Observation of antiphase coherent phonons in the warped Dirac cone of Bi2Te3

In this Rapid Communication we investigate the coupling between excited electrons and phonons in the highly anisotropic electronic structure of the prototypical topological insulator Bi2Te3. Using time and angle resolved photoemission spectroscopy we are able to identify the emergence and ultrafast temporal evolution of the longitudinal optical A1g coherent phonon mode in Bi2Te3. We observe an antiphase behavior in the onset of the coherent phonon oscillations between the amp; 915;K and the amp; 915;M high symmetry directions that is consistent with warping. The qualitative agreement between our density functional theory calculations and the experimental results reveals the critical role of the anisotropic coupling between Dirac fermions and phonon modes in the topological insulator Bi2Te

Strong Spin Dependence of Correlation Effects in Ni Due to Stoner Excitations

Using high resolution angle resolved photoemission, we observe a strong spin dependent renormalization and lifetime broadening of the quasiparticle excitations in the electronic band structure of Ni 111 in an energy window of amp; 8764;0.3 eV below the Fermi level. We derive a quantitative result for the spin dependent lifetime broadening by comparing the scattering rates of majority and minority d states, and further show that spin dependent electron correlations are instead negligible for sp states. From our analysis we experimentally determine the effective on site Coulomb interaction U caused by Stoner like interband transitions between majority and minority d states. The present results demonstrate the remarkable impact of spin dependent electron correlation effects originating from single particle excitations in a prototypical 3d transition metal, paving the way for further refinement of current many body theoretical approache

Band Renormalization of Blue Phosphorus on Au 111

Most recently, theoretical calculations predicted the stability of a novel two dimensional phosphorus honeycomb lattice named blue phosphorus. Here, we report on the growth of blue phosphorus on Au 111 and unravel its structural details using diffraction, microscopy and theoretical calculations. Most importantly, by utilizing angle resolved photoemission spectroscopy we identify its momentum resolved electronic structure. We find that Au 111 breaks the sublattice symmetry of blue phosphorus leading to an orbital dependent band renormalization upon the formation of a 4 4 superstructure. Notably, the semiconducting two dimensional phosphorus realizes its valence band maximum at 0.9 eV binding energy, however, shifted in momentum space due to the substrate induced band renormalizatio

Phasenübergang durch chemische Substitution

Kürzlich wurde entdeckt, wie sich zwei Klassen topologischer Isolatoren ineinander überführen lassen. Die Art und Weise, wie das geschieht, verspricht neue funktionelle Eigenschaften in den Materialien. So lie en sich elektrische oder spintronische Kanäle mit Spannungspulsen ein und ausschalte

Nuclear WRAP53 promotes neuronal survival and functional recovery after stroke

Failure of neurons to efficiently repair DNA double-strand breaks (DSBs) contributes to cerebral damage after stroke. However, the molecular machinery that regulates DNA repair in this neurological disorder is unknown. Here, we found that DSBs in oxygen/glucose-deprived (OGD) neurons spatiotemporally correlated with the up-regulation of WRAP53 (WD40-encoding p53-antisense RNA), which translocated to the nucleus to activate the DSB repair response. Mechanistically, OGD triggered a burst in reactive oxygen species that induced both DSBs and translocation of WRAP53 to the nucleus to promote DNA repair, a pathway that was confirmed in an in vivo mouse model of stroke. Noticeably, nuclear translocation of WRAP53 occurred faster in OGD neurons expressing the Wrap53 human nonsynonymous single-nucleotide polymorphism (SNP) rs2287499 (c.202C>G). Patients carrying this SNP showed less infarct volume and better functional outcome after stroke. These results indicate that WRAP53 fosters DNA repair and neuronal survival to promote functional recovery after stroke

Hidden spin orbital texture at the Gamma over bar located valence band maximum of a transition metal dichalcogenide semiconductor

Finding stimuli capable of driving an imbalance of spin polarised electrons within a solid is the central challenge in the development of spintronic devices. However, without the aid of magnetism, routes towards this goal are highly constrained with only a few suitable pairings of compounds and driving mechanisms found to date. Here, through spin and angle resolved photoemission along with density functional theory, we establish how the p derived bulk valence bands of semiconducting 1T HfSe2 possess a local, ground state spin texture spatially confined within each Se sublayer due to strong sublayer localised electric dipoles orientated along the c axis. This hidden spin polarisation manifests in a coupled spin orbital texture with in equivalent contributions from the constituent p orbitals. While the overall spin orbital texture for each Se sublayer is in strict adherence to time reversal symmetry TRS , spin orbital mixing terms with net polarisations at time reversal invariant momenta are locally maintained. These apparent TRS breaking contributions dominate, and can be selectively tuned between with a choice of linear light polarisation, facilitating the observation of pronounced spin polarisations at the Brillouin zone centre for all kz. We discuss the implications for the generation of spin polarised populations from 1T structured transition metal dichalcogenides using a fixed energy, linearly polarised light sourc

Robust behavior and spin texture stability of the topological surface state in Bi2Se3 upon deposition of gold

The Dirac point of a topological surface state TSS is protected against gapping by time reversal symmetry. Conventional wisdom stipulates, therefore, that only through magnetisation may a TSS become gapped. However, non magnetic gaps have now been demonstrated in Bi2Se3 systems doped with Mn or In, explained by hybridisation of the Dirac cone with induced impurity resonances. Recent photoemission experiments suggest that an analogous mechanism applies even when Bi2Se3 is surface dosed with Au. Here, we perform a systematic spin and angle resolved photoemission study of Au dosed Bi2Se3. Although there are experimental conditions wherein the TSS appears gapped due to unfavourable photoemission matrix elements, our photon energy dependent spectra unambiguously demonstrate the robustness of the Dirac cone against high Au coverage. We further show how the spin textures of the TSS and its accompanying surface resonances remain qualitatively unchanged following Au deposition, and discuss the mechanism underlying the suppression of the spectral weigh

Phi-values in protein folding kinetics have energetic and structural components

Phi-values are experimental measures of how the kinetics of protein folding is changed by single-site mutations. Phi-values measure energetic quantities, but are often interpreted in terms of the structures of the transition state ensemble. Here we describe a simple analytical model of the folding kinetics in terms of the formation of protein substructures. The model shows that Phi-values have both structural and energetic components. In addition, it provides a natural and general interpretation of "nonclassical" Phi-values (i.e., less than zero, or greater than one). The model reproduces the Phi-values for 20 single-residue mutations in the alpha-helix of the protein CI2, including several nonclassical Phi-values, in good agreement with experiments.Comment: 15 pages, 3 figures, 1 tabl

Morphological Transformations of Galaxies in the A901/02 Supercluster from STAGES

We present a study of galaxies in the Abell 901/902 Supercluster at z~0.165, based on HST ACS F606W, COMBO-17, Spitzer 24um, XMM-Newton X-ray, and gravitational lensing maps, as part of the STAGES survey. We characterize galaxies with strong externally-triggered morphological distortions and normal relatively undisturbed galaxies, using visual classification and quantitative CAS parameters. We compare normal and distorted galaxies in terms of their frequency, distribution within the cluster, star formation properties, and relationship to dark matter (DM) or surface mass density, and intra-cluster medium (ICM) density. We revisit the morphology density relation, which postulates a higher fraction of early type galaxies in dense environments, by considering separately galaxies with a low bulge-to-disk (B/D) ratio and a low gas content as these two parameters may not be correlated in clusters. We report here on our preliminary analysis.Comment: To appear in the ASP conference proceedings of the "Frank N. Bash Symposium 2007: New Horizons in Astronomy", Eds. A. Frebel, J. Maund, J. Shen, M. Siegel. 4 pages, 4 figure