Ll. Serra

Longitudinal modes of quantum dots in magnetic fields

Abstract.The far infrared longitudinal spin and density responses of two-dimensional quantum dots are discussed within local spin-density functional theory. The influence of a partial spin polarization, induced by a perpendicular static magnetic field, is taken into account in the coupling of spin and density channels. As an illustrative application, the case of a dot made of 5 electrons in parabolic confinement is discussed.We show that in the presence of massive particles such as nucleons, the standard low energy expansion in powers of meson momenta and light quark masses in general only converges in part of the low energy region. The expansion of the scalar form factor

Density functional calculations for4He droplets

\sigma(t)

Density-functional calculations of magnetoplasmons in quantum rings

, for instance, breaks down in the vicinity of

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

t=4M_\pi^2

Dipole excitation of Na clusters with a non-local energy density functional

. In the language of heavy baryon chiral perturbation theory, the proper behaviour in the threshold region only results if the multiple internal line insertions generated by relativistic kinematics are summed up to all orders. We propose a method that yields a coherent representation throughout the low energy region while keeping Lorentz and chiral invariance explicit at all stages. The method is illustrated with a calculation of the nucleon mass and of the scalar form factor to order

A density functional for liquid3He

p^4

FAR-INFRARED EDGE MODES IN QUANTUM DOTS

.

Pairing effects in metal clusters

A novel density functional, which accounts correctly for the equation of state, the static response function and the phonon-roton dispersion in bulk liquid helium, is used to predict static and dynamic properties of helium droplets. The static density profile is found to exhibit significant oscillations, which are accompanied by deviations of the evaporation energy from a liquid drop behaviour in the case of small droplets. The connection between such oscillations and the structure of the static response function in the liquid is explicitly discussed. The energy and the wave function of excited states are then calculated in the framework of time dependent density functional theory. The new functional, which contains backflow-like effects, is expected to yield quantitatively correct predictions for the excitation spectrum also in the roton wave-length range.

Transverse dipole spin modes in quantum dots

Departament de Fi´sica, Facultat de Cie`ncies, Universitat de les Illes Balears, E-07071 Palma de Mallorca, Spain~Received 2 December 1998!We have studied the structure and dipole charge-density response of nanorings as a function of the magneticfield using local-spin-density-functional theory. Two small rings consisting of 12 and 22 electrons confined bya positively charged background are used to represent the cases of narrow and wide rings. The results arequalitatively compared with experimental data existing on microrings and on antidots. A smaller ring contain-ing five electrons is also analyzed to allow for a closer comparison with a recent experiment on a two-electronquantum ring. @S0163-1829~99!02723-X#I. INTRODUCTION

Collective excitations of3He clusters

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 sizable 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 (n) related. We have found that the spin dipole mode is especially soft for even-n values. Results for selected numbers of electrons and confining potentials are discussed. @S0163-1829~99!02223-7#