxygen orbital moments instead of circulating currents

Circulating current (CC) loops within the cuprate unit cell are proposed to play a key role in the physics of the pseudogap phase. However, main experimental observations motivated by this sophisticated proposal and seemingly supporting the CC model can be explained in frames of a simple and physically clear microscopic model. We argue that instead of a well-isolated Zhang-Rice (ZR) singlet $^1A_{1g}$ the ground state of the hole center [CuO$_4$]$^{5-}$ (cluster analog of Cu$^{3+}$ ion) in cuprates should be described by a complex $^1A_{1g}$-$^{1,3}B_{2g}$-$^{1,3}E_u$ multiplet, formed by a competition of conventional hybrid Cu 3d-O 2p $b_{1g}(\sigma)\propto d_{x^2 -y^2}$ state and {\it purely oxygen nonbonding} O 2p$\pi$ states with $a_{2g}(\pi)$ and $e_{ux,y}(\pi)$ symmetry. In contrast with inactive ZR singlet we arrive at several novel competing orbital and spin-orbital order parameters, e.g., Ising-like net orbital magnetic moment, orbital toroidal moment, intra-plaquette's staggered order of Ising-like oxygen orbital magnetic moments. As a most impressive validation of the non-ZR model we explain fascinating results of recent neutron scattering measurements that revealed novel type of magnetic ordering in pseudogap phase of several hole-doped cuprates.

Calculations of EPR g factors for the isolated tetragonal Cu2+(II) centre in mechanically processed YBa2Cu3O7−δ superconductors

The g factors g∥ and g⊥ of the isolated tetragonal Cu(II)O5 cluster in YBa2Cu3O7−δ superconductors induced and suppressed by mechanical processing are calculated from the complete diagonalization (of the energy matrix) method (CDM) and the perturbation theory method (PTM). Both methods are based on the cluster approach where in addition to the contribution of the spin–orbit parameter of the central metal ion, the contribution of ligand ion via the covalence effect is taken into account. In the calculations, the structural data of the Cu(II)O5 cluster gained from x-ray diffraction are applied. The results from both the CDM and the PTM are similar and show reasonable agreement with the experimental values. It appears that both methods can be used to explain the EPR g factors for d9 ions in crystals.

Theoretical explanation of absorption spectra and ESR parameters of Cu2+ in shattuckite

The optical absorption spectra and electronic spin resonance parameters (ESR g factors g(parallel to), g(perpendicular to) and hyperfine structure constants A(parallel to), A(perpendicular to)) for Cu2+ in shattuckite crystal are calculated from the two spin-orbital coupling parameters model, high-order perturbation formulas and complete diagonalization (of energy matrix) method (CDM) of 3d(9) ion in tetragonal symmetry. The calculated results are in good agreement with the observed values. Since the ESR parameters are sensitive to the local structure of a paramagnetic impurity center, the defect structure of Cu2+ center in shattuckite crystal is estimated. The results are discussed. (C) 2012 Elsevier B.V. All rights reserved.

Theoretical calculations of the optical band positions and spin-Hamiltonian parameters for Cr3+ ions in Y2Ti2O7 crystal

The optical band positions and spin-Hamiltonian parameters (g factors g(parallel to) g(perpendicular to) and zero-field splitting D) for the trigonal Cr3+ centers in Y2Ti2O7 crystal are calculated from the complete diagonalization (of energy matrix) method based on the two-spin-orbit-parameter model. In the calculations, the contributions to spectral data from both the spin-orbit parameter of central d(n) ion and that of ligand ion are considered and the crystal field parameters used are estimated from the superposition model. The calculated results are in reasonable agreement with the experimental values. The defect structures of Cr3+ center is suggested. (C) 2012 Elsevier B.V. All rights reserved.

Quadrupole moments of spherical semi-magic nuclei within the self-consistent Theory of Finite Fermi Systems

The quadrupole moments of odd neighbors of semi-magic lead and tin isotopes and $N=50,N=82$ isotones are calculated within the self-consistent Theory of Finite Fermi Systems based on the Energy Density Functional by Fayans et al. Two sets of parameters, DF3 and DF3-a, fixed previously are used. They differ by the spin-orbit and effective tensor force parameters, the latter being significantly bigger in the DF3-a functional. Results for the two functionals turned out to be rather different. The functional DF3-a leads to quadrupole moments in reasonable agreement with the experimental ones for most nuclei examined.

High-Spin States in Transuranium Nuclei 242,244Pu

We investigate the structure of yrast bands in the transuranium nuclei 242Pu and 244Pu in the framework of the projected shell model, which is a fully quantum mechanical and microscopic approach. It is found that an appropriate modification of the standard Nilsson spin-orbital parameters in the N = 6 proton shell is necessary to correctly describe the high-spin backbending phenomenon in nucleus 244Pu. In order to test whether this modification is correct, the same modified parameters are used to calculate the yrast band of its neighboring isotope 242Pu. It is found that without this modification, a backbending will occur at spin I = 20, which is not supported by the experimental data.

Singlet-triplet splitting in double quantum dots due to spin-orbit and hyperfine interactions

We analyze the low-energy spectrum of a two-electron double quantum dot under a potential bias in the presence of an external magnetic field. We focus on the regime of spin blockade, taking into account the spin orbit interaction and hyperfine coupling of electron and nuclear spins. Starting from a model for two interacting electrons in a double dot, we derive a perturbative, effective two-level Hamiltonian in the vicinity of an avoided crossing between singlet and triplet levels, which are coupled by the spin-orbit and hyperfine interactions. We evaluate the level splitting at the anticrossing, and show that it depends on a variety of parameters including the spin orbit coupling strength, the orientation of the external magnetic field relative to an internal spin-orbit axis, the potential detuning of the dots, and the difference between hyperfine fields in the two dots. We provide a formula for the splitting in terms of the spin orbit length, the hyperfine fields in the two dots, and the double dot parameters such as tunnel coupling and Coulomb energy. This formula should prove useful for extracting spin orbit parameters from transport or charge sensing experiments in such systems. We identify a parameter regime where the spin orbit and hyperfine terms can become of comparable strength, and discuss how this regime might be reached.

Beating Analysis of Shubnikov de Haas Oscillation in In<sub>0.53</sub>Ga<sub>0.47</sub>As Double Quantum Well toward Spin Filter Applications

We recently determined the values of intrinsic spin-orbit (SO) parameters for In 0.52 Al 0.48 As/In 0.53 Ga 0.47 As(10 nm)/In 0.52 Al 0.48 As (InGaAs/InAlAs) quantum wells (QW), lattice-matched to (001) InP, from the weak localization/antilocalization analysis of the low-temperature magneto-conductivity measurements [1]. We have then studied the subband energy spectra for the InGaAs/InAlAs double QW system from beatings in the Shubnikov de Haas (SdH) oscillations. The basic properties obtained here for the double QW system provides useful information for realizing nonmagnetic spin-filter devices based on the spin-orbit interaction [2]. Copyright © 2012 The Institute of Electronics, Information and Communication Engineers.

Simulation of the f—d transitions of lanthanide ions in YPO4 using quantum-chemical calculations

We constructed an effective one-electron Hamiltonian by using the 4f/5d energies and eigenvectors obtained from the first-principles calculation with the relativistic self-consistent discrete variational Slater software package (DV-Xα). From the effective Hamiltonian, we obtained the crystal-field and spin-orbit interaction parameters for the 4f and 5d electrons of lanthanide ions (Ce3+, Pr3+, Nd3+ and Eu3+) doped in YPO4, and these parameters were used to calculate the 4fN−4fN−15d transition. Comparison with experiments shows that the obtained parameters are reasonable and the excitation spectra can be well predicted.

Cyanide/isocyanide abundances in the interstellar medium - I. Theoretical spectroscopic characterization

Modelling molecular abundances in the interstellar medium requires accurate molecular data. In this work, structural and spectroscopic properties of a series of metal cyanides/isocyanide species containing Na, Mg, Al and Si are calculated and compared using highly correlated ab initio calculations. The metal substitution effect on molecular properties is discussed. Isomerization pathways and transitions states are detailed. NaCN shows three isomeric structures, one T shaped and two linear forms, whereas the remaining compounds display two linear minimum energy geometries. For the first time, NaCN secondary minima are described. Second-order perturbation theory spectroscopic parameters are determined from an anharmonic RCCSD(T)/aug-cc-pV5Z force field. Very accurate rotational constants are calculated using a complete basis set and taking into account vibrational effects and the structure variation with core electron correlation. For l-SiCN and l-SiNC, spin–orbit parameters are also provided. Present theoretical results are compared with available experimental data attaining a good agreement.