Strong spin-orbit splitting on Bi surfaces

Using first-principles calculations and angle-resolved photoemission, we show that the spin-orbit interaction leads to a strong splitting of the surface state bands on low-index surfaces of Bi. The dispersion of the states and the corresponding Fermi surfaces are profoundly modified in the whole surface Brillouin zone. We discuss the implications of these findings with respect to a proposed surface charge density wave on Bi(111) as well as to the surface screening, surface spin-density waves, electron (hole) dynamics in surface states, and to possible applications to the spintronics.Comment: 4 pages 2 figure

Electronic structure and Fermi surface of Bi(100)

The surface electronic structure of 13000) was studied by angle-resolved photoemission and the full-potential linearized-augmented plane-wave film method. Experimentally, several electronic surface states were identified in the gaps of the projected-bulk band structure close to the Fermi level. Theory shows that these states belong to a spin-orbit split-surface band that extends through the whole Brillouin zone, and that some surface states penetrate very deeply into the bulk. In the experiment, the surface Fermi surface was found to consist of three features: an electron pocket at the (Gamma) over bar point, a hole pocket in the (Gamma) over bar-(M) over bar direction (i.e., in the direction of the surface-mirror line), and a small Fermi-surface element close to the (M) over bar' points

Electronic structure and Fermi surface of Bi(100)

The surface electronic structure of Bi(100) was studied by angle-resolved photoemission and the full-potential linearized-augmented plane-wave film method. Experimentally, several electronic surface states were identified in the gaps of the projected-bulk band structure close to the Fermi level. Theory shows that these states belong to a spin-orbit split-surface band that extends through the whole Brillouin zone, and that some surface states penetrate very deeply into the bulk. In the experiment, the surface Fermi surface was found to consist of three features: an electron pocket at the ¯Γ point, a hole pocket in the ¯Γ−¯M direction (i.e., in the direction of the surface-mirror line), and a small Fermi-surface element close to the ¯M′ points.This paper was supported by the Danish National Science Foundation

Fe/MnAs bilayers: Magnetic anisotropy and the role of the interface

International audienceWe have studied different aspects of the magnetic behavior of Fe(5 nm)/MnAs(100 nm) bilayers epitaxially grown on GaAs( 1 0 0 ). Ferromagnetic resonance (FMR) measurements were performed in order to characterize the magnetic anisotropies of the films and the interlayer coupling between them. The chemical composition of the interface was investigated by X-ray photoemission spectroscopy (XPS). The iron layer FMR spectrum is highly temperature dependent between 280K and 320K as its parameters are strongly altered in the alpha/beta phase coexistense regime of the MnAs layer, revealing a strong interlayer coupling in this T-region. Additionally, the XPS experiments demonstrate the existence of an Fe-MnAs intermixed interface. This result would explain appearance of an additional uniaxial anisotropy in the plane of the Fe films, together with a strong reduction in its magnetocrystalline anisotropy and a negligible direct exchange coupling in the MnAs ferromagnetic state. (C) 2012 Published by Elsevier B.V

Building two-dimensional metal-organic networks with tin

We show that Sn atoms combined with organic ligands can be used to build 2D coordination networks on Au(111) surfaces

Stabilization of high-spin Mn ions in tetra-pyrrolic configuration on copper

By means of Mn-Cu transmetalation, we incorporated Mn atoms in an array of TCNQ (7,7,8,8-tetracyanoquinodimethane) grown on Cu(100), forming a long range ordered and commensurate metal\u2013organic coordination network (MOCN). Preliminary Sn alloying of the Cu(100) surface allowed us to control the degree of substrate reactivity, thus preventing the chemical interaction of the Mn-TCNQ MOCN with the substrate. Mn2+ ions are stabilized in an artificial tetra-pyrrolic coordination, which mimics the macrocyle configuration of Mn-phthalocyanines/porphyrins. X-ray absorption spectroscopy at the Mn L2,3-edge indicates that the Mn ions are in a high-spin state (S = 5/2), in agreement with DFT + U calculations which also shows that the electronic structure of this Mn-TCNQ MOCN is very similar to that of the corresponding unsupported MOCN

Ubiquitous deprotonation of terephthalic acid in the self-assembled phases on Cu(100)

We performed an exhaustive study of terephthalic acid (TPA) self-assembly on a Cu(100) surface, where first-layer molecules display two sequential phase transitions in the 200-400 K temperature range, corresponding to different stages of molecular deprotonation. We followed the chemical and structural changes by means of high-resolution X-ray photoelectron spectroscopy (XPS) and variable-temperature scanning tunneling microscopy (STM), which were interpreted on the basis of density functional theory (DFT) calculations and photoemission simulations. In order to reveal the spectroscopic contributions of the molecules in different states of deprotonation, we modified the substrate reactivity by deposition of a small amount of Sn, which hampers the deprotonation reaction. We found that the characteristic molecular ribbons of the TPA/Cu(100) \u3b1-phase at a low temperature contain a significant fraction of partially deprotonated molecules, in contrast to the expectation of a fully protonated phase, where the self-assembly was claimed to be simply driven by the intermolecular double hydrogen bonds [OH efO]. On the basis of our simulations, we propose a model where the carboxylate groups of the partially deprotonated molecules form single hydrogen bonds with the carboxylic groups of the fully protonated molecules. Using real time XPS, we also monitored the kinetics of the deprotonation reaction. We show that the network of mixed single and double hydrogen bonds inhibits further deprotonation up to 3c270 K, whereas the isolated molecules display a much lower deprotonation barrier

Fe and Mo valences in Sr2FeMoO6

Sem informaçãoThe valences of Fe and Mo in Sr2FeMoO6 are investigated by means of X-ray absorption and photoemission spectroscopies. We find that the d occupations are similar to those of Fe in Fe2O3 and Mo in MoO3. Considering the covalency, however, we argue that the ground state is closer to a Fe+3(3d5)-Mo+5(4d1) configuration than to a Fe+2(3d6)-Mo+6(4d0) configuration.The valences of Fe and Mo in Sr2FeMoO6 are investigated by means of X-ray absorption and photoemission spectroscopies. We find that the d occupations are similar to those of Fe in Fe2O3 and Mo in MoO3. Considering the covalency, however, we argue that the ground state is closer to a Fe+3(3d5)–Mo+5(4d1) configuration than to a Fe+2(3d6)–Mo+6(4d0) configuration.1204161164Sem informaçãoSem informaçãoSem informaçãoFinancial support by CONICET, Fundación Antorchas, and ANPCyT of Argentina, and by LNLS of Brazil is gratefully acknowledged