301 research outputs found
Spin-orbit excitations of quantum wells
Confinement asymmetry effects on the photoabsorption of a quantum well are
discussed by means of a sum-rules approach using a Hamiltonian including a
Rashba spin-orbt coupling. We show that while the strength of the excitation is
zero when the spin-orbit coupling is neglected, the inclusion of the spin-orbit
interaction gives rise to a non zero strength and mean excitation energy in the
far-infrared region. A simple expression for these quantities up to the second
order in the Rashba parameter was derived. The effect of two-body Coulomb
interaction is then studied by means of a Quantum Monte Carlo calculation,
showing that electron-electron correlations induce only a small deviation from
the independent particle model result
Orbital current mode in elliptical quantum dots
An orbital current mode peculiar to deformed quantum dots is theoretically
investigated; first by using a simple model that allows to interpret
analytically its main characteristics, and second, by numerically solving the
microscopic equations of time evolution after an initial perturbation within
the time-dependent local-spin-density approximation. Results for different
deformations and sizes are shown.Comment: 4 REVTEX pages, 4 PDF figures, accepted in PRB:R
Quantum Monte Carlo study of circular quantum dots in presence of Rashba interaction
We present the numerical Quantum Monte Carlo results for the ground state
energy of circular quantum dots in which Rashba spin-orbit iteraction is
present. Diffusion Monte Carlo with spin propagation is applied in order to
treat the spin-orbit interaction correctly, following previous work done in the
fieldof the two-dimensional electron gas. Together with ground state energies,
also numerical results for density and spin-density profiles are given
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-orbit effects in GaAs quantum wells: Interplay between Rashba, Dresselhaus, and Zeeman interactions
The interplay between Rashba, Dresselhaus and Zeeman interactions in a
quantum well submitted to an external magnetic field is studied by means of an
accurate analytical solution of the Hamiltonian, including electron-electron
interactions in a sum rule approach. This solution allows to discuss the
influence of the spin-orbit coupling on some relevant quantities that have been
measured in inelastic light scattering and electron-spin resonance experiments
on quantum wells. In particular, we have evaluated the spin-orbit contribution
to the spin splitting of the Landau levels and to the splitting of charge- and
spin-density excitations. We also discuss how the spin-orbit effects change if
the applied magnetic field is tilted with respect to the direction
perpendicular to the quantum well.Comment: 26 pages (with 3 figures included
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
Effective Field Theory for the Quantum Electrodynamics of a Graphene Wire
We study the low-energy quantum electrodynamics of electrons and holes, in a
thin graphene wire. We develop an effective field theory (EFT) based on an
expansion in p/p_T, where p_T is the typical momentum of electrons and holes in
the transverse direction, while p are the momenta in the longitudinal
direction. We show that, to the lowest-order in (p/p_T), our EFT theory is
formally equivalent to the exactly solvable Schwinger model. By exploiting such
an analogy, we find that the ground state of the quantum wire contains a
condensate of electron-hole pairs. The excitation spectrum is saturated by
electron-hole collective bound-states, and we calculate the dispersion law of
such modes. We also compute the DC conductivity per unit length at zero
chemical potential and find g_s =e^2/h, where g_s=4 is the degeneracy factor.Comment: 7 pages, 2 figures. Definitive version, accepted for publication on
Phys. Rev.
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
- …