Nonlinear threshold electric transport has been studied at $T\simeq 30$ mK near the collective insulating transition in a dilute two-dimensional (2D) electron system in high-mobility Si MOSFET's. We found that the threshold electric field becomes steplike at the critical density, both when $H=0\mathrm{}$ and when $H\ne 0$. This steplike onset indicates a weak first-order phase transition at the 2D electron-solid-to-liquid phase boundary.

We demonstrate that a diffusive narrow wire of a length much longer than the elastic scattering length and the phase-coherence length, but of the order of the energy relaxation length, exhibits shot noise with an intensity lower than the full shot-noise level. At 4.2 K, the reduction factor is shown to vary between 0.2 and 0.45, depending on the width of the wire. The reduction is consistent with recent theoretical predictions.

Optical second-harmonic generation is used as a sensitive, nondestructive probe for the thermally activated dissociation of molecular oxygen on Si(111)7×7. Isothermal measurements show that the dissociation kinetics strongly depend on the total oxygen coverage. At room temperature the 1/e lifetime of chemisorbed ${\mathrm{O}}_2$ is ∼15 min for saturation coverage but ∼50 min for low oxygen coverage. The temperature dependence of the dissociation rates between 80 and 500 K indicates that more than one dissociation channel and/or molecular oxygen species exist on the surface.

We report the results of capacitance measurements on quantum wires in which only the lowest one-dimensional subband is occupied. The wires are generated in metal-insulator-semiconductor-field-effect-transistor-type AlAs/GaAs heterojunctions with an interdigitated gate. In such devices strong lateral confinement and a well-defined threshold voltage are achieved. In the quantum limit at very low electron density the capacitance signal recorded as a function of the gate voltage exhibits a substructure that we discuss in view of a drastic change of the effective channel width when the wire starts to be occupied. At very high magnetic fields we observe spin polarization of the lowest subband. The position of the capacitance minimum that corresponds to the minimum of the density of states between the spin-polarized subbands clearly reflects the asymmetry of the one-dimensional density of states that even persists at high magnetic fields.

Low-temperature measurements of the conductance of a long one-dimensional ballistic constriction with a narrow-wide-narrow-wide-narrow geometry are presented. The results are compared with a numerical calculation of the transmission probability for the longitudinal potential estimated from the lithographic dimensions, the carrier concentration, and the depth of the unpatterned two-dimensional electron gas. We find good agreement between measurement and this very simple model for particular gate-voltage conditions and when there is only one occupied one-dimensional subband. We suggest that there is electron phase coherence along the whole device at the measurement temperature of 35 mK.

Spin-polarized-photoemission experiments on clean Rh{001} show that the surface resonance at the $\overline{M}$ point (0.60 eV binding energy) in the surface Brillouin zone is weakly ferromagnetic at room temperature. The effect increases with decreasing temperature of the surface and disappears when the surface is covered with 0.5 layer of oxygen. The spin- and angle-resolved photoemission spectra exhibit very small exchange splitting, hence the magnetic moment of the surface atoms cannot be reliably determined, but is estimated to lie between 0.1${\mathrm{\mu }}_{\mathrm{B}}$ and 0.2${\mathrm{\mu }}_{\mathrm{B}}$.

Triplet exciton polarons in nondegenerate conjugated polymers are studied theoretically. Both electron-electron and electron-lattice interactions are taken into account in the Pariser-Parr-Pople model. The electronic and lattice structures of exciton polarons and their adiabatic energy surfaces are calculated by means of the unrestricted Hartree-Fock and the single-configuration-interaction methods. The calculated absorption spectrum of a triplet exciton polaron explains well the photoinduced absorption (PA) spectrum observed in polydiaectylene. An excitonic effect turns out to be crucial in explaining the narrow-peak profile of the observed PA spectrum. The present theory may well apply to the similar PA observed in poly(p-phenylene vinylene).

We obtain the localization-delocalization phase diagram, using finite-size scaling methods, for a random electronic tight-binding model Hamiltonian when the hopping-matrix-element ratio t between the perpendicular and the longitudinal directions varies from 0 to 1. The case t=0 is realized via a collection of uncoupled random chains, corresponding to d=1 with critical disorder ${\mathit{W}}_{\mathit{c}}$=0 and in the usual d=3 isotropic limit the critical disorder is ${\mathit{W}}_{\mathit{c}}$≃16.5. For small t we could fit our data for the critical disorder with the expression ${\mathit{W}}_{\mathit{c}}$∝${\mathit{t}}^{0.5}$, in agreement with a self-consistent perturbational theory, but for all t values we obtain the power-law relation ${\mathit{W}}_{\mathit{c}}$∝${\mathit{t}}^{\mathrm{\alpha }}$, with the exponent α≃0.611. The localization length critical exponent ν is also found and shown to vary between 1.5 and 2 with rather large error bars.

A self-consistent procedure is presented which extends the calculation of electronic densities of states of disordered systems. It is applied, by way of illustration, to a simple structural model of such a system. The n-body structural distribution functions, where n=3,4,..., which appear in the exact expression for the density of states, are approximated in an accurate, systematic way in terms of lower-order distribution functions. This yields an infinite series which is resummed using a cumulant expansion into a self-consistent form reminiscent of self-energy approximations. The resulting expression takes into account electron scattering paths in which the scatterers are far apart in real space and so can be used where electron states are expected to be extended. Numerical results demonstrate in detail how a band is formed below the free-electron continuum as the strength of the attractive atomic potential is increased.

We have investigated the possibility of pair formation in the periodic-Anderson-lattice model with a localized level having on-site Coulomb interaction, embedded in a conduction band with hybridization interaction between the localized electron and the conduction electrons. We have obtained conditions for pair formation involving the positions of the Fermi surface and the localized level. If the conduction band is free-electron-like then these conditions are always violated and pair formation is never possible. If, on the other hand, the conduction band is narrow, or hybridization occurs over a narrow momentum domain, then pairing may occur for certain relative positions of the different energies. Even then, pairing is not possible if the strength of the Coulomb interaction is large. Finite-temperature analysis gives the temperature dependence of the gap parameter and the condensation energy. A non-BCS dependence of the critical temperature on the renormalized Coulomb strength has been obtained. In the presence of a large external magnetic field the reentrant nature of the two phases is seen. Finally, except for an isolated value of the localized level the phase transition has been found to be of the first order.

Nonempirical calculations of the electronic structure and x-ray spectra of some 3d and 4d transition-metal dioxides have been performed with both the cluster ${\mathit{X}}_{\mathrm{\alpha }}$-DV method and the band linearized-muffin-tin-orbitals method in the atomic-sphere approximation. It has been shown that the inner atomic ns and np states of the nd transition metal can make an appreciable contribution to the valence band and, as a consequence, to the valence-band x-ray-photoelectron spectra of the investigated oxides. In accordance with the results of the calculations, ${\mathit{MK}}_{\mathrm{\beta }5}$ x-ray-emission spectra of the 3d transition metal oxides are formed mainly with inner atomic M3p states, but not with the vacant 4p states of the isolated metal atom, as traditionally supposed. The same conclusions about the role of the inner atomic 4p states of the 4d transition metal in forming the ${\mathit{MN}}_{4,5}$ x-ray-emission spectra of their respective oxides have been made.

X-ray photoelectron and ultraviolet-photoemission measurements have been made on ${\mathrm{Ca}}_{10}$${\mathrm{Cu}}_{90}$ and ${\mathrm{Ca}}_{10}$${\mathrm{Ag}}_{90}$ alloys. The core-level XPS spectra of Ca show strong satellites which are discussed in terms of the core-hole screening effects. It is suggested that these spectra are due to the mixing of ${\mathit{d}}^0$-, ${\mathit{d}}^1$-, and ${\mathit{d}}^2$-configurations of calcium in the final state and that bandlike effects are important. In the case of the x-ray-photoemission valence band only small differences have been observed between the alloy and the noble metal, whereas for ultraviolet-photoemission valence bands the corresponding changes are more pronounced. The energy shifts of the x-ray-photoemission valence bands are attributed to the enhancement of the p partial density of states just below the Fermi level in the case of the alloy. Also, linear-muffin-tin-orbital band calculations have been performed for the ${\mathrm{CaCu}}_5$ compound by using a superlattice with and without the Ca 2p core hole. When the core hole is created, the weight of the Ca 3d local partial density of states is increased at the Fermi level, whereas the Cu 3d band remains almost unchanged.

Dielectric losses and conductivity studies in LiF:${\mathrm{Ca}}^{2+}$ crystals were performed in the dissociation region in the frequency range from 5 to 500 kHz. Two dipolar contributions are revealed. The energy parameters of the high-frequency loss peak evidences the rotation of an impurity-cation vacancy dipole by NN→NN jumping of the bound-cation vacancy. This result is in agreement with previously reported ionic thermocurrent data of ours and directs us to the conclusion that the migration enthalpy of the bound cation vacancy decreases as a function of the ionic radius of the impurity.

An estimation of factors which can cause significant many-body effects in x-ray spectra of a given material is very important for understanding the physics behind these effects. In the present study this problem has been approached using the example of the x-ray emission spectra of elemental Ni and Ni in ${\mathrm{Ni}}_3$Mo. The spectra were calculated within the one-electron model on the basis of partial density of states obtained by various methods, namely the tight-binding method, the linear-muffin-tin-orbital method, and the method of local spherical waves. The coherent-potential-approximation method suitable for random materials was additionally considered for ${\mathrm{Ni}}_3$Mo. In the case of elemental Ni, the one-electron model fails and all applied methods result in an emission spectrum about 1.2 eV broader than the experimental spectrum. This discrepancy is not dependent on the method of calculation. For ${\mathrm{Ni}}_3$Mo, all the considered methods provide the correct basic shape of the ${\mathit{L}}_{\mathrm{\alpha }}$ spectrum, and calculated spectra differ only in details of the intensity distribution. The addition of a second element (Mo) leads to the increase of the Ni-Ni distance that results in reduction of the many-body effects. The observed broadening of the Ni spectra from ${\mathrm{Ni}}_3$Mo as compared with the spectrum of elemental Ni is due to the decrease of the correlation effects.

We have formulated a microscopic approach to the Landau theory of Fermi liquids. The method is based on the integration-over-the-coupling-constant algorithm and involves the use of suitable generalizations of Hubbard’s many-body local field. Our investigation clearly demonstrates the crucial role played in the theory by the often neglected antiparallel spin correlations. A point we also emphasize is that in order to correctly employ this procedure it is necessary to make use of the expression for the charge susceptibility as appropriate to the case of an infinitesimally polarized system. As an exemplification, we present a fully self-consistent calculation of the effective mass and the anomalous g factor for the quasi-two-dimensional electron liquid occurring in Si inversion layers. It is shown that the present development solves some serious problems plaguing earlier theories.

The ground-state crystal energies of cubic ${\mathrm{MgAl}}_2$${\mathrm{O}}_4$ (spinel) and MgO (periclase) and of rhombohedral α-${\mathrm{Al}}_2$${\mathrm{O}}_3$ (corundum) have been calculated at different volumes, relaxing the corresponding structures, by all-electron periodic Hartree-Fock methods (crystal program). Basis sets of contracted Gaussian-type functions are employed for the 18 atomic (including d) orbitals representing each of the Mg, Al, and O atoms. Mulliken net atomic charges ${\mathit{z}}_{\mathrm{Mg}}$=1.86‖e‖ (MgO), ${\mathit{z}}_{\mathrm{Al}}$=2.30‖e‖ (α-${\mathrm{Al}}_2$${\mathrm{O}}_3$), ${\mathit{z}}_{\mathrm{Mg}}$=1.74‖e‖, and ${\mathit{z}}_{\mathrm{Al}}$=2.24‖e‖ (spinel) are obtained. The elastic bulk modulus, the Murnaghan equation of state p(V) at the athermal limit, the Mg-O and Al-O bond compressibilities, and the binding energy have been derived for each phase (and the elastic constants ${\mathit{C}}_{11}$ and ${\mathit{C}}_{12}$ for spinel only). Comparison with existing experimental data is discussed. The enthalpy change for spinel decomposition into the simple oxides has been computed as a function of pressure, including a correction for the electron correlation energy based on local-density-functional theory. A decomposition pressure of 11 GPa at T=0 K is predicted, against values of 8 and 13 GPa derived from experimental thermodynamic data and from direct compression experiments, respectively.

We present a quantitative theory of the quasiparticle properties in a Fermi liquid. Our approach uses as an input our previous result for the quasiparticle energy which incorporates the vertex corrections associated with charge and spin-density fluctuations through suitably defined many-body local fields. The method is explicitly applied to the case of the quasi-two-dimensional electron liquid occurring in silicon inversion layers. In particular, we discuss results for the effective mass ${\mathit{m}}^{\mathrm{*}}$ and the modified Landé factor ${\mathit{g}}^{\mathrm{*}}$ (Wilson ratio) that are in reasonable agreement with reported findings. Our calculations are performed by making use of a self-consistent static model for the many-body local fields and are consequently free of arbitrary parameters.

It is shown that an exchange potential proposed by Slater in 1951 can be obtained as the partial functional derivative with respect to charge density of an exchange energy functional. Calculations on atomic neon demonstrate that this potential yields considerably better eigenvalues and total energies than the local-density approximation and remarkably better results when applied to valence electrons only. Its application to solids or liquids is shown to be computationally straightforward.