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Strong Rashba spin-orbit coupling (SOC) of two-dimensional electron gas (2DEG) at the oxide interface LaAIO3/SrTiO3 underlies a variety of exotic physics, but its nature is still under debate. We derive an effective Hamiltonian for the 2DEG at the oxide interface LaAIO3/SrTiO3 and find a different anisotropic Rashba SOC for the dxz and dyz orbitals. This anisotropic Rashba SOC leads to anisotropic static spin susceptibilities and also distinctive behavior of the spin Hall conductivity. These unique spin responses may be used to determine the nature of the Rashba SOC experimentally and shed light on the orbital origin of the 2DEG. [ABSTRACT FROM AUTHOR]

We propose a practical scheme to generate a pure valley current in monolayer transition-metal dichalcogenides by one-photon absorption of linearly polarized light. We show that the pure valley current can be detected by either photoluminescence measurements or the ultrafast pump-probe technique. Our method, together with the previously demonstrated generation of valley polarization, opens up the exciting possibility of ultrafast optical-only manipulation of the valley index. The tilted field effect on the valley current in experiment is also discussed. [ABSTRACT FROM AUTHOR]

It is well established that some kinds of lattice deformations in graphene monolayer, which change electron hopping in the sublattice and affect in-plane motion of electrons, may induce out-of-plane pseudomagnetic fields as large as 100 T. Here, we demonstrate that stacking misorientation in graphene bilayers mimics the effect of huge in-plane pseudomagnetic fields greater than 1000 T on the interlayer hopping of electrons. As well as addressing the similarity between the effect of in-plane pseudomagnetic fields and the twisting on the electronic band structure of the Bernal graphene bilayer, we point out that the in-plane magnetic fields (or twisting) could modify the low-energy pseudospin texture of the graphene bilayer (the pseudospin winding number is reduced from 2 to 1), thereby changing the chiralities of quasiparticles from those of spin 1 to those of spin 1/2. Our results illustrate the possibility of controllably manipulating electronic properties of Bernal graphene bilayer by introducing the in-plane magnetic field or twisting. [ABSTRACT FROM AUTHOR]

We study both the intrinsic and extrinsic spin Hall effect in spin-valley coupled monolayers of transition metal dichalcogenides. We find that whereas the skew-scattering contribution is suppressed by the large band gap, the side-jump contribution is comparable to the intrinsic one with opposite sign in the presence of scalar and magnetic scattering. Intervalley scattering tends to suppress the side-jump contribution due to the loss of coherence. By tuning the ratio of intra- to intervalley scattering, the spin Hall conductivity shows a sign change in hole-doped samples. The multiband effect in other doping regimes is considered, and it is found that the sign change exists in the heavily hole-doped regime, but not in the electron-doped regime. [ABSTRACT FROM AUTHOR]

We present a three-band tight-binding (TB) model for describing the low-energy physics in monolayers of group-VIB transition metal dichalcogenides MX2 (M=Mo, W; X=S, Se, Te). As the conduction- and valence-band edges are predominantly contributed by the dz2, dxy, and dx2-y2 orbitals of M atoms, the TB model is constructed using these three orbitals based on the symmetries of the monolayers. Parameters of the TB model are fitted from the first-principles energy bands for all MX2 monolayers. The TB model involving only the nearest-neighbor M-M hoppings is sufficient to capture the band-edge properties in the ±K valleys, including the energy dispersions as well as the Berry curvatures. The TB model involving up to the third-nearest-neighbor M-M hoppings can well reproduce the energy bands in the entire Brillouin zone. Spin-orbit coupling in valence bands is well accounted for by including the on-site spin-orbit interactions of M atoms. The conduction band also exhibits a small valley-dependent spin splitting which has an overall sign difference between MoX2 and WX2. We discuss the origins of these corrections to the three-band model. The three-band TB model developed here is efficient to account for low-energy physics in MX2 monolayers, and its simplicity can be particularly useful in the study of many-body physics and physics of edge states. [ABSTRACT FROM AUTHOR]

A pseudomagnetic field becomes an experimental reality after the observation of zero-field Landau level-like quantization in strained graphene, but it is not expected that the time-reversal symmetric pseudomagnetic fields will have any effect on the spin degree of freedom of the charge carriers. Here, we demonstrate that spin-orbit coupling (SOC) could act as a bridge between the pseudomagnetic field and spin. In quantum spin Hall (QSH) states, the direction of the spin of edge states is tied to their direction of motion because of the SOC. The pseudomagnetic field affects the clockwise and counterclockwise edge currents of the QSH states and consequently lifts the degenerate edge states of opposite spin orientation. Because of opposite signs of the pseudomagnetic field in two valleys of graphene, the one-dimensional charge carriers at the two opposite edges have different group velocities, and in some special cases, the edge states can only propagate at one edge of the nanoribbon, and the group velocity at the other edge becomes zero. [ABSTRACT FROM AUTHOR]

Theoretical research has predicted that a ripple of graphene generates an effective gauge field on its low-energy electronic structure and could lead to Landau quantization. Here, we demonstrate using a combination of an experimental method (scanning tunneling microscopy) and a theoretical approach (tight-binding approximation) that Landau levels will form when the effective pseudomagnetic flux per ripple Φ~(h²/la)Φ0 is larger than the flux quantum Φ0 (here, h is the height, l is the width of the ripple, and a is the nearest C-C bond length). The strain-induced gauge field in the ripple only results in one-dimensional (1D) Landau-level quantization along the ripple. Such 1D Landau quantization does not exist in two-dimensional systems in an external magnetic field. Its existence offers a unique opportunity to realize interesting electronic properties in strained graphene. [ABSTRACT FROM AUTHOR]

We consider the electronic structure of a slightly twisted graphene bilayer and show the coexistence of van Hove singularities (VHSs) and superlattice Dirac points in a continuum approximation. The graphene-on-graphene moiré pattern gives rise to a periodic electronic potential, which leads to the emergence of the superlattice Dirac points due to the chiral nature of the charge carriers. Because of the distinguishing real and reciprocal structures, the sublattice exchange even and sublattice exchange odd structures of the twisted graphene bilayer result in two different structures of the superlattice Dirac points. We calculate the effect of a strain on the low-energy electronic structure of the twisted graphene bilayer and demonstrate that the strain affects the position of the VHSs dramatically. [ABSTRACT FROM AUTHOR]

We theoretically study the effects of spin-orbit scattering on weak (anti)localization in two-dimensional massive Dirac systems. We clarify that weak antilocalization and localization of a single massive Dirac cone come from the diffusion of a singlet Cooperon in the massless limit and one of triplet Cooperons in the large-mass limit, respectively. Spin-orbit scattering behaves like random magnetic scattering to the triplet Cooperon, and suppresses the weak localization in the large-mass regime, different from in conventional systems where spin-orbit scattering leads to a crossover from weak localization to antilocalization. This behavior suggests an experiment to detect the weak localization of bulk subbands in topological insulator thin films, in which an enhancement of "weak antilocalization" is expected after doping heavy-element impurities. Finally, we compare the conventional electron and Dirac fermion systems in the quantum diffusion transport under ordinary, spin-orbit, and magnetic scattering. [ABSTRACT FROM AUTHOR]

We present an exact solution of a modified Dirac equation for topological insulator in the presence of a hole or vacancy to demonstrate that vacancies can induce bound states in the band gap of topological insulators. They arise due to the Z2 classification of time-reversal invariant insulators. Coexistence of the in-gap bound states and the edge or surface states in topological insulators suggests that imperfections may affect transport properties of topological insulators via additional bound states near the system boundary. [ABSTRACT FROM AUTHOR]

We study the topologically nontrivial semimetals by means of the six-band Kane model. Existence of surface states is explicitly demonstrated by calculating the local density of states (LDOS) on the material surface. In the strain-free condition, surface states are divided into two parts in the energy spectrum, one part is in the direct gap, the other part including the crossing point of surface state Dirac cone is submerged in the valence band. We also show how uniaxial strain induces an insulating band gap and raises the crossing point from the valence band into the band gap, making the system a true topological insulator. We predict the existence of helical edge states and spin Hall effect in the thin-film topological semimetals, which could be tested by future experiments. Disorder is found to significantly enhance the spin-Hall effect in the valence band of the thin films. [ABSTRACT FROM AUTHOR]

We theoretically study the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between magnetic impurities in both Dirac and Weyl semimetals (SMs). We find that the intemode process, as well as the unique threedimensional spin-momentum locking, has significant influences on the RKKY interaction, resulting in both a Heisenberg and an Ising term, and an additional Dzyaloshinsky-Moriya term if the inversion symmetry is absent. These interactions can lead to rich spin textures and possible ferromagnetism in Dirac and time-reversal symmetry-invariant Weyl SMs. The effect of anisotropic Dirac and Weyl nodes on the RKKY interaction is also discussed. Our results provide an alternative scheme to engineer topological SMs and shed new light on the application of Dirac and Weyl SMs in spintronics. [ABSTRACT FROM AUTHOR]

Using cryogenic scanning tunneling microscopy and scanning tunneling spectroscopy+ single-electron tunneling of Au nanoparticles (NPs) with 1.4 nm in radius was studied. We observe a gap ΔV ~ 2e/C (C is the capacitance of the Au particle and e the charge of an electron) around zero bias in the tunneling-conductancc spectrum, followed by a series of discrete single-electron tunneling peaks with peak spacing of EC ~ e/C at both negative and positive bias. Experimental data are well explained by taking into account both the shift o1 conductance peaks and the effect of exchange interaction of electrons on the single-electron tunneling of Au NPs. A conductance peak near zero bias was suppressed by the exchange-type zero-bias anomaly, which results in the gap Δ V ~ 2EC. According to our experiment and analysis, the shift of conductance peaks of Au NPs is attributed to self-biased gate and/or tip-induced gate. [ABSTRACT FROM AUTHOR]