Search

The article discusses the chiral induced spin selectivity effect (CISS), which is the finding that the motion of an electron within or through chiral systems depends on the spin of that electron. The article explains that while the effect has been observed experimentally, developing a quantitative theoretical description has been challenging. The article also highlights the different types of experimental measurements that have been used to study CISS, including measurements of spin-dependent transmission, tunneling currents, magnetization, and magnetic domains. The article concludes by discussing the potential applications of CISS in spintronics, electrochemistry, and biology, and expresses optimism that further research will reveal the mechanism behind the CISS effect. [Extracted from the article]

We extend to strongly correlated molecular systems the recently introduced basis-set incompleteness correction based on density-functional theory (DFT) [E. Giner et al., J. Chem. Phys. 149, 194301 (2018)]. This basis-set correction relies on a mapping between wave-function calculations in a finite basis set and range-separated DFT (RSDFT) through the definition of an effective non-divergent interaction corresponding to the electron–electron Coulomb interaction projected in the finite basis set. This enables the use of RSDFT-type complementary density functionals to recover the dominant part of the short-range correlation effects missing in this finite basis set. To study both weak and strong correlation regimes, we consider the potential energy curves of the H10, N2, O2, and F2 molecules up to the dissociation limit, and we explore various approximations of complementary functionals fulfilling two key properties: spin-multiplet degeneracy (i.e., independence of the energy with respect to the spin projection Sz) and size consistency. Specifically, we investigate the dependence of the functional on different types of on-top pair densities and spin polarizations. The key result of this study is that the explicit dependence on the on-top pair density allows one to completely remove the dependence on any form of spin polarization without any significant loss of accuracy. Quantitatively, we show that the basis-set correction reaches chemical accuracy on atomization energies with triple-ζ quality basis sets for most of the systems studied here. In addition, the present basis-set incompleteness correction provides smooth potential energy curves along the whole range of internuclear distances. [ABSTRACT FROM AUTHOR]

The excellent photocatalytic performance was attributed to upshift of d-band center, and highly energetic electrons induced by the CB flexibility alleviated the photoinduced electron recombination in defective MIL-125. [Display omitted] Solar energy is becoming the most promising option to mitigate the energy crisis in the future and can be applied in renewable and economical technologies such as water splitting and pollutants degradation. The promotion of the electronic energetic level is considered an efficient method to enhance the photocatalytic performance of semiconductor materials for solar energy conversion. The highly energetic electrons exhibit a remarkable reduction ability by virtue of the electronic spin polarization, which is associated with the conduction band (CB) position. Thus, the regulation of the CB position due to the redistribution of electrons by means of defect engineering presents potential. Here, a series of titanium-based metal–organic frameworks (Ti-based MOFs) named MIL-125-m% containing different extents of defects are reported to enable photocatalytic activity under simulated sunlight and visible light illumination for remarkably enhanced photocatalytic hydrogen evolution and pollutant degradation. The experimental results illustrated that MIL-125–5 % exhibited a superior photocatalytic hydrogen evolution rate (16507.27 μmol·g−1·h−1), much higher than that of MIL-125-0 % (1.444 μmol·g−1·h−1). The excellent photocatalytic performance was attributed to upshift of d-band center, which strengthened the adsorption of H*, facilitating the H 2 evolution reaction. In addition, the degradation rate of MIL-125-5 % was up to twice the original rate, for the highly energetic electrons induced by the CB flexibility alleviated the photoinduced electron recombination in defective MIL-125. The strategy of defect engineering provides a new path to control the flexibility of the CB position by electronic spin polarization on adjustable metal–organic frameworks (MOFs), and the photocatalytic effect is changed accordingly. [ABSTRACT FROM AUTHOR]

A sustainable future demands a successful transition from a carbon energy‐dependent economy towards renewable energy schemes, many of which ultimately rely on the development of efficient electrocatalysis that either converts chemical energy into electricity or uses electrons to produce chemical energy. In general, electrocatalysis studies focus on the interactions (e. g., electron transfer) between the catalyst surface and the reaction intermediates. However, the role of electron spin, as an intrinsic property of electrons, has commonly been overlooked. Recently, controlling the electron spin polarization at the catalyst's surface demonstrated the great potential of boosting both reaction activity and product selectivity. Molecule‐induced electron spin polarization inspired by the chiral‐induced spin selectivity (CISS) effect has started to have a remarkable impact in electrocatalysis. In this compact review, we summarize the latest studies that use molecule‐induced electron spin polarization to enhance catalytic performance. We focus on the reactions essential to the so‐called hydrogen economy, and discuss the feasibility and limitations of this effect. Finally, we share our perspective regarding the more impactful future applications. [ABSTRACT FROM AUTHOR]

Spin-polarized electron transport through zigzag-edged graphene nanoislands is studied within the framework of the Pariser-Parr-Pople Hamiltonian. By including both short- and long-range electron-electron interactions, the electron conductance is calculated self-consistently for the hexagonal model on various substrates from which we are able to identify the effects of the many-body interactions in the electron transport. For the system in its lowest antiferromagnetic (AFM) state, the long-range interactions are shown to have negligible effect on the electron transport in the low-energy region in which the conductance is found quenched mainly by the short-range interactions. As the system is excited to its second AFM state, the short- and long-range interactions are found to have opposite effects on the electron transmission, i.e., the electron transmission is found to increase with either the suppression of the long-range interactions or the enhancement of the short-range interactions. When the system moves further into the ferromagnetic state, the conductance becomes spin dependent and its resonance is shown to exhibit a blue shift in an environment with stronger long-range interactions. The distinct impact of short- and long-range electron-electron interactions are attributed to their different effects on the spin polarization in the model system. [ABSTRACT FROM AUTHOR]

Organic magnetoresistance is tightly related to the carrier spin. To explain the dependence of organic magnetoresistance on the driving voltage, we firstly study the spin polarization of a carrier with different energy through the tight-binding model. Then with a spin related hopping mechanism, we obtain the dependence of the magnetoresistance on the carrier spin. It is found that a high energy carrier will have a weak spin polarization, which results in a small magnetoresistance. By supposing the injected carrier energy is proportional to the driving voltage, our theoretical calculation is well consistent to the experimental data. [ABSTRACT FROM AUTHOR]

Construction of metal monovacancies in ZnO reduced e g occupation and induced electron spin polarization near the Fermi level. Moreover, spin-polarized orbital coupling and internal polarization electric field promoted surface redox reactions and accelerated carrier interfacial transfer, which released the restrictions of reaction condition in simultaneously photocatalytic hydrogen generation and pollutant degradation. [Display omitted] • Metal monovacancies are successfully developed in lamellar Zn-V-20. • Low eg occupancy optimizes electron configuration and spin structure. • Simultaneous hydrogen generation and pollutants degradation are enhanced. • Spin polarization proved by DFT and XAS is the reason of photocatalytic enhancement. Simultaneous hydrogen generation and pollutants removal is considered as the potential solution to the energy and environmental crisis, which can cut the consumption of expensive sacrificial electron donors and reduce the ecotoxicity of wastewater containing pollutants. However, the integration of two redox half-reactions in one system is still a challenge, limited by irreconcilable reaction conditions and low kinetics. In this study, ZnO with abundant metal monovacancies (Zn-V-m) was fabricated to manipulate the spin state by tailoring the electron occupancy of e g -orbitals, which simultaneously endowed the material with both outstanding photocatalytic oxidation and reduction performance. Compared with pristine ZnO, the prepared Zn-V-20 increases the H 2 production rate by 56.4-fold and enhances the pollutants removal efficiency by 27.5-fold. It is impressive that simultaneous hydrogen generation and pollutants degradation in one system is accomplished and accelerated. Furthermore, Zn L -edge X-ray absorption spectra (XAS) and density functional theory (DFT) calculations suggest that low electron occupancy of e g -orbitals optimizes the spin structure and leads to spin polarization, which provides the critical motivation for enhancing photocatalytic performance. This work accelerates the reaction rates of pollutants degradation and hydrogen generation at the surface interface by manipulating electron spin polarization, guiding the rational design of TMO-based catalysts for simultaneous energy recovery and wastewater purification. [ABSTRACT FROM AUTHOR]

The electronic structure and the optical properties of the HoCoSi and ErNiSi compounds are studied. Spin-polarized band calculations are performed in the local electron density approximation corrected for the strong electron-electron interactions in the 4 f shell of a rare-earth ion (LSDA + U method [11]). The optical constants are measured by ellipsometry in a wide wavelength range, and the frequency dependences of a number of spectral parameters are determined. The calculated densities of states are used to interpret the structural features of the interband optical conductivities of the intermetallic compounds. [ABSTRACT FROM AUTHOR]

The polarization vector P of scattered electrons interacting with a polarized target electrons is compared with the entanglement (or non-separability) of the electron states of the interacting electron pair. The separability S is defined as a linear function of the von Neumann entropy. The shapes of the functions P ( θ , Ω , φ ) and S ( θ , Ω , φ ) are similar and simultaneously achieve their maximum value at the scattering angle θ values close to 0 and π and simultaneously tend to zero in the case of symmetric scattering at θ ≈ π /2. In the latter case the scattered electrons are described by an asymmetric spin part of the wave function, which by definition corresponds to the spin entangled ( S ≈ 0) electron states of the interacting electron pair. Comparison of the model calculation results with experimental results of the spin polarized electron spectroscopy of the ferromagnetic solid shows qualitative agreement. The analytical expression relating polarization and separability of the two interacting particles enables use the measured polarization of scattered electrons for estimation of the spin-entanglement or separability of the two particle systems. [ABSTRACT FROM AUTHOR]

We analyze the time evolution of spin-polarized electron wave packets injected into the edge states of a two-dimensional topological insulator. In the presence of electron interactions, the system is described as a helical Luttinger liquid and injected electrons fractionalize. However, because of the presence of metallic detectors, no evidences of fractionalization are encoded in dc measurements, and in this regime the system does not show deviations from its non-interacting behavior. Nevertheless, we show that the helical Luttinger liquid nature emerges in the transient dynamics, where signatures of charge/spin fractionalization can be clearly identified. [ABSTRACT FROM AUTHOR]

A dilute two-dimensional (2D) system of interacting electrons has tendency to spontaneous spin polarization with increase of interparticle interaction. This instability, anticipated to occur with lowering carrier density and temperature, in fact has never been observed. Here, we report temperature dependence of the spin susceptibility of a 2D electron system in Si-MOS structures measured by two different techniques: (i) χ T ( T ) by direct thermodynamic measurements, which are sensitive to all the electrons, and (ii) χ ∗ ( T ) from quantum oscillations in vector field, sensitive to the itinerant electrons only. In the former case, the susceptibility strongly diverges as 1 / T 2 . In the latter case we found a weak χ ∗ ( T ) dependence, only a few percent over the range T = ( 0.1 ÷ 1 ) K , which seems to agree qualitatively with the predicted interaction corrections. We provide evidences for this difference to stem from the temperature- and magnetic field-dependent exchange with carriers between the localized and itinerant electrons coexisting in the two-phase state. [ABSTRACT FROM AUTHOR]

The spin polarization of polarons in quasi-1D organic materials has been investigated by using the extended Su-Schrieffer-Heeger (SSH) model with spin-orbit coupling. Results show that the polaron is partly spin polarized, and that the electron-electron interaction and spin-orbit coupling compete with each other during the formation of spin polarization. The dependence of spin polarization on electron-phonon coupling is also revealed. Our results demonstrate that spin polarization is well correlated with polaron localization, thus providing useful guidance for exploring magnetic effects in organic materials. [ABSTRACT FROM AUTHOR]

Abstract: We study the formation of spontaneous spin polarization in inhomogeneous electron systems with pair interaction localized in a small region that is not separated by a barrier from surrounding gas of non-interacting electrons. Such a system is interesting as a minimal model of a quantum point contact in which the electron–electron interaction is strong in a small constriction coupled to electron reservoirs without barriers. Based on the analysis of the grand potential within the self-consistent field approximation, we find that the formation of the polarized state strongly differs from the Bloch or Stoner transition in homogeneous interacting systems. The main difference is that a metastable state appears in the critical point in addition to the globally stable state, so that when the interaction parameter exceeds a critical value, two states coexist. One state has spin polarization and the other is unpolarized. Another feature is that the spin polarization increases continuously with the interaction parameter and has a square-root singularity in the critical point. We study the critical conditions and the grand potentials of the polarized and unpolarized states for one-dimensional and two-dimensional models in the case of extremely small size of the interaction region. [Copyright &y& Elsevier]

Abstract: Combining experiments and first-principle calculations, we present in this paper a detailed study of the O3 detection mechanism on the CuO (111) surface. The exchange-correlation functional is treated within both the LDA and the GGA including the spin polarization. In order to better take into account the on-site electronic interactions between 3d electrons of Cu atoms a Hubbard term U has to be added in all calculations. We show that the O3 molecule is reduced to an O2 molecule with an enthalpy of reaction of −1.11eV (−1.15eV) within LDA+U (GGA+U). Along the reaction path, the O3 molecules are first physisorbed with a large adsorption energy of −1.83eV (−1.03eV) and a significant charge transfer from the surface to the molecule. The p-doping strengthening is compared to the electrical response of a CuO based sensor under O3 exposure. [Copyright &y& Elsevier]

We study metastable-state formation in the one-dimensional model of a quantum ballistic contact, in which the contact is represented by a potential barrier with electron-electron interaction localized therein. It is shown that when the interaction parameter exceeds a critical value, a metastable state with spontaneous spin polarization of the barrier is formed. The difference between the grand potentials of the metastable and globally stable states tends to zero at the critical point; therefore, the metastable state manifests itself in transport even at low temperatures and its effect gradually increases with temperature. The main effect is a decrease in the conductance with increasing temperature, which occurs in a certain range of the barrier-region potential, similar to that observed during the formation of the well-known 0.7 conductance anomaly. [ABSTRACT FROM AUTHOR]

We analyze the spin-dependent conductance spectrum of a double quantum dot with Rashba spin-orbit and electron-electron interactions based on the Keldysh nonequilibrium Green's function formalism. A clear physical picture emerges from the single-particle analysis of electron-transfer pathways in a quantum dot molecule. It provides an insight into the mechanism that underlies the evolution of bonding resonances. This study demonstrates both numerically and analytically that the mechanism of quantum interference is altered, as either component of the Rashba spin-orbit interaction is modulated. Most importantly, the bonding state can be controlled by tuning the Rashba parameter: a bound state in the continuum becomes unbound upon gate control and vice versa, mediated by the transverse Rashba spin-orbit component. A spin-polarized current is shown to be produced by the interplay of the spin-resolved interference effect with the magnetic flux. Sharp spin polarization that arises from the negative differential conductance, observed over a wide range of values of relevant parameters, is discussed. [ABSTRACT FROM AUTHOR]

Understanding the effects of electron-electron interactions in half-metallic magnets (HMs), which have band structures with one gapped spin channel and one metallic channel, poses fundamental theoretical issues as well as having importance for their potential applications. Here we use determinant quantum Monte Carlo to study the impacts of an on-site Hubbard interaction U, finite temperature, and an external (Zeeman) magnetic field on a bilayer tight-binding model which is a half-metal in the absence of interactions, by calculating the spectral density, conductivity, spin polarization of carriers, and local magnetic properties. We quantify the effect of U on the degree of thermal depolarization, and follow relative band shifts and monitor when significant gap states appear, each of which can degrade the HM character. For this model, Zeeman coupling induces, at fixed particle number, two successive transitions: compensated half-metal with spin-down band gap → metallic ferromagnet → saturated ferromagnetic insulator. However, over much of the more relevant parameter regime, the half-metallic properties are rather robust to U. [ABSTRACT FROM AUTHOR]

We derive a spin diffusion equation for a spin-orbit coupled two-dimensional electron gas including the Hartree-Fock field resulting from first order electron-electron interactions. We find that the lifetime of the persistent spin helix, which emerges for equal linear Rashba and Dresselhaus spin-orbit interactions, can be enhanced considerably for large initial spin polarizations due to the Hartree-Fock field. The reason is a reduction of the symmetry-breaking cubic Dresselhaus scattering rate by the Hartree-Fock field. Also higher harmonics are generated and the polarization of the persistent spin helix rotates out of the (Sy,Sz) plane acquiring a finite Sx component. This effect becomes more pronounced when the cubic Dresselhaus spin-orbit interaction is large. [ABSTRACT FROM AUTHOR]

We report the correlated charge and spin density distributions in a quantum wire coupled to electron reservoirs. It is found that charging the wire because of the electron density redistribution between the wire and reservoirs results in the increase of the critical electron density, below which the spontaneous spin polarization appears. The distributions of the electron densities with spin up and spin down along the wire have components oscillating in opposite phases with the wave vector 2kF, kF being the Fermi wave vector. As a result the antiferromagnetic spin order appears, with one of the spin components spontaneously predominating. The charge density distribution is close to the Wigner order with the small amplitude of the 4kF charge-density waves. [ABSTRACT FROM AUTHOR]

Ab-initio spin-polarized Density Functional Theory plusU is used to study the electronic and magnetic properties of tetragonal doped barium titanate (Ba 1 -x Eu x O 3) system for different Europium concentrations. The Projector Augmented Wave (PAW) method and a Perdew-Zunger (LSDA) approximation, which has been used for the exchange correlation energy, have been considered taking into account a supercell model. The spin polarization as well as the Hubbard's potential have been used for the correction of the electron-electron Coulomb interactions in the rare-earth ions partially filled f -orbitals. The electronic bands-structure reveals that the band-gap energy as well as the dielectric properties decreases with the increase of the doping concentration. The modern theory of polarization also shows that the spontaneous electric polarization increases with the increase of the Europium content, whereas the states-density reveals ferromagnetic characteristics (with non-zero total magnetization), without an applied magnetic field, for the Ba 1 -x Eu x O 3 system. [ABSTRACT FROM AUTHOR]

• DFT has been performed to study the spin interactions on electronic structures, magnetic moments, and optical properties of CoFe 2 O 4. • High DOS at Fermi level manifests strong electron-electron interactions. • The calculated total spin magnetic moments 6.98 μ B is a results of high spin polarization. • The highly spin polarized CoFe 2 O 4 material can be used as spintronic devices as well as optical reflector. This report demonstrates the structural, electronic, magnetic, elastic, and optical properties of spinel CoFe 2 O 4 using generalized gradient approximation (GGA). Both the spin and non-spin polarized density functional theory (DFT) have been used to study the influence of spin interactions on electronic structures, spin magnetic moments, and optical properties. The calculated magnetic moments of CoFe 2 O 4 from spin density of states are 6.98 μ B per formula unit. The Fe and Co ions prefer high spin orientations owing to the cationic polarization because of crystal field strength and intra-atomic exchange interactions, which induces large spin magnetic moments. The high values of spin magnetic moments confirm strong spin orbit coupling due to strong electron-electron interactions and can be a promising for spintronic application. Moreover, the calculated high reflectivity of CoFe 2 O 4 material (~100%) in the Infrared-Visible-Ultraviolet region up to ~30 eV, which suggesting that the CoFe 2 O 4 can also be a good candidate for solar reflector. [ABSTRACT FROM AUTHOR]

Two-dimensional topological insulators (TIs) host gapless helical edge states that are predicted to support a quantized two-terminal conductance. Quantization is protected by time-reversal symmetry, which forbids elastic backscattering. Paradoxically, the current-carrying state itself breaks the time-reversal symmetry that protects it. Here we show that the combination of electron-electron interactions and momentum-dependent spin polarization in helical edge states gives rise to feedback through which an applied current opens a gap in the edge state dispersion, thereby breaking the protection against elastic backscattering. Current-induced gap opening is manifested via a nonlinear contribution to the system's I-V characteristic, which persists down to zero temperature. We discuss prospects for realizations in recently discovered large bulk band gap TIs, and an analogous current-induced gap opening mechanism for the surface states of three-dimensional TIs. [ABSTRACT FROM AUTHOR]

A single molecular transistor is considered in the presence of electron-electron interaction, electron-phonon interaction, an external magnetic field and dissipation. The quantum transport properties of the system are investigated using the Anderson-Holstein Hamiltonian together with the Caldeira-Leggett model that takes care of the damping effect. The phonons are first removed from the theory by averaging the Hamiltonian with respect to a coherent phonon state and the resultant electronic Hamiltonian is finally solved with the help of the Green function technique due to Keldysh. The spectral function, spin-polarized current densities, differential conductance and spin polarization current are determined. [ABSTRACT FROM AUTHOR]

Spin-orbit coupling is a single-particle phenomenon known to generate topological order, and electron-electron interactions cause ordered many-body phases to exist. The rich interplay of these two mechanisms is present in a broad range of materials and has been the subject of considerable ongoing research and controversy. Here we demonstrate that interacting two-dimensional electron systems with strong spin-orbit coupling exhibit a variety of time reversal symmetry breaking phases with unconventional spin alignment. We first prove that a Stoner-type criterion can be formulated for the spin polarization response to an electric field, which predicts that the spin polarization susceptibility diverges at a certain value of the electron-electron interaction strength. The divergence indicates the possibility of unconventional ferromagnetic phases even in the absence of any applied electric or magnetic field. This leads us, in the second part of this work, to study interacting Rashba spin-orbit coupled semiconductors in equilibrium in the Hartree-Fock approximation as a generic minimal model. Using classical Monte Carlo simulations, we construct the complete phase diagram of the system as a function of density and spin-orbit coupling strength. It includes both an out-of-plane spin-polarized phase and in-plane spin-polarized phases with shifted Fermi surfaces and rich spin textures, reminiscent of the Pomeranchuk instability, as well as two different Fermi-liquid phases having one and two Fermi surfaces, respectively, which are separated by a Lifshitz transition. We discuss possibilities for experimental observation and useful application of these novel phases, especially in the context of electric-field-controlled macroscopic spin polarizations. [ABSTRACT FROM AUTHOR]