A topological Dirac insulator in a quantum spin Hall phase : Experimental observation of first strong topological insulator

When electrons are subject to a large external magnetic field, the conventional charge quantum Hall effect \cite{Klitzing,Tsui} dictates that an electronic excitation gap is generated in the sample bulk, but metallic conduction is permitted at the boundary. Recent theoretical models suggest that certain bulk insulators with large spin-orbit interactions may also naturally support conducting topological boundary states in the extreme quantum limit, which opens up the possibility for studying unusual quantum Hall-like phenomena in zero external magnetic field. Bulk Bi$_{1-x}$Sb$_x$ single crystals are expected to be prime candidates for one such unusual Hall phase of matter known as the topological insulator. The hallmark of a topological insulator is the existence of metallic surface states that are higher dimensional analogues of the edge states that characterize a spin Hall insulator. In addition to its interesting boundary states, the bulk of Bi$_{1-x}$Sb$_x$ is predicted to exhibit three-dimensional Dirac particles, another topic of heightened current interest. Here, using incident-photon-energy-modulated (IPEM-ARPES), we report the first direct observation of massive Dirac particles in the bulk of Bi$_{0.9}$Sb$_{0.1}$, locate the Kramers' points at the sample's boundary and provide a comprehensive mapping of the topological Dirac insulator's gapless surface modes. These findings taken together suggest that the observed surface state on the boundary of the bulk insulator is a realization of the much sought exotic "topological metal". They also suggest that this material has potential application in developing next-generation quantum computing devices.Comment: 16 pages, 3 Figures. Submitted to NATURE on 25th November(2007

Atteinte urinaire et pseudo-obstruction intestinale révélatrice d’un lupus érythémateux systémique à propos d’une observation

Introduction : Le lupus érythémateux systémique est une connectivite fréquente chez les femmes en activité génitale. Au cours du lupus érythémateux systémique, la pseudo-obstruction intestinale est l’une des graves complications rares. Ainsi l’objectif de cet article est de présenter un cas clinique d’atteinte urinaire et pseudo-obstruction intestinale révélatrice d’un lupus érythémateux systémique. Observation : Une patiente âgée de 28 ans mariée, de Nationalité Guinéenne admise pour une diarrhée fébrile, asthénie, météorisme, associée à des douleurs articulaire et abdominale nécessitant une consultation et des bilans sans succès.Une échographie abdominale qui objective un épaississement diffus de la paroi colique et des anses grêles ainsi qu’une ascite de moyenne abondance. La coloscopie révèle un aspect inflammatoire spécifique de la muqueuse iléale. Conclusion : La pseudo-obstruction intestinale peut être inaugurale ou concomitante du lupus érythémateux systémique

Relation entre Maladies Parodontales et Maladies cardiovasculaires : Revue de la littérature

Introduction : La maladie parodontale (MP) est une maladie inflammatoire complexe qui détruit les tissus de soutien de la dent (parodonte) avec une étiologie multifactorielle elle a été liée au diabète, aux obstructions chroniques des voies respiratoires, aux maladies rénales chroniques, aux syndromes métaboliques, à certains types de cancers, la polyarthrite rhumatoïde et aux maladies cardiovasculaires. Les maladies cardiovasculaires (MCV) constituent un ensemble de troubles affectant le cœur et les vaisseaux sanguins, leur cause la plus courante est l’athérosclérose, qui correspond à un remaniement pathologique de la paroi interne des artères de gros et moyen calibres par accumulation de lipides, glucides complexes, éléments sanguins et dépôts calcaires, formant des plaques d’athérosclérose. Ainsi, l’objectif de cette revue de la littérature est de déterminer la relation entre les maladies parodontales et les maladies cardiovasculaires. Matériels et Méthodes : Pour ce travail une stratégie de recherche documentaire électronique a été réalisée dans 2 bases de données dont Pub Med et Google scholar. Ainsi 423 articles traitant la relation entre les maladies parodontales et les maladies cardiovasculaires publiés en anglais ou en français avec texte intégral dans la période allant de 1989 à 2016 ont été sélectionnés. Les titres et résumés des articles retrouvés grâce à la stratégie de recherche ont été passés en revue. Les articles qui n’étaient pas pertinents pour une inclusion ont été écartés dès ce stade. Les données recueillies ont subi une analyse après mise en œuvre des critères d’inclusions : Etudes réalisées chez les humains et rédigées en anglais ou en français et publiés entre 1989 à 2016. Les articles inclus étaient ceux après lecture des titres, des résumés jugés pertinents dont 35 articles traitant la relation entre les maladies parodontales et les Maladies Cardiovasculaires ont été sélectionnés. Résultat : Au total 35 articles traitant la relation entre les maladies parodontales et les Maladies cardiovasculaires ont été sélectionnés compte tenu de leurs cohérence et pertinence. La limite a été la consultation que de 2 bases de données. Les bactériémies associées aux parodontites sont responsables d’une activation de la réponse immuno-inflammatoire favorisant la formation, la maturation et la complication des plaques d’athérome. Il existe un risque accru de MCV chez les patients atteints de parodontite chronique, indépendamment des autres facteurs de risques cardiovasculaires. Le traitement parodontal réduit le niveau d’inflammation systémique et améliore la fonction endothéliale, mais ne modifie pas la dyslipidémie. Conclusion : avec une étiologie infectieuse pour les maladies et divers pour les maladies cardiovasculaires, un lien a été établi entre les deux maladies dans diverses études épidémiologiques et cliniques mais toutes fois reste controverse dans d’autre

Circular dichroism in angle-resolved photoemission spectroscopy of topological insulators

Topological insulators are a new phase of matter that exhibits exotic surface electronic properties. Determining the spin texture of this class of material is of paramount importance for both fundamental understanding of its topological order and future spin-based applications. In this article, we review the recent experimental and theoretical studies on the differential coupling of left- versus right-circularly polarized light to the topological surface states in angle-resolved photoemission spectroscopy. These studies have shown that the polarization of light and the experimental geometry plays a very important role in both photocurrent intensity and spin polarization of photoelectrons emitted from the topological surface states. A general photoemission matrix element calculation with spin-orbit coupling can quantitatively explain the observations and is also applicable to topologically trivial systems. These experimental and theoretical investigations suggest that optical excitation with circularly polarized light is a promising route towards mapping the spin-orbit texture and manipulating the spin orientation in topological and other spin-orbit coupled materials.Comment: submitted to Phys. Status Solidi RR

One-dimensional Topological Edge States of Bismuth Bilayers

The hallmark of a time-reversal symmetry protected topologically insulating state of matter in two-dimensions (2D) is the existence of chiral edge modes propagating along the perimeter of the system. To date, evidence for such electronic modes has come from experiments on semiconducting heterostructures in the topological phase which showed approximately quantized values of the overall conductance as well as edge-dominated current flow. However, there have not been any spectroscopic measurements to demonstrate the one-dimensional (1D) nature of the edge modes. Among the first systems predicted to be a 2D topological insulator are bilayers of bismuth (Bi) and there have been recent experimental indications of possible topological boundary states at their edges. However, the experiments on such bilayers suffered from irregular structure of their edges or the coupling of the edge states to substrate's bulk states. Here we report scanning tunneling microscopy (STM) experiments which show that a subset of the predicted Bi-bilayers' edge states are decoupled from states of Bi substrate and provide direct spectroscopic evidence of their 1D nature. Moreover, by visualizing the quantum interference of edge mode quasi-particles in confined geometries, we demonstrate their remarkable coherent propagation along the edge with scattering properties that are consistent with strong suppression of backscattering as predicted for the propagating topological edge states.Comment: 15 pages, 5 figures, and supplementary materia

Emergent quantum confinement at topological insulator surfaces

Bismuth-chalchogenides are model examples of three-dimensional topological insulators. Their ideal bulk-truncated surface hosts a single spin-helical surface state, which is the simplest possible surface electronic structure allowed by their non-trivial $\mathbb{Z}_2$ topology. They are therefore widely regarded ideal templates to realize the predicted exotic phenomena and applications of this topological surface state. However, real surfaces of such compounds, even if kept in ultra-high vacuum, rapidly develop a much more complex electronic structure whose origin and properties have proved controversial. Here, we demonstrate that a conceptually simple model, implementing a semiconductor-like band bending in a parameter-free tight-binding supercell calculation, can quantitatively explain the entire measured hierarchy of electronic states. In combination with circular dichroism in angle-resolved photoemission (ARPES) experiments, we further uncover a rich three-dimensional spin texture of this surface electronic system, resulting from the non-trivial topology of the bulk band structure. Moreover, our study reveals how the full surface-bulk connectivity in topological insulators is modified by quantum confinement.Comment: 9 pages, including supplementary information, 4+4 figures. A high resolution version is available at http://www.st-andrews.ac.uk/~pdk6/pub_files/TI_quant_conf_high_res.pd

Ground-state phase diagrams of the generalized Falicov-Kimball model with Hund coupling

Charge and spin orderings are studied on the simplest 1D and the 2D square lattice within the generalized Falicov-Kimball model with Hund coupling between localized and itinerant electrons. Using the restricted phase diagrams method (RPDM) a number of simple rules of formation of various sorts of ground state phases have been detected. In particular, relationships between density of current carriers (electrons or holes) and type of charge and magnetic arrangement has been determined. In 2D in the mixed valence regime only axial stripes (vertical or horizontal) have been found for intermediate values of the coupling constants. They are composed of ferromagnetic or antiferromagnetic chains interchanged with non-magnetic ones. For band fillings close to the half filling stripe phases oriented along one of the main diagonal direction are formed. The results suggest a possibility of tuning modulations of charge and magnetic superstructures with a change of doping.Comment: 10 pages, 6 figures; Fig. 2 slightly modified and the text adjusted accordingly, references adde