arXiv subjects

E. V. Chulkov

Publications and source records attributed to E. V. Chulkov.

104 records · Page 6Linked to original sources

arXiv2003

Quantum size effects in Pb islands on Cu(111): Electronic-structure calculations

The appearance of "magic" heights of Pb islands grown on Cu(111) is studied by self-consistent electronic structure calculations. The Cu(111) substrate is modeled with a one-dimensional pseudopotential reproducing the essential features, i.e. the band gap and the work function, of the Cu band structure in the [111] direction. Pb islands are presented as stabilized jellium overlayers. The experimental eigenenergies of the quantum well states confined in the Pb overlayer are well reproduced. The total energy oscillates as a continuous function of the overlayer thickness reflecting the electronic shell structure. The energies for completed Pb monolayers show a modulated oscillatory pattern reminiscent of the super-shell structure of clusters and nanowires. The energy minima correlate remarkably well with the measured most probable heights of Pb islands. The proper modeling of the substrate is crucial to set the quantitative agreement.

cond-mat.mtrl-sci↗

arXiv2003

Electron-phonon interaction at the Be(0001) surface

We present a first principle study of the electron-phonon (e-p) interaction at the Be(0001) surface. The real and imaginary part of the e-p self energy are calculated for the surface state in the binding energy range from the $\barΓ$ point to the Fermi level. Our calculation shows an overall good agreement with several photoemission data measured at high and low temperatures. Additionally, we show that the energy derivative of real part of the self-energy presents a strong temperature and energy variation close to $E_{F}$, making it difficult to measure its value just at $E_{F}$.

cond-mat.mtrl-sci↗

arXiv2003

Role of occupied d bands in the dynamics of excited electrons and holes in Ag

The role that occupied $d$ bands play in the inelastic lifetime of bulk and surface states in Ag is investigated from the knowledge of the quasiparticle self-energy. In the case of bulk electrons, $sp$ bands are taken to be free-electron like. For surface states, the surface band structure of $sp$ states is described with the use of a realistic one-dimensional hamiltonian. The presence of occupied $d$ states is considered in both cases by introducing a polarizable background. We obtain inelastic lifetimes of bulk electrons that are in good agreement with first-principles band-structure calculations. Our surface-state lifetime calculations indicate that the agreement with measured lifetimes of both crystal-induced and image-potential induced surface states on Ag(100) and Ag(111) is considerably improved when the screening of $d$ electrons is taken into account.

cond-mat.mtrl-sci↗

arXiv2002

The role of surface plasmons in the decay of image-potential states on silver surfaces

The combined effect of single-particle and collective surface excitations in the decay of image-potential states on Ag surfaces is investigated, and the origin of the long-standing discrepancy between experimental measurements and previous theoretical predictions for the lifetime of these states is elucidated. Although surface-plasmon excitation had been expected to reduce the image-state lifetime, we demonstrate that the subtle combination of the spatial variation of s-d polarization in Ag and the characteristic non-locality of many-electron interactions near the surface yields surprisingly long image-state lifetimes, in agreement with experiment.

cond-mat.mtrl-sci↗

arXiv2002

Image-potential-induced states at metal surfaces

The unequivocal observation in the early 1980s of a new class of unnocupied surface states that are bound to the vacuum level of a variety of metal surfaces has led over the last two decades to an active area of research in condensed-matter and surface physics. We discuss the key ingredients of the theory of these so-called image states, which have their origin in the long range nature of the image potential outside a solid.

cond-mat.mtrl-sci↗

arXiv2001

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.

cond-mat.mtrl-sci↗

arXiv2001

Surface and Image-Potential States on the MgB_2(0001) Surfaces

We present a self-consistent pseudopotential calculation of surface and image-potential states on $MgB_2(0001)$ for both $B$-terminated ($B-t$) and $Mg$-terminated ($Mg-t$) surfaces. We find a variety of very clear surface and subsurface states as well as resonance image-potential states n=1,2 on both surfaces. The surface layer DOS at $E_F$ is increased by 55% at $B-t$ and by 90% at the $Mg-t$ surface compared to DOS in the corresponding bulk layers.

cond-mat.mtrl-sci↗

arXiv2001

Dielectric functions and collective excitations in MgB_2

The frequency- and momentum-dependent dielectric function $ε{(\bf q,ω)}$ as well as the energy loss function Im[-$ε^{-1}{(\bf q,ω)}$\protect{]} are calculated for intermetallic superconductor $MgB_2$ by using two {\it ab initio} methods: the plane-wave pseudopotential method and the tight-binding version of the LMTO method. We find two plasmon modes dispersing at energies $\sim 2$-8 eV and $\sim 18$-22 eV. The high energy plasmon results from a free electron like plasmon mode while the low energy collective excitation has its origin in a peculiar character of the band structure. Both plasmon modes demonstrate clearly anisotropic behaviour of both the peak position and the peak width. In particular, the low energy collective excitation has practically zero width in the direction perpendicular to boron layers and broadens in other directions.

cond-mat.supr-con↗

arXiv2000

Surface-state electron dynamics in noble metals

Theoretical investigations of surface-state electron dynamics in noble metals are reported. The dynamically screened interaction is computed, within many-body theory, by going beyond a free-electron description of the metal surface. Calculations of the inelastic linewidth of Shockley surface-state electrons and holes in these materials are also presented. While the linewidth of excited holes at the surface-state band edge (${\bf k}_\parallel=0$) is dominated by a two-dimensional decay channel, within the surface-state band itself, our calculations indicate that major contributions to the electron-electron interaction of surface-state electrons above the Fermi level come from the underlying bulk electrons.

cond-mat.mtrl-sci↗

arXiv2000

First-principles calculations of hot-electron lifetimes in metals

First-principles calculations of the inelastic lifetime of low-energy electrons in Al, Mg, Be, and Cu are reported. Quasiparticle damping rates are evaluated from the knowledge of the electron self-energy, which we compute within the GW approximation of many-body theory. Inelastic lifetimes are then obtained along various directions of the electron wave vector, with full inclusion of the band structure of the solid. Average lifetimes are also reported, as a function of the electron energy. In Al and Mg, splitting of the band structure over the Fermi level yields electron lifetimes that are smaller than those of electrons in a free-electron gas. Larger lifetimes are found in Be, as a result of the characteristic dip that this material presents in the density of states near the Fermi level. In Cu, a major contribution from $d$ electrons participating in the screening of electron-electron interactions yields electron lifetimes which are well above those of electrons in a free-electron gas with the electron density equal to that of valence ($4s^1$) electrons.

cond-mat.mtrl-sci↗

arXiv1999

Self-energy of image states on copper surfaces

We report extensive calculations of the imaginary part of the electron self-energy in the vicinity of the (100) and (111) surfaces of Cu. The quasiparticle self-energy is computed by going beyond a free-electron description of the metal surface, either within the GW approximation of many-body theory or with inclusion, within the GW$Γ$ approximation, of short-range exchange-correlation effects. Calculations of the decay rate of the first three image states on Cu(100) and the first image state on Cu(111) are also reported, and the impact of both band structure and many-body effects on the electron relaxation process is discussed.

cond-mat.mtrl-sci↗

arXiv1999

Theory of inelastic lifetimes of low-energy electrons in metals

Electron dynamics in the bulk and at the surface of solid materials are well known to play a key role in a variety of physical and chemical phenomena. In this article we describe the main aspects of the interaction of low-energy electrons with solids, and report extensive calculations of inelastic lifetimes of both low-energy electrons in bulk materials and image-potential states at metal surfaces. New calculations of inelastic lifetimes in a homogeneous electron gas are presented, by using various well-known representations of the electronic response of the medium. Band-structure calculations, which have been recently carried out by the authors and collaborators, are reviewed, and future work is addressed.

cond-mat.mtrl-sci↗

arXiv1999

Role of the intrinsic surface state in the decay of image states at a metal surface

The role of the intrinsic surface state ($n=0$) in the decay of the first image state ($n=1$) at the (111) surface of copper is investigated. Inelastic linewidths are evaluated from the knowledge of the imaginary part of the electron self-energy, which we compute, within the GW approximation of many-body theory, by going beyond a free-electron description of the metal surface. Single-particle wave functions are obtained by solving the Schrödinger equation with a realistic one-dimensional model potential, and departure of the motion along the surface from free-electron behaviour is considered through the introduction of the effective mass. The decay of the first image state of Cu(111) into the intrinsic surface state is found to result in a linewidth that represents a 40% of the total linewidth. The dependence of linewidths on the momentum of the image state parallel to the surface is also investigated.

cond-mat.mtrl-sci↗

arXiv1998

Lifetimes of image-potential states on copper surfaces

The lifetime of image states, which represent a key quantity to probe the coupling of surface electronic states with the solid substrate, have been recently determined for quantum numbers $n\le 6$ on Cu(100) by using time-resolved two-photon photoemission in combination with the coherent excitation of several states (U. Höfer et al, Science 277, 1480 (1997)). We here report theoretical investigations of the lifetime of image states on copper surfaces. We evaluate the lifetimes from the knowledge of the self-energy of the excited quasiparticle, which we compute within the GW approximation of many-body theory. Single-particle wave functions are obtained by solving the Schrödinger equation with a realistic one-dimensional model potential, and the screened interaction is evaluated in the random-phase approximation (RPA). Our results are in good agreement with the experimentally determined decay times.

cond-mat.mtrl-sci↗