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The photogalvanic effects (PGEs) in low-dimensional devices have attracted great interests recently. Herein, based on non-equilibrium Green's function combined with density functional theory, we investigated spin-dependent PGE phenomena in the BiC photodetector with the linearly polarized light and zero bias. Due to the presence of strong spin–orbit interaction (SOI) and C 3 v symmetry for the BiC monolayer, the armchair and zigzag BiC photodetectors can produce robust spin-dependent PGEs which possess the cos(2 θ) and sin(2 θ) relations on the photon energies, respectively. Especially, the pristine armchair and armchair Bi-vacancy BiC photodetectors can produce fully spin polarization, and pure spin current was found in the pristine armchair and zigzag BiC photodetector, respectively. Furthermore, after introducing the Bi-vacancy, C-vacancy, Bi-doping and C-doping respectively, the BiC photodetector can produce higher spin-dependent PGEs for their C s symmetry. Additionally, the behaviors of spin-dependent photoresponse are highly anisotropic which can be tuned by the photon energy. This work suggested great potential applications of the BiC monolayer on PGE-driven photodetectors in low energy-consumption optoelectronics and spintronic devices. [ABSTRACT FROM AUTHOR]

In this work, we theoretically investigate the phenomenon of spin polarization in generalized Sierpinski gasket (SPG) triangles ( Δ N N N , Δ F N N , Δ F F N , Δ F F F) in the presence of Rashba spin–orbit interaction (RSOI) within a tight-binding framework. The geometrical construction is addressed for all four types of generalized SPG triangles using an iterative function system that begins with a fixed triangle of any arbitrary side length. The geometry of various types of fractal networks has a major impact on the degeneracy of the energy spectrum. It is shown that only the two-terminal setup in the presence of RSOI is incapable of breaking the spin degeneracy, which necessitates the use of a three-terminal setup to break the time-reversal symmetry. The effect of flip map induced anisotropic hopping integrals on three-terminal spin-resolved transmission probabilities is studied. In several cases, we find almost 100 % spin polarization in our considered lattices. We also analyze how spin polarization varies with RSOI strength and fractal generations. Our results indicate that fractal lattices might be suitable functional elements for designing future spin-based electronic devices. [ABSTRACT FROM AUTHOR]

We have theoretically investigated the Andreev reflection (AR)-induced conductance spectra through antiferromagnet/normal layer/superconductor junctions with hexagonal lattices. When the PT symmetry is broken by the staggered sublattice potential, antiferromagnet may exhibit spin polarization. A gap-edge conductance peak is usually shown, reflecting the characteristic of conventional AR. Equal-spin AR can be generated by the spin-flip scattering caused by Rashba spin–orbit coupling in the normal layer. Surprisingly, when the equal-spin AR process dominates, the conductance peak divides into two peaks near the singlet-gap energy, indicating the existence of spin-triplet pairings in the antiferromagnet. Furthermore, as the amplitudes of the conventional and equal-spin ARs can be modulated by the staggered sublattice potential and electrostatic potential, a conversion from the conductance peak to the conductance peak splitting can be realized, which can help us to distinguish between the spin-singlet and spin-triplet pairings. These findings make the antiferromagnet/superconductor junctions as promising platforms for future superconducting spintronics applications. [ABSTRACT FROM AUTHOR]

Inspired by potential application prospects of spintronics and valleytronics, a novel heterobilayer Janus structure is designed by replacing the chalcogenide atomic layers in the original bilayer MoS2. Based on first-principles calculations, it is found that the SMoS/SeMoS structure exhibits a direct band-gap semiconductor and a typical type-II band alignment with longer carrier lifetime. The transition metal (TM) atom represented by V/Cr/Mn can be stably adsorbed on the heterobilayer Janus SMoS/SeMoS sheet and effectively introduce magnetic moments (m). The calculation results demonstrate that the most stable adsorption site of the TM atom is CX(A), and the TM (V/Cr/Mn) adatom modified SMoS/SeMoS system is converted into metal (V-) or half-metal (Cr/Mn-), respectively. Under the coupling of different indirect exchange interactions, the structure exhibits stable intrinsic anti-ferromagnetic interactions for V-SMoS/SeMoS and ferromagnetic ground state for Cr/Mn-SMoS/SeMoS, respectively, and the magnetic transition temperature (T c) reaches a high temperature or even room temperature. Moreover, the robust out-of-plane magnetocrystalline anisotropy energy ensures stable long-range magnetic order. Specifically, the combination of spin injection and strong spin–orbit coupling interaction effectively breaks the time-reversal symmetry, which leads to valley polarization of the system. Based on this, the biaxial strain can effectively regulate the electronic structure, magnetic properties and valley polarization of TM-SMoS/SeMoS nanosheets with double breaking of spatial-inversion and time-reversal symmetry. [ABSTRACT FROM AUTHOR]

We study inserting Co layer thickness-dependent spin transport and spinâ€"orbit torques (SOTs) in the Pt/Co/Py trilayers by spin-torque ferromagnetic resonance. The interfacial perpendicular magnetic anisotropy (IPMA) energy density (K s = 2.7 erg/cm2, 1 erg = 10âˆ'7 J), which is dominated by interfacial spinâ€"orbit coupling (ISOC) in the Pt/Co interface, total effective spin-mixing conductance (G eff , tot â†' â†" = 0. 42 Ă— 10 15 Ω âˆ' 1 â‹... m âˆ' 2 ) and two-magnon scattering (β TMS = 0.46 nm2) are first characterized, and the damping-like torque (Îľ DL = 0.103) and field-like torque (Îľ FL = â€"0.017) efficiencies are also calculated quantitatively by varying the thickness of the inserting Co layer. The significant enhancement of Îľ DL and Îľ FL in Pt/Co/Py than Pt/Py bilayer system originates from the interfacial Rashbaâ€"Edelstein effect due to the strong ISOC between Co-3d and Pt-5d orbitals at the Pt/Co interface. Additionally, we find a considerable out-of-plane spin polarization SOT, which is ascribed to the spin anomalous Hall effect and possible spin precession effect due to IPMA-induced perpendicular magnetization at the Pt/Co interface. Our results demonstrate that the ISOC of the Pt/Co interface plays a vital role in spin transport and SOTs-generation. Our finds offer an alternative approach to improve the conventional SOTs efficiencies and generate unconventional SOTs with out-of-plane spin polarization to develop low power Pt-based spintronic via tailoring the Pt/FM interface. [ABSTRACT FROM AUTHOR]

The persistent spin helix (PSH) system is considered to have promising applications in energy-conservation spintronics because it supports an extraordinarily long spin lifetime of carriers. Here, we predict that the existence of PSH state in two-dimensional (2D) ferroelectric NbOI2 monolayers. Our first-principles calculation results show that there exists Dresselhaus-type spin-orbit coupling (SOC) band splitting near the conduction-band minimum (CBM) of the NbOI2 monolayer. It is revealed that the spin splitting near CBM merely refers to out-of-plane spin configuration in the wave vector space, which gives rise to a long-lived PSH state that can be controlled by reversible ferroelectric polarization. We believe that the coupling characteristics of ferroelectric polarization and spin texture in NbOI2 provide a platform for the realization of fully electric controlled spintronic devices. [ABSTRACT FROM AUTHOR]

We introduce a generalized Rashba coupling approximation to analytically solve confined two-dimensional electron systems with both the Rashba and Dresselhaus spin–orbit couplings in an external magnetic field. A solvable Hamiltonian is obtained by performing a simple change of basis, which has the same form as that with only Rashba coupling. Each Landau state becomes a new displaced-Fock state instead of the original Harmonic oscillator Fock state. Analytical energies are consistent with the numerical ones in a wide range of coupling strength even for a strong Zeeman splitting, exhibiting the validity of the analytical approximation. By using the eigenstates, spin polarization correctly displays a jump at the energy-level crossing point, where the corresponding spin conductance exhibits a pronounced resonant peak. As the component of the Dresselhaus coupling increases, the resonant point shifts to a smaller value of the magnetic field. In contrast to pure Rashba couplings, we find that the Dresselhaus coupling and Zeeman splittings tend to suppress the resonant spin Hall effect. Our method provides an easy-to-implement analytical treatment to two-dimensional electron gas systems with both types of spin–orbit couplings by applying a magnetic field. [ABSTRACT FROM AUTHOR]

We report a new type of spin–orbit coupling (SOC) called geometric SOC. Starting from the relativistic theory in curved space, we derive an effective nonrelativistic Hamiltonian in a generic curve embedded into flat three dimensions. The geometric SOC is O(m−1), in which m is the electron mass, and hence much larger than the conventional SOC of O(m−2). The energy scale is estimated to be a hundred meV for a nanoscale helix. We calculate the current-induced spin polarization in a coupled-helix model as a representative of the chirality-induced spin selectivity. We find that it depends on the chirality of the helix and is of the order of 0.01ℏ per nm when a charge current of 1 μA is applied. [ABSTRACT FROM AUTHOR]

It was recently noted that in certain nonmagnetic centrosymmetric compounds, spin–orbit interactions couple each local sector that lacks inversion symmetry, leading to visible spin polarization effects in the real space, dubbed "hidden spin polarization (HSP)". However, observable spin polarization of a given local sector suffers interference from its inversion partner, impeding material realization and potential applications of HSP. Starting from a single-orbital tight-binding model, we propose a nontrivial way to obtain strong sector-projected spin texture through the vanishing hybridization between inversion partners protected by nonsymmorphic symmetry. The HSP effect is generally compensated by inversion partners near the Γ point but immune from the hopping effect around the boundary of the Brillouin zone. We further summarize 17 layer groups that support such symmetry-assisted HSP and identify hundreds of quasi-2D materials from the existing databases by first-principle calculations, among which a group of rare-earth compounds LnIO (Ln = Pr, Nd, Ho, Tm, and Lu) serves as great candidates showing strong Rashba- and Dresselhaus-type HSP. Our findings expand the material pool for potential spintronic applications and shed light on controlling HSP properties for emergent quantum phenomena. [ABSTRACT FROM AUTHOR]

The fascinating Dirac cone in honeycomb graphene, which underlies many unique electronic properties, has inspired the vast endeavors on pursuing new two-dimensional (2D) Dirac materials. Based on the density functional theory method, a 2D material Zn3Si2 of honeycomb transition-metal silicide with intrinsic Dirac cones has been predicted. The Zn3Si2 monolayer is dynamically and thermodynamically stable under ambient conditions. Importantly, the Zn3Si2 monolayer is a room-temperature 2D Dirac material with a spin–orbit coupling energy gap of 1.2 meV, which has an intrinsic Dirac cone arising from the special hexagonal lattice structure. Hole doping leads to the spin polarization of the electron, which results in a Dirac half-metal feature with single-spin Dirac fermion. This novel stable 2D transition-metal-silicon-framework material holds promises for electronic device applications in spintronics. [ABSTRACT FROM AUTHOR]

This review article summarizes recent developments related to the dynamical formation of persistent spin helices in GaAs- and CdTe-based heterostructures. We start with fundamental aspects of spin-orbit interaction in quantum wells, in particular the Dresselhaus and Rashba terms and their relation to the bulk and structural inversion asymmetries, respectively. In the regime of balanced interactions, their combined impact gives rise to the formation of the persistent spin helix, i.e., a regime where a unidirectional spin grating with enhanced coherence time is established. The experimental scheme relies on ultrafast Kerr microscopy and permits to excite the spin polarization and detect it with a simultaneous spatial and temporal resolution of micrometers and picoseconds, respectively. For a microscopic understanding and a description of the results, kinetic theory of spatio-temporal spin dynamics of two-dimensional electrons is presented. In addition, Monte Carlo simulations of the spin distribution function are performed. Based on these concepts we discuss three areas with recent advances in the field of spin helices. (i) Anisotropic spin transport and spin helix dynamics in a modulation-doped GaAs quantum well is analyzed. It is observed that application of an out-of-plane electric field changes spin-orbit interaction through the Rashba component and the cubic Dresselhaus term. Remarkably, a weak in-plane electric field substantially increases spin diffusion and also affects the spin helix wavelength. (ii) In-plane magnetic fields applied in two perpendicular orientations allow for the extraction of the individual spin–orbit coupling parameters. (iii) Finally, we explore the influence of optical doping on the spin helix in a CdTe quantum well. Most importantly, a non-uniform spatio-temporal precession pattern is observed. The kinetic theory of spin diffusion allows us to model this finding by incorporating a dependence on the photo-carrier density into the Rashba and the Dresselhaus parameters. [ABSTRACT FROM AUTHOR]

We investigate theoretically the combination effect of an in-plane magnetic field and spin-orbit interactions (SOIs) on the spin and charge transport property of a quasi-one-dimensional quantum wire embedded in the (110) crystallographic plane. We find that the oscillations of the conductance induced by the SOIs become more significant and different for the spin-up and spin-down electrons in the presence of the in-plane magnetic field. The conductance exhibits a significant anisotropic behavior and electrons exhibit out-of-plane spin polarization which can be tuned by an in-plane magnetic field. These features offer us an efficient way to control SOI-induced spin transport using in-plane magnetic fields. [ABSTRACT FROM AUTHOR]

The spin-polarized linear conductance spectrum and current--voltage characteristics in a four-quantum-dot ring embodied into Aharonov--Bohm (AB) interferometer are investigated theoretically by considering a local Rashba spin--orbit interaction. It shows that the spin-polarized linear conductance and the corresponding spin polarization are each a function of magnetic flux phase at zero bias voltage with a period of 2p, and that Hubbard U cannot influence the electron transport properties in this case. When adjusting appropriately the structural parameter of inter-dot coupling and dot-lead coupling strength, the electronic spin polarization can reach a maximum value. Furthermore, by adjusting the bias voltages applied to the leads, the spin-up and spin-down currents move in opposite directions and pure spin current exists in the configuration space in appropriate situations. Based on the numerical results, such a model can be applied to the design of a spin filter device. [ABSTRACT FROM AUTHOR]

Spin-dependent transport in a triple quantum dots superlattice system with a bridge coupling to two leads is studied. There exists an odd-even parity oscillation of spin polarization at the central dot level ∊c = 0 due to the spin-dependent Fano and Dicke effects induced by the quantum interference and the Rashba spin-orbit interaction. In the case of even numbers of triple quantum dots, the device can be used as a spin switch by tuning the energy difference h between the energies of the central and the lateral dots. These results may be helpful to design and fabricate practical spintronic devices. [ABSTRACT FROM AUTHOR]

We formulate the effective Hamiltonian of Rashba spin–orbit coupling (RSOC) in (LAO/STO) heterostructures. We derive analytical expressions of properties, e.g. Rashba parameter, effective mass, band edge energy and orbital occupancy, as functions of material and tunable heterostructure parameters. While linear RSOC is dominant around the Γ-point, cubic RSOC becomes significant at the higher-energy anti-crossing region. We find that linear RSOC stems from the structural inversion asymmetry (SIA), while the cubic term is induced by both SIA and bulk asymmetry. Furthermore, the SOC strength shows a striking dependence on the tunable heterostructure parameters such as STO thickness and the interfacial electric field which is ascribed to the quantum confinement effect near the LAO/STO interface. The calculated values of the linear and cubic RSOC are in agreement with previous experimental results. [ABSTRACT FROM AUTHOR]

We have studied the characteristics of current-induced nonequilibrium spin polarization in semiconductor-nanowire/s-wave superconductor junctions with strong spin–orbit coupling. It was found that within some parameter regions the magnitude of the current-induced nonequilibrium spin polarization density in such structures will increase (or decrease) with the decrease (or increase) of the charge current density, in contrast to that found in normal spin–orbit coupled semiconductor structures. It was also found that the unusual characteristics of the current-induced nonequilibrium spin polarization in such structures can be well explained by the effect of the Andreev reflection. [ABSTRACT FROM AUTHOR]

We investigate the incident angle-dependent spin polarisation transport in a ballistic nonmagnetic nanojunction with interfacial spin–orbit (SO) coupling by means of the mode-matching approach. In the absence of interfacial SO coupling, for both delta function and square-shaped barriers, the probabilities of transmission for spin up and spin down are the same and are even functions of the injection angle. On the other hand, in the presence of interfacial SO coupling, the transmission probabilities for spin up and spin down are different and are asymmetric with respect to the direction of the normal incidence. Moreover, we study the total transmission properties and analyse the spin polarisation properties of these systems. In particular, for the case of interface with SO coupling, we find that the spin polarisation oscillates with respect to the incident angle. This characteristic offers an efficient way to achieve the spin injection device without using ferromagnets. [ABSTRACT FROM AUTHOR]

Surface states of topological noncentrosymmetric superconductors (NCSs) exhibit intricate helical spin textures, i.e., the spin orientation of the surface quasiparticles is coupled to their momentum. Using quasiclassical theory, we study the spin polarization of the surface states as a function of the spin–orbit interaction and superconducting pairing symmetry. We focus on two- and three-dimensional fully gapped and nodal NCSs. For the case of nodal systems, we show that the spin polarization of the topological flat bands is controlled by the spin polarization of the bulk normal states at the bounding gap nodes. We demonstrate that the zero-bias conductance in a magnetic tunnel junction can be used as an experimental test of the surface-state spin polarization. [ABSTRACT FROM AUTHOR]

We investigate the transitions of ground states induced by zero momentum (ZM) coupling in pseudospin-1/2 Rashba spin–orbit coupled Bose–Einstein condensates confined in a harmonic trap. In a weak harmonic trap, the condensate presents a plane wave (PW) state, a stripe state or a spin polarized ZM state, and the particle distribution of the stripe state is weighted equally at two points in the momentum space without ZM coupling. The presence of ZM coupling induces an imbalanced particle distribution in the momentum space, and leads to the decrease of the amplitude of the stripe state. When its strength exceeds a critical value, the system experiences the transition from stripe phase to PW phase. The boundary of these two phases is shifted and a new phase diagram spanned by the ZM coupling and the interatomic interactions is obtained. The presence of ZM coupling can also achieve the transition from ZM phase to PW phase. In a strong harmonic trap, the condensate exhibits a vortex lattice state without ZM coupling. For the positive effective Rabi frequency of ZM coupling, the condensate is driven from a vortex lattice state to a vortex-free lattice state and finally to a PW state with the increase of coupling strength. In addition, for the negative effective Rabi frequency, the condensate is driven from a vortex lattice state to a stripe state, and finally to a PW state. The stripe state found in the strong harmonic trap is different from that in previous works because of its nonzero superfluid velocity along the stripes. We also discuss the influences of the ZM coupling on the spin textures, and indicate that the spin textures are squeezed transversely by the ZM coupling. [ABSTRACT FROM AUTHOR]

We study of the appearance and evolution of several anomalous (i.e., G < G0 = 2e2/h) conductance plateaus in an In0.52Al0.48As/InAs quantum point contact (QPC). This work was performed at T = 4.2 K as a function of the offset bias ΔVG between the two in-plane gates of the QPC. The number and location of the anomalous conductance plateaus strongly depend on the polarity of the offset bias. The anomalous plateaus appear only over an intermediate range of offset bias of several volts. They are quite robust, being observed over a maximum range of nearly 1 V for the common sweep voltage applied to the two gates. These results are interpreted as evidence for the sensitivity of the QPC spin polarization to defects (surface roughness and impurity (dangling bond) scattering) generated during the etching process that forms the QPC side walls. This assertion is supported by non-equilibrium Green function simulations of the conductance of a single QPC in the presence of dangling bonds on its walls. Our simulations show that a spin conductance polarization α as high as 98% can be achieved despite the presence of dangling bonds. The maximum in α is not necessarily reached where the conductance of the channel is equal to 0.5G0. [ABSTRACT FROM AUTHOR]