No abstract

Topological insulators are a class of solids in which the non-trivial inverted bulk band structure gives rise to metallic surface states that are robust against impurity scattering. In three-dimensional (3D) topological insulators, however, the surface Dirac fermions intermix with the conducting bulk, thereby complicating access to the low-energy (Dirac point) charge transport or magnetic response. Here we use differential magnetometry to probe spin rotation in the 3D topological material family (Bi2Se3, Bi2Te3 and Sb2Te3). We report a paramagnetic singularity in the magnetic susceptibility at low magnetic fields that persists up to room temperature, and which we demonstrate to arise from the surfaces of the samples. The singularity is universal to the entire family, largely independent of the bulk carrier density, and consistent with the existence of electronic states near the spin-degenerate Dirac point of the 2D helical metal. The exceptional thermal stability of the signal points to an intrinsic surface cooling process, probably of thermoelectric origin, and establishes a sustainable platform for the singular field-tunable Dirac spin response.

Surfaces of three-dimensional topological insulators have emerged as one of the most remarkable states of condensed quantum matter 1-5 where exotic electronic phases of Dirac particles should arise 1,6-8 . Here we report a discovery of surface superconduc-

Raman and infrared spectra were examined for guanosine 5 -diphosphate (GDP) and guanosine 5 -triphosphate (GTP) in aqueous solution. The vibrational modes were assigned on the basis of isotopic frequency shifts and relative intensities in the Raman and infrared spectra. The observed frequency shifts on 18 O isotope labeling made it possible to identify the bands from each phosphate group (a, b, g). Frequency shifts were observed as Mg 2/ complexes with GDP and GTP. The results suggested that Mg 2/ binds to GDP in a bidentate manner to the a, b P rr O bonds and in a tridentate manner to the a, b and g P rr O bonds of MgrGTP. The results indicate that structure of Mg 2/ coordinated to GTP in aqueous solution differs somewhat to that found for MgrATP.

Growth of high-quality Bi 2 Se 3 films is crucial not only for study of topological insulators but also for manufacture of technologically important materials. We report a study of the heteroepitaxy of single-crystal Bi 2 Se 3 thin films grown on GaAs and InP substrates by use of molecular beam epitaxy. Surface topography, crystal structure, and electrical transport properties of these Bi 2 Se 3 epitaxial films are indicative of highly c-axis oriented films with atomically sharp interfaces.