78 research outputs found
Interplay of the volume and surface plasmons in the electron energy loss spectra of C
The results of a joint experimental and theoretical investigation of the C60
collective excitations in the process of inelastic scattering of electrons are
presented. The shape of the electron energy loss spectrum is observed to vary
when the scattering angle increases. This variation arising due to the electron
diffraction of the fullerene shell is described by a new theoretical model
which treats the fullerene as a spherical shell of a finite width and accounts
for the two modes of the surface plasmon and for the volume plasmon as well. It
is shown that at small angles, the inelastic scattering cross section is
determined mostly by the symmetric mode of the surface plasmon, while at larger
angles, the contributions of the antisymmetric surface plasmon and the volume
plasmon become prominent.Comment: 11 pages, 3 figure
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
Oscillation of spin polarization in a two-dimensional hole gas under a perpendicular magnetic field
Spin-charge coupling is studied for a strongly confined two-dimensional hole
gas subject to a perpendicular magnetic field. The study is based on
spin-charge coupled drift-diffusion equations derived from quantum-kinetic
equations in an exact manner. The spin-orbit interaction induces an extra
out-of-plane spin polarization. This contribution exhibits a persistent
oscillatory pattern in the strong-coupling regime.Comment: 11 pages and 1 figur
Theoretical study of interacting hole gas in p-doped bulk III-V semiconductors
We study the homogeneous interacting hole gas in -doped bulk III-V
semiconductors. The structure of the valence band is modelled by Luttinger's
Hamiltonian in the spherical approximation, giving rise to heavy and light hole
dispersion branches, and the Coulomb repulsion is taken into account via a
self-consistent Hartree-Fock treatment. As a nontrivial feature of the model,
the self-consistent solutions of the Hartree-Fock equations can be found in an
almost purely analytical fashion, which is not the case for other types of
effective spin-orbit coupling terms. In particular, the Coulomb interaction
renormalizes the Fermi wave numbers for heavy and light holes. As a
consequence, the ground state energy found in the self-consistent Hartree-Fock
approach and the result from lowest-order perturbation theory do not agree. We
discuss the consequences of our observations for ferromagnetic semiconductors,
and for the possible observation of the spin-Hall effect in bulk -doped
semiconductors. Finally, we also investigate elementary properties of the
dielectric function in such systems.Comment: 9 pages, 5 figures, title slightly changed in the course of editorial
process, a few references added, version to appear in Phys. Rev.
Optical Spin Orientation in Strained Superlattices
Optical orientation in the strained semiconductor superlattices is
investigated theoretically. The dependence of the features in spin-polarization
spectra on the structure parameters is clarified. The value of polarization in
the first polarization maximum in the SL structures is shown to grow with the
splitting between the hh- and lh- states of the valence band, the joint strain
and confinement effects on the hh1- lh1 splitting being strongly influenced by
the tunneling in the barriers. In strained structures with high barriers for
the holes initial polarization can exceed 95 %. Calculated polarization spectra
are close to the experimental spectra of polarized electron emission.Comment: 20 pages, 8 figure
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.
Theory of spin-Hall transport of heavy holes in semiconductor quantum wells
Based on a proper definition of the spin current, we investigate the
spin-Hall effect of heavy holes in narrow quantum wells in the presence of
Rashba spin-orbit coupling by using a spin-density matrix approach. In contrast
to previous results obtained on the basis of the conventional definition of the
spin current, we arrive at the conclusion that an electric-field-induced
steady-state spin-Hall current does not exist in both, pure and disordered
infinite samples. Only an ac field can induce a spin-Hall effect in such
systems.Comment: 6 pages, submitted to J. Phys.: Condens. Matte
Strain-Compensated AlInGaAs-GaAsP Superlattices for Highly-Polarized Electron Emission
Spin-polarized electron emission from the first superlattice photocathodes
developed with strain compensation is investigated. An opposite strain in the
quantum well and barrier layers is complished using an InAlGaAs/GaAsP
superlattice structure. The measured values of maximum polarization and quantum
yield for the structure with a 0.18 um-thick working layer are close to the
best results reported for any strained superlattice photocathode structure,
demonstrating the high potential of strain compensation for future photocathode
applications. An analysis of the photoemission spectra is used to estimate the
parameters responsible for the polarization losses.Comment: 10 pages, 2 figure
Spin-Hall transport of heavy holes in III-V semiconductor quantum wells
We investigate spin transport of heavy holes in III-V semiconductor quantum
wells in the presence of spin-orbit coupling of the Rashba type due to
structure-inversion asymmetry. Similarly to the case of electrons, the
longitudinal spin conductivity vanishes, whereas the off-diagonal elements of
the spin-conductivity tensor are finite giving rise to an intrinsic spin-Hall
effect. For a clean system we find a closed expression for the spin-Hall
conductivity depending on the length scale of the Rashba coupling and the hole
density. In this limit the spin-Hall conductivity is enhanced compared to its
value for electron systems, and it vanishes with increasing strength of the
impurity scattering. As an aside, we also derive explicit expressions for the
Fermi momenta and the densities of holes in the different dispersion branches
as a function of the spin-orbit coupling parameter and the total hole density.
These results are of relevance for the interpretation of possible Shubnikov-de
Haas measurements detecting the Rashba spin splitting.Comment: 6 pages, 2 figures included, some prefactor corrected, version to be
published in Phys. Rev.
Non-exponential spin relaxation in magnetic field in quantum wells with random spin-orbit coupling
We investigate the spin dynamics of electrons in quantum wells where the
Rashba type of spin-orbit coupling is present in the form of random nanosize
domains. We study the effect of magnetic field on the spin relaxation in these
systems and show that the spatial randomness of spin-orbit coupling limits the
minimum relaxation rate and leads to a Gaussian time-decay of spin polarization
due to memory effects. In this case the relaxation becomes faster with increase
of the magnetic field in contrast to the well known magnetic field suppression
of spin relaxation.Comment: published version, minor change
- …