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Thermoelectric properties of nanostructured skutterudite CoSb3 have been reported. Nanosized CoSb3 powders were synthesized through a solvothermal route. The bulk materials with average grain sizes of 250 and 150 nm were prepared by hot pressing and spark plasma sintering from the solvothermally synthesized CoSb3 powders. Both the samples show n-type conduction and the thermal conductivities are reduced compared with that of the sample prepared by the melt-annealing/hot pressing method. A thermoelectric figure of merit of 0.61 has been obtained for the unfilled CoSb3 skutterudite by spark plasma sintering, which indicates that nanostructuring is an effective way to improve the thermoelectric properties of skutterudite compounds. [ABSTRACT FROM AUTHOR]

Nanocomposites offer a promising approach to incorporate nanostructured constituents to bulk thermoelectric materials. n-type CoSb3 nanocomposites were prepared by hot pressing the mixture of nanoscale and microsized CoSb3 powders synthesized by solvothermal method and melting, respectively. Microstructure analysis shows that the bulk materials are composed of nano- and micrograins. The nanocomposite structures are effective in reducing thermal conductivity more than electrical conductivity, hence in improving the thermoelectric performance. A dimensionless figure of merit of 0.71 is obtained for the nanocomposite with 40 wt % nanopowder inclusions, about 54% increase of that without nanopowder inclusions. [ABSTRACT FROM AUTHOR]

A correction is presented for the article "Improved thermoelectric figure of merit in n-type CoSb3 based nanocomposites," from issue 91 of "Applied Physics Letters."

The band structure and intra- and interband scattering processes of the electrons at the surface of a bismuth bilayer on Bi2Se3 have been experimentally investigated by low-temperature Fourier-transform scanning tunneling spectroscopy. The observed complex quasiparticle interference patterns are compared to a simulation based on the spin-dependent joint density of states approach using the surface-localized spectral function calculated from first principles as the only input. Thereby, the origin of the quasiparticle interferences can be traced back to intraband scattering in the bismuth-bilayer valence band and Bi2Se3 conduction band and to interband scattering between the two-dimensional topological state and the bismuth-bilayer valence band. The investigation reveals that the bilayer band gap, which is predicted to host one-dimensional topological states at the edges of the bilayer, is pushed several hundred meV above the Fermi level. This result is rationalized by an electron transfer from the bilayer to Bi2Se3 which also leads to a two-dimensional electron state in the Bi2Se3 conduction band with a strong Rashba spin splitting, coexisting with the topological state and bilayer valence band. [ABSTRACT FROM AUTHOR]

The electrostatic behavior of a prototypical three-dimensional topological insulator, Bi2Se3( 111), is investigated by a scanning tunneling microscopy (STM) study of the distribution of Rb atoms adsorbed on the surface. The positively charged ions are screened by both free electrons residing in the topological surface state as well as band bending induced quantum well states of the conduction band, leading to a surprisingly short screening length. Combining a theoretical description of the potential energy with STM-based atomic manipulation, we demonstrate the ability to create tailored electronic potential landscapes on topological surfaces with atomic-scale control. [ABSTRACT FROM AUTHOR]

A combined experimental and theoretical study of doping individual Fe atoms into Bi2Se3 is presented. It is shown through a scanning tunneling microscopy study that single Fe atoms initially located at hollow sites on top of the surface (adatoms) can be incorporated into subsurface layers by thermally activated diffusion. Angle-resolved photoemission spectroscopy in combination with ab initio calculations suggest that the doping behavior changes from electron donation for the Fe adatom to neutral or electron acceptance for Fe incorporated into substitutional Bi sites. According to first principles calculations within density functional theory, these Fe substitutional impurities retain a large magnetic moment, thus presenting an alternative scheme for magnetically doping the topological surface state. For both types of Fe doping, we see no indication of a gap at the Dirac point. [ABSTRACT FROM AUTHOR]

Using angle-resolved photoelectron spectroscopy and ab initio GW calculations, we unambiguously show that the widely investigated three-dimensional topological insulator Bi2Se3 has a direct band gap at the Γ point. Experimentally, this is shown by a three-dimensional band mapping in large fractions of the Brillouin zone. Theoretically, we demonstrate that the valence-band maximum is located at the Γ point only if many-body effects are included in the calculation. Otherwise, it is found in a high-symmetry mirror plane away from the zone center. [ABSTRACT FROM AUTHOR]

The robustness of the gapless topological surface state hosted by a 3D topological insulator against perturbations of magnetic origin has been the focus of recent investigations. We present a comprehensive study of the magnetic properties of Fe impurities on the prototypical 3D topological insulator Bi2Se3 using local low-temperature scanning tunneling spectroscopy and integral x-ray magnetic circular dichroism techniques. Single Fe adatoms on the Bi2Se3 surface, in the coverage range ≈ 1% of a monolayer, are heavily relaxed into the surface and exhibit a magnetic easy axis within the surface plane, contrary to what was assumed in recent investigations on the supposed opening of a gap. Using ab initio approaches, we demonstrate that an in-plane easy axis arises from the combination of the crystal field and dynamic hybridization effects. [ABSTRACT FROM AUTHOR]

We report on the quenching of single Ni adatom moments on Te-terminated Bi2Te2Se and Bi2Te3 topological insulator surfaces. The effect is noted as a missing x-ray magnetic circular dichroism for resonant L3,2 transitions into partially filled Ni 3d states of theory-derived occupancy nd=9.2. On the basis of a comparative study of Ni and Fe using scanning tunneling microscopy and ab initio calculations, we are able to relate the element specific moment formation to a local Stoner criterion. Our theory shows that while Fe adatoms form large spin moments of ms=2.54μB with out-of-plane anisotropy due to a sufficiently large density of states at the Fermi energy, Ni remains well below an effective Stoner threshold for local moment formation. With the Fermi level remaining in the bulk band gap after adatom deposition, nonmagnetic Ni and preferentially out-of-plane oriented magnetic Fe with similar structural properties on Bi2Te2Se surfaces constitute a perfect platform to study the off-on effects of time-reversal symmetry breaking on topological surface states. [ABSTRACT FROM AUTHOR]