A new two-time-scale model of strong Langmuir turbulence has been constructed, using higher-moment fluid equations with dissipative closures designed to better simulate Vlasov theory predictions of linear wave properties, and to treat collisionless heating of particles by waves. Numerical solutions are carried out in a study of electron heating associated with collapse and burnout of a large-amplitude initial Langmuir wave and in a study of radiation-driven Langmuir turbulence interacting with ion-acoustic quasimodes in plasmas with ${\mathit{T}}_{\mathit{e}}$≊${\mathit{T}}_{\mathit{i}}$.

By reversibly manipulating the apex of the tip in a scanning tunneling microscope (STM), we can image either the O or the Cu or Ni atoms in the added rows which consistute the oxygen-induced (2×1) reconstruction of the (110) surfaces of Cu and Ni. This implies that the STM can be used to discriminate between chemically different elements on metal surfaces.

Surface freezing is able to produce thick smectic-O films at the free surface of isotropic droplets of 1-(methyl)-heptyl-terephtalidene-bis-amino cinnamate which are naturally free from solid contacts. This particular situation allows us to realize a microbalance for determining the anchoring conditions of the director onto the surface edge dislocations. The director of the film is thus found to be anchored at normal angle to the simple edge dislocations with an anchoring constant per unit length of dislocation independent of the film thickness: ${\mathit{k}}_{\mathit{a}}$∼5×${10}^{\mathrm{-}14}$ N. This value corresponds to a maximum anchoring energy ∼1/25${\mathit{k}}_{\mathit{B}}$T per molecule of the dislocation line.

High pressure x-ray diffraction experiments with synchrotron radiation in an extended pressure range up to 67 GPa reveal a novel phase transition of La: At about 60 GPa the low pressure fcc structure of La is recovered from the disorted fcc (d-fcc) phase. The reappearance of the high symmetry cubic structure at higher pressure implies that the d-fcc phase, which also appears in other lanthanides, is not a precursor of the low symmetry structures caused by the so-called f delocalization. A possible mechanism for the reentrant behavior is considered and the phase diagram of La is discussed.

Candidate structures for molecular hydrogen in the 150 GPa pressure range are examined using ab initio frozen-phonon calculations in the local density approximation. Vibronic zero-point motion yields important contributions to the relative energies of metallic versus insulating phases. A first-order insulator-metal transition is found, with features in qualitative accord with experiment. Our results imply that an observed transition in solid molecular hydrogen is an insulator-metal–molecular-orientation transition driven by the vibron zero-point motion itself.

We develop a theory for an electrochemical way of detecting the roughness of a metal surface. Here we relate the surface structure factor of a metal surface to the average reaction current measured on the metal surface and obtain its inverse too. Under the small and large time regime analysis we extract information regarding various morphological features of metal surface.

Desorption of ${\mathrm{O}}_2$ and production of ${\mathrm{CO}}_2$ from ${\mathrm{O}}_2$ coadsorbed with CO on Pt(111) at 80 K were induced by laser pulses of femtosecond and nanosecond durations. The photoyields with femtosecond pulses show highly nonlinear dependence on fluence, large enhancement of cross section, and increase of the ${\mathrm{O}}_2$ desorption to ${\mathrm{CO}}_2$ production branching ratio, when compared with desorption and reaction induced by nanosecond pulses. These differences are attributed to multiple excitations occuring within the time scale of relaxation of the excited adsorbate-surface comples, which are possible with high intensity femtosecond pulse laser irradiation.

A number of recent experiments have shown that surfactants can modify the growth mode of an epitaxial film, suppressing islanding and promoting layer-by-layer growth. Here I introduce a set of coupled equations to describe the nonequilibrium roughening of an interface covered with a thin surfactant layer. The surfactant may drive the system into a novel phase, in which the surface roughness is negative, corresponding to a flat surface.

Surface roughening of (100) InP films grown by metalorganic molecular beam epitaxy was observed by scanning force microscopy. The roughening process gives rise to periodic elongated terraces aligned in the [01¯1] direction; kinetic control by surface diffusion activation is indicated by the dependence on group III and V fluxes, and growth temperature. Below a given temperature for each set of growth parameters the surface roughness shows two distinct power law regimes dependent on the film thickness. This result supports growth models using ballistic aggregation and surface diffusion.

We report on a study of interaction effects in the tunneling density of states of a disordered two-dimensional electron gas in the strong magnetic field limit where only the lowest Landau level is occupied. Interactions in the presence of disorder are accounted for by performing finite-size self-consistent Hartree-Fock calculations. We find evidence for the formation of a pseudogap with a tunneling density of states which vanishes at the Fermi energy.

The current response to oscillating electric or magnetic fields acting on the carriers in the probes of a multichannel, mutlilead conductor is investigated. For a noninteracting system we find a frequency-dependent admittance matrix which is expressed in terms of scattering matrices. A self-consistent potential method is used to include Coulomb interactions. The low-frequency departure of the admittance away from the dc conductance is discussed in terms of phase-delay times and RC times.

The resistivity ${\mathrm{\rho }}_{\mathit{x}\mathit{x}}$ measured in large antidot arrays as a function of an applied perpendicular magnetic field B displays distinct quantum oscillations at very low temperatures. These oscillations characteristically differ from conventional Shubnikov-de Haas oscillations which are periodic in 1/B. A crossover to B periodic oscillations at low B discloses the influence of the imposed potential. Applying semiclassical periodic orbit theory to the nonintegrable (chaotic) electron motion in the antidot lattice we attribute these phenomena to the quantization of few fundamental periodic orbits.

The universal correlations which describe the response of energy levels of a disordered metallic grain to an arbitrary perturbation are shown to be equivalent to time-dependent correlations of a one-dimensional quantum Hamiltonian with inverse-square interaction. These resutls establish a direct connection between a strongly interacting quantum Hamiltonian, the nonlinear σ model of disordered electronic systems, and quantum chaotic spectra. As a consequence we have an expression for the correlation function of the quantum Hamiltonian which we believe to be exact for all space and time.

We study the response to an external perturbation of the energy levels of a disordered metallic particle, by means of the Brownian-motion model introduced by Dyson in the theory of random matrices, and reproduce the results of a recent microscopic [A. Szafer and B. L. Altshuler, Phys. Rev. Lett. 70, 587 (1993)]. This establishes the validity of Dyson’s basic assumption, that parametric correlations in the energy spectrum are dominated by ‘‘level repulsion,’’ and therefore soley dependent on the symmetry of the Hamiltonian.

We introduce a simple model of quantum percolation and analyze it numerically using transfer matrix methods. A central point of this paper is that 3 both integer and fractional plateau transitions in the quantum Hall effect are due to quantum percolation. Within this model, we obtained the localization length exponent ν=2.4±0.2, the dynamical exponent z=1, and the scaling functions for the conductivity tensor for both the integer and the fractional transitions. We show that our results agree extremely well with the experimental results for the integer plateau transition obtained by McEuen et al.

The electron-phonon scattering rate is calculated in a strong magnetic field for a two-dimensional electron gas moving in a smooth random potential within the framework of semiclassical approximation. This inelastic scattering rate is strongly influenced by the strong magnetic field and is found to be linear in temperature for a wide range of temperatures, corresponding to an effective reduction of the Debye temperature. Applying this result to the temperature scaling exponent κ for the width of the transition region between quantum Hall effect plateaus, we argue that κ=3/7 is dictated by the inelastic scattering rate and the percolation length, instead of the localization length.

We study the Coulomb blockade in a superconducting grain, connected to two normal electrodes by tunnel junctions. At small bias, the conductance of this system is due to electrons passing in pairs through the grain. The linear conductance is periodic in the gate voltage. The period and the conductance activation energy are determined by the charge 2e, rather than e. At resonance the current first grows linearly with the applied bias and then drops as the quasiparticle transport channel opens up.

By analysis of the electronic contribution to the binding in ${\mathit{A}}_3$${\mathrm{C}}_{60}$, we show that the problem of orientational ordering can be mapped onto the fcc nearest-neighbor antiferromagnetic Ising model with J at the order of 100 K. For T<1.76J, the system should be found in a state which is antiferromagnetically ordered in two dimensions and disordered in the third. This is not inconsistent with present x-ray powder data. We find that the low-temperature conduction-band structure closely resembles that of the simplest antiferromagnetically ordered (so-called bidirectional) crystal.

We succeeded in observing the two-photon absorption of germanium for both the direct and the indirect gaps, using the Vanderbilt free-electron laser. The two-photon absorption for the indirect gap was found to be 3 orders of magnetude smaller than the direct gap. The indirect-gap threshold position indicates that the two-photon absorption is assisted by an LO phonon, providing a long-delayed positive test of the Bassani-Hassan predictions.

Fourier transformation of experimental energy-dependent photoelectron diffraction data has been used to produce an essentially artifact-free image of a surface alloy. This direct method, based upon the intersection off contour arcs associated with each measurement direction, can provide vectorial atomic positions with atomic resolution. A rapid data collection mode was introduced. Surface structural sensitivity was confirmed by comparison with multiple-scattering simulations. The previously ambiguous surface geometry of c(2×2) Au/Cu(001) has been determined, with clear, non-model-dependent discrimination of the surface alloy over the overlayer structure.