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Using angle-resolved photoemission spectroscopy, we show direct evidence for charge transfer between adsorbed molecules and metal substrates, i.e., chemisorption of CO on Pt(111) and Pt-Sn/Pt(111) 2 x 2 surfaces. The observed band structures show a unique signature of charge transfer as CO atoms are adsorbed, revealing the roles of specific orbital characters participating in the chemisorption process. As the coverage of CO increases, the degree of charge transfer between CO and Pt shows a clear difference to that of Pt-Sn. With comparison to density functional theory calculation results, the observed distinct features in the band structure are interpreted as back-donation bonding states formed between the Pt molecular orbital and the 2 pi orbital of CO. Furthermore, the change in the surface charge concentration, measured from the Fermi surface area, shows that the Pt surface has a larger charge concentration change than the Pt-Sn surface upon CO adsorption. The differences between Pt and Pt-Sn surfaces are due to the effect of Pt-Sn intermetallic bonding on the interaction of CO with the surface.

International audience; Self-assembled nanolines are attractive to build the technological devices of next generation, but characterizing their electronic properties is often difficult to achieve. In this work we employ angle-resolved photoemission spectroscopy and density functional theory to clarify the electronic structure exhibited by self-assembled Bi nanolines grown on the InAs(100) surface. A surface resonance associated to the reconstructed (4 2) surface is visible in the photoemission spectra before and after the formation of the Bi nanolines. This demonstrates that Bi deposition does not necessarily drive a transition to an unreconstructed surface in the substrate, which is contrary to what was reported in previous studies. In addition, experiment and theory show the presence of a flat band located in the band gap of InAs, just above the valence band maximum. This flat band is associated to the Bi nanolines and possesses a strong orbital character, consistent with its unidimensional nature. These spectral features suggest that Bi nanolines on InAs(100) may have a strongly polarized conductivity, which makes them suitable to be exploited as nanowires in nanotechnology. The coexistence with an accumulation layer suggests an even farther functionalization.

Hybridization between $f$ electrons and conduction bands ($c$-$f$ hybridization) is a driving force for many unusual phenomena. To provide insight into it, systematic studies of CeCoIn$_5$ heavy fermion superconductor have been performed by angle-resolved photoemission spectroscopy (ARPES) in a large angular range at temperature of $T=6$ K. The used photon energy of 122 eV corresponds to Ce $4d$-$4f$ resonance. Calculations carried out with relativistic multiple scattering Korringa-Kohn-Rostoker method and one-step model of photoemission yielded realistic simulation of the ARPES spectra indicating that Ce-In surface termination prevails. Surface states, which have been identified in the calculations, contribute significantly to the spectra. Effects of the hybridization strongly depend on wave vector. They include a dispersion of heavy electrons and bands gaining $f$-electron character when approaching Fermi energy. We have also observed a considerable variation of $f$-electron spectral weight at $E_F$, which is normally determined by both matrix element effects and wave vector dependent $c$-$f$ hybridization. Fermi surface scans covering a few Brillouin zones revealed large matrix element effects. A symmetrization of experimental Fermi surface, which reduces matrix element contribution, yielded a specific variation of $4f$-electron enhanced spectral intensity at $E_F$ around $\bar{\Gamma}$ and $\bar{M}$ points. Tight-binding approximation calculations for Ce-In plane provided the same universal distribution of $4f$-electron density for a range of values of the parameters used in the model., Comment: 15 pages, 9 figures

Author(s): Rattanachata, A; Nicolai, LC; Martins, HP; Conti, G; Verstraete, MJ; Gehlmann, M; Ueda, S; Kobayashi, K; Vishik, I; Schneider, CM; Fadley, CS; Gray, AX; Minar, J; Nemsak, S | Abstract: In the last decade rare-earth hexaborides have been investigated for their fundamental importance in condensed matter, and for their applications in advanced technological fields. Among these compounds, LaB6 has a special place, being a traditional d-band metal without additional f bands. In order to understand the bulk electronic structure of the more complex rare-earth hexaborides, in this paper we investigate the bulk electronic structure of LaB6 using tender/hard x-ray photoemission spectroscopy, measuring both core-level and angle-resolved valence-band spectra. Furthermore, we compare the La 3d core level spectrum to cluster model calculations in order to understand the bulklike core-hole screening effects. The results show that the La 3d well-screened peak is at a lower binding energy compared to the main poorly screened peak; the relative intensity between these peaks depends on how strong the hybridization is between La and B atoms. We show that the recoil effect, negligible in the soft x-ray regime, becomes prominent at higher kinetic energies for lighter elements, such as boron, but is still negligible for heavy elements, such as lanthanum. In addition, we report the bulklike band structure of LaB6 determined by tender/hard x-ray angle-resolved photoemission spectroscopy (HARPES). We compare HARPES experimental results to the free-electron final-state calculations and to the more precise one-step photoemission theory including matrix element and phonon excitation effects. The agreement between the features present in the experimental ARPES data and the theoretical calculations is very good. In addition, we consider the nature and the magnitude of phonon excitations in order to interpret HARPES experimental data measured at different temperatures and excitation energies. We demonstrate that the one-step theory of photoemission and HARPES experiments provides, at present, the only approach capable of probing, both experimentally and theoretically, true "bulklike"electronic band structure of rare-earth hexaborides and strongly correlated materials.

Ferroelectric GeTe is unveiled to exhibit an intriguing multiple non-trivial topology of the electronic band structure due to the existence of triple-point and type-II Weyl fermions, which goes well beyond the giant Rashba spin splitting controlled by external fields as previously reported. Using spin- and angle-resolved photoemission spectroscopy combined with ab initio density functional theory, the unique spin texture around the triple point caused by the crossing of one spin degenerate and two spin-split bands along the ferroelectric crystal axis is derived. This consistently reveals spin winding numbers that are coupled with time reversal symmetry and Lorentz invariance, which are found to be equal for both triple-point pairs in the Brillouin zone. The rich manifold of effects opens up promising perspectives for studying non-trivial phenomena and multi-component fermions in condensed matter systems., 5 pages, 5 figures

This paper shows how the detailed dispersion of the giant Rashba split surface states in the ferroelectric \ensuremath{\alpha}--GeTe(111) can be resolved by static ARPES and surface potassium doping. The authors further confirm the Rashba mechanism for these states by moving them into the occupied part of the band structure, in good agreement with state of the art DFT calculations.

By measuring the spin polarization of GeTe films as a function of light polarization we observed that the bulk states are fully spin polarized in the initial state, in strong contrast with observations for other systems with a strong spin orbit interaction and the surface derived states in the same system. In agreement with state of the art theory, our experimental results show that fully spin polarized bulk states are an intrinsic property of the ferroelectric Rashba semiconductor amp; 945; GeTe 111 . The fact that the measured spin polarization vector does not change with light polarization can be explained by the absence of a mixing of states with a different total angular momentum J

The growth of Bi on both the In-terminated (A) face and the As-terminated (B) face of InAs(1 1 1) has been investigated by low-energy electron diffraction, scanning tunnelling microscopy, and photoelectron spectroscopy using synchrotron radiation. The changes upon Bi deposition of the In 4d and Bi 5d 5/2 photoelectron signals allow to get a comprehensive picture of the Bi/InAs(1 1 1) interface. From the early stage the Bi growth on the A face is epitaxial, contrary to that on the B face that proceeds via the formation of islands. Angle-resolved photoelectron spectra show that the electronic structure of a Bi deposit of ≈10 bi-layers on the A face is identical to that of bulk Bi, while more than ≈30 bi-layers are needed for the B face. Both bulk and surface electronic states observed are well accounted for by fully relativistic ab initio calculations performed using the one-step model of photoemission. These calculations are used to analyse the dichroic photoemission data recorded in the vicinity of the Fermi level around the Γ ¯ point of the Brillouin zone.

International audience; The goal of the present review is to cross-compare theoretical predictions with selected experimental results on bismuth thin films exhibiting topological properties and a strong Rashba effect. The theoretical prediction that a single free-standing Bi(1 1 1) bilayer is a topological insulator has triggered a large series of studies of ultrathin Bi(1 1 1) films grown on various substrates. Using selected examples we review theoretical predictions of atomic and electronic structure of Bi thin films exhibiting topological properties due to interaction with a substrate. We also survey experimental signatures of topological surface states and Rashba effect, as obtained mostly by angle- and spin-resolved photoelectron spectroscopy.

Molybdenum dichalcogenides are probably the most studied single layer TMDCs by virtue of being appealing for sundry possible applications suchlike transistors, diodes, solar cells or more fundamental studies of spin or valley pseudospin and their interactions. Tungsten-based counterparts are on the other hand evincing much stronger spin-orbit coupling due to which all the spin-related effects are more stable at room temperature and thus more feasible for application. WTe2, a type-II Weyl semimetal is in particular interesting due to having two pairs of spin-differentiated Weyl points above Fermi energy. We have conducted several experiments following the evolution of the band dispersion in the vicinity of X and Y points of the Brillouin zone of WTe2 which is substantial for understanding the fundamental properties of the structure-property relation of the system. Ab-initio set of photoemission calculations was performed using SPR-KKR package and compared to experimental results.

Here we report on our study to quantitatively describe the intensities of the valence band hard x-ray photoemission spectra (HAXPES) of a rare earth element containing 3d transition metal oxides. Using LaCoO3 as a representative model compound, we compared the experimental data to the results of ab initio one-step photoemission band structure calculations as well as to the sum of the partial density of states of the atomic constituents weighted by their tabulated photoionization cross sections. We discovered that the semicore La 5p density of states surprisingly contributes in a significant manner to the valence band spectrum: Although the La 5p partial density of states in the valence band region is negligible compared to that of the O 2p or the Co 3d, the La 5p cross section in the hard x-ray range is found to be orders of magnitude larger than that of the other subshells. This explains the long-standing issue of why the hard x-ray valence band spectra of a rare-earth element containing materials have line shapes that are very different from those taken at lower photon energies and why they cannot be described in terms of partial density of states of the subshells usually considered for the lower photon energy spectra. We infer that the contribution of the rare-earth 5p must be taken into account and cannot be ignored.

APCOM2018 - 24th International conference Applied Physics of Condensed Matter, Štrbské Pleso, Slovaquie, 20 to 22/06/2018"Solid State Physics and Radioactive Irradiation"; International audience; Thin Bi films are interesting candidates for spintronic applications due to a large spin-orbit splitting that, combined with the loss of inversion symmetry at the surface, results in a band structure that is not spin-degenerate. In recent years, applications for topological insulators based on Bi and Bi alloys have as well attracted much attention. Here we present angle-resolved photoemission spectroscopy studies of the Bi/InAs(100) interface. Bismuth deposition followed by annealing of the surface results in the formation of one full Bi monolayer decorated by Bi nanolines. We found that the building up of the interface does not affect the electronic structure of the substrate. As a consequence of weak interaction, Bi states are placed in the gaps of the electronic structure of InAs(100). We observe a strong resonance of the Bi electronic states close to the Fermi level; its intensity depends on the photon energy and the photon polarization. These states show nearly no dispersion when measured perpendicular to the nanolines, confirming their onedimensionality.

PhotoEmission Spectroscopy (PES) is a surface sensitive technique within the Ultra-Violet regime. A way to make it more bulk sensitive consists in increasing the photon energy for entering the X-ray regime. As a counterpart, this increase breaks the k-conserving dipole selection rule and results in a smearing of the measured electronic band structure caused by phonon-assisted electronic transitions. It is therefore essential to model this physical effect within ab-initio calculations. We herewith sketch the implementation of lattice vibrations within the one-step model of photoemission through the Coherent Potential Approximation (CPA). Moreover, we show a practical example with the case of Ag(001) on which the influence of photon energy and/or tempera-ture is benchmarked and interpreted.PhotoEmission Spectroscopy (PES) is a surface sensitive technique within the Ultra-Violet regime. A way to make it more bulk sensitive consists in increasing the photon energy for entering the X-ray regime. As a counterpart, this increase breaks the k-conserving dipole selection rule and results in a smearing of the measured electronic band structure caused by phonon-assisted electronic transitions. It is therefore essential to model this physical effect within ab-initio calculations. We herewith sketch the implementation of lattice vibrations within the one-step model of photoemission through the Coherent Potential Approximation (CPA). Moreover, we show a practical example with the case of Ag(001) on which the influence of photon energy and/or tempera-ture is benchmarked and interpreted.