Search

We employed first-principles calculations to investigate the structural, electronic, and magnetic properties of carbon/boron nitride nanoribbons in different sizes and doping, using twenty-eight zigzag and armchair configurations. We note that the structures present dynamic stability, with formation energies slightly higher than those of the respective undoped nanoribbons. Our electronic calculations revealed that BN-doped armchair carbon nanoribbons exhibit narrow bandgap semiconductor behavior. Most of the zigzag carbon nanoribbons doped with BN exhibited metallic behavior, in addition to exhibiting non-zero spin polarization in these cases. However, carbon-doped boron nitride nanoribbons in both configurations – zigzag and armchair – exhibited wide-gap semiconductor behavior. We also observed that the energy gap in the band structure directly depends on the doping position. The incorporation of boron and nitrogen pairs into the center of the zigzag carbon nanoribbons does not significantly alter the magnetic properties of the nanoribbons. However, when performed at or near the edges, it results in significant changes in spin polarization. Therefore, based on these results, we can consider potential applications of these nanoribbons in electronic devices. • The studied structures exhibit dynamic stability. • Doping-induced semiconductor behavior. • Band structure is directly influenced by doping position. • Doping with boron and nitrogen in nanoribbons has little impact on magnetic properties. [ABSTRACT FROM AUTHOR]

An investigation is carried on a quantum system featuring a MoS 2 zigzag nanoribbon employing double magnetic barriers. This study aims to overcome a valley polarization limitation observed in systems using a uniform magnetic field or a single magnetic barrier. A magnetic field breaks the degeneracy of the K and K ′ valleys owing to the valley Zeeman effect, but reversing the direction of the magnetic field is required to invert the valley polarization. In a double magnetic barrier system, interplay between the Fano resonance (arising from the quantum interference between the continuum state of the magnetic barrier and the Landau level) and the resonant tunneling (arising from the quantum states between two barriers) indicates the potential for achieving selective spin and valley polarization by adjusting the strength and width of the magnetic barrier. This can enhance the degree of valley polarization and enable the existence of four distinct spin and valley currents. Obtaining full spin and valley polarization is shown with the optimized parameters of this system. The experimental realization of this system should enable the control of carrier valley and spin degrees of freedom in future devices. [Display omitted] • Three-band tight-binding model using three d orbitals (dx 2 , dx2−y2, and dz2) of Mo atoms. • Double magnetic barrier is used to enhance valley and spin polarization. • Resonant tunneling effect in the K valley and Fano resonance effect in the K ′ valley. • The MoS 2 zigzag nanoribbon system with double magnetic barriers along the same direction has great advantages compared with a single magnetic barrier. [ABSTRACT FROM AUTHOR]

Trilayer graphene exhibits valley-protected gapless states when the stacking order changes from ABC to CBA and a gate voltage is applied to outer layers. Some of these states survive strong distortions of the trilayer. For example, they persist when the outer layers are partially devoid yielding a system of two trilayers of different stacking order connected by a strip of a single graphene layer. Here we investigate how these states respond to another perturbation, i.e., the presence of magnetic defects, which we model as π -vacancies. We show that the gap states hybridize with the defect states and strongly spin-split. More importantly, it is demonstrated that by changing the gate voltage value one can change the spin density of the gap states and the corresponding currents at the Fermi level. [ABSTRACT FROM AUTHOR]

The Aim of this paper is to study the properties of spin transport for ferromagnetic graphene superlattice unit cell junction taking into account the induced ac-field at different frequencies. Transfer matrix method is used for both spin alignments to calculate the conductance in terms of which spin polarization and giant magneto-resistance are also expressed. The results show that an oscillatory behavior is strongly exhibited by the three calculated quantities. These oscillations could be explained by the mutual effect between the magnetic field of the ferromagnetic insulator EuO, which causes spin filtering, and the induced photon energy of applied ac-field. The present research might have a scientific potential in the design and understanding of graphene superlattice based spin filters by optimizing the different parameters studied in this paper. • Spin-dependent transport in ferromagnetic graphene superlattice junction is studied under ac-fields with range of frequencies and different lengths. • interaction between the induced photon and the spin minibands results in oscillating behavior of the conductance. • The conductance ripples around a background average value with high spikes over semi periodic intervals of the gate voltage. • The anti-parallel spin alignment exhibits the same overall behavior with a shift towards higher gate voltages. • Energy of induced photons in selected range of frequencies enhances spin transport. [ABSTRACT FROM AUTHOR]

Abstract We study the transport properties of a quantum dot (QD) fabricated by a quantum anomalous Hall insulator. It is found that energy levels of the QD are quantized due to the quantum confinement effect, which leads to the appearance of the resonant-tunnelling phenomenon at low temperature. We also find that topological edge states form around the boundary of the QD, coexisting with the bulk states inside the QD. The electron transmission through the channels of the edge and bulk states drives the Fano interference, manifested as the asymmetric lineshape of the linear conductance spectrum. In addition, the spin polarization of this system is present. It shows that the spin-polarized current can be realized even in the absence of the external magnetic field, because of the breaking the time-reversal symmetry. Highlights • We study the transport through a quantum dot fabricated by a quantum anomalous Hall insulator. • Topological edge states form around the boundary of the QD, coexisting with the bulk states inside the QD. • Transmission through the channels of the edge and bulk states drives the Fano interference. • Spin-polarized current is realized even in the absence of the external magnetic field. • The spin filtering is found to be mainly induced by the bulk states rather than the edge states. [ABSTRACT FROM AUTHOR]

Abstract We study the tunneling conductance and magnetization of a correlated quantum dot coupled to external metallic leads, considering the occupancy dependent hybridization. Using a modified equation of motion approach and self-consistent perturbation theory we show that the assisted hopping processes can be responsible for appearance of a plateau in the linear conductance. This process breaks the particle-hole symmetry and is manifested in conductance and magnetization. In presence of the external magnetic field the correlated hybridization enhances the spin polarization. Highlights • The effect of assisted hopping on the transport properties of quantum dot was studied. • The plateau of linear conductance was obtained. • There was shown that the assisted hopping process breaks particle-hole symmetry of conductance. • There was shown that the assisted hopping enhances the spin polarization of quantum dot. [ABSTRACT FROM AUTHOR]

Abstract By applying the slave-boson mean-field approximation to the highly correlated quantum dots (QDs), we investigate the spin polarized transport properties through serial two QDs coupled with Majorana bound states (MBSs) sandwiched between two ferromagnetic (FM) leads. We demonstrate the linear conductance and transmission properties which is dependent on the QD-MBS coupling strength and the spin polarization strength. We further discuss the exact up-and down-spin transmission properties in the parallel and anti-parallel configurations. We suggest that such a theoretical model can be used to study the physical phenomenon related to the spin manipulation transport in the hybrid Majorana quantum-dot systems. Highlights • We demonstrate the linear conductance and transmission properties depending on the QD-MBS coupling and the spin polarization. • The linear conductance increases with the QD-MBS coupling and the up-spin electrons dominates that of down-spin electrons. • The up-spin (down-spin) transmission decreases (increases) with the increasing spin polarization strength under parallel configuration. • The up-spin transmission is always identical with the down-spin under anti-parallel configuration. • The obtained results can be used to the spin manipulation transport in the hybrid Majorana quantum-dot systems. [ABSTRACT FROM AUTHOR]

Abstract Based on a mono hydrogen-passivated zigzag SiC nanoribbon with width 4, we construct a heterojunction through different substitutional impurities. The left part of the heterojunction is boron-doped at the Si-edge of zigzag SiC nanoribbon, and the right part is nitrogen-doped at the C-edge. Our results show that boron and nitrogen doped zigzag SiC nanoribbons exhibit half-metallic features at ferromagnetic state, which provides the possibility to design spin nanodevices. By performing first-principle quantum transport calculations, spin-dependent transport properties in different magnetic configurations are studied. Current-voltage curves show perfect spin-filtering and negative differential resistance effects when the spin orientations of the two electrodes are opposite. In the parallel magnetization configuration of two electrodes, a strong rectifying behavior is observed and the maximum rectifying ratio reaches the order of 109. Through detailed analysis of two electrodes' band structures along with the transmission spectra, the interesting transport behaviors can be understood. Besides, the Bloch states of spin-polarized bands crossing the Fermi level can help us to understand the appearance of the negative differential resistance effect. Highlights • Spin-dependent transport in a zigzag silicon carbon nanoribbon heterojunction with boron and nitrogen impurities is studied. • In parallel magnetic configuration, strong rectifying behavior is observed and can be used as a diode. • In antiparallel magnetic configuration, the I V curves display spin filtering and NDR effects. • The half-metallic character and localized edge states give us a good starting point to design spin nanodevices. [ABSTRACT FROM AUTHOR]

Abstract We have investigated the reconstruction and electronic structure of divacancy in chiral and achiral graphene nanoribbons as the defect moves to the ribbon edge. The new healing bonds introduce strain dictating the structure and its energetics. Unlike in infinite graphene, the ribbons can take advantage of the edge flexibility in relieving stress. The total energy depends on the defect orientation and its distance to the ribbon edge, and the disposal of the divacancy through the edge results in the energy gains up to ≈7.7 eV. This energy gain is closely related to the pentagon count in the final edge morphology. The divacancy has lower energy near the edge, and thus it is more likely to occur at the edges in the thermodynamic equilibrium. We find that the zigzag portions at the edge induce spin polarization even though the whole edge is not zigzag. However, the spin polarization from discontinuous zigzag portions are not strong and can be modified by the spin polarization around the defect. Moving the divacancy closer to an edge modifies the spin polarization on one side, and the magnetic structure becomes diverse especially in the achiral ribbons. The divacancy induces defect states near E F. The defect level and the extent of its mixing with native ribbon states depend on the defect orientation and distance to the edge. Highlights • Properties of divacancy in graphene ribbon depend on its orientation and distance to edge. • Divacancy is likely to migrate and can be disposed from edge. • Divacancy self-heals by new bonds that create strain. • Unlike in infinite graphene, ribbons can take advantage of edge flexibility in stress relieving. • Zigzag portions at the edge induces spin polarization even if the whole edge is not zigzag. [ABSTRACT FROM AUTHOR]

The present study is conducted to evaluate the spin polarization in two pyrene and Triphenylene graphene nanoflakes. All calculations are performed using non-equilibrium Green's function (NEGF) method. The obtained results show that, graphene has no magnetic property and using Pyrene nanoflake results in a better spin switching at extreme magnetic fields. On the contrary, when applying magnetized electrodes, depending on the direction of magnetization of the two electrodes (either parallel or anti-parallel), different spin polarization diagrams are obtained. In this situation, it is observed that, in the case of electrodes magnetization in Triphenylene nanoflake a better spin switching is reached. [ABSTRACT FROM AUTHOR]

Aim of this study is to investigate spin transportation in double quantum ring (DQR). We developed an array of DQR to measure the transmission coefficient and analyze the spin transportation through this system in the presence of Rashba spin-orbit interaction (RSOI) and magnetic flux estimated using S-matrix method. In this article, we compute the spin transport and spin-current characteristics numerically as functions of electron energy, angles between the leads, coupling constant of the leads, RSOI, and magnetic flux. Our results suggest that, for typical values of the magnetic flux ( ϕ / ϕ 0 ) and Rashba constant ( α R ), such system can demonstrates many spintronic properties. It is possible to design a new geometry of DQR by incoming electrons polarization in a way to optimize the system to work as a spin-filtering and spin-inverting nano-device with very high efficiency. The results prove that the spin current will strongly modulate with an increase in the magnetic flux and Rashba constant. Moreover it is shown that, when the lead coupling is weak, the perfect spin-inverter does not occur. [ABSTRACT FROM AUTHOR]

The structural, electronic, and magnetic properties of (ZnO) 12 clusters doped with Cr atoms have been investigated by using spin-polarized first-principles calculations. The exohedral a3 isomer is favorable than endohedral a2 isomer. The isomer a1 and a5 respectively have the narrowest and biggest gap between highest unoccupied molecular orbital and the lowest unoccupied molecular orbital (HOMO-LUMO) of 0.473 and 1.291 eV among these five monodoped isomers. The magnetic moment may be related to the local environment around the Cr atom that the a2 isomer whose total magnetic moment is 6 μ B while the other monodoped isomers which all isomers have nearly total magnetic moments 4 μ B . For Cr-doped (ZnO) 12 on a1 or a3 isomer, the DOS of spin-up channel cross the Fermi level E F showing a finite magnitude near the Fermi level which might be useful for half metallic character. For the bidoped cases, the exohedral isomers are found to be most favorable. Including all bipoed isomers of substitutional, exohedral and endohedral bidoped clusters, the total magnetic moment of the ferromagnetic (antiferromagnetic) state is 8 (0) μ B and the HOMO-LUMO gap of antiferromagnetic state is slightly larger than that of ferromagnetic state. The magnetic coupling between the Cr atoms in bidoped configurations is mainly governed by the competition between direct Cr and Cr atoms antiferromagnetic interaction and the ferromagnetic interaction between two Cr atoms via O atom due to strong p-d hybridization. Most importantly, we show that the exohedral bidoped (ZnO) 12 clusters favor the ferromagnetic state, which may have the future applications in spin-dependent magneto-optical and magneto-electrical devices. [ABSTRACT FROM AUTHOR]

We performed a systematic study of the electronic structures and magnetic properties of SnS 2 monolayer doped with non-magnetic elements in groups IA, IIA and IIIA based on the first-principles methods. The doped systems exhibit half-metallic and metallic natures depending on the doping elements. The formation of magnetic moment is attributable to the cooperative effect of the Hund's rule coupling and hole concentration. The spin polarization can be stabilized and enhanced through confining the delocalized impurity states by biaxial tensile strain in hole-doped SnS 2 monolayer. Both the double-exchange and p-p exchange mechanisms are simultaneously responsible for the ferromagnetic ground state in those hole-doped materials. Our results demonstrate that spin polarization can be induced and controlled in SnS 2 monolayers by non-magnetic doping and tensile strain. [ABSTRACT FROM AUTHOR]

Using first principles study, through Density Functional Theory combined with Non Equilibrium Green's Function Formalism, electronic properties of endohedral N@C 20 fullerene molecule joining Au electrodes (Au-N@C 20 ) was addressed in the presence of spin property. The electronic transport behavior across the Au-N@C 20 molecular junction was investigated by spin resolved transmission, density of states, molecular orbitals, differential conductance and current-voltage ( I-V ) characteristics. Spin asymmetric variation was clearly observed in the results due to single N atom encapsulated in the C 20 fullerene cage, where the N atom played an essential role in the electronic behavior of Au-N@C 20 . This N@C 20 based molecular bridge, exhibiting a spin dependent I-V variation, revealed a metallic behavior within the bias range from −1 V to 1 V. The induced magnetic moment, spin polarization and other relevant quantities associated with the spin resolved transport were elucidated. [ABSTRACT FROM AUTHOR]

We study thermally induced spin resolved current in a zigzag silicene nanoribbon when the left and right leads are respectively affected by ferromagnetic (FM) and anti-ferromagnetic (AFM) exchange fields (FM/normal/AFM junction). We show that pure spin current is generated due to the leads temperature difference and the junction can work as a spin Seebeck diode. The pure spin current can be easily controlled by a perpendicular electric field and the junction, in this case, can work as a spin current switch. In addition, we study the effect of a single vacancy and show that the vacancy can slightly destroy the pure spin current property which leads to induce a weak spin polarized current. In the presence of both vacancy and electric field, current with high and tunable spin polarization can be achieved. [ABSTRACT FROM AUTHOR]

We study the symmetry, magnetization, temperature and electrostatic gating effect on the selective spin-valley polarized transport through the zigzag silicene nanoribbon (ZSiNR) coupled to two ferromagnetic (FM) leads, which are supposed to be in either parallel (P) or anti-parallel (AP) configuration. The transport properties show evident even-odd behavior and are not affected by the zigzag-chain number N when |EF|M. When |EF|V0. As the temperature rises, the spin/valley dependent conductance and the spin-valley polarization are smoothed. The above results have potential applications in fabricating spin-valleytronic devices based on FM-normal-FM ZSiNR junctions. [ABSTRACT FROM AUTHOR]

Based on non-equilibrium Green's function and density functional theory, a first-principles study of the spin-polarized transport properties and magnetism of 1,3-dimethylpropynylidene molecule sandwiched in two Ag electrodes is performed. Strong spin-polarized negative differential resistance and spin filtration effect are present. We also find that the net spin moments of molecular magnet abnormally decrease driven by electric field because the molecular orbitals around Fermi level have opposite spin direction and that non-spin-polarized electrical read out of spin states for single molecular magnets is possible. [ABSTRACT FROM AUTHOR]

We studied the effect of a defect of superlattice on the spin and valley dependent transport properties in silicene, where there is an abnormal barrier in height. It is found that the transmission resonance is greatly suppressed, because the symmetry of superlattice structure is destroyed by the defect. The spin-up and spin-down electrons near the K and K ′ valleys are dominated by different effective superlattices and defects. Therefore, the conductances are strongly dependent on the spin and valley of electron. By adjusting the defect strength properly, the spin and valley polarizations could be dramatically enhanced in a wide energy region. Furthermore, the result suggests an application of the structure as a defect-controlled switch. [ABSTRACT FROM AUTHOR]

The tight-binding model including the spin-orbit coupling (SOC) is used to study electronic and optical properties of zigzag silicene nanoribbons (ZSiNRs) in magnetic and electric fields. The SOC affects the low-energy bands and induces new selection rules leading to richer optical spectra. Except an increase in bandgaps, perpendicular magnetic field further exhibits spin-polarized Landau levels, in which electron's probability density of band-edge states distributes like a standing-wave. Landau levels could enhance the DOS and increases absorption frequency and strength. Perpendicular electric field ( F z ) increases bandgap and thus absorption frequency, but it does not change band symmetry, edge-states, and selection rules. Moreover, F z enhances the split of spin-polarized states inducing more absorption peaks. Parallel electric field ( F x ) leads to an overlap between conduction and valence bands and destroys band symmetry and Landau levels. Consequently, F x exhibits new selection rules and enriches absorption spectra. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) valley materials with valley-polarized band structures have received extensive discussions for their potential applications in the emerging valleytronics, while 2D materials with both spontaneous valley polarization and spin polarization are quite rare. Here, we predict a new 2D ferromagnetic semiconductor MnCoO 6 Bi 2 possessing spontaneous valley polarization by first-principles calculations. The results show that MnCoO 6 Bi 2 has large valley polarization strength of 254 meV and ferromagnetic Curie temperature of 214 K, which is sufficient for the observation of anomalous valley Hall effects. In addition, the band structure with valley polarization can be well maintained under external biaxial strains between −6% and 6%. Our findings provide an ideal platform for exploring the valleytronic physics in 2D magnetic materials. [ABSTRACT FROM AUTHOR]

Due to the symmetry breaking, Janus two-dimensional materials possess novel electronic properties such as energy valley and spin polarization. In this research, we predicted the Zeeman-type spin splitting and Rashba splitting of monolayer Janus ZrNX (X = Br, I). The Rashba spin splitting and valley splitting can be greatly tuned by the magnetic proximity effect of monolayer H–VTe 2 , which are dependent on the stacking configurations. There is strong interlayer coupling between Janus ZrNX and VTe 2 , leading to a sizable valley splitting of 87 meV. The valley splitting can be significantly enlarged by the vertical compression strain, because of the increases of effective Zeeman field and in-plane orbital component. In addition, a helical gap is opened and the dispersion relation of Rashba spin-orbit coupling is obviously modified by in-plane biaxial strain. The Rashba constant and helical gap increase with the in-plane tensile strain, which leads from the larger potential energy difference and magnetic moment of surface V atoms. The greatly tunable spin/valley splittings in ZrNBr/VTe 2 heterostructure are of some signification for the development of spintronics/valleytronics and the realization of new functional devices. • The valley polarization and Rashba SOC of monolayer Janus ZrNX (X = Br, I) are demonstrated. • The valley splitting and Rashba splitting of ZrNBr/VTe 2 heterostructure are effectively regulated by stacking configurations. • The factor of greater valley splitting is larger in-plane orbital composition and strong effective Zeeman field. • The helical gap is found and can be manipulated by biaxial strain. [ABSTRACT FROM AUTHOR]

In this work we have theoretically studied the band structure and Landau level spectrum of AB Bernal-stacked twisted double bilayer graphene with Rashba spin–orbit interaction. Using the low energy effective theory, we have studied the flat bands bandwidth as a function of twist angle, inter layer coupling strength, interlayer potential difference, and spin–orbit interaction strength. We find that the tunable Rashba spin–orbit interaction strength enhances the flatness of the flatbands. We further predicted an unusual strong spin polarization and multiple crossings of Landau levels with increasing interlayer coupling, Rashba spin–orbit interaction strength, and external bias voltage. • Considered Bernalstacked twisted double bilayer graphene with spinorbit interaction. • Noticed tunable Rashba spinorbit interaction strength enhances flatness of flatbands. • Predicted an unusual strong spin polarization and multiple crossings of Landau levels. • Our results show the tDBG system will be promising material for spintronic devices. [ABSTRACT FROM AUTHOR]

The photogalvanic effect (PGE) enables materials to generate photocurrent under zero bias and has a high polarization sensitivity in a broadband range, showing potential applications in the low-power two dimensional (2D) optoelectronic devices. Here, we compare the PGE for zigzag antimonene nanoribbons (SbNR) edge-modified by H, Cr and Co atoms in the visible range based on quantum transport calculations. It is found that the photoresponse and extinction ratio of Cr-SbNR and Co-SbNR are spin-polarized compared to those of H-SbNR. A cosine dependence on the polarization angle is found for photocurrent generated under the illumination of linearly polarized light in all three systems. Calculation indicates Co modification has a more significant effect on improving the photoresponse and polarization sensitivity of the device than Cr modification. These results show that in the visible range, antimonene nanoribbon edge-modified by Co atoms might be a promising candidate for photodetection in spintronic devices. [Display omitted] • The PGE results of zigzag antimonene nanoribbons edge-modified by Cr and Co atoms are spin-polarized. • The photoresponse and polarization sensitivity of Cr and Co systems are strongly related to the spin state. • Enhanced PGE is observed in antimonene nanoribbon passivated by Co atoms. • Co-modified device might be a promising candidate for photodetection in visible range. [ABSTRACT FROM AUTHOR]

Zigzag graphene nanoribbons (ZGNRs) are known to exhibit metallic behavior. Depending on structural properties such as edge status, doping and width of nanoribbons, the electronic properties of these structures may vary. In this study, changes in electronic properties of crystal by doping Lithium (Li) atom to ZGNR structure are analyzed. In spin polarized calculations are made using Density Functional Theory (DFT) with generalized gradient approximation (GGA) as exchange correlation. As a result of calculations, it has been determined that Li atom affects electronic properties of ZGNR structure significantly. It is observed that ZGNR structure exhibiting metallic behavior in pure state shows half-metal and semiconductor behavior with Li atom. [ABSTRACT FROM AUTHOR]

The magnetic and spin transport properties of a carbon chain between two armchair graphene nanoribbon (AGNR) electrodes were studied using tight-binding Hamiltonian, mean-field Hubbard model and Landauer–Butikker formalism. The results showed that only odd-numbered carbon chains show intrinsic magnetic moments in chain–graphene junctions. It was also found that the electronic, magnetic and spin transport properties of carbon chain–graphene junctions strongly depend on the position and the length of the carbon chains between AGNR electrodes. Interestingly, we found a fully spin-polarized transmission near the Fermi energy in all odd-numbered carbon chain–graphene junctions, regardless of their lengths and without any magnetic field and magnetic electrodes. [ABSTRACT FROM AUTHOR]

We calculate the spatially resolved tunnelling conductance of topological superconductors (TSCs) based on ferromagnetic chains, measured by means of spin-polarised scanning tunnelling microscopy (SPSTM). Our analysis reveals novel signatures of MFs arising from the interplay of their strongly anisotropic spin-polarisation and the magnetisation content of the tip. We focus on the deep Yu–Shiba–Rusinov (YSR) limit where only YSR bound states localised in the vicinity of the adatoms govern the low-energy as also the topological properties of the system. Under these conditions, we investigate the occurrence of zero/finite bias peaks (ZBPs/FBPs) for a single or two coupled TSC chains forming a Josephson junction. Each TSC can host up to two Majorana fermions (MFs) per edge if chiral symmetry is preserved. Here we retrieve the conductance for all the accessible configurations of the MF number of each chain. Our results illustrate innovative spin-polarisation-sensitive experimental routes for arresting the MFs by either restoring or splitting the ZBP in a predictable fashion via: (i) weakly breaking chiral symmetry, e.g. by the SPSTM tip itself or by an external Zeeman field and (ii) tuning the superconducting phase difference of the TSCs, which is encoded in the 4 π -Josephson coupling of neighbouring MFs. [ABSTRACT FROM AUTHOR]

We evaluate the spin polarization (Edelstein or inverse spin galvanic effect) and the spin Hall current induced by an applied electric field by including the weak localization corrections for a two-dimensional electron gas. We show that the weak localization effects yield logarithmic corrections to both the spin polarization conductivity relating the spin polarization and the electric field and to the spin Hall angle relating the spin and charge currents. The renormalization of both the spin polarization conductivity and the spin Hall angle combine to produce a zero correction to the total spin Hall conductivity as required by an exact identity. Suggestions for the experimental observation of the effect are given. [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]

The tunneling conductance spectra of a ferromagnetic semimetal/metal junction, where there were electrons and holes with the same spin directions as the essential conducting particle, was theoretically studied based on a scattering approach in a ballistic regime. The main area of interest was to perform a high spin polarization by considering the effect of the interfacial scattering at the interface that was composed of normal and spin-flip scattering, the particle effective mass mismatch on the reflection and transmission probabilities, and spin polarization of conductance. It was found that the spin polarization of conductance decreased with increasing spin-flip scattering. Interestingly, the normal scattering can cause the spin polarization of the conductance to reach a maximum value in the presence of both kinds of scattering. When the particle effective mass mismatch was considered, the spin polarization of conductance was large when the electron effective mass in the valence band was smaller than that in the conduction band. However, in this calculation, the results of a ferromagnetic semimetal/metal junction behaved similarly to those of a ferromagnetic metal/metal junction. [ABSTRACT FROM AUTHOR]

We simulate the electron transport in a vertical bi-layer nanowire in order to study an influence of the lateral confinement's shape on a spin polarization of wire's conductance. The active part of considered quantum wire constitutes a double inverted heterojunction In 0.52 Al 0.48 As / In 0.53 Ga 0.47 As which nanostructure can be fabricated in molecular beam epitaxy process while the lateral confinement potential can be finally formed by means of cleaved overgrowth or surface oxidization methods giving the desired rectangular and smooth lateral confinement. In calculations we take into account interaction between charge carriers using DFT within local spin density approximation. We show that if the magnetic field is perpendicular to the wire axis, the pseudogaps are opened in energy dispersion relation E ( k ) what in conjunction with spin Zeeman shift of spin-up and spin-down subbands may enhance the spin polarization of conductance with reference to a single layer wire. For nanowire with rectangular lateral confinement potential we found that the electron density has two maximums localized at wire edges in each layers. This modificates strongly all magnetosubbands giving up to four energy minimums in lowest subband and considerably diminishes widths of pseudogaps what translates into low maximal spin polarization of conductance, not exceeding 40%. This drawback is absent in wire with smooth lateral confinement. However, in order to gain a large spin polarization simultaneous tuning of magnetic field as well as the Fermi energies in both layers of nanowire are required. [ABSTRACT FROM AUTHOR]

We have studied the electronic structure and magnetism of the single transitional metal element X =Sc, V, Cr, Mn, Fe, Ni, Cu-doped CoO systems by first-principles calculations. At X =Sc, Cr, Cu, the binding energy of the doped systems is lower than pure CoO, suggesting that these systems are energetically stable. In the Sc, V, Cr, Mn, Fe, Ni, Cu-doped 2×2×2 CoO supercells, the total magnetic moments are 3.03, 5.64, 6.80, 7.70, 6.93, 2.30 and 1.96 μ B , respectively. At X =Cr and Fe, the doped CoO systems are half-metallic with a high spin polarization. The large magnetic moment and high spin polarization in the Cr and Fe-doped CoO are important for the design of the spintronic devices. [ABSTRACT FROM AUTHOR]

We study ballistic electron transport through single or double barriers on monolayer MoS 2 , of width d , in the presence of a ferromagnetic field M or an antiferromagnetic field F . The total conductance g c , its spin-up and spin-down components, and the polarization oscillate with d or the distance b between two barriers. The corresponding oscillation periods are different. The conductance g c versus M decreases in a fluctuating manner with a steep decline at certain value of M . As a function of M the spin polarization P s oscillates before it becomes 100% while the valley polarization P v oscillates and steadily increases. [ABSTRACT FROM AUTHOR]

We investigate the spin-polarized electronic and magnetic properties of bilayer SnSe with transition-metal (TM) atoms doped in the interlayer by using a first-principles method. It shows that Ni dopant cannot induce the magnetism in the doped SnSe sheet, while the ground state of V, Cr, Mn, Fe and Co doped systems are magnetic and the magnetic moment mainly originates from 3 d TM atom. Two types of factors, which reduce the magnetic moment of TM atoms doped in bilayer SnSe, are identified as spin-up channel of the 3 d orbital loses electrons to SnSe sheet and spin-down channel of the 3 d orbital gains electrons from 4 s orbital. The spin polarization is found to be 100% at Fermi level for the Mn and Co atoms doped system, while the Ni-doped system is still a semiconductor with a gap of 0.26 eV. These results are potentially useful for development of spintronic devices. [ABSTRACT FROM AUTHOR]

We evaluate the spin polarization (Edelstein or inverse spin galvanic effect) and the spin Hall current induced by an applied electric field by including the weak localization corrections for a two-dimensional electron gas. We show that the weak localization effects yield logarithmic corrections to both the spin polarization conductivity relating the spin polarization and the electric field and to the spin Hall angle relating the spin and charge currents. The renormalization of both the spin polarization conductivity and the spin Hall angle combine to produce a zero correction to the total spin Hall conductivity as required by an exact identity. Suggestions for the experimental observation of the effect are given. [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]

We calculate the spatially resolved tunnelling conductance of topological superconductors (TSCs) based on ferromagnetic chains, measured by means of spin-polarised scanning tunnelling microscopy (SPSTM). Our analysis reveals novel signatures of MFs arising from the interplay of their strongly anisotropic spin-polarisation and the magnetisation content of the tip. We focus on the deep Yu–Shiba–Rusinov (YSR) limit where only YSR bound states localised in the vicinity of the adatoms govern the low-energy as also the topological properties of the system. Under these conditions, we investigate the occurrence of zero/finite bias peaks (ZBPs/FBPs) for a single or two coupled TSC chains forming a Josephson junction. Each TSC can host up to two Majorana fermions (MFs) per edge if chiral symmetry is preserved. Here we retrieve the conductance for all the accessible configurations of the MF number of each chain. Our results illustrate innovative spin-polarisation-sensitive experimental routes for arresting the MFs by either restoring or splitting the ZBP in a predictable fashion via: (i) weakly breaking chiral symmetry, e.g. by the SPSTM tip itself or by an external Zeeman field and (ii) tuning the superconducting phase difference of the TSCs, which is encoded in the 4 π -Josephson coupling of neighbouring MFs. [ABSTRACT FROM AUTHOR]

We investigate the electron transport through one double-helical molecule with four terminals, by considering one terminal to be the source and others to be the drains. It is found that notable spin polarizations simultaneously occur during the processes of intra-chain electron tunneling and inter-chain electron reflection. More importantly, in these two processes, the spin polarizations always show similar strengths and opposite directions. Based on these results, we consider that the spin polarization and spin separation can be co-realized in this system. [ABSTRACT FROM AUTHOR]

The strain effects on the edge-state transport of the zigzag monolayer for a molybdenum disulfide nanoribbon are investigated numerically using a six-band tight-binding model with KWANT, where the strain effect was absorbed into the modified hopping coefficients. For metallic edge-states in a zigzag nanoribbon, introducing both an intrinsic spin–orbit coupling and local exchange field effects breaks the spin degeneracy and spin inversion symmetry to enable spin selective transport. Changes in the energy dispersion of the metallic edge-states due to uniaxial strain are asymmetric with respect to the strain direction. Transitions from metallic to insulating edge modes occur for a tensile strain of approximately 5% along the x -direction, but no such transition has been observed up to a tensile strain of 10% along the y -direction. The edge-current transmission and spin-polarized edge-currents are determined primarily by details of the energy dispersion of edge-states and are strongly affected by the incident energy of carriers for a given strain. The fully spin-polarized edge-currents can be obtained by modulating both the Fermi energy and gate potential. The results provide useful information to implement a spin-polarized current as a potential solution for wearable spin devices. [Display omitted] • The strain effects on the edge-state transport for a molybdenum disulfide nanoribbon. • Asymmetric change of the energy dispersion of the edge states with respect to the strain direction. • Transitions from metallic to insulating edge modes due to tensile strains. • The spin-polarized edge currents in a three terminal field effect transistor. [ABSTRACT FROM AUTHOR]

The recombination dynamics of photoexcited holes is studied in an In 0.53 Ga 0.47 As/InP quantum well in a quantizing magnetic field. The experimental data are analyzed in a framework of the four level system formed in the valence band by Landau levels. As a result, the characteristic times including the inter-Landau level transfer time, the spin relaxation time, and the interband recombination time are obtained. The inverse population of higher energy Landau level is found due to the slow transfer between Landau levels as compared to the fast interband recombination. It is demonstrated that optical spin injection led to about 50% spin polarization in the inversely populated Landau level, while the lowest energy Landau level is unpolarized. [ABSTRACT FROM AUTHOR]

The electronic states of a mesoscopic ring are assessed using the Green functions approach and the equation of motion method. We put forward the Green's function formalism to evaluate precisely persistent charge and spin currents in a ring exhibiting nearest-neighbors (NN) and next-nearest (NNN) neighbors Rashba spin–orbit interactions. Our present scheme circumvents direct diagonalization of the Hamiltonian, allowing to determine numerically persistent currents with both spin–orbit interactions simultaneously. Our results for the spin currents show that the NN Rashba interaction breaks the spin degeneracy producing a square-like shape; while the NNN Rashba interaction creates an energy-dependent splitting of the levels that generates a pattern of small peaks. The merging of both interactions rises a periodic squared-peaked pattern at half integer values of the quantum flux, which suggests the possibility of controlling the spin current magnitude and polarization by modulating the NNN Rashba parameter. • Next Nearest-Neighbors Rashba coupling breaks the spin degeneracy. • Charge persistent currents slightly changes due to Next Nearest-Neighbors Rashba SOC. • Spin persistent currents have localized peaks due to Next Nearest-Neighbors SOC. • The values of these peaks are large despite the small strength of the NNN SOC. • The spin currents suggest some spin control possibilities, by manipulating NNN SOC. [ABSTRACT FROM AUTHOR]

We study spin polarization and conductance of the asymmetric quantum point contact. We consider both Rashba coupling and lateral spin–orbit interaction induced by laterally asymmetric confinement potential. We show that in longitudinally symmetric quantum point contact, the spin polarization is not accompanied by the appearance of the conductance plateau at 0.5 G 0 ( G 0 = 2 e 2 / h ) . In longitudinally asymmetric quantum point contact the above plateau arises due to the presence of resonant states within the using one-electron approximation. An explanation of the experimental fact that the plateau exists only for a limited range of variation of the gate voltage is given. [ABSTRACT FROM AUTHOR]

We report on a theoretical investigation of spin-polarized transport in a δ -doped magnetically modulated semiconductor nanostructure, which can be experimentally realized by depositing a ferromagnetic stripe on the top of a semiconductor heterostructure and by using the atomic layer doping technique such as molecular beam epitaxy (MBE). It is shown that although such a nanostructure has a zero average magnetic filed, a sizable spin polarization exists due to the Zeeman splitting mechanism. It is also shown that the degree of spin polarization varies sensitively with the weight and/or position of the δ -doping. Therefore, one can conveniently tailor the behaviour of the spin-polarized electron by tuning the δ -doping, and such a device can be employed as a controllable spin filter for spintronics. [ABSTRACT FROM AUTHOR]

The structural, electronic and magnetic properties of 8-hydroxyquinoline-based small molecules TMQ x (TM=Cr, Mn, Fe, Co, Ni, Cu and Zn, and x =2 or 3) are systemically studied from first principles. These small molecules are spin-polarized semiconductors except for NiQ 2 , ZnQ 2 , and CoQ 3 . For TMQ 2 , the magnetic moments can be expressed as 8- nµ B ( n is the number of 3 d electrons of TM ions. For Mn, Fe, Co, and Ni, n =5, 6, 7, and 8 respectively) and 10- nµ B ( n =9 and 10 for Cu and Zn, respectively). For TMQ 3 , the magnetic moments can be expressed as 6- nµ B ( n =3, 4, 5, 6 for Cr, Mn, Fe, and Co, respectively). The magnetism can be explained by the spin-polarized filling of splitting d orbitals on the basis of the crystal field theory. This provides theoretical insight for better understanding of 8-hydorquinoline-based complexes (TMQ x ). [ABSTRACT FROM AUTHOR]

Achieving an efficient spin-filter effect and large magneto-resistance in molecular junctions is very important in spintronics. By employing the non-equilibrium Green's function formalism combined with the density functional theory, this study investigated the atomic structures and spin-resolved transport properties of molecular junctions consisting of nitrogen (N 2) sandwiched between two cobalt (Co) electrodes with different crystal lattices as a function of stretching distance. In the case of face-centred cubic Co electrodes, our calculations showed that the transport properties depend strongly on the stretching process, which changes the contact between the N 2 and Co electrodes. Specifically, the maximum spin polarization is due to the configuration of N 2 molecules sitting in parallel with the protruding Co atoms. Furthermore, the Co d xz,yz orbitals interact with the N p x,y orbitals, which contribute to the high transmission coefficient at the Fermi level for spin-down electrons. Meanwhile, the Co s-d z 2 hybridization orbitals, which interact weakly with the N p orbitals, contribute to the small transmission coefficient at the Fermi level. This can also be verified by the molecular junction model adopting simple monatomic Co chain electrodes, which also show a perfect spin-filter effect and achieve an ideal magnetoresistance. In contrast, in the case of hexagonal Co electrodes, the spin-filter effect disappears. However, the effect appears again by adding one more Co atom to the central point contact. Our findings show that the spin-resolved electronic transport of molecular junctions depends on the stretching process and the nature of the electrodes, which can help in the future design of molecular devices based on the spin degree of freedom. • The variation of atomic contact structures responds to the mechanical strain in the adiabatic approximation. • The spin-resolved transport properties depend on the stretching process and the nature of electrodes. • A perfect spin-filter device with ideal magneto-resistance is designed using N 2 sandwiched between monatomic Co chain. • The interaction between N p x,y and Co d xz,yz is Recognized and Verified in terms of the monatomic chain electrode model. • Developing a strategy turns the spin-filter effect. [ABSTRACT FROM AUTHOR]

We study the interplay of both Rashba and Dresselhaus spin-orbit couplings (SOCs) and a uniform perpendicular magnetic field B on the transport of a spin-polarized electron along a curved quantum wire. Eigenenergies and eigenfunctions of the system were analytically solved in the presence of both SOCs for a confinement radius R . From the transmission coefficients, the spin transport properties such as spin polarization, probability current density and spin conductance were computed numerically to determine their dependence on the SOCs, B and R . We find the condition for B that if it is beyond R 1 / 3 , no spin reversal will occur. Our results show that for a sufficiently large SOC strength, regardless of its inversion asymmetry origin, the effect of the external magnetic field is reduced. Finding the optimal effective SOC strength is essential in achieving suitable magneto-transport properties for possible spintronic device applications. [ABSTRACT FROM AUTHOR]

Abstract: The spin polarized electron transport properties and spin polarized tunneling current have been investigated analytically in a diluted magnetic semiconductor core–shell quantum dot in the presence of applied electric and magnetic fields. Assuming the electron wave function to satisfy WKB approximation, the electron energy eigenvalues have been calculated. The spin polarized tunneling current and the spin dependent tunneling coefficient are obtained by taking into account the exchange interaction and Zeeman splitting. Numerical estimates made for a specific diluted magnetic semiconductor, viz., core–shell quantum dot establishes the possibility of a nano-spin filter for a particular biasing voltage and applied magnetic field. [Copyright &y& Elsevier]

Abstract: We have theoretically investigated the conductance and the conductance spin-polarization (P G ) with combined magneto-electric potential structure in monolayer graphene. The results show that P G could be enhanced and hence reach maximum (P G±=±1) no matter which one of the four barrier parameters is increased. These four barrier parameters are the intensity (β) and the width (w) of the magnetic barriers, the intensity (U) and the width (b) of the potential barriers. The above results indicate that it is easy to realize the spin filtering. The peak value of the conductance and its corresponding energy could be controlled by adjusting the corresponding four barrier parameters. Additionally, switching effect and low energy spin-up injection could be realized in the structure under certain specific conditions. [Copyright &y& Elsevier]

Abstract: We performed a spin polarized density-function theory study of the stabilities, electronic and magnetic properties of zigzag silicene nanoribbons (ZSiNRs) substitutionally doped with a single N or B atom located at various sites ranging from edge to center of the ribbon. From minimization of the formation energy, it is found that the substitutional doping is favorable at edge of the ribbon. A single N or B atom substitution one edge Si atom of ZSiNRs can greatly suppress the spin-polarizations of the impurity atom site and its vicinity region, and leads to a transition from antiferromagnetic (AFM) state to ferromagnetic (FM) state, which is attributed to the splitting of the original spin degenerate edge bands. A single N atom doped ZSiNRs still keep semiconductor property but a single B atom doped ZSiNRs exhibit a half-metallic character. Our results reveal that substitution doped ZSiNRs have potential applications in Si-based nanoelectronics, such as field effect transisitors (FETs), negative differential resistance (NDR) and spin filter (SF) devices. [Copyright &y& Elsevier]

Abstract: Effect of gate voltage on spin transport properties of electrons through the metal / / metal junction was investigated using the non-equilibrium Green׳s function technique. The influence of position, type and contacts of M atoms was calculated using the tunneling theory. The results have indicated that molecule becomes magnetic by encapsulating M atoms and the effect of gate voltage is dramatic on magnetic moment of molecules. Spin polarization can be more than 90% with the proper gate voltage. [Copyright &y& Elsevier]

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]