Magnetic phases of one-dimensional lattices with 2 to 4 fermions per site

We study the spectral and magnetic properties of one-dimensional lattices filled with 2 to 4 fermions (with spin 1/2) per lattice site. We use a generalized Hubbard model that takes account all interactions on a lattice site, and solve the many-particle problem by exact diagonalization. We find an intriguing magnetic phase diagram which includes ferromagnetism, spin-one Heisenberg antiferromagnetism, and orbital antiferromagnetism.Comment: 8 pages, 6 figure

Density Functional Theory of Multicomponent Quantum Dots

Quantum dots with conduction electrons or holes originating from several bands are considered. We assume the particles are confined in a harmonic potential and assume the electrons (or holes) belonging to different bands to be different types of fermions with isotropic effective masses. The density functional method with the local density approximation is used. The increased number of internal (Kohn-Sham) states leads to a generalisation of Hund's first rule at high densities. At low densitites the formation of Wigner molecules is favored by the increased internal freedom.Comment: 11 pages, 5 figure

Magnetism in one-dimensional quantum dot arrays

We employ the density functional Kohn-Sham method in the local spin-density approximation to study the electronic structure and magnetism of quasi one-dimensional periodic arrays of few-electron quantum dots. At small values of the lattice constant, the single dots overlap, forming a non-magnetic quantum wire with nearly homogenous density. As the confinement perpendicular to the wire is increased, i.e. as the wire is squeezed to become more one-dimensional, it undergoes a spin-Peierls transition. Magnetism sets in as the quantum dots are placed further apart. It is determined by the electronic shell filling of the individual quantum dots. At larger values of the lattice constant, the band structure for odd numbers of electrons per dot indicates that the array could support spin-polarized transport and therefore act as a spin filter.Comment: 11 pages, 6 figure

Order-disorder transition in nanoscopic semiconductor quantum rings

Using the path integral Monte Carlo technique we show that semiconductor quantum rings with up to six electrons exhibit a temperature, ring diameter, and particle number dependent transition between spin ordered and disordered Wigner crystals. Due to the small number of particles the transition extends over a broad temperature range and is clearly identifiable from the electron pair correlation functions.Comment: 4 pages, 5 figures, For recent information on physics of small systems see http://www.smallsystems.d

Predictors of employment in young adults with psychiatric work disability

AIM: Mental disorders are the leading cause of work disability among young adults in the industrialized world. Factors predicting employment after long-term psychiatric work disability are largely unknown. METHODS: We linked personal and clinical information from the benefit applications and medical certificates of 1163 young adults (18-34 years) with a new-onset fixed-term psychiatric disability pension in 2008 with employment records between 2005 and 2013. The outcomes were starting employment during and being employed at the end of follow-up. RESULTS: Of the participants, 48% had been employed during and 22% were employed at the end of follow-up. Sustained employment history, university education (master's degree) and no recorded psychological symptoms in childhood were associated with both subsequent employment outcomes. Women and participants under 25 years were more likely to start employment. Depression and other mental disorders (vs psychotic diagnose) and having no comorbid mental disorders or substance abuse were associated with employment at the end of follow-up. CONCLUSIONS: Sustained employment history, university education and no recorded psychological symptoms during childhood predict a return to employment among young adults after a fixed-term psychiatric work disability pension. Pro-active interventions in psychological problems during childhood could enhance employment after a period of work disability

Hartree-Fock dynamics in highly excited quantum dots

Time-dependent Hartree-Fock theory is used to describe density oscillations of symmetry-unrestricted two-dimensional nanostructures. In the small amplitude limit the results reproduce those obtained within a perturbative approach such as the linearized time-dependent Hartree-Fock one. The nonlinear regime is explored by studying large amplitude oscillations in a non-parabolic potential, which are shown to introduce a strong coupling with internal degrees of freedom. This excitation of internal modes, mainly of monopole and quadrupole character, results in sizeable modifications of the dipole absorption.Comment: 4 pages, 4 embedded figure

Persistent Currents in Small, Imperfect Hubbard Rings

We have done a study with small, imperfect Hubbard rings with exact diagonalization. The results for few-electron rings show, that the imperfection, whether localized or not, nearly always decrease, but can also \emph{increase} the persistent current, depending on the character of the imperfection and the on-site interaction. The calculations are generally in agreement with more specialized studies. In most cases the electron spin plays an important role.Comment: 6 pages, 4 figure

Spectral properties of rotating electrons in quantum dots and their relation to quantum Hall liquids

The exact diagonalization technique is used to study many-particle properties of interacting electrons with spin, confined in a two-dimensional harmonic potential. The single-particle basis is limited to the lowest Landau level. The results are analyzed as a function of the total angular momentum of the system. Only at angular momenta corresponding to the filling factors 1, 1/3, 1/5 etc. the system is fully polarized. The lowest energy states exhibit spin-waves, domains, and localization, depending on the angular momentum. Vortices exist only at excited polarized states. The high angular momentum limit shows localization of electrons and separation of the charge and spin excitations.Comment: 14 pages 18 figure