For the first time, absolute cross sections for electron-impact excitation of a multiply charged ion have been measured using an electron-energy-loss technique. Cross sections for e+${\mathrm{Si}}^{3+}$(3s ${}_{}{}^2{}_{}{}^{}$${\mathit{S}}_{1/2}$)→e+${\mathrm{Si}}^{3+}$(3p ${}_{}{}^2{}_{}{}^{}$${\mathit{P}}_{1/2,3/2}$)-8.88 eV have been measured with an accuracy of ±20% (at 90% confidence level) over a narrow energy range (±0.6 eV) about the threshold energy with an energy resolution of 0.2 eV. Results are in good agreement with close-coupling calculations.

We consider the behavior of solitons described by the nonlinear Schrödinger equation with periodic perturbation (not necessarily small) whose period ${\mathit{Z}}_{\mathit{a}}$ is much shorter than the characteristic period of the solitons, ${\mathit{Z}}_0$. The soliton behaves like the guiding-center motion of a charged particle in a magnetic field, smooth and adiabatic. However, when ${\mathit{Z}}_{\mathit{a}}$ approaches ${\mathit{Z}}_0$, resonances appear between the periodic perturbations and the characteristic frequencies of the solitons which induce the generation of dispersive waves and/or splitting of solitons.

We have demonstrated the formation of stable, symmetric, compact-torus (CT) plasma rings and the subsequent stable, twofold radial compression in coaxial conical electrodes with the ring accelerator experiment. The CT is compressed by J×B forces from a capacitor bank discharging across the conical electrodes. During compression, the force of the ${\mathbf{B}}_{\mathrm{\theta }}$ acceleration field balances the force of the CT poloidal field against the cones, in good agreement with a 2D code. Power amplification factors of ∼100 may be possible with an opening switch based on this technique.

Phase transitions in fractal porous media are studied using a spin model with correlated dilution parametrized by a microscopic porosity p and a Hausdorf dimension D. For D>${\mathit{D}}_{\mathrm{crit}}$ ther is a percolation transition for the pore space at some ${\mathit{p}}_{\mathit{c}}$ and, for p>${\mathit{p}}_{\mathit{c}}$, the spins in the pore space exhibit two critical points at the bulk transition temperature, ${\mathit{T}}_{\mathit{c}0}$ and at ${\mathit{T}}_{\mathit{c}}$<${\mathit{T}}_{\mathit{c}0}$. The correlation-length exponent at ${\mathit{T}}_{\mathit{c}}$ is larger than in the corresponding pure system. The qualitative features of the model resemble those of the superfluid transition in aerogel.

Exploiting the computational efficiency of the cell-dynamical-system modeling of spinodal decomposition, a large three-dimensional, critically quenched binary-alloy system was studied. The primary result is the conclusive determination of the time-asymptotic scaled form factor, which satisfies Porod’s law, Tomita’s sum rule, and the exponent inequality for the small-wave-number limit by Yeung.

From symmetry arguments we construct a simple Langevin model to describe driven interfaces such as lattice sandpile models composed of discrete grains in the presence of white noise. The model exhibits generic scale invariance (or ‘‘self-organized criticality’’) with calculable exponents in all dimensions. For spatial dimensions 1<d≤2 it undergoes a roughening transition between two distinct phases with algebraic correlations. The transition is Kosterlitz-Thouless-like in d=2.

A quartz-crystal microbalance has been utilized to probe sliding-friction effects in Kr monolayers undergoing solidification on Au and Ag surfaces. Solid layers are observed to be far more sensitive to surface morphology than liquids. The behavior of liquid layers is consistent with a frictional force whose magnitude is a nonlinear function of the sliding velocity.

We present an investigation of the macroscopic spreading behavior of polydimethylsiloxane droplets on solid surfaces of adjustable spreading power. This is obtained through chemical grafting of mixed self-assembled monolayers on silicon wafers. Between partial wetting and high-energy-type total wetting, we identify for the first time a new regime in which the whole spreading kinetics is highly sensitive to the layer polarizability. This new regime can be interpreted in terms of oscillating van der Waals interactions, and identified with the pseudo partial wetting recently predicted.

A tight-binding molecular-dynamics scheme is shown to have the efficiency and accuracy to study complex Si systems. We first establish the reliability of the scheme by showing that simulation results of liquid Si are nearly identical to ab initio (Car-Parrinello) results. The ability of the method to study complex systems is demonstrated by calculating defect formation energies and atomic configurations around vacancies and self-interstitials, with simulation unit cells of up to 512 atoms. The calculated formation energies compare well with first-principles results.

We have measured optical absorption and reflectance in the visible and near infrared in hydrogen up to 230 GPa between 77 and 295 K. Our data show no evidence that hydrogen metallizes near 150 GPa, as has been recently reported from reflectance data. We analyze both experiments and conclude that the metallization of hydrogen remains an open question.

The energy flow in a system of hot electrons, hot LO phonons, and a bath of acoustic phonons is studied using nonequilibrium Green functions. In lowest order, Kogan’s formula for the energy-loss rate is obtained. When coupled modes are included we find, in sharp contrast to Das Sarma and co-workers, that the energy-loss rate is significantly suppressed by coupled-mode formation and quasiparticlelike modes do not contribute to the energy-loss rate.

We present the first study of the dynamics of an extended electronic wave packet in a solid. The wave packet is created in a GaAs/AlGaAs double-quantum-well structure by ultrashort pulse excitation. We observe the oscillatory motion of the wave packet between the two wells by using time-resolved degenerate four-wave-mixing and pump-and-probe spectroscopy.

We studied the transport properties of the Anderson localization model for a disordered metal using a new numerical method in which the time evolution of the current in response to a constant electric field which is turned on abruptly at t=0 is calculated directly. We report results on the current response of a sample of ${128}^2$ sites in the one-orbital-per-site Anderson model near the metal-insulator transition. We find the current response out to times of the order of 1000 times the inverse bandwidth. We discuss scaling and the values of the critical exponents ν and z (usually thought to be 3).

We have studied the Kondo effect in thin films of AuFe, through measurements of the temperature dependence of the resistivity, Δρ(T). At low temperatures, we find Δρ=-B ln(T), as expected for the Kondo effect. We have also found that the factor B becomes smaller as the film thickness is reduced. This result is discussed in terms of the effect of the film thickness on the conduction-electron screening cloud which forms around the magnetic impurities, and the associated crossover from three- to two-dimensional behavior. Studies of bilayer films, which seem to support this interpretation, are also described.

Suppression and shift of period-doubling bifurcation due to a periodic perturbation is experimentally observed in the strain dynamics of a magnetically driven magnetostrictive ribbon. First experimental verification of the predicted scaling law relating the shift of the bifurcation point to the perturbation amplitude is made. The predicted switchlike nonlinearities in the perturbing signal around the bifurcation point are also observed.

Critical currents injected from an external source into the superconducting microladder are obtained as a function of magnetic flux at constant temperature for the uniform-current mode. We find a new, first-order, phase-transition boundary in temperature–magnetic-flux space which divides the superconducting region into two domains: one supporting both injected and persistent currents, the other a persistent current only. This boundary is distinctly different from the second-order phase-transition boundary.

High-conductance Nb/${\mathrm{AlO}}_{\mathit{x}}$/Al/${\mathrm{AlO}}_{\mathit{x}}$/Nb tunnel-junction devices with the Al thickness varying from 3 to 20 nm have been fabricated using a whole-wafer processing route. Current-voltage measurements show a step in the subgap structure corresponding to the difference in the energy gaps V=2(${\mathrm{\Delta }}_{\mathrm{Nb}}$-${\mathrm{\Delta }}_{\mathrm{Al}}$) of the two superconductors. The measured ${\mathrm{\Delta }}_{\mathrm{Al}}$ is large and persists to temperatures considerably in excess of the equilibrium critical temperature of the Al. This is interpreted as arising from a tunnel-induced gap enhancement which is an order of magnitude larger than has been seen previously.

The geometry of a flux lattice pinned by superconducting layers is studied. Under variation of magnetic field the lattice undergoes an infinite sequence of continuous transitions corresponding to different ways of selection of shortest distances. All possible lattices form a hierarchical structure identified as the hierarchy of Farey numbers. It is shown that dynamically accessible lattices are characterized by pairs of consecutive Fibonacci numbers.

The infrared singularities of the recently introduced marginal-Fermi-liquid theory are treated within a perturbative renormalization-group approach. Marginal Fermi liquids are stable in a limited range of the parameters; otherwise non-Fermi-liquid behavior is obtained. Experimental ramifications on the conductivity and spin relaxation are discussed.

We report heat-capacity measurements on untwinned ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ single crystals in magnetic fields H≤7 T, for both H?c and H⊥c. Adding Gaussian fluctuations to a BCS-like step, we obtain a fit for H=0, T≊${\mathit{T}}_{\mathit{c}}$ that is consistent with a 3D, two-component order parameter in the strong-coupling limit. However, the H≠0 data are inconsistent with this approach. A finite-size-scaling analysis, assuming critical behavior and an H-dependent length, satisfactorily describes the data.