Addition energies in semiconductor quantum dots: Role of electron-electron interaction

We show that the addition spectra of semiconductor quantum dots in the presence of magnetic field can be studied through a theoretical scheme that allows an accurate and practical treatment of the single particle states and electron-electron interaction up to large numbers of electrons. The calculated addition spectra exhibit the typical structures of Hund-like shell filling, and account for recent experimental findings. A full three dimensional description of Coulomb interaction is found to be essential for predicting the conductance characteristics of few-electron semiconductor structures.Comment: LaTeX 2.09, RevTeX, 3 pages, 3 Postscript figure

Quasiparticle band structure

Many body effects influence the energy-versus-momentum relation that is measured in angle resolved photoemission experiments and the quasiparticle band structure may be significantly different from what is deduced within the independent particle model. In the case of cobalt many body effects are even more drastic than an energy renormalization giving rise to a quenching of quasiparticle peaks. Augmenting ab-initio band structure with many-body e-e interactions we have obtained spin- and k-dependent self-energies, hole spectral functions and quasiparticle energies to be compared with photoemission spectra; our results show that e-e correlations are responsible for strong spin-dependent energy renormalizations

Reentrant metallicity in the Hubbard model: the case of honeycomb nanoribbons

Based on the cluster perturbation solution of the Hubbard Hamiltonian for a 2D honeycomb lattice, we present quasi-particle band structures of nanoribbons at half filling as a function of on-site electron-electron (e-e) repulsion. We show that, at moderate values of e-e interaction, ribbons with armchair-shaped edges exhibit an unexpected semimetallic behavior, recovering the original insulating character only at larger values of U

Graphene-mediated exchange coupling between a molecular spin and magnetic substrates

Using first-principles calculations we demonstrate sizable exchange coupling between a magnetic molecule and a magnetic substrate via a graphene layer. As a model system we consider cobaltocene (CoCp2) adsorbed on graphene deposited on Ni(111). We find that the magnetic coupling is antiferromagnetic and is influenced by the molecule structure, the adsorption geometry, and the stacking of graphene on the substrate. We show how the coupling can be tuned by the intercalation of a magnetic monolayer, such as Fe or Co, between graphene and Ni(111). We identify the leading mechanism responsible for the coupling to be the spatial and energy matching of the frontier orbitals of CoCp2 and graphene close to the Fermi level. Graphene plays the role of an electronic decoupling layer while allowing effective spin communication between molecule and substrate

Interfacial magnetic structure in Fe/NiO(001)

Using nuclear resonant scattering of synchrotron radiation and density functional theory calculations we haveresolved the magnetic properties of the different Fe phases present at the Fe/NiO(001) interface, an epitaxialferromagnetic/antiferromagnetic system. We have detected the presence of an interfacial antiferromagneticFeO-like phase with a significantly increased magnetic moment compared to the case of a sharp interface.Already a few atomic layers above the interface, the Fe atoms have a bulk-like metallic character and the reversalof their magnetization is strongly influenced by the antiferromagnetic layer

First-principle theory of correlated transport through nano-junctions

We report the inclusion of electron-electron correlation in the calculation of transport properties within an ab initio scheme. A key step is the reformulation of Landauer's approach in terms of an effective transmittance for the interacting electron system. We apply this framework to analyze the effect of shortrange interactions on Pt atomic wires and discuss the coherent and incoherent correction to the mean-field approach

First-principles calculation of x-ray dichroic spectra within the full-potential linearized augmented planewave method: An implementation into the Wien2k code

X-ray absorption and its dependence on the polarization of light is a powerful tool to investigate the orbital and spin moments of magnetic materials and their orientation relative to crystalline axes. Here, we present a program for the calculation of dichroic spectra from first principles. We have implemented the calculation of x-ray absorption spectra for left and right circularly polarized light into the Wien2k code. In this package, spin-density functional theory is applied in an all-electron scheme that allows to describe both core and valence electrons on the same footing. The matrix elements, which define the dependence of the photo absorption cross section on the polarization of light and on the sample magnetization, are computed within the dipole approximation. Results are presented for the L2,3 and M4,5 egdes of CeFe2 and compared to experiments