666 research outputs found

### Spin and density longitudinal response of quantum dots in time-dependent local-spin-density approximation

The longitudinal dipole response of a quantum dot has been calculated in the
far-infrared regime using local spin density functional theory. We have studied
the coupling between the collective spin and density modes as a function of the
magnetic field. We have found that the spin dipole mode and single particle
excitations have a sizeable overlap, and that the magnetoplasmon modes can be
excited by the dipole spin operator if the dot is spin polarized. The frequency
of the dipole spin edge mode presents an oscillation which is clearly filling
factor ($\nu$) related. We have found that the spin dipole mode is especially
soft for even $\nu$ values, becoming unstable for magnetic fields in the region
$1 < \nu \leq 2$. Results for selected number of electrons and confining
potentials are discussed. An analytical model which reproduces the main
features of the microscopic spectra has been developed.Comment: We have added some new references and minor changes on the mnuscript
have been mad

### The Fano-Rashba effect

We analyze the linear conductance of a semiconductor quantum wire containing
a region where a local Rashba spin-orbit interaction is present. We show that
Fano lineshapes appear in the conductance due to the formation of quasi bound
states which interfere with the direct transmission along the wire, a mechanism
that we term the Fano-Rashba effect. We obtain the numerical solution of the
full Schr\"odinger equation using the quantum-transmitting-boundary method. The
theoretical analysis is performed using the coupled-channel model, finding an
analytical solution by ansatz. The complete numerical solution of the
coupled-channel equations is also discussed, showing the validity of the ansatz
approach.Comment: 5 pages, proceedings of ICN+T 2006 (Basel, Switzerland, 30/7-4/9),
accepted, to appear in J. Phys.: Conf. Se

### Far-infrared edge modes in quantum dots

We have investigated edge modes of different multipolarity sustained by
quantum dots submitted to external magnetic fields. We present a microscopic
description based on a variational solution of the equation of motion for any
axially symmetric confining potential and multipole mode. Numerical results for
dots with different number of electrons whose ground-state is described within
a local Current Density Functional Theory are discussed. Two sum rules, which
are exact within this theory, are derived. In the limit of a large neutral dot
at B=0, we have shown that the classical hydrodynamic dispersion law for edge
waves \omega(q) \sim \sqrt{q \ln (q_0/q)} holds when quantum and finite size
effects are taken into account.Comment: We have changed some figures as well as a part of the tex

### Optical response of two-dimensional few-electron concentric double quantum rings: A local-spin-density-functional theory study

We have investigated the dipole charge- and spin-density response of
few-electron two-dimensional concentric nanorings as a function of the
intensity of a perpendicularly applied magnetic field. We show that the dipole
response displays signatures associated with the localization of electron
states in the inner and outer ring favored by the perpendicularly applied
magnetic field. Electron localization produces a more fragmented spectrum due
to the appearance of additional edge excitations in the inner and outer ring.Comment: To be published in Physical Review

### Far-infrared edge modes in quantum dots

We have investigated edge modes of different multipolarity sustained by
quantum dots submitted to external magnetic fields. We present a microscopic
description based on a variational solution of the equation of motion for any
axially symmetric confining potential and multipole mode. Numerical results for
dots with different number of electrons whose ground-state is described within
a local Current Density Functional Theory are discussed. Two sum rules, which
are exact within this theory, are derived. In the limit of a large neutral dot
at B=0, we have shown that the classical hydrodynamic dispersion law for edge
waves \omega(q) \sim \sqrt{q \ln (q_0/q)} holds when quantum and finite size
effects are taken into account.Comment: We have changed some figures as well as a part of the tex

### Structure and far-infrared edge modes of quantum antidots at zero magnetic field

We have investigated edge modes of different multipolarity sustained by
quantum antidots at zero magnetic field. The ground state of the antidot is
described within a local density functional formalism. Two sum rules, which are
exact within this formalism, have been derived and used to evaluate the energy
of edge collective modes as a function of the surface density and the size of
the antidot.Comment: Typeset using Revtex, 8 pages and 6 Postscript figure

### Brueckner-Hartree-Fock study of circular quantum dots

We calculate ground state energies in the Brueckner-Hartree-Fock theory for
$N$ electrons (with $N\le 20$) confined to a circular quantum dot and in
presence of a static magnetic field. Comparison with the predictions of
Hartree-Fock, local-spin-density and exact configuration-interaction theories
is made. We find that the correlations taken into account in
Brueckner-Hartree-Fock calculations give an important contribution to the
ground state energies, specially in strongly confined dots. In this
high-density range, corresponding in practice to self-assembled quantum dots,
the results of Brueckner-Hartree-Fock calculations are close to the exact
values and better than those obtained in the local-spin-density approximation.Comment: Regular articl

### Scissors modes in triaxial metal clusters

We study the scissors mode (orbital M1 excitations) in small Na clusters,
triaxial metal clusters ${\rm Na}_{12}$ and ${\rm Na}_{16}$ and the
close-to-spherical ${{\rm Na}_9}^+$, all described in DFT with detailed ionic
background. The scissors modes built on spin-saturated ground and
spin-polarized isomeric states are analyzed in virtue of both macroscopic
collective and microscopic shell-model treatments. It is shown that the mutual
destruction of Coulomb and the exchange-correlation parts of the residual
interaction makes the collective shift small and the net effect can depend on
details of the actual excited state. The crosstalk with dipole and spin-dipole
modes is studied in detail. In particular, a strong crosstalk with spin-dipole
negative-parity mode is found in the case of spin-polarized states. Triaxiality
and ionic structure considerably complicate the scissors response, mainly at
expense of stronger fragmentation of the strength. Nevertheless, even in these
complicated cases the scissors mode is mainly determined by the global
deformation. The detailed ionic structure destroys the spherical symmetry and
can cause finite M1 response (transverse optical mode) even in clusters with
zero global deformation. But its strength turns out to be much smaller than for
the genuine scissors modes in deformed systems.Comment: 17 pages, 5 figure

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