48 research outputs found
Formalism for Multiphoton Plasmon Excitation in Jellium Clusters
We present a new formalism for the description of multiphoton plasmon
excitation processes in jellium clusters. By using our method, we demonstrate
that, in addition to dipole plasmon excitations, the multipole plasmons
(quadrupole, octupole, etc) can be excited in a cluster by multiphoton
absorption processes, which results in a significant difference between plasmon
resonance profiles in the cross sections for multiphoton as compared to
single-photon absorption. We calculate the cross sections for multiphoton
absorption and analyse the balance between the surface and volume plasmon
contributions to multipole plasmons.Comment: 29 pages, 1 figur
Structure and properties of small sodium clusters
We have investigated structure and properties of small metal clusters using
all-electron ab initio theoretical methods based on the Hartree-Fock
approximation and density functional theory, perturbation theory and compared
results of our calculations with the available experimental data and the
results of other theoretical works. We have systematically calculated the
optimized geometries of neutral and singly charged sodium clusters having up to
20 atoms, their multipole moments (dipole and quadrupole), static
polarizabilities, binding energies per atom, ionization potentials and
frequencies of normal vibration modes. Our calculations demonstrate the great
role of many-electron correlations in the formation of electronic and ionic
structure of small metal clusters and form a good basis for further detailed
study of their dynamic properties, as well as structure and properties of other
atomic cluster systems.Comment: 47 pages, 16 figure
Electron--phonon coupling and anharmonic effects in metal clusters
The periods of the harmonic oscillations of the ion core of charged sodium
clusters around the equilibrium shapes are considered. It is found that these
periods are of the order of magnitude of the experimentally measured relaxation
times of the plasmons, which suggests the importance of the electron-ion
coupling and stresses the role played by the electron-phonon interaction in the
dissipation of the plasmon energy. The relation of the process to fission is
briefly discussed.Comment: 6 pages, no figures, to appear in EPLetter
Electron attachment to SF6 and lifetimes of SF6- negative ions
We study the process of low-energy electron capture by the SF6 molecule. Our
approach is based on the model of Gauyacq and Herzenberg [J. Phys. B 17, 1155
(1984)] in which the electron motion is coupled to the fully symmetric
vibrational mode through a weakly bound or virtual s state. By tuning the two
free parameters of the model, we achieve an accurate description of the
measured electron attachment cross section and good agreement with vibrational
excitation cross sections of the fully symmetric mode. An extension of the
model provides a limit on the characteristic time of intramolecular vibrational
relaxation in highly-excited SF6-. By evaluating the total vibrational spectrum
density of SF6-, we estimate the widths of the vibrational Feshbach resonances
of the long-lived negative ion. We also analyse the possible distribution of
the widths and its effect on the lifetime measurements, and investigate
nonexponential decay features in metastable SF6-.Comment: 22 pages, 10 figures, submitted to Phys. Rev.
Spin-orbit interaction in three-dimensionally bounded semiconductor nanostructures
The structural inversion asymmetry-induced spin-orbit interaction of
conduction band electrons in zinc-blende and wurtzite semiconductor structures
is analysed allowing for a three-dimensional (3D) character of the external
electric field and variation of the chemical composition. The interaction,
taking into account all remote bands perturbatively, is presented with two
contributions: a heterointerface term and a term caused by the external
electric field. They have generally comparable strength and can be written in a
unified manner only for 2D systems, where they can partially cancel each other.
For quantum wires and dots composed of wurtzite semiconductors new terms
appear, absent in zinc-blende structures, which acquire the standard Rashba
form in 2D systems.Comment: 18 pages, 1 figur
Evolution of electronic and ionic structure of Mg-clusters with the growth cluster size
The optimized structure and electronic properties of neutral and singly
charged magnesium clusters have been investigated using ab initio theoretical
methods based on density-functional theory and systematic post-Hartree-Fock
many-body perturbation theory accounting for all electrons in the system. We
have systematically calculated the optimized geometries of neutral and singly
charged magnesium clusters consisting of up to 21 atoms, electronic shell
closures, binding energies per atom, ionization potentials and the gap between
the highest occupied and the lowest unoccupied molecular orbitals. We have
investigated the transition to the hcp structure and metallic evolution of the
magnesium clusters, as well as the stability of linear chains and rings of
magnesium atoms. The results obtained are compared with the available
experimental data and the results of other theoretical works.Comment: 30 pages, 10 figures, 3 table
Spin-orbit terms in multi-subband electron systems: A bridge between bulk and two-dimensional Hamiltonians
We analyze the spin-orbit terms in multi-subband quasi-two-dimensional
electron systems, and how they descend from the bulk Hamiltonian of the
conduction band. Measurements of spin-orbit terms in one subband alone are
shown to give incomplete information on the spin-orbit Hamiltonian of the
system. They should be complemented by measurements of inter-subband spin-orbit
matrix elements. Tuning electron energy levels with a quantizing magnetic field
is proposed as an experimental approach to this problem.Comment: Typos noticed in the published version have been corrected and
several references added. Published in the special issue of Semiconductors in
memory of V.I. Pere
Quadratic response theory for spin-orbit coupling in semiconductor heterostructures
This paper examines the properties of the self-energy operator in
lattice-matched semiconductor heterostructures, focusing on nonanalytic
behavior at small values of the crystal momentum, which gives rise to
long-range Coulomb potentials. A nonlinear response theory is developed for
nonlocal spin-dependent perturbing potentials. The ionic pseudopotential of the
heterostructure is treated as a perturbation of a bulk reference crystal, and
the self-energy is derived to second order in the perturbation. If spin-orbit
coupling is neglected outside the atomic cores, the problem can be analyzed as
if the perturbation were a local spin scalar, since the nonlocal spin-dependent
part of the pseudopotential merely renormalizes the results obtained from a
local perturbation. The spin-dependent terms in the self-energy therefore fall
into two classes: short-range potentials that are analytic in momentum space,
and long-range nonanalytic terms that arise from the screened Coulomb potential
multiplied by a spin-dependent vertex function. For an insulator at zero
temperature, it is shown that the electronic charge induced by a given
perturbation is exactly linearly proportional to the charge of the perturbing
potential. These results are used in a subsequent paper to develop a
first-principles effective-mass theory with generalized Rashba spin-orbit
coupling.Comment: 20 pages, no figures, RevTeX4; v2: final published versio
Tunnelling Studies of Two-Dimensional States in Semiconductors with Inverted Band Structure: Spin-orbit Splitting, Resonant Broadening
The results of tunnelling studies of the energy spectrum of two-dimensional
(2D) states in a surface quantum well in a semiconductor with inverted band
structure are presented. The energy dependence of quasimomentum of the 2D
states over a wide energy range is obtained from the analysis of tunnelling
conductivity oscillations in a quantizing magnetic field. The spin-orbit
splitting of the energy spectrum of 2D states, due to inversion asymmetry of
the surface quantum well, and the broadening of 2D states at the energies, when
they are in resonance with the heavy hole valence band, are investigated in
structures with different strength of the surface quantum well. A quantitative
analysis is carried out within the framework of the Kane model of the energy
spectrum. The theoretical results are in good agreement with the tunnelling
spectroscopy data.Comment: 29 pages, RevTeX, submitted in Phys.Rev.B. Figures available on
request from [email protected]