Intrinsic Spin Splitting Research Articles

Mechanisms of manipulating valley splitting in MoTe2/MnS2 van der Waals heterostructure by electric field and strains.

In this study, we discuss the tunability of valley splitting using first-principles calculations with a monolayer MoTe2 and layered ferromagnetic MnS2 heterostructure as an example. We observe that, due to the magnetic proximity effect (MPE) at the interface, a monolayer of MoTe2 can exhibit a significant valley splitting of 55.2 meV. The production of the interlayer dipoles with spin-adapted configuration could be the origin of MPE at the interface. Furthermore, the valley splitting can be regulated continuously by the perpendicular electric field and biaxial strain. Interestingly, the valley splitting increases with the increasing induced magnetic moments in MoTe2 by applying an electric field while the inverse laws are presented by applying biaxial strains, which indicates that the mechanisms of valley splitting manipulating in these two ways are quite different. The calculation results suggest that the electric field influences the electric dipole distributions at the interface, which determines the induced magnetic moments in monolayer MoTe2, and results in valley splitting variations. However, biaxial strains not only affect MPE at the interface but also the intrinsic spin splitting caused by spin-orbital coupling (SOC) effects of monolayer MoTe2 itself and the latter is even the dominating mechanism of valley splitting variations.

Optical manipulation of Rashba-split 2-dimensional electron gas

In spintronics, the two main approaches to actively control the electrons’ spin involve static magnetic or electric fields. An alternative avenue relies on the use of optical fields to generate spin currents, which can bolster spin-device performance, allowing for faster and more efficient logic. To date, research has mainly focused on the optical injection of spin currents through the photogalvanic effect, and little is known about the direct optical control of the intrinsic spin-splitting. To explore the optical manipulation of a material’s spin properties, we consider the Rashba effect. Using time- and angle-resolved photoemission spectroscopy (TR-ARPES), we demonstrate that an optical excitation can tune the Rashba-induced spin splitting of a two-dimensional electron gas at the surface of Bi2Se3. We establish that light-induced photovoltage and charge carrier redistribution - which in concert modulate the Rashba spin-orbit coupling strength on a sub-picosecond timescale - can offer an unprecedented platform for achieving optically-driven spin logic devices.

Adsorption of heavy-element monolayers of Tl, Pb, and Bi at silicene: A DFT study

This report investigates the adsorption of monolayers of X (Tl, Pb, Bi) at silicene and the dynamical stability of the system. Based on the density functional theory calculations it is shown that, X atoms bond strongly with the substrate giving rise to new X–Si hybrid states, which results in preferred surface configurations of X@silicene. Born-Oppenheimer quantum dynamics of the favorable structures were carried out at set temperature of 200 and 500 K for X@silicene supported on MoS2. The simulations predict that, the 1 × 1 phases of Tl, and Bi are dynamical stable at 200 K, while at 500 K the adsorbed atoms group in 3- or 4-atom patterns suggesting a possible 3×3 reconstruction. In contrast, Pb@silicene–1 × 1 is still predicted stable at 500 K. All structures exhibit a giant spin splitting (GSS) present in the metallic bands, which shows that, a heavy-element adsorption can be an effective method for giving rise to GSS at surfaces of 2D materials with no intrinsic spin splitting.

Spin response and collective modes in simple metal dichalcogenides

Transition-metal dichalcogenide monolayers are interesting materials in part because of their strong spin-orbit coupling. This leads to intrinsic spin splitting of opposite signs in opposite valleys, so the valleys are intrinsically spin polarized when hole doped. We study spin response in a simple model of these materials, with an eye to identifying sharp collective modes (i.e., spin waves) that are more commonly characteristic of ferromagnets. We demonstrate that such modes exist for arbitrarily weak repulsive interactions, even when they are too weak to induce spontaneous ferromagnetism. The behavior of the spin response is explored for a range of hole dopings and interaction strengths.

Anomalous Hall effect in 2H -phase MX2 transition-metal dichalcogenide monolayers on ferromagnetic substrates ( M = Mo, W, and X = S, Se, Te)

We study the anomalous Hall effect in monolayers of transition-metal dichalcogenides 2H-$MX_2$ ($M$=Mo, W, and $X$=S, Se, Te) under a proximity effect of ferromagnetic substrate. If a proximity-induced exchange field is introduced, the spin-polarized energy bands in $K$ and $K'$ valleys are shifted in the opposite directions, and it causes the Hall effect by breaking time-reversal symmetry. The induced Hall effect is the most prominent in the valence band which has a large intrinsic spin splitting. Moreover, we find that tilting the magnetization from the perpendicular direction gives rise to a sensitive change in the Hall conductivity only in the electron side, and it is attributed to the mixing of the Berry phase by the in-plane field in the nearly degenerate conduction bands.

Spin Hall Effects Due to Phonon Skew Scattering.

A diversity of spin Hall effects in metallic systems is known to rely on Mott skew scattering. In this work its high-temperature counterpart, phonon skew scattering, which is expected to be of foremost experimental relevance, is investigated. In particular, the phonon skew scattering spin Hall conductivity is found to be practically T independent for temperatures above the Debye temperature T_{D}. As a consequence, in Rashba-like systems a high-T linear behavior of the spin Hall angle demonstrates the dominance of extrinsic spin-orbit scattering only if the intrinsic spin splitting is smaller than the temperature.

Gate-controlled supercurrent reversal in MoS2-based Josephson junctions

Motivated by recent experiments revealing superconductivity in , we investigate the Josephson effect in the monolayer in the presence of an exchange splitting. We show that the supercurrent reversal known as transition can occur by varying the doping via gate voltages. This is in contrast to common superconductor/ferromagnet/superconductor junctions in which successive transitions take place with the variation of junction length or temperature. In fact for the case of we find that both the amplitude and the period of oscillations show a dependence on the doping which explains the predicted doping-induced supercurrent reversal. These effects comes from the dependence of density and Fermi velocity on the doping strength beside the intrinsic spin-splitting in the valence band which originates from spin-orbit interaction.

Spin-orbit-mediated spin relaxation in monolayer MoS2

We study the intra-valley spin-orbit mediated spin relaxation in monolayers of MoS2 within a two bands effective Hamiltonian. The intrinsic spin splitting of the valence band as well as a Rashba-like coupling due to the breaking of the out-of-plane inversion symmetry are considered. We show that, in the hole doped regime, the out-of-plane spin relaxation is not very efficient since the spin splitting of the valence band tends to stabilize the spin polarization in this direction. We obtain spin lifetimes larger than nanoseconds, in agreement with recent valley polarization experiments.

Absence of intrinsic spin splitting in one-dimensional quantum wires of tetrahedral semiconductors

The energy bands of three-, two-, and one-dimensional (1D) structures are generally split at certain wave-vector values into spin components, a spin splitting (SS) that occurs even without an external magnetic field and reflects the effect of spin-orbit interaction on certain symmetries. We show via atomistic theory that 1D quantum wires made of conventional zinc-blende semiconductors have unexpected zero SS for all electron and hole bands if the wire is oriented along (001) (belonging to ${D}_{2d}$ symmetry), and for some of bands if the wire is oriented along (111) (belonging to ${C}_{3v}$ symmetry). We find that the predicted absence of a Dresselhaus SS in both (001)-oriented and (111)-oriented 1D wires is immune to perturbations lowering their original ${D}_{2d}$ and ${C}_{3v}$ structural symmetries, such as alloying of the matrix around the wire or application of an external electric field. Indeed, such perturbations induce only a Rashba SS. We find that the scaling of the SS with the wave vector is dominated by a linear term plus a minor cubic term.

Effect of spin-orbit coupling on the spectrum of two-dimensional electrons in a magnetic field

The electron states in semiconductors with zinc-blende structure in an external magnetic field are studied taking into account the intrinsic spin splitting. The Hamiltonian of the spin-orbit coupling is written out using the method of invariants. Effects of modification of the energy spectrum of two-dimensional electrons in single and double quantum wells in a magnetic field oriented parallel to the interface planes are considered.

Weak anti-localisation in 2-D 100-electron gases in GaAS

2-dimensional electrons in GaAs has a strong spin-orbit interaction, which leads to anti-localisation. The origin of this spin-orbit effect in GaAs lies in the band structure, where an intrinsic spin splitting is rooted in the lack of inversion symmetry. The weak localization at small magnetic fields clearly shows this. We have studied this experimentally at various temperatures in 2 different MBE grown GaAlAs/GaAs structures: A triangular 100 oriented quantum well and a symmetrical 100 oriented quantum well.

Electron spin-flip Raman scattering in asymmetric quantum wells: Spin orientation

We present Raman scattering measurements of intrasubband single-particle excitations (SPE) in the two-dimensional gas confined in a GaAs AlGaAs quantum well. The intrinsic spin-splitting in the conduction subband of the quantum well may be determined from the spin-flip SPE observed in depolarized Raman scattering. From measurements on samples of varying carrier density, we analyse the dependence of the spin-splitting and its anisotropy on electron wavevector. The results of tight binding calculations support our conclusions about the origin of the spin orientation in a quantum well.

Weak localization corrections to spin and particle transport in semiconductor quantum wells. Effects of the spin orbit interaction

We studied weak localization corrections to spin and particle transport parameters of III-V semiconductor quantum wells. The intrinsic spin splitting of electron energies in the conduction band was taken into account. At the region of times larger than the D'yakonov-Perel' spin relaxation time we found drastically different localization behaviours of the spin and particle diffusion coefficients. We also have shown that the weak localization corrections are strongly dependent on the crystal orientation of material within the quantum well. In particular, no antilocalization behaviour was found for the particle diffusion in case of [011] orientation in contrast to [111] and [001] oriented quantum wells. Possible experimental detection is suggested.

Raman scattering on modulation-doped quantum wells: Intrinsic spin splitting of the GaAs conduction band

The spin splitting of the conduction band in GaAs is directly observed through the splitting of the intrasubband electronic Raman spectra. Its dependence on the magnitude and orientation of the wavevector is discussed in terms of a simple band structure model.