Electron energy-loss and X-ray absorption spectroscopy of cuprate superconductors and related compounds

We investigate the adsorption of Cs on the As-rich $c(2\ifmmode\times\else\texttimes\fi{}8)/(2\ifmmode\times\else\texttimes\fi{}4)$ reconstruction of GaAs(001) at low coverages using a combination of theoretical and experimental techniques. Density-functional-theory local-density-approximation total-energy calculations and x-ray diffraction experiments find only minimal Cs-induced surface relaxation and identify three preferential adsorption sites within the partially disordered overlayer. These sites are, in order of decreasing occupation probability, the arsenic dimer bridge D site, the gallium dangling bond ${T}_{2}^{\ensuremath{'}}$ site, and the arsenic ${T}_{3}$ trench site. Detailed analysis of the wave functions and electronic charge densities allows us to clarify the bonding mechanisms at the three sites. At the gallium site, the bonding is strongly ionic and involves significant charge transfer to a new Cs-induced state reminiscent of the ${p}_{z}$ orbital of the gallium atom in the ${\mathrm{sp}}^{{}_{2}}$ configuration. In sharp contrast, at the arsenic sites, the charge transfer is minimal and the bonding rather occurs through mixing with a relatively delocalized state of the clean surface. The ionization energy decreases are estimated and compared for the three sites.

Early stages of cesium adsorption on the As-rich c(2×8) reconstruction of GaAs(001): Adsorption sites and Cs-induced chemical bonds

http://dipc.ehu.es/etxenike/admin/documentos/archivos/publicaciones/419SSR2013.pdf

Vibrational spectroscopy and theory of alkali metal adsorption and co-adsorption on single-crystal surfaces

We employ dynamical mean-field theory (DMFT) with a quantum Monte Carlo atomic solver to investigate the finite-temperature Mott transition in the Hubbard model with nearest-neighbor hopping on a triangular lattice at half-filling. We estimate the value of the critical interaction to be ${U}_{c}=12.0\ifmmode\pm\else\textpm\fi{}0.5$ in units of the hopping amplitude $t$ through the evolution of the magnetic moment, spectral function, internal energy, and specific heat as the interaction $U$ and temperature $T$ are varied. This work also presents a comparison between DMFT and finite-size determinant quantum Monte Carlo calculations and a discussion of the advantages and limitations of both methods.

/pdf/dynamical-mean-field-study-of-the-mott-transition-in-the-4wefvzdhav.pdf

Dynamical mean-field study of the Mott transition in the half-filled Hubbard model on a triangular lattice

Coulomb interactions in carbon nanotubes

Correlation effects in photoemission from adsorbates: Hydrogen on narrow-band metals.

Study of the electronic bonding of Cl Si(100) by synchrotron radiation photoemission spectroscopy and many-body calculations

One-particle densities of states for finite square clusters are calculated with the one- and three-band Hubbard model, within the generalized unrestricted Hartree-Fock approximation. Cluster-size and free-or periodic-boundary-conditions effects are studied. Changes induced by doping in both the density of states and the chemical potential position are presented. From the general accordance with experimental data and other theoretical results, we conclude that the unrestricted Hartree-Fock approach is valid. The prediction of the Hubbard model on the chemical potential behavior upon doping is discussed on the light of experimental findings

Doping dependence of the density of states for CuO2 clusters in the Hubbard model.

The single-particle spectral-weight function of the ionic Hubbard model (IHM) at half-filling shows an abrupt change of regime at a critical value of the coupling constant (Hubbard U). Specifically, this function jumps at the Fermi points kF = ± π/2 from a two-peak to a four-peak structure accompanied by a (non-vanishing) minimum of the single-particle charge gap. This jump separates a weak-coupling regime, the band insulating phase, from a strong-coupling regime which evolves gradually into the Mott–Hubbard phase. We take advantage of this critical behaviour to model several quasi-one-dimensional materials in terms of the IHM instead of the simpler one-band Hubbard model. For instance, the two regimes are physically realized in the angle-resolved photoelectron spectra of (TaSe4)2I, and the blue-bronze K0.3MoO3, respectively.

María del Carmen Refolio Refolio

Papers

Correlation effects in photoemission from adsorbates: Hydrogen on narrow-band metals.

Study of the electronic bonding of Cl Si(100) by synchrotron radiation photoemission spectroscopy and many-body calculations

Doping dependence of the density of states for CuO2 clusters in the Hubbard model.

Modelling one-dimensional insulating materials with the ionic Hubbard model

The dynamic form factor of a one-level adsorbate: Cluster - Bethe lattice approach in configuration space.