arXiv subjects

J. M. Pitarke

Publications and source records attributed to J. M. Pitarke.

At least 55 records · Page 3Linked to original sources

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

Plasmon bands in metallic nanostructures

The photonic band structure of a three-dimensional lattice of metal spheres is calculated using an embedding technique, in the frequency range of the Mie plasmons. For a small filling factor of the spheres, Maxwell-Garnett theory gives an almost exact description of the dipole modes, and the multipole modes are fairly dispersionless. For a larger filling factor, crystal field effects modify the multipole frequencies, which show dispersion. These multipole bands are enclosed between the dipole modes. For touching spheres, there is a wide continuum of plasmon modes between zero frequency and the bulk metal plasmon frequency, which yield strong absorption of incident light. These plasmon modes are responsible for the blackness of colloidal silver.

cond-mat.mtrl-sci↗

arXiv2004

Exchange and correlation effects in the relaxation of hot electrons in noble metals

We report extensive first-principles calculations of the inelastic lifetime of low-energy electrons in the noble metals Cu, Ag, and Au. The quasiparticle self-energy is computed with full inclusion of exchange and correlation (xc) effects, in the framework of the GWΓapproximation of many-body theory. Although exchange and correlation may considerably reduce both the screening and the bare interaction of hot electrons with the Fermi gas, these corrections have opposite signs. Our results indicate that the overall effect of short-range xc is small and GWΓlinewidths are close to their xc-free G^0W^0 counterparts, as occurs in the case of a free-electron gas.

cond-mat.mtrl-sci↗

arXiv2004

Comment on "Diffusion Monte Carlo study of jellium surfaces: Electronic densities and pair correlation functions"

In a fixed-node diffusion Monte Carlo calculation of the total energy of jellium slabs, Acioli and Ceperley [Phys. Rev. B {\bf 54}, 17199 (1996)] reported jellium surface energies that at low electron densities were significantly higher than those predicted in the local-density approximation (LDA) of density-functional theory. Assuming that the fixed-node error in the slab and the bulk calculations cancel out, we show that their data yield surface energies that are considerably closer to the LDA and in reasonable agreement with those obtained in the random-phase approximation.

cond-mat.mtrl-sci↗

arXiv2004

Ultrafast electron dynamics in metals

During the last decade, significant progress has been achieved in the rapidly growing field of the dynamics of {\it hot} carriers in metals. Here we present an overview of the recent achievements in the theoretical understanding of electron dynamics in metals, and focus on the theoretical description of the inelastic lifetime of excited hot electrons. We outline theoretical formulations of the hot-electron lifetime that is originated in the inelastic scattering of the excited {\it quasiparticle} with occupied states below the Fermi level of the solid. {\it First-principles} many-body calculations are reviewed. Related work and future directions are also addressed.

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↗

arXiv2004

Nonlinear, band-structure, and surface effects in the interaction of charged particles with solids

A survey is presented of various aspects of the interaction of charged particles with solids. In the framework of many-body perturbation theory, we study the nonlinear interaction of charged particles with a free gas of interacting electrons; in particular, nonlinear corrections to the stopping power are analyzed, and special emphasis is made on the separate contributions that are originated in the excitation of either electron-hole pairs, single plasmons, or double plasmons. Ab initio calculations of the electronic energy loss of ions moving in real solids are also presented, and the energy loss of charged particles interacting with simple metal surfaces is addressed.

cond-mat.mtrl-sci↗

arXiv2003

Effects of the crystal structure in the dynamical electron density-response of hcp transition metals

We present an all-electron study of the dynamical density-response function of hexagonal close-packed transition metals Sc and Ti. We elucidate various aspects of the interplay between the crystal structure and the electron dynamics by investigating the loss function, and the associated dielectric function, for wave-vector transfers perpendicular and parallel to the hexagonal plane. As expected, but contrary to recent work, we find that the free-electron-like aspects of the dynamical response are rather isotropic for small wave vectors. The crystal local-field effects are found to have an impact on the plasmon energy for small wave vectors, which gives rise to an interplay with the exchange-correlation effects built into the many-body kernel. The loss function lineshape shows a significant dependence on propagation direction; in particular, for propagation on the hexagonal plane the plasmon hybridizes substantially with fine structure due to d-electron transitions, and its dispersion curve becomes difficult to establish, beyond the small wave vector limit. The response is calculated in the framework of time-dependent density functional theory (TDDFT), based on a full-potential linearized augmented-plane-wave (LAPW) ground-state, in which the exchange-correlation effects are treated in the local-density approximation.

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

Surface effects on the electronic energy loss of charged particles entering a metal surface

Surface effects on the electronic energy loss of charged particles entering a metal surface are investigated within linear-response theory, in the framework of time-dependent density functional theory. Interesting phenomena occur in the loss spectra originated by the boundary (bregenzung) effect, which is as a consequence of the orthogonality of surface and bulk excitation modes. Our calculations indicate that the presence of a non-abrupt electron-density profile at the surface severely affects the nature of surface excitations, as deduced from comparison with simplified models.

cond-mat.mtrl-sci↗

arXiv2002

Metal Surface Energy: Persistent Cancellation of Short-Range Correlation Effects beyond the Random-Phase Approximation

The role that non-local short-range correlation plays at metal surfaces is investigated by analyzing the correlation surface energy into contributions from dynamical density fluctuations of various two-dimensional wave vectors. Although short-range correlation is known to yield considerable correction to the ground-state energy of both uniform and non-uniform systems, short-range correlation effects on intermediate and short-wavelength contributions to the surface formation energy are found to compensate one another. As a result, our calculated surface energies, which are based on a non-local exchange-correlation kernel that provides accurate total energies of a uniform electron gas, are found to be very close to those obtained in the random-phase approximation and support the conclusion that the error introduced by the local-density approximation is small.

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

Many-body approach to the nonlinear interaction of charged particles with an interacting free electron gas

We report various many-body theoretical approaches to the nonlinear decay rate and energy loss of charged particles moving in an interacting free electron gas. These include perturbative formulations of the scattering matrix, the self-energy, and the induced electron density. Explicit expressions for these quantities are obtained, with inclusion of exchange and correlation effects.

cond-mat.mtrl-sci↗

arXiv2001

Lifetime of d-holes at Cu surfaces: Theory and experiment

We have investigated the hole dynamics at copper surfaces by high-resolution angle-resolved photoemission experiments and many-body quasiparticle GW calculations. Large deviations from a free-electron-like picture are observed both in the magnitude and the energy dependence of the lifetimes, with a clear indication that holes exhibit longer lifetimes than electrons with the same excitation energy. Our calculations show that the small overlap of d- and sp-states below the Fermi level is responsible for the observed enhancement. Although there is qualitative good agreement of our theoretical predictions and the measured lifetimes, there still exist some discrepancies pointing to the need of a better description of the actual band structure of the solid.

cond-mat.str-el↗

arXiv2001

Optical absorption and energy-loss spectra of aligned carbon nanotubes

Optical-absorption cross-sections and energy-loss spectra of aligned multishell carbon nanotubes are investigated, on the basis of photonic band-structure calculations. A local graphite-like dielectric tensor is assigned to every point of the tubules, and the effective transverse dielectric function of the composite is computed by solving Maxwell's equations in media with tensor-like dielectric functions. A Maxwell-Garnett-like approach appropriate to the case of infinitely long anisotropic tubules is also developed. Our full calculations indicate that the experimentally measured macroscopic dielectric function of carbon nanotube materials is the result of a strong electromagnetic coupling between the tubes. An analysis of the electric-field pattern associated with this coupling is presented, showing that in the close-packed regime the incident radiation excites a very localized tangential surface plasmon.

cond-mat.mtrl-sci↗

arXiv2001

Energy loss of charged particles interacting with simple metal surfaces

Self-consistent calculations of the energy-loss spectra of charged particles moving near a plane-bounded free electron gas are reported. Energy-loss probabilities are obtained, within linear-response theory, from the knowledge of the density-response function of the inhomogeneous electron system. Self-consistent single-particle wave functions and energies are obtained by solving the Kohn-Sham equation of density-functional theory, and the electronic response is then computed either in the random-phase approximation or with the use of an adiabatic local-density approximation. Special emphasis is placed on the various contributions from collective and electron-hole excitations to the energy loss of charged particles moving parallel with the surface. The effect of the electronic selvage at a metal surface on the energy-loss spectra is also discussed, by comparing our full self-consistent calculations with those obtained for electron densities that drop abruptly to zero at the surface.

cond-mat.mtrl-sci↗