Spin-orbit Interaction Parameter Research Articles

Bismuth induced enhancement of Rashba spin–orbit interaction in GaAsBi/GaAs heterostructures

The incorporation of heavy atoms into semiconductor heterostructures is a promising way to enhance the spin–orbit interaction of carriers moving in two-dimensional channels. We investigated the strength of spin–orbit interaction in a sample containing an epitaxially grown GaAsBi channel. Time- and spatially resolved Kerr rotation measurements revealed the existence of Rashba-type spin–orbit effective magnetic fields experienced by the photo-injected spins diffusing in the GaAsBi layer. The spin–orbit interaction parameters deduced from both experiments and theory suggest that, as a result of an increase in the spin–orbit split-off energy due to Bi, the offset energies of the valence band and spin split-off band at the GaAsBi/GaAs interface work constructively to enhance the Rashba spin–orbit interaction parameter, which is one order of magnitude larger than those arising from conventional GaAs/AlGaAs and InGaAs/GaAs interfaces.

Rotational and deperturbation analysis of the interacting A2Π1/2, v = 11 ∼ B2Σ+, v = 6 states of yttrium monoxide (YO) molecule

The YO molecules in gas-phase were formed by the reaction of the laser produced yttrium plasma with molecular oxygen and subsequently cooled by free-jet expansion. The YO molecules were studied by laser-induced excitation and dispersed fluorescence (DF) spectroscopy at 0.1 cm-1 spectral resolution. The B2Σ+ state was observed in vibrations v=5 and 6 from the X2Σ+ ground state. The anomalously low spin-rotation constant of the B2Σ+, v=6 level compared to the v=0-5 vibrational levels of the B state indicated perturbation. Investigation of the wavelength filtered excitation spectra led to the observation of the A2Π1/2, v=11 spin-orbit component lying 28.5 cm-1 below the B2Σ+, v=6 state. The deperturbation analysis of the interacting pair of B2Σ+, v=6 ∼ A2Π1/2,v=11 states was carried out by incorporating the spin-orbit, spin-electronic and L-uncouple interaction parameters as off-diagonal matrix elements in the 2Σ+-2Π Hamiltonian. The molecular constants of v=11 of the A and v=6 of the B states followed the vibrational trend after deperturbation. The e-parity level of the B2Σ+, v=6 and A2Π1/2, v=11 crossed after J=25.5 and deperturbation analysis estimated J-dependent configuration mixing up to ∼50% for the e-parity and 16% for the f-parity levels. The value of the configuration mixing coefficient of the interacting A and the B states, obtained from the intensity analysis of the observed vibronic bands in the DF spectra, is in agreement with the depertubation analysis. In addition, the Ω=½ spin-orbit components of the A2Π state was observed in v=12 and 13 vibrations and were found to be unperturbed.

Coupled superconducting spin qubits with spin-orbit interaction

Superconducting spin qubits, also known as Andreev spin qubits, promise to combine the benefits of superconducting qubits and spin qubits defined in quantum dots. While most approaches to control these qubits rely on controlling the spin degree of freedom via the supercurrent, superconducting spin qubits can also be coupled to each other via the superconductor to implement two-qubit quantum gates. We theoretically investigate the interaction between superconducting spin qubits in the weak tunneling regime and concentrate on the effect of spin-orbit interaction (SOI), which can be large in semiconductor-based quantum dots and thereby offers an additional tuning parameter for quantum gates. We find analytically that the effective interaction between two superconducting spin qubits consists of Ising, Heisenberg, and Dzyaloshinskii-Moriya interactions and can be tuned by the superconducting phase difference, the tunnel barrier strength, or the SOI parameters. The Josephson current becomes dependent on SOI and spin orientations. We demonstrate that this interaction can be used for fast controlled phase-flip gates with a fidelity >99.99%. We propose a scalable network of superconducting spin qubits which is suitable for implementing the surface code.

Spectroscopic characterization of singlet-triplet doorway states of aluminum monofluoride.

Aluminum monofluoride (AlF) possesses highly favorable properties for laser cooling, both via the A1Π and a3Π states. Determining efficient pathways between the singlet and the triplet manifold of electronic states will be advantageous for future experiments at ultralow temperatures. The lowest rotational levels of the A1Π, v = 6 and b3Σ+, v = 5 states of AlF are nearly iso-energetic and interact via spin-orbit coupling. These levels thus have a strongly mixed spin-character and provide a singlet-triplet doorway. We here present a hyperfine resolved spectroscopic study of the A1Π, v = 6//b3Σ+, v = 5 perturbed system in a jet-cooled, pulsed molecular beam. From a fit to the observed energies of the hyperfine levels, the fine and hyperfine structure parameters of the coupled states and their relative energies as well as the spin-orbit interaction parameter are determined. The standard deviation of the fit is about 15MHz. We experimentally determine the radiative lifetimes of selected hyperfine levels by time-delayed ionization, Lamb dip spectroscopy, and accurate measurements of the transition lineshapes. The measured lifetimes range between 2 and 200ns, determined by the degree of singlet-triplet mixing for each level.

Determination of the Rashba and Dresselhaus Spin–Orbit Interaction Parameters and g‐Factor from the Critical Points of the Spectrum in a 2D Electron Gas in an In‐Plane Magnetic Field

A 2D electron gas with spin–orbit interaction (SOI) is known to form an anisotropic system with van Hove singularities controllable by a parallel magnetic field. The conductivity tensors of this system in the presence of both Rashba and Dresselhaus SOIs is studied. It is found that the diagonal elements of the conductivity tensor have sharp dips when the Fermi level passes through the singularity point of a spectrum. The energy position of these dips at different orientations of the magnetic field allows one to determine both SOI constants and the Landé g‐factor. The dependencies of the surface charge concentration on the Fermi level show a sharp change in the slope near the minimum of the spectrum due to the jumps of the density of states, while the van Hove singularities are not noticeable. In a zero magnetic field, the conductivity tensor has off‐diagonal terms which change the sign when the Fermi level passes the saddle points of the spectrum. The off‐diagonal terms evidence the appearance of the Hall voltage caused by the anisotropy of the Fermi surface and the scattering process.

High-resolution Fourier-transform spectroscopy and deperturbation analysis of the A1Π(v = 1) level in 12C18O

The A1Π(v = 1) level of the 12C18O isotopologue was precisely reinvestigated with two complementary spectroscopic techniques. High resolution B1Σ+ → A1Π(0, 1), (1, 1) and C1Σ+ → A1Π(0, 1) emission bands were recorded in the visible region, 20,700 – 26,100 cm−1, with a 1.71 m Fourier-transform spectrometer (Bruker IFS 125-HR) installed at the University of Rzeszów. The resulting line centre accuracy of isolated and medium to strong lines is 0.005 cm−1. In addition, high-resolution spectra of the A1Π ⟵ X1Σ+(1, 0), B1Σ+⟵ X1Σ+(0, 0) and (1, 0) as well as C1Σ+⟵ X1Σ+(0, 0) bands were recorded between 66,200 and 95,250 cm−1 using the vacuum-ultraviolet Fourier-transform spectrometer installed at the DESIRS beamline of the SOLEIL synchrotron. The wavenumber accuracy for isolated and strong spectral lines is 0.01 cm−1. A data set of 626 spectral lines belonging to seven bands was incorporated into a global deperturbation analysis. Significantly improved deperturbed molecular constants for the A1Π(v = 1), a´3Σ+(v = 10), D1Δ(v = 1), and I1Σ−(v = 2) levels, term values of the B1Σ+(v = 0, 1) and C1Σ+(v = 0) Rydberg states as well as the accompanying spin-orbit and rotation-electronic (L-uncoupling) interaction parameters were obtained. The experimental ro-vibrational term values of the A1Π(v = 1) level and its perturbers were also determined. The mixed composition of interacting states is expressed in terms of their 1Π percentage character.

Knight Shift and Leading Superconducting Instability from Spin Fluctuations in Sr_{2}RuO_{4}.

Recent nuclear magnetic resonance studies [A. Pustogow etal., Nature 574, 72 (2019)] have challenged the prevalent chiral triplet pairing scenario proposed for Sr_{2}RuO_{4}. To provide guidance from microscopic theory as to which other pair states might be compatible with the new data, we perform a detailed theoretical study of spin fluctuation mediated pairing for this compound. We map out the phase diagram as a function of spin-orbit coupling, interaction parameters, and band structure properties over physically reasonable ranges, comparing when possible with photoemission and inelastic neutron scattering data information. We find that even-parity pseudospin singlet solutions dominate large regions of the phase diagram, but in certain regimes spin-orbit coupling favors a near-nodal odd-parity triplet superconducting state, which is either helical or chiral depending on the proximity of the γ band to the van Hove points. A surprising near degeneracy of the nodal s^{'} and d_{x^{2}-y^{2}} wave solutions leads to the possibility of a near-nodal time-reversal symmetry broken s^{'}+id_{x^{2}-y^{2}} pair state. Predictions for the temperature dependence of the Knight shift for fields in and out of plane are presented for all states.

Chirality-Induced Spin Selectivity: The Role of Electron Correlations.

Chirality-induced spin selectivity, discovered about two decades ago in helical molecules, is a nonequilibrium effect that emerges from the interplay between geometrical helicity and spin-orbit interactions. Several model Hamiltonians building on this interplay have been proposed, and while these can yield spin-polarized transport properties that agree with experimental observations, they simultaneously depend on unrealistic values of the spin-orbit interaction parameters. It is likely, however, that a common deficit originates from the fact that all these models are uncorrelated or single-electron theories. Therefore, chirality-induced spin selectivity is here addressed using a many-body approach, which allows for nonequilibrium conditions and a systematic treatment of the correlated state. The intrinsic molecular spin polarization increases by 2 orders of magnitude, or more, compared to the corresponding result in the uncorrelated model. In addition, the electronic structure responds to varying external magnetic conditions which, therefore, enables comparisons of the currents provided for different spin polarizations in one or both of the leads between which the molecule is mounted. Using experimentally feasible parameters and room temperature, the obtained normalized difference between such currents may be as large as 5-10% for short molecular chains, clearly suggesting the vital importance of including electron correlations when searching for explanations of the phenomenon.

Topological insulator with negative spin-orbit coupling and transition between Weyl and Dirac semimetals in InGaN-based quantum wells

We study the influence of negative spin-orbit coupling on the topological phase transition and properties of the topological insulator state in InGaN-based quantum wells grown along c axis of the wurtzite lattice. The realistic eight-band k·p method with relativistic and nonrelativistic linear-k terms is employed. Our calculations show that the negative spin-orbit coupling in InN is not an obstacle to obtain the topological insulator phase in InN/InGaN and InGaN/GaN quantum wells. The bulk energy gap in the topological insulator state can reach 2 meV, which allows experimental verification of the edge state transport in these materials. The topological phase transition occurs due to the band inversion between the highest light hole subband and the lowest conduction subband, and almost always is mediated by the two-dimensional Weyl semimetal, arising from an anticrossing of these subbands at zero in-plane wave vector. However, for certain InGaN/GaN quantum wells, we find that the magnitude of this anticrossing vanishes, leading to the appearance of the Dirac semimetal. The novel transition between the Weyl and Dirac semimetals originates from vanishing of the average in-plane spin-orbit interaction parameter, which decouples the conduction subband from the light hole subband at zero in-plane wave vector.

Quantum confinement and heavy surface states of Dirac fermions in bismuth (111) films: An analytical approach

Recent high-resolution angle-resolved photoemission spectroscopy experiments have given a reason to believe that pure bismuth is a topologically nontrivial semimetal. We derive an analytic theory of surface and size-quantized states of Dirac fermions in Bi(111) films taking into account the new data. The theory relies on a new phenomenological momentum-dependent boundary condition for the effective Dirac equation. The boundary condition is described by two real parameters that are expressed by a linear combination of the Dresselhaus and Rashba interface spin-orbit interaction parameters. In semi-infinite Bi(111), near the $\overline{\mathrm{M}}$ point the surface states possess anisotropical parabolic dispersion with very heavy effective mass in the $\overline{\mathrm{\ensuremath{\Gamma}}}\text{\ensuremath{-}}\overline{\mathrm{M}}$ direction order of ten free electron masses and light effective mass in the $\overline{\mathrm{M}}\text{\ensuremath{-}}\overline{\mathrm{K}}$ direction order of one hundredth of free electron mass. In Bi(111) films with equivalent surfaces, the surface states from top and bottom surfaces are not split. In such a symmetric film with arbitrary thickness, the bottom of the lowest quantum confinement subband in the conduction band coincides with the bottom of the bulk conduction band in the $\overline{\mathrm{M}}$ point.

Optical spectroscopic investigation of Ba3Tb(PO4)3 single crystals for visible laser applications

Optical spectroscopic characterization of Ba3Tb(PO4)3 single crystals grown by the Czochralski technique was performed in order to evaluate the potential for visible laser application. Powder X-ray diffraction patterns at different temperatures were recorded to calculate the thermal expansion for temperatures between 298 and 1073 K. Refractive indices in the visible spectral region were determined and fitted into a Sellmeier equation. Absorption spectra were measured in the UV and visible range to obtain the ground-state absorption cross-sections, which were used for a Judd-Ofelt analysis. Electrostatic and spin-orbit interaction parameters were fitted, allowing for more precise Judd-Ofelt calculations. The Judd-Ofelt intensity parameters were calculated and employed to study the radiative transition probabilities, branching ratios and radiative lifetime associated to the potential upper laser level 5D4. The fluorescence spectrum shows several lines in the visible range, which can be assigned to 5D4 → 7FJ (J=6,5,4,3,2,1,0) transitions of Tb3+. These data enabled the determination of the branching ratio of the transitions from the 5D4 excited state. The stimulated emission cross-section of the 5D4 → 7F5 transition was found to be 5.9 × 10−22 cm2 at a wavelength of 549.6 nm by using the Füchtbauer-Ladenburg equation. Fluorescence decay curves were recorded to obtain the fluorescence lifetime. The resulting value of 3.17 ms is in reasonable agreement with the theoretical value of 3.54 ms pointing towards a high radiative quantum efficiency of 90% despite a high doping ion density of 3.5 × 1021 cm−3 and revealing the low effect of detrimental inter-ionic processes in Tb3+.

Capsize of polarization in dilute photonic crystals

We investigate, experimentally and theoretically, polarization rotation effects in dilute photonic crystals with transverse permittivity inhomogeneity perpendicular to the traveling direction of waves. A capsize, namely a drastic change of polarization to the perpendicular direction is observed in a one-dimensional photonic crystal in the frequency range 10 ÷ 140 GHz. To gain more insights into the rotational mechanism, we have developed a theoretical model of dilute photonic crystal, based on Maxwell’s equations with a spatially dependent two dimensional inhomogeneous dielectric permittivity. We show that the polarization’s rotation can be explained by an optical splitting parameter appearing naturally in Maxwell’s equations for magnetic or electric fields components. This parameter is an optical analogous of Rashba like spin-orbit interaction parameter present in quantum waves, introduces a correction to the band structure of the two-dimensional Bloch states, creates the dynamical phase shift between the waves propagating in the orthogonal directions and finally leads to capsizing of the initial polarization. Excellent agreement between theory and experiment is found.

Fourier-transform spectroscopy of 13C17O and deperturbation analysis of the A1Π (υ=0–3) levels

The high-resolution B1Σ+→A1Π (0, 0) and (0, 3) emission bands of the less-abundant 13C17O isotopologue have been investigated by Fourier-transform spectroscopy in the visible region using a Bruker IFS 125HR spectrometer at an accuracy 0.003cm-1. These spectra are combined with high-resolution photoabsorption measurements of the 13C17O B1Σ+←X1Σ+ (0, 0), B1Σ+←X1Σ+ (1, 0) and C1Σ+←X1Σ+ (0, 0) bands recorded with an accuracy of 0.01cm-1 using the vacuum ultraviolet Fourier-transform spectrometer, installed on the DESIRS beamline at the SOLEIL synchrotron. In the studied 17,950–22,500cm-1 and 86,800–92,100cm-1 regions, 480 transitions have been measured. These new experimental data were combined with data from the C→A and B→A systems, previously analyzed in 13C17O. The frequencies of 1003 transitions derived from 12 bands were used to analyze the perturbations between the A1Π (υ=0–3) levels and rovibrational levels of the d3Δi, e3Σ-, a'3Σ+, I1Σ- and D1Δ states as well as to a preliminary investigation of weak irregularities that appear in the B1Σ+ (υ=0) level. Deperturbed molecular constants and term values of the A1Π state were obtained. The spin-orbit and L-uncoupling interaction parameters as well as isotopologue-independent spin-orbit and rotation-electronic perturbation parameters were derived.

Sizable band gap in organometallic topological insulator

Based on first principle calculation when Ceperley–Alder and Perdew–Burke–Ernzerh type exchange-correlation energy functional were adopted to LSDA and GGA calculation, electronic properties of organometallic honeycomb lattice as a two-dimensional topological insulator was calculated. In the presence of spin–orbit interaction bulk band gap of organometallic lattice with heavy metals such as Au, Hg, Pt and Tl atoms were investigated. Our results show that the organometallic topological insulator which is made of Mercury atom shows the wide bulk band gap of about ∼120meV. Moreover, by fitting the conduction and valence bands to the band-structure which are produced by Density Functional Theory, spin–orbit interaction parameters were extracted. Based on calculated parameters, gapless edge states within bulk insulating gap are indeed found for finite width strip of two-dimensional organometallic topological insulators.

Optical properties and spectroscopic study of different modifier based Pr3 +:LiFB glasses as optical amplifiers

In this paper, we report the preparation and optical characterization of Pr3+ doped lithium fluoro borate (LiFB) glasses for six different chemical compositions of Li2B4O7-BaF2-NaF-MO (where M=Mg, Ca, Cd and Pb), Li2B4O7-BaF2-NaF-MgO-CaO and Li2B4O7-BaF2-NaF-CdO-PbO. The structural and optical properties of these glasses were characterized by X-ray powder diffraction (XRD), scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), optical absorption and photoluminescence techniques. The optical absorption spectra of Pr3+ ions in LiFB glasses have been recorded in the UV–VIS-NIR region. The optical absorption data are used to calculate various spectroscopic parameters such as Racah (E1, E2, E3) and spin-orbit interaction (ξ4f) parameters. Judd-Ofelt (J-O) (Ωλ where λ=2, 4 and 6) intensity parameters were determined by applying J-O theory, which in turn used to calculate the radiative properties such as radiative transition probabilities (A), radiative lifetimes (τR), integrated absorption cross-sections (Σ) and branching ratios (βr) for all emission levels of Pr3+ ion in different LiFB glass matrices. By using the J-O theory and luminescence parameters, stimulated emission cross sections (σp) of prominent transitions, 3P0→3H4 and 1D2→3H4 of Pr3+ ion in all LiFB glasses were calculated. 3P0→3H4 possesses higher branching ratios and stimulated emission cross-sections for the Pr3+:LiFB(Mg-Ca) glass, which can be used as a best laser excitation. The optical gain parameter (σpxτR) was noticed higher in Pr3+:LiFB(Mg-Ca) and Pr3+:LiFB(Cd-Pb) glasses for the transition 3P0→3H4 transition, and these glasses have potential for optical amplification at 488 nm wavelength.

Gate-controlled switching between persistent and inverse persistent spin helix states

We demonstrate gate-controlled switching between persistent spin helix (PSH) state and inverse PSH state, which are detected by quantum interference effect on magneto-conductance. These special symmetric spin states showing weak localization effect give rise to a long spin coherence when the strength of Rashba spin-orbit interaction (SOI) is close to that of Dresselhaus SOI. Furthermore, in the middle of two persistent spin helix states, where the Rashba SOI can be negligible, the bulk Dresselhaus SOI parameter in a modulation doped InGaAs/InAlAs quantum well is determined.

Magnetization of interacting electrons in anisotropic quantum dots with Rashba spin–orbit interaction

Magnetization of anisotropic quantum dots in the presence of the Rashba spin–orbit interaction has been studied for three and four interacting electrons in the dot for non-zero values of the applied magnetic field. We observe unique behaviors of magnetization that are direct reflections of the anisotropy and the spin–orbit interaction parameters independently or concurrently. In particular, there are saw-tooth structures in the magnetic field dependence of the magnetization, as caused by the electron–electron interaction, that are strongly modified in the presence of large anisotropy and high strength of the spin–orbit interactions. We also report the temperature dependence of magnetization that indicates the temperature beyond which these structures due to the interactions disappear. Additionally, we found the emergence of a weak sawtooth structure in magnetization for three electrons in the high anisotropy and large spin–orbit interaction limit that was explained as a result of merging of two low-energy curves when the level spacings evolve with increasing values of the anisotropy and the spin–orbit interaction strength.

Note: Cold spectra of the electronic transition A(2)Σ(+)-X(2)Π of N2O(+) radical: High resolution analysis of the bands 000-100, 100-100, and 001-101.

In this note, three vibrational bands of the electronic transition A(2)Σ(+)-X(2)Π of the N2O(+) radical (000-100, 100-100, and 001-101) were theoretically analysed. Starting from Hamiltonian models proposed for this kind of molecule, their parameters were calculated using a Levenberg-Marquardt fit procedure in order to reduce the root mean square deviation from the experimental transitions below to 0.01 cm(-1). The main objective of this work is to obtain new and reliable values for rotational constant B″ and the spin-orbit interaction parameter A of the analysed vibrational levels of the X(2)Π electronic state of this molecule.

Theory of unconventional spin states in surfaces with non-Rashba spin-orbit interaction

Surface states in Tl/Si(111) and Bi/Si(111) show non-Rashba-type spin splitting. We study spin-transport properties in these surface states. First we construct tight-binding Hamiltonians for Tl/Si and Bi/Si surfaces, which respect crystallographic symmetries. As a result, we find specific terms in the Tl/Si surface Hamiltonian responsible for non-Rashba spin splitting. Using this model we calculate current-induced spin polarization in the Tl/Si Hamiltonian in order to see the effect of non-Rashba spin-orbit interaction. We found that the induced spin polarization is in-plane and perpendicular to the current, which is consequently the same with Rashba systems. We find that it follows from crystallographic symmetries. Furthermore, we numerically find bound states at the junction between two surface regions which have different signs of the spin-orbit interaction parameters in the Bi/Si system and in the Tl/Si system. We explain these numerical results with the results of our analytical calculations.

Real-time dynamics of spin-dependent transport through a double-quantum-dot Aharonov-Bohm interferometer with spin-orbit interaction

The spin-resolved nonequilibrium real-time electron transport through a double-quantum-dot (DQD) Aharonov-Bohm (AB) interferometer with spin-orbit interaction (SOI) is explored. The SOI and AB interference in the real-time dynamics of spin transport is expressed by effective magnetic fluxes. Analytical formulas for the time-dependent currents, for initially unpolarized spins, are presented. In many cases, there appear spin currents in the electrodes, for which the spins in each electrode are polarized along characteristic directions, predetermined by the SOI parameters and by the geometry of the system. Special choices of the system parameters yield steady-state currents in which the spins are fully polarized along these characteristic directions. The time required to reach this steady state depends on the couplings of the DQD to the leads. The magnitudes of the currents depend strongly on the SOI-induced effective fluxes. Without the magnetic flux, the spin-polarized current cannot be sustained to the steady states, due to the phase rigidity for this system. For a nondegenerate DQD, transient spin transport can be produced by the sole effects of SOI. We also show that one can extract the spin-resolved currents from measurements of the total charge current.