The motion of a particle with an arbitrary dispersion law in both high- and low-frequency fields is studied. Low-frequency dynamics is described using an effective Hamiltonian. The case of the conduction-band electrons in quantum superlattice is examined in detail. The validity of the calculation scheme presented is observed.

We have rigorously calculated the bare electron-phonon scattering rates in semiconductor quantum wires in the presence of an external magnetic field. The magnetic field has several interesting effects on the scattering rates. It drastically reduces acoustic-phonon scattering (by orders of magnitude at easily achievable field strengths), but increases longitudinal-optical and surface optical-phonon scattering. It also enhances the difference between the acoustic-phonon scattering rates at energies just below and above a subband minimum. The latter effect may cause negative differential mobility to appear in quantum wires at electric fields far below the threshold for intervalley transfer.

We show that many-body effects and band-gap renormalization can be easily produced in strained-layer quantum wells with internal built-in piezoelectric fields, under photoexcitation. Our observation was made at low temperature by comparing the behavior of ${\mathrm{Ga}}_{0.92}$${\mathrm{In}}_{0.08}$As-GaAs strained-layer quantum wells grown along the (111) and (001) directions and tuning the densities of photoinjected carriers over several decades. Comparison between experimental data and the results of Hartree calculations including the charge space effects reveals that many-body interactions are photoinduced.

It is argued that a short-range interaction induces a quasi-Landau-level structure in the filling-factor dependence of the ground-state energy of electrons in the lowest Landau level. The discussion is based on exact numerical results obtained from small-system calculations, and the adiabatic principle of Greiter and Wilczek. It is shown that by attaching a single negative flux quantum to each electron adiabatically, the noninteracting electron ground states occupying higher Landau levels are smoothly transformed into the ground states of a hard-core boson gas in the lowest Landau level. This implies a close correspondence between the noninteracting fermions and the hard-core bosons in the lowest Landau level. Numerical results suggest the possibility of a smooth transition from hard-core bosons to fermions with a short-range interaction, by continuously varying the interaction potential.

We report low-temperature (77 K) electroreflectance and photoreflectance measurements of the ${\mathit{E}}_1$-like optical transitions on a series of Ge/Si heterostructures (superlattices and quantum wells). For single and double quantum wells of any thickness, as well as for thick-layer superlattices (period ∼100 Å) the spectra can be understood in terms of quantum-confined bulk-Ge ${\mathit{E}}_1$ states. For thin (∼10 Å) multiple quantum wells and superlattices, zone-folding effects dominate the spectra. Actual confinement of the electronic states is determined by measuring the Raman spectrum of each sample in and out of resonance with a given transition.

The band structure of ${\mathrm{In}}_{0.53}$${\mathrm{Ga}}_{0.47}$P/${\mathrm{In}}_{0.50}$${\mathrm{Al}}_{0.50}$P multiple quantum wells grown by molecular-beam epitaxy has been determined from pressure-dependent-photoluminescence measurements at low temperature. The photoluminescence signals from the direct-gap well and the indirect barrier were monitored as a function of pressure up to 4 GPa. High pressure transformed the multiple quantum well from a type I to a staggered aligned type II at 1.1 GPa. This transition was evidenced by the appearance of a photoluminescence signal due to the recombination of carriers separated in momentum and space. The simultaneous detection of this transition and that of the barrier material, allowed the direct determination of a valence-band offset energy of (0.24±0.05) eV, without requiring any information on parameters of the bulk materials. Considering that the total band-gap discontinuity for this heterostructure system is 0.50 eV at 20 K, an approximate band-gap splitting of 52:48 is determined to be the band lineup at the InGaP/InAlP interface. Variations in the pressure coefficients of the indirect transitions in the barrier indicated that the valence band alignment changes with pressure at a rate of ≊18 meV/GPa, due to shifting of the heavy- and light-hole states with biaxial strain generated by applying pressure in the epilayers.

The dependence of physically observable quantities such as electron-phonon scattering rates on the boundary conditions for the optical phonons confined in polar semiconductor quantum wells, quantum wires, and quantum dots are examined wihin the dielectric continuum approach. Calculations of the confined phonons and of their contributions to the scatterintg rates are made using the boundary conditions of Maxwell’s equations at the interfaces and the condition that the ionic displacements go to zero there. These results are compared with the results obtained using only the condition that Maxwell’s equations be satisfied (the usual dielectric continuum model). We find that in the absence of phonon dispersion the rates of scattering by the confined phonons in these two cases are identical even though the individual phonons differ. We attribute this result to the fact that physically observable quantities involve sums over complete sets of states. As a part of the present work we have derived an interesting relation between the contributions of the confined phonons and the interface phonons to the scattering rates in nanostructures. This relation is useful in, for example, obtaining the rates of scattering by the confined modes for geometries of low symmetry where straightforward sums are difficult.

We study the effect of an external magnetic field on a defect which tunnels incoherently between two locations in a mesoscopic metal. The magnetic field influences the energy asymmetry (bias), and the polaron effect due to the conduction electrons. Both effects contribute to the magnetic-field dependence of the tunneling rate. For a two-level system that has zero bias in the absence of a magnetic field, we find that the modification of the polaron effect dominates at low fields (cyclotron frequency ${\mathrm{\omega }}_{\mathit{c}}$ small compared to ${\mathit{Kk}}_{\mathit{B}}$T/g, where K is the dimensionless electron-defect coupling constant, T is the temperature, and g is the dimensionless conductance). This leads to a small increase in the disorder-averaged tunneling rate. At higher magnetic fields, the change in the bias can significantly suppress the disorder-averaged tunneling rate.

Pairs of particles of definite total and relative angular momentum provide a natural description for a two-dimensional electron gas in a strong magnetic field. Two body operators take a simple form when expressed in terms of pair creation and destruction operators. The pair formalism is applied to the study of edge-wave excitations. For ν=1 the operators which create edge excitations are identified and the role the interaction potential plays in the long wavelength limit is clarified. This picture also describes edge excitations on the ν=1/m Laughlin states.

We propose a unified transport theory for the two-dimensional electron gas in the dissipative quantum Hall regime in the presence of a long-range disorder. We find that the evolution of the longitudinal conductivity peaks as a function of the disorder can be described by a single parameter ${\mathrm{\beta }}^{\mathrm{-}1}$ which is determined by the typical gradient of the electron-density fluctuations. In the case of a relatively strong disorder we utilize the edge-states-network model to describe transport in a half-filled Landau level. In the fractional quantum Hall regime we apply the network model to the system of composite fermions, finding the universal values of the resistivity at even-denominator filling fractions. The breakdown of the network model takes place at weak disorder because the edge channels develop into wide compressible strips and at strong disorder because of the destruction of the incompressible strips, isolating the edge channels. We find the limits of the applicability of the network model in terms of β. In the limit of very weak disorder the system is effectively a Fermi liquid of composite fermions. We calculate the conductivity in this regime by considering the motion of noninteracting fermions in a spatially varying magnetic field arising from the density fluctuations. The resistivity is found to scale linearly with the magnetic field with the slope given by ${\mathrm{\beta }}^{\mathrm{-}1}$. Although the presence of nonlocal transport makes measurements of the resistivity difficult, we find qualitative and, in some cases, quantitative agreement with experiment.

Angle-resolved photoemission experiments using synchrotron radiation have been performed on an As-rich GaAs(1¯ 1¯ 1¯)-2×2 surface over the photon energy range 10–70 eV. The occupied bulk and surface band structures of the surface were investigated using theoretical structure plots involving the linear-muffin-tin-orbital (LMTO) calculated initial bands and free-electron-like final states. Based on a three-step model, the calculations suggest that this surface is rich in surface umklapp effects and that many strong transitions may be explained as surface umklapp transitions involving mainly the surface reciprocal lattice vector ${\mathbf{g}}_{2\times 2}$=2π/a(-1/3,2/3,-1/3). In general, the combination of the LMTO initial bands and the free-electron-like final states allow us to satisfactorily identify the observed emission features, deviations in energy being <0.5 eV.

The one-particle Green’s function, the density of states, and the thermodynamic quantities (susceptibility and specific heat) are evaluated for tunnel-coupled quantum wells with asymmetric scattering in the presence of a transverse quasiclassical magnetic field. The oscillations of the susceptibility and of the specific heat have different periods and widths and depend sensitively on the level splitting between the left and right levels. Peculiar characteristics appear in the density of states when the splitting due to tunneling is comparable to the difference in the broadening between wells of equal width. When the tunneling splitting is stronger than this difference two sets of peaks arise with the same width. In the opposite case, the peaks have different widths but are superposed.

Shubnikov–de Haas oscillations and cyclotron resonance absorption are considered for quasiclassical magnetic fields and very low temperatures in tunnel-coupled quantum wells with asymmetric short-range scattering. The two sets of Landau levels, separated by the splitting ${\mathrm{\Delta }}_{\mathit{T}}$ between the left and right levels, lead to two series of peaks with different periods and widths. In addition, the conductivity shows oscillations as function of ${\mathrm{\Delta }}_{\mathit{T}}$. The cyclotron resonance peak shows peculiar characteristics when both sets of Landau levels cross the Fermi energy.

Based on the idea of constant-momentum-transfer averaging (CMTA) of Lagally et al. and facing the problem of CMTA pointed out by Pendry, in the present work we propose the use of the quasikinematic low-energy electron-diffraction (QKLEED) calculations in comparison with the experimental CMTA curves in surface structure determinations. In QKLEED, the influences of the zero-angle scattering on the CMTA curves are treated so that they have essentially no influence on correctly determining the structural parameters, and the mean complex atomic scattering factors are introduced as the effective scattering factors. In addition, an experimental design is proposed for obtaining CMTA curves containing the least influence of multiple scattering. The whole QKLEED/CMTA method has been carefully and systematically tested, and its capability of determining surface structures is demonstrated on the Cu(001)(1×1), Si(111)(√3 × √3 )R30°-Al, and Si(111)(√3 × √3 )R30°-Ag surfaces.

In the present work, the atomic structure of the Si(111)(√3 × √3 )R30°-Ag surface is investigated with the quasikinematic low-energy electron-diffraction approach in conjunction with the constant-momentum-transfer-averaging technique. Our results support the honeycomb-chained-triangle model. The topmost layer of the model consists of Ag atoms arranged as ‘‘honeycomb chained trimers.’’ Below the Ag layer is a Si-trimer layer and then bulklike Si double layers follow. In the optimized model of this work the √3 × √3 reconstruction extends down to the fifth Si layer, and there is an oscillatory multilayer relaxation in the selvage region. We give all structural parameters of the model.

Second-harmonic generation exploiting evanescent field interaction has been investigated for a planar dielectric waveguide covered with a thin organic layer. The coherent nature of the frequency-doubling process in such a structure was studied experimentally by systematic ablation of the nonlinear film in an in situ setup. An increase in the conversion efficiency by two orders of magnitude has been observed for a nonoptimized second-order susceptibility of the coverage layer.

The structure and phase behavior of the clean Pt(111) surface has been studied between 300 K and 0.92${\mathit{T}}_{\mathit{m}}$ via x-ray scattering. The surface is unreconstructed at low temperatures (T<0.65${\mathit{T}}_{\mathit{m}}$). For temperatures greater than ${\mathit{T}}_{\mathit{c}}$=0.65${\mathit{T}}_{\mathit{m}}$, we find that the top layer undergoes a continuous commensurate-incommensurate transformation into a translationally and orientationally disordered discommensuration-fluid phase, which is isotropically compressed relative to the bulk (111) planes. A disordered arrangement of discommensurations separates regions of ideal face-centered-cubic ABC stacking from regions of faulted ABA stacking. As the temperature is increased, the compression of the surface layer increases and the incommensurability (δ) follows a power-law versus reduced temperature with an exponent equal to 1/3. For temperatures increasing above 0.75${\mathit{T}}_{\mathit{m}}$, sixfold orientational ordering of the discommensurations develops and increases.

When an external force acts on an adsorbate structure, the structure may slide or flow relative to the substrate. The mechanism behind this sliding motion is of fundamental importance for the understanding of friction and lubrication between two flat macroscopic surfaces, and is also related to the question of what boundary condition should be used for the velocity field at a solid-liquid interface when solving the Navier-Stokes equations of fluid dynamics. Here I study the friction which occurs when adsorbate structures slide on surfaces. I present results of simulations based on Langevin or Brownian-motion dynamics, where the dependence of the linear sliding friction on the temperature and on the coverage is studied. I also present results for the nonlinear (in the external driving force) sliding friction, which is found to exhibit hysteresis giving rise to the well-known phenomenon of ‘‘stick-and-slip’’ motion. The theory predicts that for a class of sliding systems the ratio ${\mathit{f}}_{\mathit{k}}$/${\mathit{f}}_{\mathit{s}}$ between the kinetic and the static friction coefficient should equal 1/2, in good agreement with experimental data.

The linear-muffin-tin-orbital method is used to study the adsorption of a monolayer of Fe atoms on the β-SiC(100) surface. Adsorption energies of Fe on both Si- and C-terminated (100) surfaces are calculated. It is found that Fe can adsorb on both the Si- and C-terminated (100) surfaces. In the case of a clean Si-terminated surface, the 2${\mathit{p}}_{3/2}$ core level of the surface Si atoms shifts downward, since the surface Si atom loses more of its electrons than does the bulk Si atom. When a monolayer of Fe atoms adsorbs on this surface, the 2${\mathit{p}}_{3/2}$ core level shifts upward; this is due to the fact that charge transfers from Fe to the surface Si atom. In addition, the layer projected density of states is also studied.

We study the quantized electronic energy levels in a three-dimensional icosahedral billiard modeling a faceted metal cluster. The first 2000 levels are determined numerically. The magic numbers are compared with experimental data and with the results for a spherical model. We discuss the supershell structure and propose its study as a test of cluster sphericity. We compare our results with the predictions of the semiclassical trace formula and point out the relevance of diffractive orbits.