Spin-orbit Coupling Research Articles

Actinyl Electronic Structure Probed by XAS: The Role of Many-Body Effects.

A detailed analysis of the wave functions for the M5 to 5f excitations in the linear actinyls, UO22+, NpO22+, and PuO22+, and the theoretical X-ray absorption spectra obtained with these wave functions in comparison with experimental M5-edge high-resolution X-ray absorption near-edge structure (HR-XANES) spectra is presented. The wave functions include full treatment of scalar and spin-orbit relativistic effects through the use of a Dirac-Coulomb Hamiltonian; many-body effects are included in determining the wave functions. The character of the excited states and of the active spaces to describe the wave functions for these states are investigated and analyzed. It is shown that the excited states cannot, in general, be described with a single configuration but have an essential multiconfiguration character. The characterization of the properties of the excited states and the X-ray absorption spectra was achieved through the use of novel methods.

Cluster Odd-Parity Multipoles by Staggered Orbital Ordering in Locally Noncentrosymmetric Crystals

Odd-parity multipoles in crystals manifest themselves not only in their peculiar electronic orderings but also in unconventional parity-violating physical phenomena. We here report the emergence of odd-parity multipoles by considering staggered orbital orderings in a locally noncentrosymmetric crystal system with the global inversion center but without the inversion center at each lattice site. We show that various odd-parity multipoles, such as the electric toroidal monopole, electric dipole, and electric toroidal quadrupole, are realized depending on the type of orbital orderings in the one-dimensional zigzag chain. Such odd-parity multipoles give rise to an antisymmetric spin splitting in the electronic band structure with the aid of the relativistic spin–orbit coupling. We also show that similar states with odd-parity multipoles are realized in other locally noncentrosymmetric crystals, such as the two-dimensional honeycomb and three-dimensional diamond structures.

Competition between d-wave superconductivity and magnetism in uniaxially strained Sr2RuO4

The pairing symmetry of Sr2RuO4 is a long-standing fundamental question in the physics of superconducting materials with strong electronic correlations. We use the functional renormalization group to investigate the behavior of superconductivity under uniaxial strain in a two-dimensional realistic model of Sr2RuO4 obtained with density functional theory and incorporating the effect of spin-orbit coupling. We find a dominant dx2−y2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${d}_{{{{{\\rm{x}}}}}^{2}-{{{{\\rm{y}}}}}^{2}}$$\\end{document} superconductor mostly hosted by the dxy-orbital, with no other closely competing superconducting state. Within this framework, we reproduce the experimentally observed enhancement of the critical temperature under strain and propose a simple mechanism driven by the density of states to explain our findings. We also investigate the competition between superconductivity and spin-density wave ordering as a function of interaction strength. By comparing theory and experiment, we discuss constraints on a possible degenerate partner of the dx2−y2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${d}_{{{{{\\rm{x}}}}}^{2}-{{{{\\rm{y}}}}}^{2}}$$\\end{document} superconducting state.

Strain-tuned electronic and valley-related properties in Janus monolayers of SWSiX2 (X = N, P, As)

Abstract Exploring novel two-dimensional (2D) valleytronic materials has an essential impact on the design of spintronic and valleytronic devices. Our first principles calculation results reveal that the Janus SWSiX2 (X = N, P, As) monolayer has excellent dynamical and thermal stability. Owing to strong spin-orbit coupling (SOC), the SWSiX2 monolayer exhibits a valence band spin splitting of up to 0.49 eV, making it promising 2D semiconductor for valleytronic applications. The opposite Berry curvatures and optical selection rules lead to the coexistence of valley and spin Hall effects in the SWSiX2 monolayer. Moreover, the optical transition energies can be remarkably modulated by the in-plane strains. Large tensile (compressive) inplane strains can achieve spin flipping in the SWSiN2 monolayer, and induce both SWSiP2 and SWSiAs2 monolayers transit from semiconductor to metal. Our research provides new 2D semiconductor candidates for designing high-performance valleytronic devices.

Iodine Clusters in the Atmosphere I: Computational Benchmark and Dimer Formation of Oxyacids and Oxides.

The contribution of iodine-containing compounds to atmospheric new particle formation is still not fully understood, but iodic acid and iodous acid are thought to be significant contributors. While several quantum chemical studies have been carried out on clusters containing iodine, there is no comprehensive benchmark study quantifying the accuracy of the applied methods. Here, we present the first study in a series that investigate the role of iodine species in atmospheric cluster formation. In this work, we have studied the iodic acid, iodous acid, iodine tetroxide, and iodine pentoxide monomers and their dimers formed with common atmospheric precursors. We have tested the accuracy of commonly applied methods for calculating the geometry of the monomers, thermal corrections of monomers and dimers, the contribution of spin-orbit coupling to monomers and dimers, and finally, the accuracy of the electronic energy correction calculated at different levels of theory. We find that optimizing the structures either at the ωB97X-D3BJ/aug-cc-pVTZ-PP or the M06-2X/aug-cc-pVTZ-PP level achieves the best thermal contribution to the binding free energy. The electronic energy correction can then be calculated at the ZORA-DLPNO-CCSD(T0) level with the SARC-ZORA-TZVPP basis for iodine and ma-ZORA-def2-TZVPP for non-iodine atoms. We applied this methodology to calculate the binding free energies of iodine-containing dimer clusters, where we confirm the qualitative trends observed in previous studies. However, we identify that previous studies overestimate the stability of the clusters by several kcal/mol due to the neglect of relativistic effects. This means that their contributions to the currently studied nucleation pathways of new particle formation are likely overestimated.

Rashba splitting in polar-nonpolar sandwich heterostructure: a DFT study

In this study, we employ density functional theory based first-principles calculations to investigate the spin-orbit effects in the electronic structure of a polar-nonpolar sandwich heterostructure namely LaAlO3 / SrTiO3 / LaAlO3 . Our focus on the Ti-3d bands reveals an inverted ordering of the SrTiO3 - t2g orbital near the n-type interface, which is consistent with earlier experimental work. In contrast, toward the p-type interface, the orbital ordering aligns with the natural ordering of SrTiO3 orbitals, influenced by crystal field splitting. In the presence of SOC, a notable inter-orbital coupling between t2g and eg orbitals is observed within the tetragonal slab, a phenomenon not reported before in the SrTiO3 -based 2D systems. Additionally, our observations highlight that the cubic Rashba splitting in this system surpasses the linear Rashba splitting, contrary to experimental findings. This comprehensive analysis contributes to a refined understanding of the role of orbital mixing in Rashba splitting in the sandwich oxide heterostructures.

Josephson diode effect in a ballistic single-channel nanowire

When time-reversal and inversion symmetry are broken, superconducting circuits may exhibit a so-called diode effect, where the critical currents for opposite directions of the current flow differ. In recent years, this effect has been observed in a multitude of systems, and the different physical ingredients that may yield such an effect are well understood. On a microscopic level, the interplay between spin–orbit coupling and a Zeeman field may give rise to a diode effect in a single Josephson junction. However, so far, there is no analytical description of the effect within a simple model. Here, we study a single-channel nanowire with Rashba spin–orbit coupling and in the presence of a Zeeman field. We show that the different Fermi velocities and spin projections of the two pseudo-spin bands lead to a diode effect. Simple analytical expressions for the diode efficiency can be obtained in limiting cases.

Search for an antiferromagnetic Weyl semimetal in (MnTe) m (Sb2Te3) n and (MnTe) m (Bi2Te3) n superlattices

The interaction between topology and magnetism can lead to novel topological materials including Chern insulators, axion insulators, and Dirac and Weyl semimetals. In this work, a family of van der Waals layered materials using MnTe and Sb2Te3 or Bi2Te3 superlattices as building blocks are systematically examined in a search for antiferromagnetic Weyl semimetals, preferably with a simple node structure. The approach is based on controlling the strength of the exchange interaction as a function of layer composition to induce the phase transition between the topological and the normal insulators. Our calculations, utilizing a combination of first-principles density functional theory and tight-binding analyses based on maximally localized Wannier functions, clearly indicate a promising candidate for a type-I magnetic Weyl semimetal. This centrosymmetric material, Mn10Sb8Te22 (or (MnTe) m (Sb2Te3) n with m = 10 and n = 4), shows ferromagnetic intralayer and antiferromagnetic interlayer interactions in the antiferromagnetic ground state. The obtained electronic bandstructure also exhibits a single pair of Weyl points in the spin-split bands consistent with a Weyl semimetal. The presence of Weyl nodes is further verified with Berry curvature, Wannier charge center, and surface state (i.e. Fermi arc) calculations. Other combinations of the MnSbTe-family materials are found to be antiferromagnetic topological or normal insulators on either side of the Mn:Sb ratio, respectively, illustrating the topological phase transition as anticipated. A similar investigation in the homologous (MnTe) m (Bi2Te3) n system produces mostly nontrivial antiferromagnetic insulators due to the strong spin–orbit coupling. When realized, the antiferromagnetic Weyl semimetals in the simplest form (i.e. a single pair of Weyl nodes) are expected to provide a promising candidate for low-power spintronic applications.

Coherent spin qubit shuttling through germanium quantum dots

Quantum links can interconnect qubit registers and are therefore essential in networked quantum computing. Semiconductor quantum dot qubits have seen significant progress in the high-fidelity operation of small qubit registers but establishing a compelling quantum link remains a challenge. Here, we show that a spin qubit can be shuttled through multiple quantum dots while preserving its quantum information. Remarkably, we achieve these results using hole spin qubits in germanium, despite the presence of strong spin-orbit interaction. In a minimal quantum dot chain, we accomplish the shuttling of spin basis states over effective lengths beyond 300 microns and demonstrate the coherent shuttling of superposition states over effective lengths corresponding to 9 microns, which we can extend to 49 microns by incorporating dynamical decoupling. These findings indicate qubit shuttling as an effective approach to route qubits within registers and to establish quantum links between registers.

Spin-dependent shot noise in 8-Pmmn borophene based-superlattice

The effect of the Rashba spin-orbit interaction on the shot noise, spin/valley polarization in 8-Pmmn borophene-based superlattice are studied theoretically, by applying the transfer-matrix approach. The spin-dependent transmission probability can be easily controlled by the number of superlattice barriers, the strength of the Rashba, and the incident electron angle. The Fano factor without spin rotation as well as with spin rotation shows an oscillatory pattern versus the strength of the Rashba, and the oscillatory behavior becomes more pronounced as the number of barriers increases. Also, the Fano factor shows a strong dependence on the superlattice direction and number of barriers. The spin and valley polarizations can be easily controlled by the number of barriers and the direction of superlattice. Our findings in this work could provide useful for valleytronics/spintronics systems based on the 8-Pmmn borophene.

Half-metallic ferromagneticWeyl fermions related to dynamic correlations in the zinc-blende compound VAs

Abstract The realization of 100% polarized topological Weyl fermions in halfmetallic ferromagnets is of particular importance for fundamental research and spintronic applications. Here, we theoretically investigate the electronic and topological properties of the zinc-blende compound VAs, which was deemed as a halfmetallic ferromagnet related to dynamic correlations. Based on the combination of density functional theory and dynamical mean field theory, we uncover that the halfmetallic ferromagnet VAs exhibit attractive Weyl semimetallic behaviors which are very close to the Fermi level in the DFT + U regime with effect U values ranging from 1.5 eV to 2.5 eV. Meanwhile, we also investigate the magnetization-dependent topological properties; the results show that the change of magnetization directions only slightly affects the positions of Weyl points, which is attributed to the weak spin-orbital coupling effects. The topological surface states of VAs projected on semiinfinite (001) and (111) surfaces are investigated. The Fermi arcs of all Weyl points are clearly visible on the projected Fermi surfaces. Our findings suggest that VAs is a fully spin-polarized Weyl semimetal with many-body correlated effects in the effective U values range from 1.5 to 2.5 eV.

Zero‐Dimensional Interstitial Electron‐Induced Spin–Orbit Coupling Dirac States in Sandwich Electride

Zero‐Dimensional Interstitial Electron‐Induced Spin–Orbit Coupling Dirac States in Sandwich Electride

Sb-loaded MnOx/TiO2/CNTs catalysts for selective catalytic reduction of NOx: insight to the SO2 and H2O tolerance

PurposeThis paper aims to synthesize and test Mn-Sb/TiO2-CNT catalysts with different Sb/Mn molar ratios to be used in NH3-SCR reaction.Design/methodology/approachA series of Sb-loaded carbon nanotubes (CNTs)-based Mn/TiO2 catalysts were prepared by the incipient wetness co-impregnation method and tested for the selective catalytic reduction (SCR) of NOx with NH3.FindingsThe Sb-loaded Mn/TiO2-CNTs catalyst outperformed other catalysts and presented the highest activity in the temperature regime of 100–400°C. The catalyst loaded with Sb also showed good SO2 and H2O resistance and exhibited better thermal stability. A stepwise study of SO2 addition evidenced that Mn-Sb/TiO2-CNTs catalyst exhibited better SO2 resistance than the base catalyst Mn/TiO2, where the Sb doping greatly inhibited the sulphating of active phase of the catalyst.Originality/valueIn Sb-loaded catalysts, the formed SOx species fused with SbOx instead of MnOx. This favoured interaction of SO2 with SbOx successfully prevents the MnOx from being sulphated by SO2 which substantially improves the SO2 tolerance of Sb-loaded catalysts.

Automated workflow for analyzing thermodynamic stability in polymorphic perovskite alloys

In this first-principles investigation, we explore the polymorphic features of pseudo-cubic alloys, focusing on the impact of mixing organic and inorganic cations on their structural and electronic properties, configurational disorder, and thermodynamic stability. Employing an automated cluster expansion within the generalized quasichemical approximation (GQCA), our results reveal how the effective radius of the organic cation (rMA = 2.15 Å, rFA = 2.53 Å) and its dipole moment (μMA = 2.15 D, μFA = 0.25 D), influences Glazer’s rotations in the A1−xCsxPbI3 (A = MA, FA) sublattice, with MA-based alloy presenting a higher critical temperature (527 K) and being stable for x > 0.60 above 200 K, while its FA analog has a lower critical temperature (427.7 K) and is stable for x < 0.15 above 100 K. Additionally, polymorphic motifs magnify relativistic effects, impacting the thermodynamic behavior of the systems. Our methodology leverages the SimStack framework, an automated scientific workflow that enables the nuanced modeling of polymorphic alloys. This structured approach allows for comprehensive calculations of thermodynamic properties, phase diagrams, optoelectronic insights, and power conversion efficiencies while meticulously incorporating crucial relativistic effects like spin-orbit coupling (SOC) and quasi-particle corrections. Our findings advocate for the rational design of thermodynamically stable compositions in solar cell applications by calculating power conversion efficiencies using a spectroscopic limited maximum efficiency model, from which we obtained high efficiencies of about 28% (31–32%) for MA1−xCsxPbI3 with 0.50 < x < 1.00 (FA1−xCsxPbI3 with 0.0 < x < 0.20) as thermodynamically stable compositions at room temperature. The workflow’s significance is highlighted by a Colab-based notebook, which facilitates the analysis of raw data output, allowing users to delve into the physics of these complex systems. Our work underscores the pivotal role of composition and polymorphic degrees in determining the stability and optoelectronic properties of MHP alloys. It demonstrates the effectiveness of the SimStack workflow in advancing our understanding of these materials.

Optical properties of meso-tetra(sulphonatophenyl) porphyrins (TPPS 4) and their Fe 3+, Mn 3+, Zn 2+ complexes with different pH values studied using by picosecond pulse trains

Applying picosecond pulse trains propagating in meso-tetra(sulphonatophenyl) porphyrins and their Fe 3+, Mn 3+, Zn 2+ complexes, we studied the nonlinear dynamics at different pH values. The pulse train at wavelength 532nm is comprised of 20 subpulses with 70ps width and 13ns spacing. We simplified the energy structures of porphyrins and metalloporphyrins to five-level models. In solving coupled rate equations and two-dimensional paraxial field, we used Crank-Nicholson numerical method to do the calculations. The results revealed that in irregular metalloporphyrins with central paramagnetic ion Mn 3+ or Fe 3+, the central ion would act as electron acceptor, which leads to charge transfer of unpaired metal electron to the porphyrin ring π conjugated system, and strengthen the spin–orbit coupling of electronic systems and weaken the transition prohibition between electronic states in porphyrins. However regular metalloporphyrins with central diamagnetic ion Zn 2+ has similar optical properties to free base porphyrins, and Zn 2+ TPPS 4 has much longer excited state lifetimes and slower intersystem crossing. In solutions, hydrogen bond would be formed to porphyrin, which can change the transitions of π electrons and thus the charge transfer can be strengthened in the porphyrin ring. In weak intensity region with linear absorption, nonprotonated porphyrins with high pH value show better optical limiting (OL) effect. Conversely in high intensity region, protonated porphyrins with low pH value show better OL effect. Besides, increasing interaction distances of porphyrins and metalloporphyrins with laser pulses is another important factor to raise the OL effects.

Phonon-mediated spin transport in quantum paraelectric metals

The concept of ferroelectricity is now often extended to include continuous inversion symmetry-breaking transitions in various metals and doped semiconductors. Paraelectric metals near ferroelectric quantum criticality, which we term ‘quantum paraelectric metals,’ possess soft transverse optical phonons which can have Rashba-type coupling to itinerant electrons in the presence of spin-orbit coupling. We find through the Kubo formula calculation that such Rashba electron-phonon coupling has a profound impact on electron spin transport. While the spin Hall effect arising from non-trivial electronic band structures has been studied extensively, we find here the presence of the Rashba electron-phonon coupling can give rise to spin current, including spin Hall current, in response to an inhomogeneous electric field even with a completely trivial band structure. Furthermore, this spin conductivity displays unconventional characteristics, such as quadrupolar symmetry associated with the wave vector of the electric field and a thermal activation behavior characterized by scaling laws dependent on the phonon frequency to temperature ratio. These findings shed light on exotic electronic transport phenomena originating from ferroelectric quantum criticality, highlighting the intricate interplay of charge and spin degrees of freedom.

Spin–Orbit Coupling Free Nonlinear Spin Hall Effect in a Triangle-Unit Collinear Antiferromagnet with Magnetic Toroidal Dipole

We investigate emergent conductive phenomena triggered by collinear antiferromagnetic orderings. We show that an up-down-zero spin configuration in a triangle cluster leads to linear and nonlinear spin conductivities even without the relativistic spin–orbit coupling; the linear spin conductivity is Drude-type, while the nonlinear spin conductivity has Hall-type characterization. We demonstrate the emergence of both spin conductivities in a breathing kagome system consisting of a triangle cluster. The nonlinear spin conductivity becomes larger than the linear one when the Fermi level lies near the region where a small partial band gap opens. Our results indicate that collinear antiferromagnets with triangular geometry give rise to rich spin conductive phenomena.

A DFT insight of the electronic, thermodynamic, and thermoelectric properties of RuO2

In this study, we explore the structural, electronic, thermodynamic, and thermoelectric properties of RuO2 using density functional theory. The derived equilibrium structural parameters agree with other theoretical and experimental results. The widely used modified Becke–Johnson (mBJ-GGA) potential is adopted for accurate electronic band gap estimation. To incorporate the effect of the extended orbital of the Ru atom, spin-orbit coupling has been used in combination with the mBJ potential. The investigation of electronic properties revealed an indirect semi-conducting nature with a band gap along the W-L symmetry. The calculated band gaps are 1.685 and 1.658 eV from mBJ and mBJ + SOC, respectively. The dynamical stability is tested and verified by calculating the phonon dispersion curve. We have employed the quasiharmonic approximation-based Gibbs2 package to determine the pressure and temperature-dependent thermodynamical parameters, such as cell volume, Debye temperature, heat capacity, entropy, and thermal expansion coefficient. This study uses the BoltzTraP simulation algorithm to determine the thermoelectric parameters such as the Seebeck coefficient, electrical conductivity, and thermal conductivity.

Toward Accurate Spin-Orbit Splittings from Relativistic Multireference Electronic Structure Theory.

Most nonrelativistic electron correlation methods can be adapted to account for relativistic effects, as long as the relativistic molecular spinor integrals are available, from either a four-, two-, or one-component mean-field calculation. However, relativistic multireference correlation methods remain a relatively unexplored area, with mixed evidence regarding the improvements brought by perturbative treatments. We report, for the first time, the implementation of state-averaged four-component relativistic multireference perturbation theories to second and third order based on the driven similarity renormalization group (DSRG). With our methods, named 4c-SA-DSRG-MRPT2 and 3, we find that the dynamical correlation included on top of 4c-CASSCF references can significantly improve the spin-orbit splittings in p-block elements and potential energy surfaces when compared to 4c-CASSCF and 4c-CASPT2 results. We further show that 4c-DSRG-MRPT2 and 3 are applicable to these systems over a wide range of the flow parameter, with systematic improvement from second to third order in terms of both improved error statistics and reduced sensitivity with respect to the flow parameter.

Three-Carrier Spin Blockade and Coupling in Bilayer Graphene Double Quantum Dots.

The spin degrees of freedom is crucial for the understanding of any condensed matter system. Knowledge of spin-mixing mechanisms is not only essential for successful control and manipulation of spin qubits, but also uncovers fundamental properties of investigated devices and material. For electrostatically defined bilayer graphene quantum dots, in which recent studies report spin-relaxation times T_{1} up to 50ms with strong magnetic field dependence, we study spin-blockade phenomena at charge configuration (1,2)↔(0,3). We examine the dependence of the spin-blockade leakage current on interdot tunnel coupling and on the magnitude and orientation of externally applied magnetic field. In out-of-plane magnetic field, the observed zero-field current peak could arise from finite-temperature cotunneling with the leads; though involvement of additional spin- and valley-mixing mechanisms are necessary for explaining the persistent sharp side peaks observed. In in-plane magnetic field, we observe a zero-field current dip, attributed to the competition between the spin Zeeman effect and the Kane-Mele spin-orbit interaction. Details of the line shape of this current dip, however, suggest additional underlying mechanisms are at play.