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. Understanding the temporal evolution of quasi particles (electron and holes) on metal surfaces is of paramount importance to describe many important phenomena such as the dynamics of charge and energy transfer, quantum interference, localization and many others. This temporal evolution is characterized by a finite lifetime, τ , which refers to the time the quasi particle retains its identity. While the lifetime of an excited electron or hole is determined by many-body interactions, namely electron-electron (e-e) and electron-phonon (e-p) scattering processes, the peak width in an experiment might also be influenced by electron-defect scattering on crystal or surface imperfections [1]. However, it was demonstrated in recent STM [2] and photoemission experiments [3] that these defect contributions can be minimized, making it possible to analyze the pure lifetime broadening due to the formation of a hole in the sp surface state band in the L-gap of the (111)-surface of noble metals.These Shockley-type surface states form a twodimensional (2D) electron gas and the e-e contribution to the hole lifetime has been rationalized in terms of a dominant contribution from intraband transitions within the 2D surface state band, screened by the underlying 3D bulk electron system, and in terms of interband transitions (bulk states → surface state) [2]. On the other hand an appropriate calculation of the e-p contribution to the lifetime broadening of surface states is still lacking. The present work is an attempt in this direction.The strength of the e-p coupling is described by the electron mass enhancement parameter λ, which is, in general, energy and momentum dependent. Many properties of metals [4], such as resistivity, specific heat and superconductivity, reflect the e-p coupling and can be expressed in terms of the Fermi surface-averaged λ-value. It also reflects the high temperature behavior of the broadening Γ ep = 2πλk B T , and the e-p contribution to the renormalization of the mass m * = m(1 + λ). The anisotropy of λ is well known [5] and is revealed in e.g. cyclotron resonance measurements [6].Typically, the phonon contribution to the decay of surface states is estimated using the Debye phonon model. Within this model the Eliashberg spectral function of the e-p interaction is proportional to the quadratic density of phonon states α 2 F (ω) = λ(ω/ω D ) 2 , where ω D is the Debye energy, λ is usually obtained from measurements or th...

First-principles calculations of the damping rate of vibrational and translational modes of single hydrogen atoms and molecules chemisorbed on metal surfaces are presented. The decay into electron-hole pair excitations is considered. The metal is described in the so-called jellium model, and the calculations are based on the Kohn-Sham density functional formalism extended to the quasi-static regime. For the actual evaluation of the damping an embedding scheme is used, which through explicit tests is shown to be appropriate. In particular in the homogeneous limit, a comparison is made with an exact phase-shift formula. The local electron density is found to be a key parameter for the damping rate, in particular in situations with no dramatic electron structure at the Fermi level. Adsorbates that induce states around the Fermi level should exhibit an enhanced damping rate. A direct relation between the friction coefficient of an adparticle and the vibrational damping rate is derived. The calculated rate values imply that the electronic mechanism is able to accommodate typical thermal energies of hydrogen atoms impinging on metal surfaces. From this result and comparisons with observed lifetime broadenings of vibrational spectral lines it is concluded that electron-hole pairs provide an important channel for energy transfer at metal surfaces.

We show that electron correlations lead to a bad metallic state in chalcogenides FeSe and FeTe despite the intermediate value of the Hubbard repulsion U and Hund's rule coupling J. The evolution of the quasi particle weight Z as a function of the interaction terms reveals a clear crossover at U ≃ 2.5 eV. In the weak coupling limit Z decreases for all correlated d orbitals as a function of U and beyond the crossover coupling they become weakly dependent on U while strongly depend on J. A marked orbital dependence of the Z's emerges even if in general the orbital-selective Mott transition only occurs for relatively large values of U . This two-stage reduction of the quasi particle coherence due to the combined effect of Hubbard U and the Hund's J, suggests that the iron-based superconductors can be referred to as Hund's correlated metals. The role of electron correlations in the iron-based superconductors is still a debated issue, naturally intertwined with the search for the origin of high critical temperatures. We present results that improve the qualitative understanding of how electron correlation influences fundamental electron properties of these compounds, such as the metallicity, which in turn might be important also for the understanding of the pairing mechanism. We choose two candidates of the chalogenides, FeSe and FeTe and employ f irst principles electron structure calculations combined with advanced many-body methods taking into account the local electron correlation. The chalcognides have in contrast to the pnictides a simpler atomic structure, thus easier to synthesize and also to study theoretically. In addition they are non toxic in contrast to the pnictides containing arsenic.In previously known superconductors we can identify either weakly correlated materials, like elemental superconductors or binary alloys, including MgB 2 , or highlycorrelated compound like the copper oxides and heavy fermion materials. In the first set of compounds superconductivity is explained within the Bardeen-CooperSchrieffer framework and its extensions, and it occurs as a pairing instability of a normal metal. In the second set it is widely believed that correlations revolutionize the electronic properties and that both the metallic state and the pairing mechanism deviate from standard paradigms.The iron-based pnictides and chalcognides superconductors do not fit this simple classification. The common labeling "intermediate correlation", referring to properties such as Fermi surface topology or absence of Hubbard bands [1], suggests modest effects of correlations. Conversely, the metallic state appears much less coherent than what these observations imply [2,3]. A magnetic counterpart of this dualism is the localized an itinerant nature of the spin-density-wave state of the parent compound.The characteristic property of the band structure is that several of the five d-bands cross the Fermi level. The multi-orbital nature leads to several exotic electronic properties such as orbital-selectivity [4][5][6][7][8][9] and ...

We present a self-consistent numerical approach to solve the Gutzwiller variational problem for general multi-band models with arbitrary on-site interaction. The proposed method generalizes and improves the procedure derived by Deng et al., Phys. Rev. B. 79 075114 (2009), overcoming the restriction to density-density interaction without increasing the complexity of the computational algorithm. Our approach drastically reduces the problem of the high-dimensional Gutzwiller minimization by mapping it to a minimization only in the variational density matrix, in the spirit of the Levy and Lieb formulation of DFT. For fixed density the Gutzwiller renormalization matrix is determined as a fixpoint of a proper functional, whose evaluation only requires ground-state calculations of matrices defined in the Gutzwiller variational space. Furthermore, the proposed method is able to account for the symmetries of the variational function in a controlled way, reducing the number of variational parameters. After a detailed description of the method we present calculations for multi-band Hubbard models with full (rotationally invariant) Hund's rule on-site interaction. Our analysis shows that the numerical algorithm is very efficient, stable and easy to implement. For these reasons this method is particularly suitable for first principle studies -- e.g., in combination with DFT -- of many complex real materials, where the full intra-atomic interaction is important to obtain correct results.Comment: 19 pages, 7 figure

Theoretical calculations and scanning-tunneling spectroscopy measurements of the hole lifetime broadening, Ϫ1 , in a quantum-well state for 0.95 and 1.0 monolayers of Na on Cu͑111͒ are reported. A model potential is proposed for calculating quantum-well states in a monolayer on metal surfaces. The inelastic electron-electron contribution, e-e Ϫ1 , is evaluated within the GW approximation by using eigenfunctions and eigenenergies obtained with this model potential. The electron-phonon contribution, e-ph Ϫ1 , is computed by employing Debye and Einstein models as well as a first-principle ultrasoft pseudopotential method. The obtained theoretical results are in excellent agreement with experimental data, both showing a surprisingly large difference in the lifetime broadening for 0.95 and 1.0 monolayers which is attributed mostly to changes in the electronic structure.