We report bulk Rashba spin splitting (RSS) and associated Dirac surface state in (Bi$_{0.9}$Sb$_{0.1})_2$Se$_3$, exhibiting dominant $p$-type conductivity. We argue from the synchrotron diffraction studies that origin of the bulk RSS is due to a structural transition to a non-centrosymmetric $R3m$ phase below $\sim$ 30 K. The Shubnikov-de Haas Van (SdH) oscillations observed in the magnetoresistance curves at low temperature and the Landau level fan diagram, as obtained from these oscillations, confirm the presence of nontrivial Dirac surface state. The magnetization data at low temperature exhibit substantial orbital magnetization consistent with the bulk RSS. The existance of both the bulk RSS and Dirac surface states are confirmed by first principles density functional theory calculations. Coexistence of orbital magnetism, bulk RSS, and Dirac surface state is unique for $p$-type (Bi$_{0.9}$Sb$_{0.1})_2$Se$_3$, making it an ideal candidate for spintronic applications.
The transport properties of a magnetic two dimensional electron gas consisting of a modulation doped n type HgMnTe/HgCdTe quantum well, QW, have been investigated. By analyzing the Shubnikov-de Haas oscillations and the node positions of their beating patterns, we have been able to separate the gate voltage dependent Rashba spin-orbit splitting from the temperature dependent giant Zeeman splitting. It has been experimentally demonstrated that the Rashba spin-orbit splitting is larger than or comparable to the $sp-d$ exchange interaction induced giant Zeeman splitting in this magnetic 2DEG even…
In the two-dimensional electron gas (2DEG) emerging at the transition metal oxide surface and interface, it has been pointed out that the Rashba spin-orbit interaction, the momentum-dependent spin splitting due to broken inversion symmetry and atomic spin-orbit coupling, can have profound effects on electronic ordering in the spin, orbit, and charge channels, and may help give rise to exotic phenomena such as ferromagnetism-superconductivity coexistence and topological superconductivity. Although a large Rashba splitting is expected to improve experimental accessibility of such phenomena, it h…
Spin-spin correlation function response in the low electronic density regime and externally applied electric field is evaluated for 2D metallic crystals under Rashba-type coupling, fixed number of particles and two-fold energy band structure. Intrinsic Zeeman-like effect on electron spin polarization, density of states, Fermi surface topology and transverse magnetic susceptibility are analyzed in the zero temperature limit. A possible magnetic state for Dirac electrons depending on the zero field band gap magnitude under this conditions is found.
We study the magneto-optical (MO) response of polar semiconductor BiTeI with giant bulk Rashba spin splitting at various carrier densities. Despite being non-magnetic, the material is found to yield a huge MO activity in the infrared region under moderate magnetic fields (<3 T). By comparison with first-principles calculations, we show that such an enhanced MO response is mainly due to the intraband transitions between the Rashba-split bulk conduction bands in BiTeI, which give rise to distinct novel features and systematic doping dependence of the MO spectra. We further predict an even more p…
The electronic structure of Bi2Se3 is studied by angle-resolved photoemission and density functional theory. We show that the instability of the surface electronic properties, observed even in ultra-high-vacuum conditions, can be overcome via in-situ potassium deposition. In addition to accurately setting the carrier concentration, new Rashba-like spin-polarized states are induced, with a tunable, reversible, and highly stable spin splitting. Ab-initio slab calculations reveal that these Rashba state are derived from the 5QL quantum-well states. While the K-induced potential gradient enhances …
The recent epitaxial growth of 1T-phase of PtSe2 monolayer (ML) has opened a possibility for its novel applications, in particular for spintronics device. However, in contrast to 2H-phase of transition-metal dichalcogenides (TMDs), the absence of spin splitting in the PtSe2 ML may limit the functionality for spintronics application. Through fully-relativistic density-functional theory calculations, we show that large spin splitting can be induced in the PtSe2 ML by introducing a substitutional halogen impurity. Depending on the atomic number (Z) of the halogen dopants, we observe an enhancemen…
The spin-splitting energy bands induced by the relativistic spin-orbit interaction in solids provide a new opportunity to manipulate the spin-polarized electrons on the sub-picosecond time scale. Here, we report one such example in a bulk Rashba-type polar semiconductor BiTeBr. Strong terahertz electromagnetic waves are emitted after the resonant excitation of the interband transition between the Rashba-type spin-splitting energy bands with a femtosecond laser pulse circularly polarized. The phase of the emitted terahertz waves is reversed by switching the circular polarization. This suggests …
We propose that existence of local orbital angular momentum (OAM) on the surfaces of high-Z materials play a crucial role in the formation of Rashba-type surface band splitting. Local OAM state in a Bloch state produces asymmetric charge distribution (electric dipole). Presence of surface electric field aligns the electric dipole and results in chiral OAM states and the relevant Rashba- type splitting. Therefore, the band splitting originates from electric dipole interaction, not from the Zeeman splitting as proposed in the original Rashba picture. The characteristic spin chiral structure of R…
First-principles calculations were carried out to explore the possible coupling between spin-polarized electronic states and ferroelectric polarization in monolayers of transition-metal dichalcogenides MX 2 (M = Mo, W; X = S, Se, Te) with distorted octahedrally coordinated 1T structures.For d^2 metal ions, two competing metal clustering effects can take place, where metal ions are arranged in trimers or zigzag chains. Among these, the former structural distortion comes along with an improper ferroelectric phase which persists in the monolayer limit. Switchable Rashba-like spin-polarization fea…
The origin of the g-factor of the two-dimensional (2D) electrons and holes moving in the periodic crystal lattice potential with the perpendicular magnetic and electric fields is discussed. The Pauli equation describing the Landau quantization accompanied by the Rashba spin-orbit coupling (RSOC) and Zeeman splitting (ZS) for 2D heavy holes with nonparabolic dispersion law is solved exactly. The solutions have the form of the pairs of the Landau quantization levels due to the spinor-type wave functions. The energy levels depend on amplitudes of the magnetic and electric fields, on the g-factor …
A new family of the low-buckled Dirac materials which includes silicene, germanene, etc. is expected to possess a more complicated sequence of Landau levels than in pristine graphene. Their energies depend, among other factors, on the strength of the intrinsic spin-orbit (SO) and Rashba SO couplings and can be tuned by an applied electric field $E_z$. We studied the influence of the intrinsic Rashba SO term on the energies of Landau levels using both analytical and numerical methods. The quantum magnetic oscillations of the density of states are also investigated. A specific feature of the osc…
The beating pattern of Shubnikov-de Haas oscillations in 2D electron system in the presence of a Rashba zero-field spin splitting is reproduced. It is shown, taking into account the Zeeman splitting, that the explicit formulae for the node position well describes the experimental data. The spin-orbit interaction strength obtained is found to be magnetic field independent in an agreement with the basic assumptions of the Rashba model.
The compositional as well as structural asymmetries in Janus transition metal dichalcogenides (J-TMDs) and their van der Waals heterostructures (vdW HSs) induce an intrinsic Rashba spin-splitting. We investigate the variation of band-gaps and the Rashba parameter in three different Janus heterostructures having AB-stacked Mo$XY$/W$XY$ ($X$, $Y$ = S, Se, Te; $X\neq Y$) geometry with a $Y-Y$ interface, using first-principles calculations. We consider the effect of external electric field and in-plane biaxial strain in tuning the strength of the intrinsic electric field, which leads to remarkable…
We study the transport properties for a Luttinger-liquid (LL) quantum wire in the presence of both Rashba spin-orbit coupling (SOC) and a weak external in-plane magnetic field. The bosonized Hamiltonian of the system with an externally applied longitudinal electric field is established. And then the equations of motion for the bosonic phase fields are solved in the Fourier space, with which the both charge and spin conductivities for the system are calculated analytically based on the linear response theory. Generally, the ac conductivity is an oscillation function of the strengths of electron…
Near-surface two-dimensional electron gases on the topological insulator Bi$_2$Te$_2$Se are induced by electron doping and studied by angle-resolved photoemission spectroscopy. A pronounced spin-orbit splitting is observed for these states. The $k$-dependent splitting is strongly anisotropic to a degree where a large splitting ($\approx 0.06$ Å$^{-1}$) can be found in the $\barΓ\bar{M}$ direction while the states are hardly split along $\barΓ\bar{K}$. The direction of the anisotropy is found to be qualitatively inconsistent with results expected for a third-order anisotropic Rashba Hamiltonian…
The interaction between magnetic impurities and the gapless surface state is of critical importance for realizing novel quantum phenomena and new functionalities in topological insulators. By combining angle-resolved photoemission spectroscopic experiments with density functional theory calculations, we show that surface deposition of Cr atoms on Bi$_2$Se$_3$ does not lead to gap opening of the surface state at the Dirac point, indicating the absence of long-range out-of-plane ferromagnetism down to our measurement temperature of 15 K. This is in sharp contrast to bulk Cr doping, and the origi…
The spin-degeneracy of Bloch bands in a crystal can be lifted when spin-orbit (SO) coupling is present and inversion symmetry is absent. In two-dimensional electron systems (2DES) spin-degeneracy is lifted by Rashba interaction terms - symmetry invariants that are scalar products of spin and orbital axial vectors. Rashba interactions are symmetry allowed whenever a 2DES is not invariant under reflections through the plane it occupies. In this paper, we use a tight-binding model informed by ab initio electronic structure calculations to develop a theory of Rashba splitting in the t2g bands of t…
We report the observation of superconductivity with multiple magnetic ordering and Rashba-type spin-orbit coupling in a layered polar semimetal EuAuBi. Magnetic transition is observed at 4 K, followed by a superconducting transition at 2.2 K, which is sensitive to the crystal surface conditions. The upper critical field Hc2 of 9.8 T for the out-of-plane field is three times higher than that for the in-plane field, which can be associated with the two-dimensional structure or the surface state. On the basis of first-principles calculations, it is found that the characteristic Hc2 possibly refle…
