We study the effect of a magnetic field B on the luminescence spectrum of a doped symmetric quantum-well wire. We compute the nonlocal electron-hole interaction in the system within a random-phase approximation for the screening. Two effects due to B compete in the spectrum: (i) the symmetry is broken implying a coupling between distinct subbands of the wire that produces an enhancement of the Fermi edge singularity; (ii) particles with different wave vectors become separated from each other, which tends to quench the singularity. When temperature increases, higher bands are more populated and other singularities associated with the single-particle density of states become comparable to the Fermi-edge singularity.

Quantum-dot structures can exhibit bistability between two conduction states connected with S-shaped current-voltage characteristics. In this work, a dynamical model for the electric transport in this structure is proposed. Switching times of about 5 ps at threshold are found for small sample capacitances. On the other hand, it seems to take more than 1 ns before the steady state is reached when the device switches from the high to the low conducting state. In addition, relaxation-type oscillations are predicted under current-controlled conditions if the capacitance of the structure is large enough.

Surface yield measurements with single-alignment high-energy ion scattering, at normal incidence, are used to show that the Cu(110)-(2×3)-N surface is reconstructed according to an additional-row model, where the first-layer density of Cu atoms is increased to 4/3 monolayers. A surface-reconstruction model involving missing rows can be excluded. We also find that 2/3 of the second- and third-layer atoms are displaced laterally, from their bulklike positions, by 0.30 and 0.07 Å, respectively. Off-normal-incidence measurements indicate additional vertical atomic displacements in the second and third layers.

A semiempirical phenomenological equation is proposed to interpret the Monte Carlo simulation experiments of the kinetics of physisorption and chemisorption with attractive and repulsive lateral interaction on a homogeneous solid.

We propose a method for using reflection high-energy electron-diffraction (RHEED) measurements to determine step-adatom kinetics during growth by step flow. Analytical results are obtained for the adatom sticking coefficients at the steps in terms of the steady-state in-phase RHEED specular intensity at two distinct misorientations. Calculated results based on estimated values for these intensities in the step-flow regime indicate the presence of a pronounced barrier at the down step, providing support for previous conjectures. Extension of these results to lower temperatures, including the region below the critical temperature where the majority of RHEED studies reported have been made, should be possible but will involve calculations of a more complicated nature.

It is demonstrated that one of the most common methods used to determine surface energies from thin-film total-energy calculations introduces a computational error that increases linearly with the thickness of the film. This linear divergence is shown to have had a major impact on a recent calculation of the Li(111) surface energy, using one- to five-layer-thick films.

We present quantum-mechanical calculations of conductance oscillations produced by modulating an applied-potential step ${\mathit{V}}_3$ in one of the branches of a multiply connected system. We show that these oscillations arise from partial reflections of the wave function at the sharp steps defining the different potential regions. Quantum interference between the different branches is shown to be negligible in spite of a great deal of coherence present in ballistic multiply connected systems.

We show that the degree of quantum interference in the conductance of a structure, produced by modulating an applied potential step ${\mathit{V}}_{\mathit{T}}$ along one of the branches in a multiply connected system, depends strongly on the constriction geometry. We illustrate this by calculating the conductance G for both open-end and partially closed-end structures. Open-end structures, such as those studied in our paper, exhibit weak interference effects. However, significant interference effects are shown to be present in partially closed nanostructures, which more realistically model typical structures in experiments.

We present Lanczos numerical scaling results for the nearest-level-spacing distribution function P(S) favoring a recently proposed random-matrix theory (RMT), which extends the usual RMT appropriate for disordered metals to the Anderson metal-insulator transition. In the three-dimensional (d=3) tight-binding random-matrix ensemble at the mobility edge we obtain a reasonable overall P(S) fit of the form P(S)=${\mathit{BSe}}^{\mathrm{-}\mathit{A}\mathit{S}\mathrm{\alpha }}$, where A and B are constants and α≊1.31, close to the theoretical value of 2-2/d. We study in more detail the tail of this distribution which is compatible with a lower value of α. These results are also shown to hold for the critical number variance 〈[δN(E)${]}^2$〉 which obeys the asymptotic law 〈[δN(E)${]}^2$〉∝〈N(E)${\mathrm{〉}}^{2\mathrm{-}\mathrm{\alpha }}$.

We have measured the thermal expansion of the Kondo insulator ${\mathrm{SmB}}_6$ from 5 to 80 K using a sensitive capacitance dilatometer. There is a pronounced negative anomaly in the linear expansion coefficient α, of electronic origin, which achieves a local minimum of -5×${10}^{\mathrm{-}6}$ ${\mathrm{K}}^{\mathrm{-}1}$ at 45 K. We interpret this anomaly as a Schottky-like contribution arising from transitions across a semiconducting energy gap ${\mathit{E}}_{\mathit{g}}$≃140 K. Although there are several energy scales in the problem, a Grüneisen analysis indicates that the thermodynamics is driven by a single energy, which we identify as the gap energy.

Microwave photoconductivity is shown to be a powerful method to detect low-energy excitation of the electronic density in antidot arrays. From the experiments on size-tunable field-effect confined antidots, we can deduce the electronic density and the frequency dependence of the low-energy excitation (magnetoplasma modes around the antidots) as a function of the gate voltage. The observed dependence of the magnetoplasmon frequencies on the depletion radius can be analyzed by using the depletion radius obtained from magnetotransport experiments on the same structures.

We time-resolve the transient, photoinduced transmission near the direct band edge of crystalline germanium (at 295 K) with 120-fs, tunable, infrared pulses from a 76-MHz optical parametric oscillator. The data show a rich collection of phenomena including band-gap renormalization, carrier-carrier scattering, carrier cooling, and Γ→L intervalley scattering. An apparent carrier-density dependence in the measured intervalley scattering time is attributed to plasma screening of the Coulomb enhanced continuum absorption.

Using the time-dependent local-density approximation (TDLDA) within a self-consistent-linear response theory, we calculate the elementary excitation energies and the associated inelastic light-scattering spectra of a strongly coupled two-component plasma in a double-quantum-well system with electron occupation of symmetric and antisymmetric subbands. We find, consistent with the results of a recent experimental Raman-scattering study, that the intersubband spin-density excitations tend to merge with the single-particle excitations (i.e., the excitonic shift decreases monotonically) as the Fermi energy increases beyond the symmetric-antisymmetric energy gap ${\mathrm{\Delta }}_{\mathrm{SAS}}$. However, our TDLDA calculation does not show the abrupt suppression of the excitonic shift seen experimentally at a finite value of the subband occupancy parameter η==${\mathrm{\Delta }}_{\mathrm{SAS}}$/${\mathit{E}}_{\mathit{F}}$.

Inelastic light scattering was used to study the dispersion and magnetic-field dependence of both inter-Laudau and intersubband magnetoplasma modes in a wide parabolic quantum well. The intersubband magnetoplasmon energy (∼11 meV) was found to be much greater than expected from a simple self-consistent Hartree calculation (∼2 meV). The value is in fact very close to the bare harmonic energy of the well. This striking example of the absence of corrections to the single-particle energy from electron-electron interactions is the result of Kohn’s theorem. In a magnetic field, the intersubband magnetoplasmon energy is constant except at the field where the inter-Landau energy crosses the intersubband energy. After the crossover, the intersubband energy shifts to a lower value. This is interpreted as a shift in oscillator strength from a bulklike to a surfacelike magnetoplasma mode.

We predict the observation of negative differential resistence (NDR) in interband tunneling devices (ITD’s) of well width smaller then 100 Å. This strong NDR results from the nature of tunneling in ITD’s, and is not related to resonant tunneling. It is inherent to the ITD structure, and should be experimentally observed in any symmetric ITD (including polytype structures). The mechanism is given in terms of simple physical arguments. Rigorous calculations of the current-voltage characteristics of narrow-well ITD’s are then made in the framework of the effective-mass approximation.

Following a recent experiment by Du et al., we study theoretically the energy gaps and collective excitations of the most prominent sequence of the fractional quantum Hall effect (FQHE) at filling factor ν=p/(2+1) around ν=1/2. Our theoretical study is carried out by mapping a FQHE system to the corresponding integer system with gauge interaction. We investigate in detail the effects of Coulomb interaction and gauge interaction on the collective excitation and energy gap. Consistent with the experimental result, the energy gaps are found to be roughly linear with ΔB, the deviation of the magnetic field from half filling. This linear dependence is attributed to the intimate connection between the ground state at ν=p/(2p+1) and the wave function of p-filled Landau levels.

We present a structural model for the metal-induced Si(111)3×1 reconstruction. Fivefold Si rings form one-dimensional π-bonded chains along 〈11¯0〉. These chains are separated by empty channels that can accommodate 1/3 monolayer of metal atoms. We propose that the π-bonded chains undergo a strong disturbance resulting in the formation of alternating dimers consistent with published scanning tunneling microscope images [K. J. Wan et al., Phys. Rev. B 46, 13 635 (1992)]. Unlike previous models, this model accounts for most experimental observations, including a large band gap and chemical passivation.

We study the response of the transmission eigenvalue spectrum of disordered metallic conductors to an arbitrary external perturbation. For systems without time-reversal symmetry we find an exact nonperturbative solution for the two-point correlation function, which exhibits a universal behavior characteristic of disordered conductors. Systems with orthogonal and symplectic symmetries are studied in the hydrodynamic regime.

We have studied the mechanism of visible photoluminescence (PL) from surface-oxidized Si crystallites of 3.7 nm diameter. Under intense laser-pulse illumination, two PL bands are clearly observed: a fast-decay blue-green PL band and a slow-decay red PL band. Time-resolved PL-spectrum measurements indicate that carriers generated in the core state are rapidly localized into the lower-energy surface states. Spectroscopic analysis indicates that the slow-decay red PL is caused by the hopping-limited recombination process in the surface-localized state of the crystallite, while the blue-green PL is caused by the band-edge emission from the core state of the crystallite.

We report on Raman scattering by intersubband excitations in GaAs-AlAs superlattices which exhibit electric-field domains resulting from sequential resonant tunneling. In regions where two domains coexist, the scattering intensity varies linearly with the applied voltage. This behavior, consistent with the standard domain picture, can be explained by a model relying on the electric-field dependence of the cross section and the domain size.