We report measurements of the effect of the presence of ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ on the wetting of ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ to a cesium-plated substrate; ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ induces the wetting of the mixture film to cesium at low temperatures where a pure ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ film does not wet. The wetting is hysteretic and reentrant with wetting at low temperatures. A lower wetting temperature is measured as a function of the amount of ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ in the apparatus and as a function of the estimated ${}_{}{}^3{}_{}{}^{}\mathrm{-}_{}^4{}_{}{}^{}$He ratio in the mixture film.

In this Letter we show that a coherent low energy electron beam (<100 eV) can be used to obtain real space images of structures and defects buried deep below the surface of the sample. The elastic strain fields of such buried structures, extending to the free surface, are found to give rise to localized phase shifts in the reflected electron waves, resulting in excellent image contrast under slight objective lens defocus conditions. We can now image the formation and evolution of buried interfaces and defects in situ, and in real time. Because of the very low electron energies used, this imaging method is nondestructive.

An atomic-force microscope study of interstitial impurities in the quasi-one-dimensional charge-density-wave system ${\mathrm{NbSe}}_3$ at room temperature (in the normal phase) exhibits long-range periodic lattice modulations. The amplitudes and wavelengths are strong functions of the impurity concentration, and in the case of vanadium successive wavelengths of 6${\mathit{b}}_0$, 4${\mathit{b}}_0$, and 3${\mathit{b}}_0$ are observed. The drastic changes in the long-range structure of the system caused by small changes in the impurity concentration are an indication of the complex electric susceptibility of a system on the verge of becoming unstable against charge-density-wave formation.

A simple model for the sintering of materials made of connected fractal aggregates, such as aerogels, is proposed. The densification at small scales is described by an increase of the lower cutoff length accompanied by a decrease of the upper cutoff length, in order to conserve the total mass of the system. General scaling laws are derived which relate the structural characteristics to the mean bulk density. The theory explains quite satisfactorily a large number of experiments on gradually densified silica aerogels.

We present a novel Monte Carlo simulation of electrochemical deposition that shows a smooth transition between diffusion limited aggregation and dense-branching morphology. The essential element of the simulation is to divide the growth field into two areas, a ‘‘space charge’’ region surrounding the aggregate in which particle motion is biased to branch tips, and a second region surrounding the first in which particle motion follows unbiased random walks. The interface between these areas is stable to perturbations of wavelength smaller than the size of the space charge region.

Many compounds have twinned domains with plane walls sufficiently regular to allow Bragg diffraction of light. For a coherence light source we have shown that diffraction peaks in the twinned orthorhombic phase of ${\mathrm{DyVO}}_4$ and related compounds have speckle features arising from randomness in domain topology. They evolve with changes in temperature and ordering field, and show qualitative differences between pure ${\mathrm{DyVO}}_4$, where the interfaces are expected to be relatively smooth, and Dy(${\mathrm{As}}_{0.154}$${\mathrm{V}}_{0.846}$)${\mathrm{O}}_4$, where random strains are expected to roughen and pin the interfaces.

We have used interfacial force microscopy (IFM) to monitor the mechanical deformation of single nanometer-size grains in Au thin films. Our results show that protruding grains, which represent early-stage delamination, display multiple deformation mechanisms including grain-boundary sliding and intragranular plasticity. The unprecedented load-displacement control capability of the IFM provides data that are used for the first time to quantitatively distinguish and evaluate individual deformation processes.

A symmetric phase-field model is used to study directional solidification in two and three dimensions. Numerical evidence of tip-splitting, breathing modes, solitary modes, and other non-steady-state behavior is seen in 2D. A simple model for the breathing modes is proposed. Finally, 3D simulations indicate a hexagonal ordering of cells.

Picosecond time-resolved infrared absorption measurements of CO/Cu(100) following visible and ultraviolet laser pumping allow a determination of the time scales for photoexcited carriers and lattice phonons to couple to the CO frustrated translation vibrational mode.

We study irreversible interpolymeric reaction rates k in polymer solutions as a function of concentration φ. At high dilution, kinetics obey mean field theory, and screening of excluded-volume repulsions as φ increases results in a growth, k∼${\mathrm{\phi }}^{3\mathit{g}/4\mathrm{}}$, where g is the monomer contact exponent. Screening effects cause a transition to diffusion-controlled kinetics at a value ${\mathrm{\phi }}^{\mathrm{*}\mathrm{*}}$, beyond which (for entangled solutions) k decreases as k∼${\mathrm{\phi }}^{\mathrm{-}(5/8+\gamma )}$, γ being the entanglement exponent. Thus k is peaked at ${\mathrm{\phi }}^{\mathrm{*}\mathrm{*}}$ which, in agreement with experiment, is distinct from the overlap threshold.

We have performed a Monte Carlo study of a classical three dimensional Coulomb glass. We use finite size scaling to demonstrate the existence of a spin-glass-like phase transition and determine its critical exponents. We find that the transition temperature is well below the bar energy scale; we attribute this to pairs of nearby sites binding into weakly interacting effective dipoles. We have also studied the density of states as a function of temperature; we find that the Coulomb gap begins to develop well above the transition temperature and is nearly fully formed at ${\mathit{T}}_{\mathit{c}}$.

We present an efficient approach for calculating spectral corrections of finite disordered systems beyond the diffusion approximation. For both ballistic (but not perfectly clean) and diffusive systems we find new regimes of spectral correlations. We address the nonuniversal features of these correlations and interpret them in terms of semiclassical concepts.

We derive from first principles the existence of deep level localized electronic gap states, induced by hedgehog solitons, in the two-dimensional Hubbard model. These arise naturally as excitations in a new topological magnetic condensate of the many-electron system associated with ${\mathrm{\pi }}_1$(SO(3)). The condenstate exhibits local spin 1/2 magnetic moments as well as topological ‘‘spin flux.’’ This flux emerges microscopically from a homotopically nontrivial phase rotation of the electron spinor field and leads to an intriguing relativistic structure for the Mott-Hubbard gap.

The evolution of charging energies of few-electron artifical atoms (quantum dots) with magnetic field is calculated and compared with results of the single-electron capacitance spectroscopy of Ashoori et al. The evidence for magnetic field induced spin and angular momentum transitions in the strongly interacting artifical atom is presented.

The conductance of a weakly interacting electron gas in the presence of a single scatterer is found at arbitrary strength of the scattering potential. At weak interaction, a simple renormalization group approach can be used instead of the standard bosonization procedure. Our technique allows us to take into account the backscattering of electrons that leads to deviations of the low-temperature conductance from the behavior typical for Luttinger liquid. In the presence of magnetic field, the backscattering may give rise to a peak in differential conductance at bias equal to the Zeeman energy.

Epitaxial thin films of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathit{x}}$ with low cation and oxygen disorder exhibit two features in the temperature dependence of the microwave surface impedence which are consistent with a weak s-wave superconducting state associated with the CuO chains. First, both the microwave surface resistance and the magnetic field penetration depth exhibit a weak exponential temperature dependence below 30 K corresponding to an energy gap of about 6 meV. Second, the penetration depth exhibits a small bump at about 60 K, which is consistent with a two-band BCS calculation using 6 meV for the smaller gap.

We study underdamped Josephson junction series arrays that are globally coupled through a resistive shunting load and driven by an rf bias current. We find coherent, ordered, partially ordered, and turbulent regimes in the I-V characteristics. The ordered regime corresponds to giant Shapiro steps. In the turbulent regime there is a saturation of the broadband noise for a large number of junctions. This corresponds to a breaking of the law of large numbers already seen in globally coupled maps. Coexisting with this, we find an emergence of novel pseudosteps in the I-V characteristics.

We examine the effect of an impurity on the nearby tunneling conductance in an anisotropically gapped superconductor. The variation of the conductance has pronounced spatial dependence which depends strongly on the Fermi surface location of gap extrema. In particular, different gap symmetries produce profoundly different spatial features in the conductance. These effects may be detectable with a scanning-tunneling-microscope study of the surface of a high-temperature superconductor.

The evolution of the magnetic flux density in the cavity and wall of tubes of high-${\mathit{T}}_{\mathit{c}}$ superconductors subjected to an azimuthal field in the presence of axial fields provides dramatic evidence of cutting and cross-flow of the flux lines in the weak link regime.

Vortices in ${\mathrm{Bi}}_2$${\mathrm{Sr}}_{1.8}$${\mathrm{CaCu}}_2$${\mathrm{O}}_{\mathit{x}}$ thin films were directly observed by Lorentz microscopy as the sample temperature T was raised from 4.5 K under fixed magnetic fields H. Each time T was raised, vortices moved, eventually to settle in a new static configuration. Vortices began to form a regular lattice at a temperature depending on H. The vortex-lattice image remained visible until it gradually faded away around an irreversibility temperature ${\mathit{T}}^{\mathrm{*}}$(H). Careful examination of the disappearance temperature indicates that the vortex lattice may persist up to some temperature above ${\mathit{T}}^{\mathrm{*}}$(H).