We have performed ab initio calculations of the energies of antiphase boundaries as well as complex and superlattice intrinsic stacking faults in nine intermetallic compounds observed in the face-centered-cubic L$1_2$ and ${\mathit{DO}}_{22}$ structures. The calculations were performed by means of a Green’s function technique based on the linear-muffin-tin-orbitals method within the tight-binding and atomic-sphere approximations.

We propose a simple method to evaluate the energies of ideal metal surfaces as a function of orientation based on cluster energy expansion. By symmetry only clusters with even-number corners will be present. It is found that the energy expansion converges rapidly and in most cases can be truncated at the pair interaction level. The parameters can be determined from a limited number of low-index surface energies obtained from first-principles calculations. The equilibrium crystal shape at T=0 is then predicted and the step energy on major facets is derived for some fcc metals.

We study the mobility of a particle coupled to a one-dimensional interacting fermionic system, namely, a Luttinger liquid. We bosonize the Luttinger liquid and find the effective interaction between the particle and the bosonic system. We show that the dynamics of this system is completely equivalent to the acoustic polaron problem where the interaction has purely electronic origin. This problem has a zero-mode excitation, or soliton, in the strong-coupling limit, which corresponds to the the formation of a polarization cloud due to the fermion-fermion interaction around the particle. We find that, due to the scattering of the residual bosonic modes, the soliton has a finite mobility and diffusion coefficient at finite temperatures that depend on the fermion-fermion interaction. We show that at low temperatures the mobility and the diffusion coefficient are proportional to ${\mathit{T}}^{\mathrm{-}4}$ and ${\mathit{T}}^5$, respectively, and at high temperatures the mobility vanishes as ${\mathit{T}}^{\mathrm{-}1}$ while the diffusion increases as T.

We carry out a numerical study of the transmittance in a three-dimensional disordered Anderson model and study the weakly localized regime in the vicinity of the mobility edge, by the vector-recursion method of Godin and Haydock. This regime is straddled by stochastic resonant states and characterized by negative magnetoresistance. These stochastic resonances are very different in character to the strong fluctuations in the extended regime which arise due to lead-sample mismatch at the boundary.

We have studied the singlet exciton decay by picosecond photoinduced absorption in films of ${\mathrm{C}}_{60}$, under pressures up to 62 kbar. The picosecond decay of excitons excited in the absorption tail continues to be dominated by broad distributions of lifetimes at high pressure. These results suggest that the distributions of lifetimes do not arise from variations in tunneling or hopping rates between ${\mathrm{C}}_{60}$ molecules as was originally suggested, but arise from distributions of recombination rates at different sites in the sample.

The specific heat of Grafoil, an artificial graphite made by Union Carbide, has been measured at temperatures as low as 100 mK, thus extending substantially the range investigated up to the present. An unusual contribution to the specific heat is found which obeys a ${\mathit{T}}^{\mathrm{\alpha }}$ law (with α negative and smaller than 1). This effect is attributed to localized electronic states associated with defects in the crystal structure of the graphite sample. We compare our results to those obtained in doped semiconductors and to the theoretical predictions of Bhatt and Lee.

In o-${\mathrm{TaS}}_3$ and in ${\mathrm{NbSe}}_3$ doped with Ta, but not in undoped ${\mathrm{NbSe}}_3$, driving the charge-density wave with an ac current produced broad-band noise out of phase with the current. The cross spectrum between this out-of-phase noise and the in-phase noise is small, so the two noises do not represent different aspects of a single fluctuating parameter. The out-of-phase noise appears to represent fluctuations in the magnitude of the nonlinear dielectric behavior (the overshoot phenomenon) which, surprisingly, survive repeated resetting of the polarization.

We have investigated the strongest infrared absorption mode in silicon oxide films obtained at low temperatures (anodic and plasma oxides). The asymmetric stretching transverse mode of the Si-${\mathrm{O}}_4$ tetrahedra, centered at 1070 ${\mathrm{cm}}^{\mathrm{-}1}$, exhibits an interesting multiple-resonance structure on the high-energy side of the infrared spectrum. A transverse-optical (TO) mode at 1200 ${\mathrm{cm}}^{\mathrm{-}1}$ and a longitudinal-optical (LO) mode at 1150 ${\mathrm{cm}}^{\mathrm{-}1}$, both modes associated with a LO-TO frequency splitting, and another longitudinal-optical mode at 1250 ${\mathrm{cm}}^{\mathrm{-}1}$, associated also with a LO-TO splitting of the 1250- and 1070-${\mathrm{cm}}^{\mathrm{-}1}$ peaks are also observed. An important increase in the intensity of the multiple-resonance feature, attributed to the water concentration present during the oxidation process, is observed. This effect is related to the increase in the short-range disorder in silicon oxide films attributed to OH and ${\mathrm{H}}_2$O incorporation during growth. In addition, x-ray-photoelectron-spectroscopy measurements reflect the influence of this short-range disorder on the O 1s and Si 2p core-level and valence-band spectra.

We report a direct observation by electroluminescence (EL) spectroscopy of ballistic-electron transport in double-barrier resonant-tunneling GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As p-i-n diodes. The samples studied contain two confined electron states (e1 and e2) and consequently two resonances in the current versus bias characteristic. When biased for electron tunneling through e2, an analysis of EL intensities permits a quantitative determination of the ratio (1:16 and 1:203 for the two samples studied) of the ballistic current flowing directly through e2 to the current flowing sequentially through e1.

We have studied the in-plane magnetoresistance of coupled double-quantum-well structures, in which each well has a different mobility and where the values of carrier concentration can be varied independently. Resistance resonances, observed at zero magnetic field, were suppressed with an in-plane magnetic field of 1 T, provided the field was perpendicular to the current. The magnetoresistance showed structure which changed systematically with front-gate and back-gate voltages, and was due to the deformation of both wave functions and Fermi surfaces in the in-plane magnetic field.

Schottky-barrier height (SBH) for intimate Al/Si contacts is investigated in relation to the interfacial crystallographic alignment, which is observed by transmission-electron microscopy. Epitaxial and rotational Al films are obtained by low-temperature molecular-beam epitaxy on both Si(111) and (100) surfaces, by controlling the surface structures. The SBH measurements for n- and p-type samples reveal that the absence of epitaxial alignment at the interfaces significantly lowers the Fermi-level pinning position for the contacts on both (111) and (100) surfaces.

Shubnikov–de Haas-like oscillations of the tunnel current were observed at 4.2 K in GaAs/AlAs/GaAs single-barrier heterostructures with 50-, 35-, and 25-Å-thick barriers and 600-Å spacer layers. An accumulation layer was formed at the emitter side of the barriers under external bias. Analysis of the experimental data showed that the concentration of two-dimensional (2D) electrons in the accumulation layer could not be determined from the oscillation period. Only the total number of 2D states on the emitter side of the barrier, below the Fermi level of the emitter bulk, could be determined.

A magneto-optical study of acceptors in varying degrees of confinement in GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As quantum wells (QW’s) is presented. A model for the splitting of the acceptor bound exciton (BE) and the allowed BE transitions in the presence of a magnetic field is presented. Our experimental results for the acceptor BE emission agree with calculated g values for bound holes, e.g., ${\mathit{g}}_{3/2}$=0.61 and ${\mathit{g}}_{1/2}$=0.35 for a 150-Å-wide QW. Furthermore, the energy separation between the acceptor ${\mathit{m}}_{\mathit{j}}$=±3/2 1S(${\mathrm{\Gamma }}_6$) ground state and the excited ${\mathit{m}}_{\mathit{j}}$=±3/2 2S(${\mathrm{\Gamma }}_6$) state as a function of applied magnetic field is derived from selective photoluminescence and resonant-Raman-scattering measurements. Finally, these experimental results are compared with theoretical predictions for the confined acceptor states.

The adsorption position of sulfur atoms in the sulfur-passivated GaAs(001) surface is investigated by soft-x-ray standing-wave triangulation using two types of noncentrosymmetric (11¯1) and (111) diffraction planes inclined by 54° to the (001) surface. The sulfur atoms are at the bridge site on the Ga-terminated GaAs(001) surface, forming bonds with the underlying Ga atoms. The sulfur atomic layer is approximately 1.1 Å above the underlying Ga atomic layer. The existence of symmetric sulfur-sulfur dimers lining up in the [11¯0] direction is not confirmed for the 2×1 reconstructed S/GaAs(001) surface.

We show that the coherent mixing of different transverse modes, due to forward scattering of carriers by soft impurity or boundary potentials leads to a nonlinear, asymmetric current response of quantum point contacts (QPC’s). The oscillating contribution to the current is sensitive both to driving voltage and to gate voltage in direct analogy to the electrostatic Aharonov-Bohm effect. Our calculations are in good agreement with recent experimental data showing small-scale conductivity nonlinearities and asymmetry in QPC’s.

The donor binding energies and density of impurity states of a hydrogenic impurity in a quantum dot are presented within the effective-mass approximation following a variational procedure. The emphasis is placed on the dependence of the binding energy on the volume of the dot and on the impurity position. We show that the results for the donor binding energy in the quantum dot goes to the exact limits of a square-cross-sectional quantum-well wire and a quantum well when appropriate limits are considered. Comparing the donor binding energies for cubic and spherical quantum dots, we found that the values are very close provided the dots have similar volumes.

We calculate using linear-response theory the admittance of a quantum dot out of equilibrium. The interaction between two electrons with opposite spins simultaneously residing on the resonant level is modeled by an Anderson Hamiltonian. The electron correlations lead to the appearance of another feature in the frequency dependence of the conductance. For certain parameter values there are two crossover frequencies between capacitive and inductive behavior of the imaginary part of the admittance. The experimental implications of the obtained results are briefly discussed.

The general expression for the persistent current of one-dimensional noninteracting electrons in a disorder potential with smooth scattering data is derived for zero temperature. On the basis of this expression the parity effects are discussed. It is shown that the electron-electron interaction may give rise to an unusual size dependence of the current amplitude due to renormalized backscattering from the disorder potential.

The symmetry of surface states on metal surfaces is investigated by group-theoretical methods. The surface states are represented in the linear-combination-of-atomic-orbitals approximation. This approach yields a qualitative characterization of surface states with respect to their orbital composition, charge distribution, position of nodal planes, etc., simply on the basis of existing bulk-band-structure calculations. Symmetry selection rules are easily derived and examples are given, where erroneous assignments and ambiguities in the literature could be clarified by the present method.

The ${\mathrm{Cu}}_{83}$${\mathrm{Pd}}_{17}$ alloy is known to be chemically ordered (fcc L$1_2$) at low temperature and to exhibit a disordering transition at ${\mathit{T}}_{\mathit{c}}$=778 K. Using thermal-energy atom scattering, a vicinal surface of ${\mathrm{Cu}}_{83}$${\mathrm{Pd}}_{17}$(110) (miscut 1.8°) was found to undergo a single-step–double-step morphological transition when crossing the bulk critical temperature.