Impurities and electronic localization in graphene bilayers

We analyze the electronic properties of bilayer graphene with Bernal stacking and a low concentration of adatoms. Assuming that the host bilayer lies on top of a substrate, we consider the case where impurities are adsorbed only on the upper layer. We describe non-magnetic impurities as a single orbital hybridized with carbon's pz states. The effect of impurity doping on the local density of states with and without a gated electric field perpendicular to the layers is analyzed. We look for Anderson localization in the different regimes and estimate the localization length. In the biased system, the field induced gap is partially filled by strongly localized impurity states. Interestingly, the structure, distribution and localization length of these states depend on the field polarization.Comment: 7 pages, 6 figure

Dinámica de meandros y riesgos hidrogeomorfológicos en Alcalá de Ebro y Cabañas de Ebro (Zaragoza)

[Resumen] Alcalá de Ebro y Cabañas de Ebro constituyen los enclaves de máximo riesgo hidrogeomorfológico del curso medio del Ebro. Las dos localidades se ubican dentro de la llanura de inundación y en sendas orillas cóncavas de meandros pronunciados. Se analiza la dinámica reciente del cauce de meandros libres en este sector aguas arriba de Zaragoza, así como los riesgos derivados de dicha dinámica, que han requerido sucesivas actuaciones de defensa[Abstract] Alcalá de Ebro & Cabañas de Ebro are the most threatened places with hydrogeomorphological risk in the middle Ebro. Both towns are placed in the floodplain and on each concave bank of sharp meanders. The recent dynamics of the free meanders river bed upstream from Zaragoza is analysed, as well as the risks derived that dynamics, which have required several successive protection works

Bilayer graphene under pressure: Electron-hole Symmetry Breaking, Valley Hall Effect, and Landau Levels

The electronic structure of bilayer graphene under pressure develops very interesting features with an enhancement of the trigonal warping and a splitting of the parabolic touching bands at the K point of the reciprocal space into four Dirac cones, one at K and three along the T symmetry lines. As pressure is increased, these cones separate in reciprocal space and in energy, breaking the electron-hole symmetry. Due to their energy separation, their opposite Berry curvature can be observed in valley Hall effect experiments and in the structure of the Landau levels. Based on the electronic structure obtained by Density Functional Theory, we develop a low energy Hamiltonian that describes the effects of pressure on measurable quantities such as the Hall conductivity and the Landau levels of the system.Comment: 11 pages, 9 figure

Globalizíación, Class Actions y Derecho de Trabajo

[Excerpt] El objeto principal de este artículo consiste en analizar la larga experiencia acumulada al otro lado del Atlántico, en Estados Unidos, en material de demandas extraterritoriales contra empresas norteamericanas ya desde los años setenta. Realizaremos una síntesis de los rasgos característicos de las class actions en ese país, en primer lugar, seguida por una breve Mirada al context internacional del Derecho del trabajo y la jurisprudencia en EE.UU., de los efectos extraterritoriales del Derecho del trabajo estadounidense, en segundo término, y un análisis pormenorizado de tales litigious en Europa

Towards spin injection from silicon into topological insulators: Schottky barrier between Si and Bi2Se3

A scheme is proposed to electrically measure the spin-momentum coupling in the topological insulator surface state by injection of spin polarized electrons from silicon. As a first approach, devices were fabricated consisting of thin (<100nm) exfoliated crystals of Bi2Se3 on n-type silicon with independent electrical contacts to silicon and Bi2Se3. Analysis of the temperature dependence of thermionic emission in reverse bias indicates a barrier height of 0.34 eV at the Si-Bi2Se3 interface. This robust Schottky barrier opens the possibility of novel device designs based on sub-band gap internal photoemission from Bi2Se3 into Si

Triple-Star Candidates Among the Kepler Binaries

We present the results of a search through the photometric database of eclipsing Kepler binaries (Prsa et al. 2011; Slawson et al. 2011) looking for evidence of hierarchical triple star systems. The presence of a third star orbiting the binary can be inferred from eclipse timing variations. We apply a simple algorithm in an automated determination of the eclipse times for all 2157 binaries. The "calculated" eclipse times, based on a constant period model, are subtracted from those observed. The resulting O-C (observed minus calculated times) curves are then visually inspected for periodicities in order to find triple-star candidates. After eliminating false positives due to the beat frequency between the ~1/2-hour Kepler cadence and the binary period, 39 candidate triple systems were identified. The periodic O-C curves for these candidates were then fit for contributions from both the classical Roemer delay and so-called "physical" delay, in an attempt to extract a number of the system parameters of the triple. We discuss the limitations of the information that can be inferred from these O-C curves without further supplemental input, e.g., ground-based spectroscopy. Based on the limited range of orbital periods for the triple star systems to which this search is sensitive, we can extrapolate to estimate that at least 20% of all close binaries have tertiary companions.Comment: 19 pages, 13 figures, 3 tables; ApJ, 2013, 768, 33; corrected Fig. 7, updated references, minor fixes to tex