G. Nicolay

Role of Bulk and Surface Phonons in the Decay of Metal Surface States

We present a comprehensive theoretical investigation of the electron-phonon contribution to the lifetime broadening of the surface states on Cu(111) and Ag(111), in comparison with high-resolution photoemission results. The calculations, including electron and phonon states of the bulk and the surface, resolve the relative importance of the Rayleigh mode, being dominant for the lifetime at small hole binding energies. Including the electron-electron interaction, the theoretical results are in excellent agreement with the measured binding energy and temperature dependent lifetime broadening.

Temperature Dependence of the Kondo Resonance and Its Satellites in CeCu2Si2

We present high-resolution photoemission spectroscopy studies on the Kondo resonance of the strongly correlated Ce system CeCu2Si2. By exploiting the thermal broadening of the Fermi edge we analyze position, spectral weight, and temperature dependence of the low-energy 4f spectral features, whose major weight lies above the Fermi level E(F). We also present theoretical predictions based on the single-impurity Anderson model using an extended noncrossing approximation, including all spin-orbit and crystal field splittings of the 4f states. The excellent agreement between theory and experiment provides strong evidence that the spectral properties of CeCu2Si2 can be described by single-impurity Kondo physics down to T approximately 5 K.

Electron-phonon coupling and its evidence in the photoemission spectra of lead.

We present a detailed study of the influence of strong electron-phonon coupling on the photoemission spectra of lead. Representing the strong-coupling regime of superconductivity, the spectra of lead show characteristic features that demonstrate the correspondence of physical properties in the normal and the superconducting state, as predicted by the Eliashberg theory. These features appear on an energy scale of a few meV and are accessible for photoemission only by using modern spectrometers with high-resolution in energy and angle.

Atomic correlations in itinerant ferromagnets: Quasi-particle bands of nickel

The Gutzwiller theory is demonstrated to resolve most of the long-standing discrepancies between experiment and theory on the quasi-particle bands of ferromagnetic nickel. This is confirmed by new angle-resolved photoelectron spectroscopy data along various high-symmetry lines of the bulk Brillouin zone obtained under full control of the three-dimensional momentum. Our findings support the view of itinerant ferromagnetism as a consequence of atomic correlations.

Lifetime of holes and electrons at metal surfaces; electron-phonon coupling

Abstract Surface chemical reactions are influenced by inherent dissipative processes which involve energy transfer between the conduction electrons and the ionic motion. We will discuss how it is possible to model this electron–phonon coupling in order to estimate its importance. A relevant quantity for this investigation is the lifetime of surface localized electron states. A surface state, quantum-well state or surface image state is located in a surface projected band gap and becomes relatively sharp in energy. This makes a comparison between calculations and experimental data most attractive, with a possibility to resolve the origin of the lifetime broadening. We point out the importance of taking into account the phonon spectrum, electron surface state wave functions and the screening of the electron–ion potential.

Fast epitaxy of Au and Ag on WSe2

Abstract Evaporation of Ag and Au on single crystal surfaces of the layered compound WSe 2 leads to epitaxial growth of (111) noble metal surfaces even at deposition rates several orders of magnitude higher than previously reported. The metal overlayers are studied by atomic force microscopy, low energy electron diffraction, angle-resolved photoemission and electron energy loss spectroscopy.

Quantitative line shape analysis of the Kondo resonance of cerium compounds

Abstract By use of high-resolution photoelectron spectroscopy we investigate the 4f spectral function of the heavy fermion compound CeRu2Si2 in the energy range close to the Fermi level. A normalization method proposed by Greber et al. (Phys. Rev. Lett. 79 (22) (1997) 4465) allows to resolve the Kondo resonance and its crystal field satellites. We discuss the applicability of this method with respect to a quantitative analysis of the data, and compare our experimental results to non-crossing approximation (NCA) calculations in the frame of the single impurity Andersson model (SIAM).

Investigation of the BCS density of states on a conventional superconductor by high-resolution photoelectron spectroscopy

Abstract The superconducting phase transition of the conventional A15 superconductor V3Si occurs at a transition temperature of Tc=17.1 K. According to the BCS theory, the zero-temperature gap width in the electronic density of states (DOS) is given by 1.75kBTc=2.5 meV, a value which is by a factor of the order of ten smaller than for High Temperature Superconductors (HTSC). We have investigated the DOS on polycrystalline V3Si surfaces by photoemission spectroscopy (PES) with an instrumental energy resolution of 3 meV (monochromatized He I). For the first time in photoemission spectra on a conventional superconductor, we could clearly detect the opening of a gap around the Fermi level and the signatures of the BCS DOS on this energy scale. A quantitative analysis of the data — based on a least-squares modelation by the theoretical BCS DOS — is in excellent agreement with the results of other experimental methods.

Photoemission Investigation of theL¯-Gap Surface States on Clean and Rare Gas-Covered Noble Metal (111)-Surfaces

High resolution photoemission spectroscopy is used to investigate the linewidth and dispersion of the L¯-gap surface states on (111)-surfaces of noble metals. The effect of a coverage of rare gases is demonstrated.

SELF-ENERGY EFFECTS IN THE UNOCCUPIED AND OCCUPIED ELECTRONIC STRUCTURE OF Cu

We report on self-energy effects in the electronic structure of Cu as a prototype weakly correlated system containing electron states of different localization. The unoccupied and occupied excited states were mapped fully resolved in the three-dimensional k using very-low-energy electron diffraction and photoemission, respectively. The self-energy corrections to the density-functional theory show distinct band- and k-dependence. These results are well described by quasiparticle GW calculations, especially for less localized states. We find correlation of the self-energy effects with spatial overlap of the one-electron wave function with the electron density, and elucidate the essential physics of this effect based on the electron-gas exchange correlation behavior.