9,739 research outputs found
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
Spin-orbit effects on the Larmor dispersion relation in GaAs quantum wells
We have studied the relevance of spin-orbit coupling to the dispersion 00009
relation of the Larmor resonance observed in inelastic light scattering and
electron-spin resonance experiments on GaAs quantum wells. We show that the
spin-orbit interaction, here described by a sum of Dresselhaus and
Bychkov-Rashba terms, couples Zeeman and spin-density excitations. We have
evaluated its contribution to the spin splitting as a function of the magnetic
field , and have found that in the small limit, the spin-orbit
interaction does not contribute to the spin splitting, whereas at high magnetic
fields it yields a independent contribution to the spin splitting given by
, with being the intensity of the
Bychkov-Rashba and Dresselhaus spin-orbit terms.Comment: To be published in Physical Review
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 () related. We have found that the spin dipole mode is especially
soft for even values, becoming unstable for magnetic fields in the region
. 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
Quasi-ordinary power series and their zeta functions
The main objective of this paper is to prove the monodromy conjecture for the
local Igusa zeta function of a quasi-ordinary polynomial of arbitrary dimension
defined over a number field. In order to do it, we compute the local
Denef-Loeser motivic zeta function of a quasi-ordinary
power series of arbitrary dimension over an algebraically closed field of
characteristic zero from its characteristic exponents without using embedded
resolution of singularities. This allows us to effectively represent
such that almost all the candidate poles given
by are poles. Anyway, these candidate poles give eigenvalues of the
monodromy action of the complex of nearby cycles on In particular
we prove in this case the monodromy conjecture made by Denef-Loeser for the
local motivic zeta function and the local topological zeta function. As a
consequence, if is a quasi-ordinary polynomial defined over a number field
we prove the Igusa monodromy conjecture for its local Igusa zeta function.Comment: 74 page
Quasi-ordinary singularities and Newton trees
In this paper we study some properties of the class of nu-quasi-ordinary
hypersurface singularities. They are defined by a very mild condition on its
(projected) Newton polygon. We associate with them a Newton tree and
characterize quasi-ordinary hypersurface singularities among nu-quasi-ordinary
hypersurface singularities in terms of their Newton tree. A formula to compute
the discriminant of a quasi-ordinary Weierstrass polynomial in terms of the
decorations of its Newton tree is given. This allows to compute the
discriminant avoiding the use of determinants and even for non Weierstrass
prepared polynomials. This is important for applications like algorithmic
resolutions. We compare the Newton tree of a quasi-ordinary singularity and
those of its curve transversal sections. We show that the Newton trees of the
transversal sections do not give the tree of the quasi-ordinary singularity in
general. It does if we know that the Newton tree of the quasi-ordinary
singularity has only one arrow.Comment: 32 page
Finite size effects in adsorption of helium mixtures by alkali substrates
We investigate the behavior of mixed 3He-4He droplets on alkali surfaces at
zero temperature, within the frame of Finite Range Density Functional theory.
The properties of one single 3He atom on 4He_N4 droplets on different alkali
surfaces are addressed, and the energetics and structure of 4He_N4+3He_N3
systems on Cs surfaces, for nanoscopic 4He drops, are analyzed through the
solutions of the mean field equations for varying number N3 of 3He atoms. We
discuss the size effects on the single particle spectrum of 3He atoms and on
the shapes of both helium distributions.Comment: 12 pages, and 12 figures (PNG format
Vertically coupled double quantum rings at zero magnetic field
Within local-spin-density functional theory, we have investigated the
`dissociation' of few-electron circular vertical semiconductor double quantum
ring artificial molecules at zero magnetic field as a function of inter-ring
distance. In a first step, the molecules are constituted by two identical
quantum rings. When the rings are quantum mechanically strongly coupled, the
electronic states are substantially delocalized, and the addition energy
spectra of the artificial molecule resemble those of a single quantum ring in
the few-electron limit. When the rings are quantum mechanically weakly coupled,
the electronic states in the molecule are substantially localized in one ring
or the other, although the rings can be electrostatically coupled. The effect
of a slight mismatch introduced in the molecules from nominally identical
quantum wells, or from changes in the inner radius of the constituent rings,
induces localization by offsetting the energy levels in the quantum rings. This
plays a crucial role in the appearance of the addition spectra as a function of
coupling strength particularly in the weak coupling limit.Comment: 18 pages, 8 figures, submitted to Physical Review
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