Low-field magnetotransport measurements of topological insulators such as Bi2Se3 are important for revealing the nature of topological surface states by quantum corrections to the conductivity, such as weak-antilocalization. Recently, a rich variety of high-field magnetotransport properties in the regime of high electron densities (∼1019 cm−3) were reported, which can be related to additional two-dimensional layered conductivity, hampering the identification of the topological surface states. Here, we report that quantum corrections to the electronic conduction are dominated by the surface states for a semiconducting case, which can be analyzed by the Hikami-Larkin-Nagaoka model for two coupled surfaces in the case of strong spin-orbit interaction. However, in the metallic-like case this analysis fails and additional two-dimensional contributions need to be accounted for. Shubnikov-de Haas oscillations and quantized Hall resistance prove as strong indications for the two-dimensional layered metallic behavior. Temperature-dependent magnetotransport properties of high-quality Bi2Se3 single crystalline exfoliated macro and micro flakes are combined with high resolution transmission electron microscopy and energy-dispersive x-ray spectroscopy, confirming the structure and stoichiometry. Angle-resolved photoemission spectroscopy proves a single-Dirac-cone surface state and a well-defined bulk band gap in topological insulating state. Spatially resolved core-level photoelectron microscopy demonstrates the surface stability.
We demonstrate that quantum scattering of fast atoms and molecules under grazing angles of incidence can be exploited to study the structure of organic molecules on metal surfaces. Making use of keV H and He atoms as well as H2 molecules, the surface structures of the chiral amino acid alanine adsorbed on a Cu(110) surface is studied. We present a detailed investigation on the (3×2) phase of a monolayer of enantiopure and racemic alanine on Cu(110), revealing the formation of an elongated surface unit cell of c(n×2) symmetry with n=3.16±0.04 for the sticking out methyl groups of the alanine molecules.
Fast atoms with energies from 500 eV up to several keV are grazingly scattered from a Fe(110) surface covered with defined superstructures of sulfur or oxygen atoms. For scattering along low index azimuthal directions, we observe defined diffraction patterns in the angular distributions for scattered projectiles. From the analysis of those patterns, we derive the widths of low indexed axial channels and the corrugation of the interaction potential across these channels. This allows us to estimate the positions of adsorbed atoms on the Fe(110) surface. By demonstration, for adsorbate induced superstructures on a metal surface, we show that fast atom diffraction, first observed for insulators, can be applied to studies on surface structures for a wide range of materials.
Excitation functions A(N)(p(p),Theta(c.m.)) of the analyzing power in pp--> elastic scattering have been measured with a polarized atomic hydrogen target for projectile momenta p(p) between 1000 and 3300 MeV/ c. The experiment was performed for scattering angles 30 degrees =Theta(c.m.)=90 degrees using the recirculating beam of the proton storage ring COSY during acceleration. The resulting excitation functions and angular distributions of high internal consistency have significant impact on the recent phase shift solution SAID SP99, in particular, on the spin triplet phase shifts between 1000 and 1800 MeV, and demonstrate the limited predictive power of single-energy phase shift solutions at these energies.
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