Spin Hall effect in spin-valley coupled monolayer transition-metal dichalcogenides

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. Multiband effect in other doping regime is considered, and it is found that the sign change exists in the heavily hole-doped regime, but not in the electron-doped regime

Massive Dirac fermions and spin physics in an ultrathin film of topological insulator

We study transport and optical properties of the surface states which lie in the bulk energy gap of a thin-film topological insulator. When the film thickness is comparable with the surface state decay length into the bulk, the tunneling between the top and bottom surfaces opens an energy gap and form two degenerate massive Dirac hyperbolas. Spin dependent physics emerges in the surface bands which are vastly different from the bulk behavior. These include the surface spin Hall effects, spin dependent orbital magnetic moment, and spin dependent optical transition selection rule which allows optical spin injection. We show a topological quantum phase transition where the Chern number of the surface bands changes when varying the thickness of the thin film.Comment: 7 pages, 5 figure

A Theory of Common Dealing with the Internet as an Innovative Distribution Channel

After the emergence of the Internet, an interesting question arises that what is its impact on the firms’ channel and pricing strategies. This paper applies game theory to study the strategic interactions between rational manufacturers, retailers, and consumers, and it generates the following results: 1. The presence of the Internet allows imperfectly competitive manufacturers to better coordinate their pricing, targeting, and channel strategies, thereby minimizing the agency costs involved in common dealing at the traditional outlets, which in turn enhances the manufacturers’ profits. 2. Exclusive dealing may and may not become more prevalent in the presence of the Internet. It all depends on the ratio of the population of switchers to the entire population of consumers. 3. The presence of the Internet allows a monopolistic manufacturer to screen consumers by serving different people at different outlets. Screening is less effective, however, in the case of imperfect competition. 4. A dynamic adjustment process is obtained which describes how a manufacturer should optimally change his channel and pricing strategies when the population of the Internet purchasers grows over time

Effective continuous model for surface states and thin films of three dimensional topological insulators

Two-dimensional effective continuous models are derived for the surface states and thin films of the three-dimensional topological insulator (3DTI). Starting from an effective model for 3DTI based on the first principles calculation [Zhang \emph{et al}, Nat. Phys. 5, 438 (2009)], we present solutions for both the surface states in a semi-infinite boundary condition and in the thin film with finite thickness. An effective continuous model was derived for surface states and the thin film 3DTI. The coupling between opposite topological surfaces and structure inversion asymmetry (SIA) give rise to gapped Dirac hyperbolas with Rashba-like splittings in energy spectrum. Besides, the SIA leads to asymmetric distributions of wavefunctions along the film growth direction, making some branches in the energy spectra much harder than others to be probed by light. These features agree well with the recent angle-resolved photoemission spectra of Bi$_{2}$Se $_{3}$ films grown on SiC substrate [Zhang et al, arXiv: 0911.3706]. More importantly, we use the effective model to fit the experimental data and determine the model parameters. The result indicates that the thin film Bi$_{2}$Se$_{3}$ lies in quantum spin Hall region based on the calculation of the Chern number and the $Z_{2}$ invariant. In addition, strong SIA always intends to destroy the quantum spin Hall state.Comment: 12 pages, 7 figures, references are update