Intervalley coupling by quantum dot confinement potentials in monolayer transition metal dichalcogenides

Monolayer transition metal dichalcogenides (TMDs) offer new opportunities for realizing quantum dots (QDs) in the ultimate two-dimensional (2D) limit. Given the rich control possibilities of electron valley pseudospin discovered in the monolayers, this quantum degree of freedom can be a promising carrier of information for potential quantum spintronics exploiting single electrons in TMD QDs. An outstanding issue is to identify the degree of valley hybridization, due to the QD confinement, which may significantly change the valley physics in QDs from its form in the 2D bulk. Here we perform a systematic study of the intervalley coupling by QD confinement potentials on extended TMD monolayers. We find that the intervalley coupling in such geometry is generically weak due to the vanishing amplitude of the electron wavefunction at the QD boundary, and hence valley hybridization shall be well quenched by the much stronger spin-valley coupling in monolayer TMDs and the QDs can well inherit the valley physics of the 2D bulk. We also discover sensitive dependence of intervalley coupling strength on the central position and the lateral length scales of the confinement potentials, which may possibly allow tuning of intervalley coupling by external controlsComment: 17 pages, 14 figure

Topological magnetic phase in LaMnO3_3 (111) bilayer

Candidates for correlated topological insulators, originated from the spin-orbit coupling as well as Hubbard type correlation, are expected in the ($111$) bilayer of perovskite-structural transition-metal oxides. Based on the first-principles calculation and tight-binding model, the electronic structure of a LaMnO$_3$ ($111$) bilayer sandwiched in LaScO$_3$ barriers has been investigated. For the ideal undistorted perovskite structure, the Fermi energy of LaMnO$_3$ ($111$) bilayer just stays at the Dirac point, rendering a semi-metal (graphene-like) which is also a half-metal (different from graphene nor previous studied LaNiO$_3$ ($111$) bilayer). The Dirac cone can be opened by the spin-orbit coupling, giving rise to nontrivial topological bands corresponding to the (quantized) anomalous Hall effect. For the realistic orthorhombic distorted lattice, the Dirac point moves with increasing Hubbard repulsion (or equivalent Jahn-Teller distortion). Finally, a Mott gap opens, establishing a phase boundary between the Mott insulator and topological magnetic insulator. Our calculation finds that the gap opened by spin-orbit coupling is much smaller in the orthorhombic distorted lattice ($\sim$$1.7$ meV) than the undistorted one ($\sim$$11$ meV). Therefore, to suppress the lattice distortion can be helpful to enhance the robustness of topological phase in perovskite ($111$) bilayers.Comment: 8 pages, 8 figure

Tunable Intrinsic Plasmons due to Band Inversion in Topological Materials

The band inversion has led to rich physical effects in both topological insulators and topological semimetals. It has been found that the inverted band structure with the Mexican-hat dispersion could enhance the interband correlation leading to a strong intrinsic plasmon excitation. Its frequency ranges from several $\mathrm{meV}$ to tens of $\mathrm{meV}$ and can be effectively tuned by the external fields. The electron-hole asymmetric term splits the peak of the plasmon excitation into double peaks. The fate and properties of this plasmon excitation can also act as a probe to characterize the topological phases even in the lightly doped systems. We numerically demonstrate the impact of the band inversion on plasmon excitations in magnetically doped thin films of three-dimensional strong topological insulators, V- or Cr-doped (Bi, Sb)$_2$Te$_3$, which support the quantum anomalous Hall states. Our work thus sheds some new light on the potential applications of topological materials in plasmonics.Comment: 6 pages, 5 figures, Accepted in PR

Intrinsic spin Hall effect in monolayers of group-VI dichalcogenides: A first-principles study

Using first-principles calculations within density functional theory, we investigate the intrinsic spin Hall effect in monolayers of group-VI transition-metal dichalcogenides MX2 (M = Mo, W and X = S, Se). MX2 monolayers are direct band-gap semiconductors with two degenerate valleys located at the corners of the hexagonal Brillouin zone. Because of the inversion symmetry breaking and the strong spin-orbit coupling, charge carriers in opposite valleys carry opposite Berry curvature and spin moment, giving rise to both a valley- and a spin-Hall effect. The intrinsic spin Hall conductivity (ISHC) in p-doped samples is found to be much larger than the ISHC in n-doped samples due to the large spin-splitting at the valence band maximum. We also show that the ISHC in inversion-symmetric bulk dichalcogenides is an order of magnitude smaller compared to monolayers. Our result demonstrates monolayer dichalcogenides as an ideal platform for the integration of valleytronics and spintronics.Comment: published version (7 pages, 6 figures

Scattering universality classes of side jump in anomalous Hall effect

The anomalous Hall conductivity has an important extrinsic contribution known as side jump contribution, which is independent of both scattering strength and disorder density. Nevertheless, we discover that side jump has strong dependence on the spin structure of the scattering potential. We propose three universality classes of scattering for the side jump contribution, having the characters of being spin-independent, spin-conserving and spin-flip respectively. For each individual class, the side jump contribution takes a different unique value. When two or more classes of scattering are present, the value of side jump is no longer fixed but varies as a function of their relative disorder strength. As system control parameter such as temperature changes, due to the competition between different classes of disorder scattering, the side jump Hall conductivity could flow from one class dominated limit to another class dominated limit. Our result indicates that magnon scattering plays a role distinct from normal impurity scattering and phonon scattering in the anomalous Hall effect because they belong to different scattering classes