We report imbibition experiments investigating the effect of evaporation on the interface roughness and mean interface height. We observe a new exponent characterizing the scaling of the saturated surface width. Further, we argue that evaporation can be usefully modeled by introducing a gradient in the strength of the disorder, in analogy with the gradient percolation model of Sapoval et al. By incorporating this gradient we predict a new critical exponent and a novel scaling relation for the interface width. Both the exponent value and the form of the scaling agree with the experimental results.

It is shown that a runaway electron population accelerates along the main magnetic field in a Sweet-Parker current sheet. After a characteristic distance the entire current is carried by runaways. The thickness of this runaway sheet is much smaller than the original Ohmic sheet. The influence of microinstabilities is discussed.

Emission of whistler waves by a density modulated electron beam is studied in a laboratory plasma and compared to excitation by loop antenna. Single and double pole excitation are predicted by a simple linear model which agrees with the experiments. The fraction of the power of the modulated beam radiated by the whistler wave has been measured and is of the order of ${10}^{\mathrm{-}5}$.

Correlation radiometry has been applied to detect for the first time electron temperature fluctuations in the core of a magnetically confined plasma by means of electron cyclotron emission. Broadband fluctuations are observed in the frequency range up to 150 kHz with levels below 1.4%. Apparent temperature fluctuations due to the finite optical depth are subtracted; the remaining electron temperature fluctuation level is significant. On the basis of reasonable considerations, the results indicate that electron temperature fluctuations can contribute to the anomalous electron heat flux.

We used high-temperature scanning tunneling microsopy to observe, in real time, the step rearrangement induced by a (7×7) reconstructive phase transition on a vicinal Si(111) surface misoriented toward [1¯ 1¯2]. A new transient step bunching is found between a high-temperature phase consisting of single-layer steps with nonreconstructed terraces and a low-temperature phase of a mixture of single- and triple-layer steps with (7×7) reconstructed terraces. The transient step bunching indicates that the free energy of the (7×7) reconstructed step edge is larger than that of the nonreconstructed step edge just below the phase transition temperature.

Atomistic molecular dynamics simulations were used to study defects which arise in the rotator phase of n-heneicosane (${\mathrm{C}}_{21}$${\mathrm{H}}_{44}$). Chain-setting angle trajectories reveal sine-Gordon soliton motion which is in excellent agreement with defect motions hypothesized for this class of materials. Until now, these nonlinear waves have evaded detection by both experiment and simulation. Thus, this work supports the previous analytic models and provides a first glimpse into the microscopic details of how these pulses can affect the overall rotation of long chain segments in a crystal.

Using the Car-Parrinello method, we have obtained unforeseen structures for the low-lying isomers of ${\mathrm{Si}}_{45}$ and other midsized Si clusters. They are formed by two shells of atoms, the outer one (cage) being fullerenelike and inner one (core) consisting of a few atoms saturating dangling bonds. These novel structures provide for the first time a consistent interpretation of the available experimental data, including the reactivity trends and the structural transition at a size of ∼25 atoms.

We report the first successful molecular dynamics simulations of fullerene annealing and fragmentation. The molecular vibrational dynamics, which we find to play a central role in these processes, is simulated by following constant energy trajectories under specially generated initial conditions. Employing this scheme with a carbon tight-binding potential, we have observed sequential ${\mathrm{C}}_2$ loss from ${\mathrm{C}}_{60}$, as well as the rearrangement of carbon-carbon bonds on the fullerene cage. Our successful approach is a departure from previously employed constant temperature schemes.

A new phase with spontaneous atomic ordering on the sublattice is found in ${\mathrm{Al}}_{0.48}$${\mathrm{In}}_{0.52}$As grown on exact (001)InP substrate by molecular-beam epitaxy. The atomic arrangement is a periodic sequence of {111}A planes in a unit of ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{In}}_{1\mathrm{-}\mathit{x}}$/${\mathrm{Al}}_{\mathit{y}}$${\mathrm{In}}_{1\mathrm{-}\mathit{y}}$/${\mathrm{Al}}_{\mathit{z}}$${\mathrm{In}}_{1\mathrm{-}\mathit{z}}$ on the group-III sublattice. The surface reconstruction during growth is (2×3). A CuPt-type ordered phase is observed in crystals grown at higher temperatures, where the reconstruction is (2×1). This correlation with respect to periodicity and direction between the reconstructions and the types of ordered phase unequivocally demonstrates that surface reconstruction plays a central role in ordered structure formation. Band-gap reductions of ∼80 and ∼30 meV are observed for the new ordered phase and the CuPt-type phase, respectively.

A full phase field model of eutectic growth is proposed, which incorporates the generic features of a eutectic phase diagram and reduces to the sharp-interface model in the appropriate limit. Large scale two-dimensional simulations are presented for the isothermal solidification of a uniformly undercooled eutectic melt, in which the Avrami exponent is 3. The results of this study identify three possible growth mechanisms: diffusion limited growth, lamellar growth, and spinodal decomposition.

The problem of describing the velocity field of quantized vortices on a torus is solved exactly by use of Riemann’s bilinear relations of 1857. The solution is used to discuss the behavior of superfluids on porous media. The close connection between topology and quantization of circulation is emphasized as well as its implications for a successful theory of the experiments.

Synchrotron x-ray scattering has been used to investigate the structure and growth of xenon films physisorbed on the Ag(111) surface. For growth under quasiequilibrium conditions, the bulk Xe-Xe spacing is reached at monolayer completion and fcc films of thickness ≥220 Å are observed. Under kinetic growth conditions, intensity oscillations in the specular reflectivity as a function of time demonstrate nearly layer-by-layer growth. Modeling of the intensity at a fixed coverage allows profiling of the Xe/vacuum interface as well as a direct determination of the film’s thickness and layer spacings.

Scanning tunneling microscopy (STM) has been used to investigate the interaction of nanoscale structural elements associated with rutile ${\mathrm{TiO}}_2$(100)-(1×3). These are the 1×3 reconstruction, vicinal off-cut steps in the [001] direction, and up-down steps in the [010] direction. The STM data image the microfacet morphology of the 1×3 reconstruction suggested by diffraction measurements. They also provide an explanation for the stabilization of the up-down steps by the vicinal off-cut, which involves maximizing the area of the (110) microfacets at the expense of high-energy (001) step edges.

Atomic-scale mechanisms for surfactant-mediated layer-by-layer growth in homoepitaxy are investigated theoretically. Starting with minimal assumptions on relative bond strengths, we demonstrate that four possible mechanisms can be operative in enhancing layered growth: (1) a high density of islands at the initial growth stage of each layer, (2) a reduced activation barrier for atoms to cross steps, (3) incorporation into a growing island, and (4) an effective increase in the migration rate on top of the island. We assess the relative importance of these processes by computer simulations.

We have measured the magnetoresistance (MR) and Hall coefficient of state-of-the-art graphite nanotubule bundles. The apparent Hall coefficient is positive in the temperature and field ranges studied. At low temperatures, the conductivity σ shows two dimensional weak localization behavior and the MR is negative; above 60 K and MR is positive and σ increases approximately linearly with temperature, which is mainly due to an increase in the carrier concentration. The results show that a bundle of graphite nanotubules may best be described as a semimetal.

Low-energy quasiparticle excitations in the vortex state of the superconductor ${\mathrm{V}}_3$Si have been investigated using the de Haas–van Alphen effect. Quantum oscillations persist to surprisingly low values of ${\mathit{B}}_0$/${\mathit{B}}_{\mathit{c}2}$∼0.6 and T/${\mathit{T}}_{\mathit{c}}$∼0.001. The superconducting state introduces a field-dependent quasiparticle damping which has a value ħ${\mathrm{\tau }}^{\mathrm{-}1}$≊0.25Δ at the lowest fields investigated, considerably less than the superconducting gap Δ. Quantum oscillations are attributed to the presence of a gapless excitation spectrum and may be a universal characteristic of superconductors in the vortex state.

We have calculated the single-particle density of states N(ω) and the spectral weight A(p,ω) for the doped two-dimensional Hubbard model by combining quantum Monte Carlo simulations with the maximum-entropy analytic continuation technique. We present results for various values of the doping, temperature, and Coulomb repulsion U. For sufficiently strong Coulomb repulsions and near half filling, a Mott-Hubbard pseudogap exists. In this case, we find that a peak develops at the top of the lower Hubbard band near the Fermi level at temperatures of order of the hopping t. The structure of this peak is similar to that seen in the infinite dimensional Hubbard model.

We carried out magnetotransport measurements and scaling analysis to report on a new magnetic-field-induced metal-insulator transition in two dimensions, where the separatrix between insulating and conducting states appears at a critical magnetic field. In the insulating state, a giant magnetoresistance is observed over a wide range of magnetic field. At the transition, the resistance remains nearly constant over two decades of temperature. In the conducting state a quantum Hall plateau is observed at h/2${\mathit{e}}^2$. The critical exponent is in agreement with those of similar transitions in the quantum Hall regime, possibly reflecting a symmetry between the delocalization processes in 2D.

We study the time evolution of wave packets of noninteracting electrons in a two-dimensional disordered system in strong magnetic field. For wave packets built from states near the metal-insulator transition in the center of the lowest Landau band we find that the return probability to the origin p(t) decays algebraically, p(t)∼${\mathit{t}}_2^{\mathrm{-}\mathit{D}}$/2, with a nonconventional exponent ${\mathit{D}}_2$/2. ${\mathit{D}}_2$ is the generalized dimension describing the scaling of the second moment of the wave function. We show that the corresponding spectral measure is multifractal and that the exponent ${\mathit{D}}_2$/2 equals the generalized dimension D${\mathrm{̃}}_2$ of the spectral measure.

A femtosecond-resolved Faraday spectroscopy has been developed to directly monitor spin dynamics in magnetically tunable semiconductor quantum wells. Tunable terahertz quantum beating of the optical polarization is observed from coherent excitation of the spin states Zeeman split by a single ultrathin magnetic tunneling barrier. Subsequent spin-flip scattering of a photoinjected spin-polarized excitons deposits a magnetic ‘‘imprint’’ in the barrier which is orientation dependent and persists for orders of magnitude longer than the carrier lifetime.