No abstract

Spin density functional theory is used to calculate the ground state electronic structures of circular parabolic quantum dots. We find that such dots either have a spin configuration determined by Hund's rule or make a spin-density-wave-like state with zero total spin. The dependence of the spin-density-wave amplitudes on the density of the two-dimensional electron gas is studied. [S0031-9007(97)03740-X]

Theoretical approaches to one-dimensional and quasi-one-dimensional quantum rings with a few electrons are reviewed. Discrete Hubbard-type models and continuum models are shown to give similar results governed by the special features of the one-dimensionality. The energy spectrum of the many-body states can be described by a rotation-vibration spectrum of a 'Wigner molecule' of 'localized' electrons, combined with the spin-state determined from an effective antiferromagnetic Heisenberg Hamiltonian. The persistent current as a function of the magnetic flux through the ring shows periodic oscillations arising from the 'rigid rotation' of the electron ring. For polarized electrons the periodicity of the oscillations is always the flux quantum Φ0. For nonpolarized electrons the periodicity depends on the strength of the effective Heisenberg coupling and changes from Φ0 first to Φ0/2 and eventually to Φ0/N when the ring gets narrower.

Photoelectron (PES) spectra from aluminum cluster anions, Al − n (12 ≤ n ≤ 15), at various temperature regimes, were studied using ab-initio molecular dynamics simulations and experimentally. The calculated PES spectra, obtained via shifting of the simulated electronic densities of states by the self-consistently determined values of the asymptotic exchange-correlation potential, agree well with the measured ones, allowing reliable structural assignments and theoretical estimation of the clusters' temperatures. PACS: 36.40.Cg, 36.40.Mr, 71.24.+q

We study atoms trapped with a harmonic confinement in an optical lattice characterized by a flat band and Dirac cones. We show that such an optical lattice can be constructed which can be accurately described with the tight binding or Hubbard models. In the case of fermions the release of the harmonic confinement removes fast atoms occupying the Dirac cones while those occupying the flat band remain immobile. Using exact diagonalization and dynamics we demonstrate that a similar strong occupation of the flat band does not happen in bosonic case and furthermore that the mean field model is not capable for describing the dynamics of the boson cloud.

It was recently argued that in small quantum dots the electrons could crystallize at much higher densities than in the infinite two-dimensional electron gas. We compare predictions that the onset of spin polarization and the formation of Wigner molecules occurs at a density parameter rs ≈ 4 a * B to the results of a straight-forward diagonalization of the Hamiltonian matrix. PACS 73.20.Dx, 71.45.Gm, 85.30.Vw

Addition energy spectra at 0 T of circular and ellipsoidally deformed few-electron vertical quantum dots are measured and compared to results of model calculations within spin-density functional theory. Because of the rotational symmetry of the lateral harmonic confining potential, circular dots show a pronounced shell structure. With the lifting of the single- particle level degeneracies, even a small deformation is found to radically alter the shell structure leading to significant modifications in the addition energy spectra. Breaking the circular symmetry with deformation also induces changes in the total spin. This "piezo-magnetic" behavior of quantum dots is discussed, and the addition energies for a set of realistic deformation parameters are provided. For the case of the four-electron ground state at 0 T, a spin-triplet to spin-singlet transition is predicted, i.e. Hund's first rule no longer applies. Application of a magnetic field parallel to the current confirms that this is the case, and also suggests that the anisotropy of an elliptical dot, in practice, may be higher than that suggested by the geometry of the device mesa in which the dot is located.Comment: 11 pages, 5 figures (original figures available on request

Energies of atoms, H through Ar, embedded in a homogeneous electron gas are calculated within the density-functional scheme as a function of the electron-gas density. The energy-versus-density curves and the induced densities of states are analyzed and discussed in terms of the interaction properties of an atom with its environment. The low-density limit of the immersion energy is related to the electron-atom scattering length. The results should prove useful in detailed investigations of the recently suggested "quasiatom" or "effective-medium" approaches to chemical binding. The lowest-order estimates of the binding energies of diatomic molecules and chemisorbed atoms are obtained.