Electron transport through a multilevel quantum dot with intradot Coulomb repulsion is discussed theoretically. Based on the calculated local density of states, we argue that characteristic peaks should be seen in differential conductance if the dot has a group of closely spaced levels. These peaks provide a hallmark of Kondo-type correlation. Our proposal is especially pertinent if one realizes that Kondo temperature in a multilevel system may be enhanced by orders of magnitude over that for a single-level system.

Since the initial report on the epitaxial growth of α-Fe films on hydrogen-terminated Si(111) surfaces at 300 K, two in-plane orientation relationships, twinned and aligned epitaxy, have been suggested. In this paper, the epitaxial growth of Fe on Si(111) is further examined in detail by x-ray-diffraction θ-2θ scans, x-ray-diffraction φ scans, transmission electron microscopy, and reflection high-energy electron diffraction. Twinned epitaxy at the Fe/Si interface is established, i.e., (111${)}_{\mathrm{\alpha }\mathrm{-}\mathrm{Fe}}$∥(111${)}_{\mathrm{Si}}$ and [1¯10${]}_{\mathrm{\alpha }\mathrm{-}\mathrm{Fe}}$∥[11¯0${]}_{\mathrm{Si}}$. As the film thickness increases, the formation of twins in the epitaxial α-Fe films is observed. The apparent ‘‘aligned epitaxy’’ is the result of twinning in the α-Fe film. The formation of twins in the epitaxial α-Fe film is attributed to the limited mobility at 300 K. The dominance of twinned epitaxy at the interface suggests that the influence of the second-nearest-neighbor interaction between Fe and Si atoms near the interface is important.

Reconstructed surfaces on Sb/GaAs(001) have been investigated in situ by reflection high-energy electron diffraction (RHEED) and core-level photoelectron spectroscopy by heating a sample prepared by depositing Sb on an As-terminated GaAs(001) surface at room temperature (RT). Before Sb desorption, the halo RHEED pattern changes into 1×4, 1×3, and 2×4 patterns from RT to 560 °C, which is in contrast to Sb/GaAs(110) that shows only a 1×1 pattern. It is found that the GaAs surface with a 2×4 pattern is terminated by a monolayer of Sb, and that these superstructure changes are caused by As atom desorption followed by Sb atom substitution.

The Ag growth of Si(100)-2×1 has been investigated by real-time in situ photoreflectance spectroscopy, in the spectral range 1.1–5.4 eV. For the lowest coverages, the interface displays a nonmetallic character, due to the covalent bonding between the Ag atoms and the Si atoms. When the Ag coverage increases, the additional deposits become suddenly metallic and the differential reflectance spectra display typical features: rapid increase of the signal in the red and near-infrared range because of the optical response of the conduction electrons; appearance and growing of a plasma resonance in the thin Ag deposits. Moreover, the following of the signal during the Ag growth permits accurate determination of the beginning of the metallic behavior.

We have investigated the photoluminescence of ${\mathrm{Ga}}_{0.8}$${\mathrm{In}}_{0.2}$As quantum wells where the top barrier is defined by the surface of ${\mathrm{Ga}}_{0.8}$${\mathrm{In}}_{0.2}$As layers. The spectra of surface quantum wells are compared to the emission of GaAs/${\mathrm{Ga}}_{0.8}$${\mathrm{In}}_{0.2}$As/GaAs quantum wells with varying GaAs top barrier thicknesses. Due to the increase of the confinement potential in the surface quantum wells we observe a significant blueshift of the emission line (of about 20 meV) compared to the emission line of quantum wells with a thick semiconductor barrier. The experimentally observed energy shift and line broadening for surface quantum wells as well as the onset of the blueshift for quantum wells with thin top barrier layers can be modeled by assuming a 5-eV electron affinity. For quantum wells with top barrier thicknesses below 10 nm we observe a decrease of the emission intensity due to nonradiative recombination at the surface.

High-quality single-crystal Co/Cr(001) superlattices with layer thicknesses of 5–50 Å have been grown by molecular-beam epitaxy. In contrast to other investigations we found that hcp Co grows with its (11.0) plane parallel to Cr(001). The Co layers exhibit a remarkable expansion of ≊6% perpendicular to the film plane, indicating a structural change in direction to the bcc phase. However, in-plane diffraction experiments confirmed that the hexagonal symmetry remains for Co layer thicknesses down to 4 Å.

High-resolution, polarization-dependent C K-edge near-edge x-ray absorption fine structure spectra of benzene and pyridine on ZnO(101¯0) indicate that both species are oriented by the substrate. At 180 K benzene lies flat on the surface to within 10°, while at 295 K pyridine adopts an upright geometry with the ring close to parallel to the (112¯0) plane. These geometries are similar to those found on metal surfaces.

For Tb(0001), a surface core-level shift of the 4${\mathit{f}}^7$ photoemission multiplet of ${\mathrm{\delta }}_{\mathit{s}}$=0.26±0.03 eV is determined. This value is by more than a factor of 2 smaller than the result of a recent self-consistent SLAB calculation, but agrees with the prediction of a thermochemical model. It is demonstrated that the larger values of ${\mathrm{\delta }}_{\mathit{s}}$ reported previously for polycrystalline samples originate from contributions of low-coordinated surface sites. Implications of the present findings for an improved understanding of the surface electronic structure of rare-earth metals are briefly discussed.

Angle-resolved electron distribution curves have been measured for two different excitation energies on heteroepitaxial ${\mathrm{C}}_{60}$(111) films. At ħω=29 eV, the limited ${\mathit{k}}_{\mathrm{\parallel }}$ resolution together with broadening induced by vibronic excitations results in a weak dependence of the peak positions and line shapes of the photoemission features on the emission angle. We demonstrate that at the low photon energy of ħω=8.1 eV the ${\mathit{k}}_{\mathrm{\parallel }}$ resolution becomes sufficient to resolve two bands in the feature derived from the highest-occupied molecular orbital which show a dispersion of the order of 400 meV.

We have observed a persistent photoconductivity effect (PPC) in ${\mathrm{C}}_{60}$ thin films at the record high temperature of 260 °C. ${\mathrm{C}}_{60}$ is the first noncompound semiconductor known to exhibit the effect well above room temperature. Our available data seem to rule out macroscopic potential barriers as a possible origin for PPC in ${\mathrm{C}}_{60}$. The effect may, instead, be associated with the distortions that the ${\mathrm{C}}_{60}$ molecule experiences in the presence of localized charge.

The optical conductivity of ${\mathrm{BaC}}_{60}$ is calculated using a model of an atom embedded inside a finite shell of jellium. The investigations are carried out within the framework of time-dependent local-density theory. The optical conductivity of ${\mathrm{C}}_{60}$ shows a strong collective resonance (plasmon) at 17.6 eV, which is nearly degenerate with the Ba 5p-d giant dipole resonance, leading to strong interference effects in ${\mathrm{BaC}}_{60}$. Molecular multiple-scattering effects appear as prominent oscillations in the Ba 4d photoionization spectrum of ${\mathrm{BaC}}_{60}$, without any reduction of the overall intensity of the collective 4d-f giant dipole resonance. The oscillations also show up in the various partial photoionization cross sections of the central Ba atom and the ${\mathrm{C}}_{60}$ shell.

The local approximation is applied to the spinless Falicov-Kimball model in one and two dimensions. The local approximation may be viewed as a zeroth-order expansion in 1/d that is exact in the weak-coupling limit. The local approximation rapidly becomes inaccurate as a function of interaction strength in one dimension, but is accurate in two dimensions. This result indicates that the 1/d expansion converges rapidly for the Falicov-Kimball model in d≥2 and that exact solutions of many-body problems in infinite dimensions are quantitatively relevant for physical dimensions.

The electronic structure and the cohesive properties of the ${\mathrm{NiTi}}_2$-type structure are studied by using first-principles calculations based on the linear-muffin-tin-orbital method. The relative structural stability of the ${\mathrm{NiTi}}_2$ compound among the three different (${\mathrm{MoPt}}_2$-, ${\mathrm{MoSi}}_2$-, and ${\mathrm{NiTi}}_2$-type) structures is studied, bringing to light the effects of the shape approximation to the potential or of the self-consistency. Our calculations are also used to study the stability of the ${\mathrm{NiTi}}_2$-type structure as a function of the number of valence electrons per atom.

We present a study of the photoexcitation mechanism of poly-3-alkylthienylene and poly-3-alkylthienylenevinylene polymer solutions. We study the photoinduced absorption under steady-state and far from steady-state conditions. By calculating the analytical dependence of the photoinduced signal on the pump intensity and on the chop frequency we distinguish a bimolecular recombination mechanism for both single chain and aggregated chain solutions. The results are discussed assuming that a weak reversible charge transfer between the photoexcited polymer and the solvent takes place.

We have investigated the electronic structure of well-characterized samples of ${\mathrm{La}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{FeO}}_3$ (x=0.0–0.4) by x-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy, bremsstrahlung isochromat (BI) spectroscopy, and Auger electron spectroscopy. We find systematic behavior in the occupied and unoccupied density of states reflecting changes in the electronic structure on hole doping via Sr substitution as well as providing estimates for different interaction strengths. The spectral features, particularly of the unoccupied states obtained from BI spectra, indicate the probable reason for the absence of an insulator-metal transition in this series. Analysis of the Auger spectra provides the estimates of the on-site effective Coulomb interaction strengths in Fe 3d and O 2p states. The parameter values for the bare charge-transfer energy Δ and the Fe 3d–O 2p hybridization strength ${\mathit{t}}_{\mathrm{\sigma }}$ for ${\mathrm{LaFeO}}_3$ are obtained from an analysis of the Fe 2p core-level XPS in terms of a model many-body calculation. We discuss the character of the ground state in ${\mathrm{LaFeO}}_3$ as well as the nature of the doped hole states in ${\mathrm{La}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{FeO}}_3$, based on these parameter values.

A local approach to the study of complex systems with low symmetry is examined. The approach leads to the direct calculation of the local density of states (DOS) via the local Green’s function. The feasibility and reliability of the method are established by subjecting the method to a severe test, using it to calculate the bulk DOS of the crystalline GaP in a layer-by-layer approach. In this case, the calculation of the Green’s function only involves a series of inversions of matrices whose dimensions are given by the number of orbitals per layer unit cell.

We have studied the electronic structures of rare-earth trihalides ${\mathrm{LaF}}_3$, ${\mathrm{LaCl}}_3$, ${\mathrm{CeF}}_3$, ${\mathrm{CeCl}}_3$, and ${\mathrm{GdF}}_3$ by x-ray photoemission spectroscopy (XPS), bremsstrahlung isochromat spectroscopy (BIS), and electron-energy-loss spectroscopy (EELS). The double peak structures of the rare-earth 3d core-level XPS can be understood within the Anderson impurity model as being due to the charge transfer from the ligand 2p level to the rare-earth unfilled 4f level. The parameters obtained from fitting these core-level spectra using the Gunnarsson-Schönhammer-model approach are consistent with the valence-band XPS and the conduction-band BIS spectra. In the higher binding-energy side (10–40 eV) of 3d XPS, several more satellites are observed. Through comparing with other core-level XPS and EELS, we find that they are mainly loss structures arising from the interband transition, the rare-earth 5p excitation, and the charge-transfer transition, but there are some contributions from the ‘‘intrinsic’’ plasmon excitations as well.

We consider a numerical mean-field study, at the unrestricted Hartree-Fock level, of a Gaussian site-disordered Anderson-Hubbard model on a simple cubic lattice. The phase diagram at half filling is obtained, including magnetic and metallic-insulating phases, and all relevant phase boundaries are found to occur in a relatively weak-coupling regime. Variation with filling fraction y is also considered, with particular reference to the y-differential disorder-induced enhancement of electron interactions that lead to site-differential local-moment formation. The inhomogeneous distribution of local charges and magnetic moments over the sites is found to influence strongly the distribution and character of pseudoparticle states. This enables a simple microscopic rationalization of the metal-insulator transition and its phase boundaries in terms of an interplay between disorder and electron interactions, giving in addition a natural explanation for the two-fluid-like coexistence of delocalized charge-carrying states and strong-local-moment sites.

The variational Monte Carlo (VMC) method, using Jastrow-Slater (JS) wave functions, is used to study the partially polarized interacting electron gas for densities spanning the range encountered in bulk metals. We concentrate on a spin polarization ζ=0.42 which allows direct comparison of polarized and unpolarized states for a fixed total number of electrons in the simulation supercell. The radial distribution functions ${\mathit{g}}_{++}$(r), ${\mathit{g}}_{\mathrm{-}\mathrm{-}}$(r), and ${\mathit{g}}_{+\mathrm{-}}$(r) are given particular attention and compared with a model developed by Perdew and Wang (PW) that satisfies known constraints. At high density the agreement with the PW model is good. At the lower densities (electron-gas parameter ${\mathit{r}}_{\mathit{s}}$=4–8) there are differences that can be roughly characterized as the PW model giving a somewhat more extended exchange-correlation hole than the VMC calculations. These discrepancies could be due to limitations either of the PW model or of the JS wave functions used here. Both the VMC and PW results are contrasted with the Hartree-Fock result for parallel spins.