Orbital Effects Research Articles

Systematic Analysis Method for Nonlinear Response Tensors

We propose a systematic analysis method for identifying essential parameters in various linear and nonlinear response tensors without which they vanish. By using the Keldysh formalism and the Chebyshev polynomial expansion method, the response tensors are decomposed into the model-independent and dependent parts, in which the latter is utilized to extract the essential parameters. An application of the method is demonstrated by analyzing the nonlinear Hall effect in the ferroelectric SnTe monolayer for example. It is shown that in this example the second-neighbor hopping is essential for the nonlinear Hall effect whereas the spin–orbit coupling is unnecessary. Moreover, by analyzing terms contributing to the essential parameters in the lowest order, the appearance of the nonlinear Hall effect can be interpreted by the subsequent two processes: the orbital magneto-current effect and the linear anomalous Hall effect by the induced orbital magnetization. In this way, the present method provides a microscopic picture of responses. By combining with computational analysis, it stimulates further discoveries of anomalous responses by filling in a missing link among hidden degrees of freedom in a wide variety of materials.

On Evaluating the Imaging Performance and Orbital Determination Under Perturbations of Orbital Inclination and RAAN in the Lunar-Based SAR

The imaging performance of the lunar-based SAR (LBSAR) is susceptible to the orbital perturbation effects. In particular, the perturbations of orbital inclination and right ascension of ascending node (RAAN) could give rise to the temporally varying orbit drift of LBSAR and further lead to Doppler errors in the radio signal. As a result, the LBSAR image performance might be influenced by such effects. This study comprehensively probes into the phase error induced by perturbations of orbital inclination and RAAN, and its effects on the LBSAR imaging performance are further explored. It is found the LBSAR imaging performance in terms of focusing quality and geometric fidelity are affected by the perturbations of orbital inclination and RAAN, wherein the deterioration of focusing quality is closely associated with the synthetic aperture time. In this regard, the azimuth resolution on a decameter level is optimum for Earth observation of LBSAR with satisfactory image quality. Regarding the geometric fidelity, the accuracy requirement for the orbit determination of the LBSAR under perturbations of the orbital inclination and RAAN is proposed. The analysis results show that the LBSAR orbit determination in terms of the position and velocity determinations are most strenuous in the z-direction. Finally, point target responses are simulated to illustrate the preceding analysis.

Investigation of the Timing and Spectral Properties of an Ultraluminous X-Ray Pulsar NGC 7793 P13

Abstract We perform both timing and spectral analyses using the archival X-ray data taken with Swift, XMM-Newton, NICER, and NuSTAR from 2016 to 2020 to study an ultraluminous pulsar, NGC 7793 P13, that showed a long period of super-Eddington accretion. We use the Rayleigh test to investigate the pulsation at different epochs, and confirm the variation of the pulse profile with finite Gaussian mixture modeling and a two-sample Kuiper test. Taking into account the periodic variation of the spin periods caused by the orbital Doppler effect, we further determine an orbital period of ∼65 days and show that no significant correlation can be detected between the orbital phase and the pulsed fraction. The pulsed spectrum of NGC 7793 P13 in the 0.5–20 keV range can be simply described using a power law with a high-energy exponential cutoff, while the broadband phase-averaged spectrum of the same energy range requires two additional components to account for the contribution of a thermal accretion disk and the Comptonization photons scattered into the hard X-rays. We find that NGC 7793 P13 stayed in the hard ultraluminous state and the pulsed spectrum was relatively soft when the source was faint at the end of 2019. Moreover, an absorption feature close to 1.3 keV is marginally detected from the pulsed spectra and it is possibly associated with a cyclotron resonant scattering feature.

Enhancing magnetic coupling through protonation of benzylideneaniline-bridged diradicals and comparison with stilbene- and azobenzene-based diradicals.

Taking nitroxide radicals as spin sources, we explore the intramolecular magnetic coupling interactions of the trans- and cis-forms of benzylideneaniline (BA)-bridged diradicals, in which the central -CH[double bond, length as m-dash]N- unit can undergo single protonation to convert to its protonated counterpart or vice versa. The calculated results for these two pairs of diradicals (protonated versus unprotonated trans and cis forms) verify that the signs of their magnetic coupling constants J do not change, but the magnitudes significantly increase after protonation. In the structure, the better conjugation of the protonated trans diradical and two reduced CCNC and CCCN torsion angles of the protonated cis one make for a more efficient spin transport, promoting the spin polarization, thus leading to larger spin couplings. In terms of mechanism, the proton-induced magnetic enhancement should be attributed to strong participation of the coupler BA through its lowest unoccupied molecular orbital (LUMO) with a lower energy level after protonation, and the small HOMO-LUMO (HOMO: highest occupied molecular orbital) gap of the coupler BA through protonation is crucial in explaining such remarkable spin-coupling enhancement. Furthermore, different linking modes of the radical groups to the couplers are also considered to confirm our conclusions. In addition, we also make a comparison of the magnetic coupling strengths among their isoelectronic analogues of BA-, AB- and stilbene-bridged nitroxide diradicals before or after protonation, and find a linear correlation among them. It should be noted that the magnetic behaviors of all these diradicals obey the spin alternation rule and singly occupied molecular orbital (SOMO) effect. This work provides helpful information for the rational design of promising magnetic molecular switches.

A theoretical electronic structure with a feasibility study of laser cooling of LaNa molecules with a spin orbit effect.

The electronic structure with the spin orbit effect of the molecule LaNa has been studied in the present work using the Multi-Reference Configuration Interaction MRCI calculations including Davidson correction (+Q). Adiabatic potential energy curves (PECs) have been investigated for the lowest low-lying spin free states in the Λ representation and spin orbit states of Ω = 0+/-, 1, 2, 3, and 4 along with their spectroscopic constants Re, Te, ωe, and Be, the dissociation energy De, the dipole moment μe, and the ionic character fionic of the LaNa molecule at the equilibrium bond length. The permanent dipole moment curves (PDMCs) for the investigated states are calculated in addition to the electronic transition dipole moments between the lowest electronic states where the Franck-Condon factor (FCF) has been calculated for the X1Σ+-11Π and for many spin orbit transitions. For these transitions the dipole moments are used in order to determine the Einstein coefficient of spontaneous emission Aν'ν, the radiative lifetime τ and the branching ratio Rν'ν. Employing the canonical function approach, the rovibrational parameters Eν, Bν, Dν, Rmin and Rmax have also been calculated for the lowest vibrational levels of different bound states in both Λ and Ω representations. To the best of our knowledge, the data reported in the present work are presented for the first time in the literature with a discussion on the candidacy of this molecule for laser cooling.

The first-principles investigation of structural and electronic properties of B3-HgSe amalgam

The present study integrates the theoretical investigation of structural and electronic behavior of B3-HgSe amalgam as one of the mercury chalcogenides prototypes. The ground state parameters evaluated by Murnaghan equation of states are in good agreement with experimental as well as previously reported results. The electronic band structure of B3-HgSe amalgam exhibits zero band gap at Γ-point with Dirac cone configuration. In addition, the spin orbital effect on electronic band structure is incorporated which reveals B3-HgSe amalgam as a potential candidate for the tuning band gap applications of spintronics. The density of states and charge density reveal the hybridization of “s”, “p” and “d” orbitals with the dominance characteristics of Hg-d orbital.

Effects of pebble accretion on the growth and composition of planetesimals in the inner Solar system

ABSTRACT Recent work has shown that aside from the classical view of collisions by increasingly massive planetesimals, the accretion of mm to m-sized ‘pebbles’ can also reproduce the mass–orbit distribution of the terrestrial planets. Here, we perform N-body simulations to study the effects of pebble accretion on to growing planetesimals of different diameters located in the inner Solar system. The simulations are run to occur during the lifetime of the gas disc while also simultaneously taking Jupiter’s growth into account. We find that pebble accretion can increase the mass in the solid disc by at least a few times its initial mass with reasonable assumptions that pebbles fragment to smaller sized grains at the snow line and that gas-disc-induced orbital migration effects are in force. Such a large contribution in mass by pebbles would seem to imply that the isotopic composition of the inner Solar system should be similar to the pebble source (i.e. outer Solar system). This implication appears to violate the observed nucleosynthetic isotopic dichotomy of the sampled Solar system. Thus, pebble accretion played little or no role in terrestrial planet formation.

Magnetic response of metallic nanoparticles: Geometric and weakly relativistic effects

While the large paramagnetic response measured in certain ensembles of metallic nanoparticles has been assigned to orbital effects of conduction electrons, the spin-orbit coupling has been pointed out as a possible origin of the anomalously large diamagnetic response observed in other cases. Such a relativistic effect, arising from the inhomogeneous electrostatic potential seen by the conduction electrons, might originate from the host ionic lattice, impurities, or the self-consistent confining potential. Here we theoretically investigate the effect of the spin-orbit coupling arising from the confining potential, quantifying its contribution to the zero-field magnetic susceptibility and gauging it against the ones generated by other weakly-relativistic corrections. Two ideal geometries are considered in detail, the sphere and the half-sphere, focusing on the expected increased role of the spin-orbit coupling upon a symmetry reduction, and the application of these results to actual metallic nanoparticles is discussed. The matrix elements of the different weakly-relativistic corrections are obtained and incorporated in a perturbative treatment of the magnetic field, leading to tractable semi-analytical and semiclassical expressions for the case of the sphere, while a numerical treatment becomes necessary for the half-sphere. The correction to the zero-field susceptibility arising from the spin-orbit coupling in a single sphere is quite small, and it is dominated by the weakly-relativistic kinetic energy correction, which in turn remains considerably smaller than the typical values of the nonrelativistic zero-field susceptibility. Moreover, the spin-orbit contribution to the average response for ensembles of nanoparticles with a large size dispersion is shown to vanish. The symmetry reduction in going from the single sphere to the half-sphere does not translate into a significant (...)

Exploring failure mode and enhancement mechanism of doped rare-earth elements iron-based/alumina-ceramic interface

This work implements a first-principles calculations method to explore the effects of rare-earth element dopants on the properties of the α-Al2O3 (0001)/γ-Fe (111) interface. The results show that the work of adhesion (Wad) of the doped-x (x=Ce, Y, Sc, La, Er, Yb, Gb, and Nd) Fe/Al2O3 interface is obviously greater than that of the non-doped interface, especially the doped-Y interface with the maximum binding strength, is selected as the model of tensile test. In contrast to the non-doped Fe/Al2O3 interface, the critical strain and tensile stress of the doped-Y interface increased from 0.5% to 8% and 6.88 to 13.55 GPa, respectively, indicating the introduction of rare-earth Y changed the failure mode of the Fe/Al2O3 interface from brittle to toughness fracture, significantly improving the mechanical performance of the Fe/Al2O3 interface. Further, electronic structure revealed that electron at local location being exhausted early induced by stretching is the signal of the structural failure. Furthermore, it is also found that the doped-Y atom segregate towards the middle of the Fe/Al2O3 interface, resulting in the Y-(p, d) orbits hybridized with O-s orbit in the range from −23.58 to −19.83 eV and Y-(s, p and d) orbits hybridized with Fe-s orbit in the range from −7.52 to −3.51 eV. As a result, the segregation behavior of the doped-Y atom appears to act as an adhesive at the Fe/Al2O3 interface, and then the electron orbital hybridization effect produced among atoms is enhancement mechanism of interface.

In-plane magnetic field-driven symmetry breaking in topological insulator-based three-terminal junctions

Topological surface states of three-dimensional topological insulator nanoribbons and their distinct magnetoconductance properties are promising for topoelectronic applications and topological quantum computation. A crucial building block for nanoribbon-based circuits are three-terminal junctions. While the transport of topological surface states on a planar boundary is not directly affected by an in-plane magnetic field, the orbital effect cannot be neglected when the surface states are confined to the boundary of a nanoribbon geometry. Here, we report on the magnetotransport properties of such three-terminal junctions. We observe a dependence of the current on the in-plane magnetic field, with a distinct steering pattern of the surface state current towards a preferred output terminal for different magnetic field orientations. We demonstrate that this steering effect originates from the orbital effect, trapping the phase-coherent surface states in the different legs of the junction on opposite sides of the nanoribbon and breaking the left-right symmetry of the transmission across the junction. The reported magnetotransport properties demonstrate that an in-plane magnetic field is not only relevant but also very useful for the characterization and manipulation of transport in three-dimensional topological insulator nanoribbon-based junctions and circuits, acting as a topoelectric current switch.

Electronic Structure of Pyrochlore Iridate Pr2Ir2O7: Interplay Between Spin-Orbit Coupling and Hubbard Potential

We have investigated the electronic structure of pyrochlore iridate Pr2Ir2O7 compound with Fd-3m space group using first-principle density functional theory calculations. [Formula: see text] calculations show that the PrAFM–IrNM state in Pr2Ir2O7 compound is energetically more favorable than the other phases. Combining of the interaction of electronic correlation (U) and spin-orbit coupling (SO) leads to three different phases for this material. (1) An anti-ferromagnetic metal is found by the [Formula: see text] ([Formula: see text][Formula: see text]eV) approximation without taking into account the spin orbit interaction. (2) A metal-semimetal transition appears, when the spin-orbit coupling is applied. (3) A semi-conductor characteristic with a narrow gap increases slightly by varying the Hubbard potential of nonmagnetic Ir atoms from 0.5[Formula: see text]eV to 1.5[Formula: see text]eV. The effect of the spin orbit (SO) coupling and the interaction (U) clearly influences the Fermi region of the calculated band structures and densities of states of this system. The hydrostatic pressure effect on the energy gap has shown a further advantage in predicting the desired gap value for this kind of materials. The optical properties, including the dielectric function, refractive index, reflectivity and real part of optical conductivity, are calculated for radiation up to 8[Formula: see text]eV. Overall, however, for both [Formula: see text] values of Pr2Ir2O7, the compound shows similar optical characteristics.

Design of optimal low-thrust manoeuvres for remote sensing multi-satellite formation flying in low Earth orbit

This paper presents a strategy for optimal manoeuvre design of multi-satellite formation flying in low Earth orbit environment, with the aim of providing a tool for mission operation design. The proposed methodology for formation flying manoeuvres foresees a continuous low-thrust control profile, to enable the operational phases. The design is performed starting from the dynamic representation described in the relative orbital elements, including the main orbital perturbations effects. It also exploits an interface with the classical radial-transversal-normal description to include the maximum delta-v limitation and the safety condition requirements. The methodology is applied to a remote sensing mission study, Formation Flying L-band Aperture Synthesis, for land and ocean application, such as a potential high-resolution Soil Moisture and Ocean Salinity (SMOS) follow-on mission, as part of a European Space Agency mission concept study. Moreover, the results are applicable to a wide range of low Earth orbit missions, exploiting a distributed system, and in particular to Formation Flying L-band Aperture Synthesis (FFLAS) as a follow-on concept to SMOS.

New photometric studies for two deep, low-mass ratio overcontact binaries: Y Sex and V1363 Ori

We present new photometry for two contact binaries, Y Sex and V1363 Ori, which were observed by three small telescopes in China. By using the W-D method, the absolute parameters are updated from new BVR light curves and previous radial velocity curves. Results identify that two binaries are deep, low-mass ratio (DLMR) overcontact binaries with q ⩽ 0.25 and f ⩾ 50%. From the temperature-luminosity diagram, the primary components are slightly evolved main-sequence stars, whose evolutionary ages are ∼2.51 Gyr for Y Sex and ∼3.56 Gyr for V 1363 Ori, respectively. From the (O − C) curves, it is found that the orbital periods may be undergoing secular increase with cyclic variations, which may be interpreted either by magnetic activity cycles or by the light-time orbit effect. With period increasing, this kind of DLMR overcontact binaries, such as Y Sex and V1363 Ori, will evolve into the rapid-rotating single stars.

Functionalized tellurene; a candidate large-gap 2D topological insulator

The discovery of group IV and V elemental xene’s with topologically non-trivial characters in their honeycomb lattice structure (HLS) has led to extensive efforts in realising analogous behaviour in group VI elemental monolayers. Theoretically; it was concluded that, group VI elemental monolayers cannot exist in HLS. However, some recent experimental evidence suggests that group VI elemental monolayers can be realised in HLS. In this letter, we report HLS of group VI elemental monolayer (such as, tellurene) can be realised to be dynamically stable when functionzalised with oxygen. The functionalization leads to, peculiar orbital filtering effects and broken spatial inversion symmetry which gives rise to the non-trivial topological character. The exotic quantum behaviour of this system is characterized by, spin–orbit coupling induced large-gap (≈0.36 eV) with isolated Dirac cone along the edges indicating potential room temperature spin-transport applications. Further investigations of spin Hall conductivity and the Berry curvatures unravel high conductivity as compared to previously explored xene’s alongside the potential valley Hall effects. The non-trivial topological character is quantified in terms of the invariant as ν = 1 and Chern number C = 1. Also, for practical purposes, we report that, hBN/TeO/hBN quantum-wells can be strain engineered to realize a sizeable non-trivial gap (≈0.11 eV). We finally conclude that, functionalization of group VI elemental monolayer with oxygen gives rise to, exotic quantum properties which are robust against surface oxidation and degradations while providing viable electronic degrees of freedom for spintronic/valleytronic applications.

Substituent Effects on Aluminyl Anions and Derived Systems: A High-Level Theory.

Aluminyl anions are low-valent aluminum species bearing a lone pair of electrons and a negative charge. These systems have drawn recent synthetic interest for their nucleophilic nature, allowing for the activation of σ-bonds, and have been proposed as a pathway to hydrogen energy storage. In this research, we provide high-level ab initio geometries and energies for both the simplest aluminyl anion (AlH2-) and several substituted derivatives. Geometries are reported using the gold-standard CCSD(T)/aug-cc-pV(T+d)Z level of theory. Energies were extrapolated to the complete basis set limit through the focal point approach, utilizing coupled-cluster methods through perturbative quadruples and basis sets up to five-ζ quality. Geometries were rationalized using electrostatic, steric, and orbital donation effects. The donation from substituents to Al is accompanied by back-donation effects, a property traditionally thought of in transition-metal systems. Stereoelectronic effects through the secondary orbital interaction play a fundamental role in stabilizing these low-valent aluminum compounds and would likely also affect the feasibility of their use within several industrial applications. The energetic analysis of the formation of each substituted anion is rationalized as the result of three energetic schemes. The effectiveness of these schemes for determining the relative formation energies is discussed.

Fluoromaticity: The Molecular Orbital Contributions of Fluorine Substituents to the π-Systems of Aromatic Rings.

The addition of fluorine atoms to an aromatic ring brings about an additional set of π-bonding and antibonding orbitals culminating after the addition of the sixth fluorine with a new set of π-aromatic-like orbitals that affect the molecule in a way that we will refer to hereafter as “fluoromaticity”. Depending on the number and position of the fluorine atoms, the contributed π-orbitals can even further stabilize the ring leading to smaller bond lengths within the ring and higher resistance to addition reactions. This added ring stability partially explains the high thermostability and chemical resistance found in polymers containing fluorinated aromatics in their architecture. A similar molecular orbital effect is seen with the addition of other halogen atoms to aromatic rings, though to a much smaller degree and not resulting in the additional ring stability.

The FFLO State in the Dimer Mott Organic Superconductor κ-(BEDT-TTF)2Cu[N(CN)2]Br

The superconducting phase diagram for a quasi-two-dimensional organic superconductor, κ-(BEDT-TTF)2Cu[N(CN)2]Br, was studied using pulsed magnetic field penetration depth measurements under rotating magnetic fields. At low temperatures, Hc2 was abruptly suppressed even by small tilts of the applied fields owing to the orbital pair-breaking effect. In magnetic fields parallel to the conducting plane, the temperature dependence of the upper critical field Hc2 exhibited an upturn and exceeded the Pauli limit field HP in the lower temperature region. Further analyses with the second derivative of the penetration depth showed an anomaly at 31–32 T, which roughly corresponded to HP. The origin of the anomaly should not be related to the orbital effect, but the paramagnetic effect, which is almost isotropic in organic salts, because it barely depends on the field angle. Based on these results, the observed anomaly is most likely due to the transition between the Bardeen-Cooper-Schrieffer (BCS) and the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) states. Additionally, we discuss the phase diagram and physical parameters of the transition by comparing them with other FFLO candidates.

Electrical conductivity in the Hubbard model: Orbital effects of magnetic field

Calculation of conductivity in the Hubbard model is a challenging task. Recent years have seen much progress in this respect and numerically exact solutions are now possible in certain regimes. In this paper we discuss the calculation of conductivity for the square lattice Hubbard model in the presence of a perpendicular magnetic field, focusing on orbital effects. We present the relevant formalism in all detail and in full generality, and then discuss the simplifications that arise at the level of the dynamical mean field theory (DMFT). We prove that the Kubo bubble preserves gauge and translational invariance, and that in the DMFT the vertex corrections cancel regardless of the magnetic field. We present the DMFT results for the spectral function and both the longitudinal and Hall conductivity in several regimes of parameters. We analyze thoroughly the quantum oscillations of the longitudinal conductivity and identify a high-frequency oscillation component, arising as a combined effect of scattering and temperature, in line with recent experimental observations in moir\'e systems.

Universal Magnetic Oscillations of dc Conductivity in the Incoherent Regime of Correlated Systems.

Using the dynamical mean field theory we investigate the magnetic field dependence of dc conductivity in the Hubbard model on the square lattice, fully taking into account the orbital effects of the field introduced via the Peierls substitution. In addition to the conventional Shubnikov-de Haas quantum oscillations, associated with the coherent cyclotron motion of quasiparticles and the presence of a well-defined Fermi surface, we find an additional oscillatory component with a higher frequency that corresponds to the total area of the Brillouin zone. These paradigm-breaking oscillations appear at elevated temperature. This finding is in excellent qualitative agreement with the recent experiments on graphene superlattices. We elucidate the key roles of the off-diagonal elements of the current vertex and the incoherence of electronic states, and explain the trends with respect to temperature and doping.

Orbital asymmetric hybridization enhances surface Lewis acid-base reactions of charged clay catalysts

A strong electric field of 108–10 V/m could be produced from the surface charges of clay. In this study, the asymmetric hybridization of atomic orbitals in the electric field at the clay surface substantially enhances the Lewis acid-base reactions between the surface O and Cu2+/Ca2+/Mg2+/H2O. This has been confirmed by cationic adsorption kinetics, energies, critical coagulation concentrations (CCCs) and infrared spectral analyses of –OH and Si-O stretches for H2O and clay crystal respectively. The enhanced Lewis acid-base reaction energy for Cu2+, Ca2+ and Mg2+ at charged clay surface is found in an order of Cu2+(−27.21 kJ/mol) > Ca2+(−15.51 kJ/mol) > Mg2+(−6.061 kJ/mol). For surface H2O, a new blueshift adsorption peak (3612 cm−1) is observed in the infrared spectral analyses which indicate a strong Lewis acid-base reaction for H2O at charged clay surface. This study indicates that, for the catalytic activities of charged clay catalysts, the background cation types and concentrations, the electric field intensity and the orbital asymmetric hybridization effect at charged clay surface would be coupled and intertwined. Importantly, in those factors/effects the electric field and its initiated orbital asymmetric hybridization of surface atoms/cations should play the critical roles, and thus these two key factors should be emphasized in clay catalyst design.