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Using surface x-ray diffraction in combination with ab initio calculations, we demonstrate that the atomic structure of ultrathin BaTiO3 (BTO) films grown on Me(001) surfaces (Me=Fe, Pd, Pt) depends on subtle modifications of the interface chemical composition. A complete reversal of the surface termination from a BaO- [BTO on Fe(001)] to a TiO2-terminated film [BTO on Pt(001)] is observed which goes in parallel with the adsorption of submonolayer amounts of oxygen at metal hollow sites of the interface. Our results may suggest a new route to an overall control of both the surface and the interface geometry in BaTiO3/metal contacts.

The effect of electron-impurity scattering on momentum and spin relaxation times in graphene is studied by means of relativistic ab initio calculations. Assuming carbon and silicon adatoms as natural impurities in graphene, we are able to simulate fast spin relaxation observed experimentally. We investigate the dependence of the relaxation times on the impurity position and demonstrate that C or Si adatoms act as real-space spin hot spots inducing spin-flip rates about 5 orders of magnitude larger than those of in-plane impurities. This fact confirms the hypothesis that the adatom-induced spin-orbit coupling leads to fast spin relaxation in graphene.

First-principles and model calculations show that the Dirac surface state of the topological insulator Bi(2)Te(3) survives upon moderate Mn doping of the surface layers but can lose its topological character as a function of magnetization direction. The dispersion depends considerably on the direction of the Mn magnetization: for perpendicular magnetization, a gap of 16 meV opens up at the Dirac point; for in-plane magnetization, a tiny gap can be opened or closed in dependence on the magnetization azimuth. The ground state is ferromagnetic, with a critical temperature of 12 K. The results provide a path towards a magnetic control of the topological character of the Dirac surface state and its consequences to spin-dependent transport properties.

We present an ab initio description of the thermal transport phenomenon called the spin Nernst effect. It refers to generation of a spin accumulation or a pure spin current transverse to an applied temperature gradient. This is similar to the intensively studied spin Hall effect described by intrinsic and extrinsic mechanisms due to an applied electric field. Analogously, several contributions are present for the spin Nernst effect. Here we investigate the extrinsic skew scattering mechanism which is dominant in the limit of dilute alloys. Our calculations are based on a fully relativistic Korringa-Kohn-Rostoker method and a solution of the linearized Boltzmann equation. As a first application, we consider a Cu host with Au, Ti, and Bi impurities.

Using surface x-ray diffraction and ab initio calculations we present a model of the BaTiO3(001)-(2×1) surface structure, which has not been considered so far. While the crystal is terminated by two TiO2 layers similarly to SrTiO3(001)-(2×1), we find that one out of two surface layer Ti-atoms resides in a tetragonal pyramidal oxygen environment. This peculiar geometry leads to a metallic and magnetic surface involving local magnetic moments up to 2μ(B) in magnitude located at surface Ti and O atoms. Our results are important for the understanding of the intrinsic surface metallicity of insulating oxides in general.

Different computational scheme for calculating surface integrals in anisotropic Brillouin zones are compared. An example of the transport distribution function (plasma frequency) of the thermoelectric material Bi(2)Te(3) near the band edges is discussed. The layered structure of the material together with the rhombohedral symmetry causes a strong anisotropy of the transport distribution function for the directions in the basal plane (in-plane) and perpendicular to the basal plane (out-of-plane). It is shown that a thorough reciprocal space integration is necessary to reproduce the in-plane/out-of-plane anisotropy. A quantitative comparison can be made at the band edges, where the transport anisotropy is given in terms of the anisotropic mass tensor., (© 2011 IOP Publishing Ltd Printed in the UK & the USA)

Strong chemical interaction between bacterial surface protein layers and calcium atoms deposited in situ on top was revealed by means of photoemission spectroscopy. The interaction appears to mainly happen at the oxygen site of the peptide bonds and involves a large charge transfer from Ca 4s states into the peptide backbone. Chemical kinetics of this reaction was characterized using time-dependent valence band photoemission, and the reaction rate constant was determined., (© 2011 American Chemical Society)

A fully relativistic description of the spin-orbit induced spin Hall effect is presented that is based on Kubo's linear response formalism. Using an appropriate operator for the spin-current density a Kubo-Středa-like equation for the spin Hall conductivity (SHC) is obtained. An implementation using the Korringa-Kohn-Rostoker band structure method in combination with the coherent potential approximation allow detailed investigations on various alloy systems. A decomposition of the SHC into intrinsic and extrinsic contributions is suggested. Accompanying calculations for the skew-scattering contribution of the SHC using the Boltzmann equation demonstrate the equivalence to the Kubo formalism in the dilute alloy regime and support the suggested decomposition scheme.

We present an ab initio description of the spin Hall effect in metals. Our approach is based on density functional theory in the framework of a fully relativistic Korringa-Kohn-Rostoker method and the solution of a linearized Boltzmann equation including the scattering-in term (vertex corrections). The skew scattering mechanism at substitutional impurities is considered. Spin-orbit coupling in the host as well as at the impurity atom and the influence of spin-flip processes are fully taken into account. A sign change of the spin Hall effect in Cu and Au hosts is obtained as a function of the impurity atom, and even light elements like Li can cause a strong effect. It is shown that the gigantic spin Hall effect in Au can be caused by skew scattering at C and N impurities which are typical contaminations in a vacuum chamber.

High-quality films of copper phthalocyanine (CuPc) prepared in situ were used as a model to characterize unoccupied states of organic molecular semiconductors. We demonstrate that a combination of high-resolution near-edge x-ray absorption together with first-principles calculations constitutes a reliable tool for the detection and identification of particular molecular orbitals.

The influence of the finite thickness and structure, amorphous or crystalline, of Fe electrodes on the tunneling magnetoresistance (TMR) ratio is investigated by ab initio calculations in Fe/MgO/Fe tunnel junctions. An amorphous Fe layer in direct contact with the MgO barrier causes a low TMR ratio of only 44%. By inserting crystalline Fe monolayers between the barrier and the amorphous Fe the TMR ratio increases rapidly and reaches the same level as for semi-infinite Fe electrodes. Even one crystalline Fe monolayer is sufficient to achieve a giant TMR ratio exceeding 500%. Omitting the amorphous Fe has nearly no influence on the results if there are more than two monolayers of crystalline Fe next to the barrier. The results demonstrate that the reservoirs can even be nonmagnetic. The TMR emerges from the interplay of symmetry selection in the barrier and spin filtering at the electrode-barrier interface.

From the basis of ab initio electronic structure calculations which include the effects of thermally excited magnetic fluctuations, we predict Mn-stabilized cubic zirconia to be ferromagnetic above 500 K. We find this material, which is well known both as an imitation diamond and as a catalyst, to be half-metallic with the majority and minority spin Mn impurity states lying in zirconia's wide gap. The Mn concentration can exceed 40%. The high-Tc ferromagnetism is robust to oxygen vacancy defects and to how the Mn impurities are distributed on the Zr fcc sublattice. We propose this ceramic as a promising future spintronics material.

Using density functional theory we perform theoretical investigations of the electronic properties of a freestanding one-dimensional organometallic vanadium-benzene wire. This system represents the limiting case of multidecker Vn(C6H6)(n+1) clusters which can be synthesized with established methods. We predict that the ground state of the wire is a 100% spin-polarized ferromagnet (half-metal). Its density of states is metallic at the Fermi energy for the minority electrons and shows a semiconductor gap for the majority electrons. We find that the half-metallic behavior is conserved up to 12% longitudinal elongation of the wire. Ab initio electron transport calculations reveal that finite size vanadium-benzene clusters coupled to ferromagnetic Ni or Co electrodes will work as nearly perfect spin filters.