arXiv subjects

V. M. Silkin

Publications and source records attributed to V. M. Silkin.

50 records · Page 3Linked to original sources

arXiv2005

Dynamical response function of a compressed lithium monolayer

Since recent both theoretical and experimental results have proved that the simple behaviour light alkaline metals present at equilibrium breaks when high pressures are applied, they have become an important object of study in Condensed Matter Physics. On the other hand, development of new techniques in the atomic manipulation allows the growth of atomic monolayers (ML's), therefore rising the interest to analyze low dimensional systems under different conditions. In particular, new \textit{ab initio} calculations performed for a lithium ML show that its electronic properties experience important modifications under pressure, which could lead to significant modifications in its dynamical response function. In this article we perform \textit{ab initio} calculations of the dynamical response function of a lithium ML analyzing its evolution with increasing applied pressure. We show that besides the well known intraband and interband plasmons, rising electronic density induces characteristic features of acoustic plasmons related to the presence of two types of carriers at the Fermi level.

cond-mat.mtrl-sci↗

arXiv2005

Induced Charge-Density Oscillations at Metal Surfaces

Induced charge-density (ICD) oscillations at the Cu(111) surface caused by an external impurity are studied within linear response theory. The calculation takes into account such properties of the Cu(111) surface electronic structure as an energy gap for three-dimensional (3D) bulk electrons and a $s-p_z$ surface state that forms two-dimensional (2D) electron system. It is demonstrated that the coexistence of these 2D and 3D electron systems has profound impact on the ICD in the surface region. In the case of a static impurity the characteristic ICD oscillations with the $1/ρ^2$ decay as a function of lateral distance, $ρ$, are established in both electron systems. For the impurity with a periodically time-varying potential, the novel dominant ICD oscillations which fall off like $\sim1/ρ$ are predicted.

cond-mat.soft↗

arXiv2005

Acoustic surface plasmons in the noble metals Cu, Ag, and Au

We have performed self-consistent calculations of the dynamical response of the (111) surface of the noble metals Cu, Ag, and Au. Our results indicate that the partially occupied surface-state band in these materials yields the existence of acoustic surface plasmons with linear dispersion at small wave vectors. Here we demonstrate that the sound velocity of these low-energy collective excitations, which had already been predicted to exist in the case of Be(0001), is dictated not only by the Fermi velocity of the two-dimensional surface-state band but also by the nature of the decay and penetration of the surface-state orbitals into the solid. Our linewidth calculations indicate that acoustic surface plasmons should be well defined in the energy range from zero to $\sim 400$ meV.

cond-mat.mtrl-sci↗

arXiv2005

Role of elastic scattering in electron dynamics at ordered alkali overlayers on Cu(111)

Scanning tunneling spectroscopy of p(2x2) Cs and Na ordered overlayers on Cu(111) reveals similar line widths of quasi two-dimensional quantum well states despite largely different binding energies. Detailed calculations show that 50% of the line widths are due to electron-phonon scattering while inelastic electron-electron scattering is negligible. A frequently ignored mechanism for ordered structures, i.e., enhanced elastic scattering due to Brillouin zone back folding, contributes the remaining width.

cond-mat.mtrl-sci↗

arXiv2004

Theory of acoustic surface plasmons

Recently, a novel low-energy collective excitation has been predicted to exist at metal surfaces where a quasi two-dimensional (2D) surface-state band coexists with the underlying three-dimensional (3D) continuum. Here we present a model in which the screening of a semiinfinite 3D metal is incorporated into the description of electronic excitations in a 2D electron gas through the introduction of an effective 2D dielectric function. Our self-consistent calculations of the dynamical response of the 3D substrate indicate that an acoustic surface plasmon exists for all possible locations of the 2D sheet relative to the metal surface. This low-energy excitation, which exhibits linear dispersion at low wave vectors, is dictated by the nonlocality of the 3D dynamical response providing incomplete screening of the 2D electron-density oscillations.

cond-mat.mtrl-sci↗

arXiv2004

Surface plasmons in metallic structures

Since the concept of a surface collective excitation was first introduced by Ritchie, surface plasmons have played a significant role in a variety of areas of fundamental and applied research, from surface dynamics to surface-plasmon microscopy, surface-plasmon resonance technology, and a wide range of photonic applications. Here we review the basic concepts underlying the existence of surface plasmons in metallic structures, and introduce a new low-energy surface collective excitation that has been recently predicted to exist.

cond-mat.mtrl-sci↗

arXiv2004

Novel low-energy collective excitation at metal surfaces

A novel collective excitation is predicted to exist at metal surfaces where a two-dimensional surface-state band coexists with the underlying three-dimensional continuum. This is a low-energy acoustic plasmon with linear dispersion at small wave vectors. Since new modern spectroscopies are especially sensitive to surface dynamics near the Fermi level, the existence of surface-state induced acoustic plasmons is expected to play a key role in a large variety of new phenomena and to create situations with potentially new physics.

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↗

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↗