The front of an electron beam (${\mathit{t}}_{\mathrm{rise}}$≊20 ns, ${\mathit{V}}_{\mathit{b}}$=200 V, ${\mathit{I}}_{\mathit{b}}$≤2 A) injected into a uniform, magnetized plasma (${\mathit{n}}_{\mathit{e}}$≊2×${10}^{11}$ ${\mathrm{cm}}^{\mathrm{-}3}$,${\mathit{kT}}_{\mathit{e}}$<0.2 eV, ${\mathit{B}}_0$=90 G) is observed to erode rapidly because of scattering of the beam electrons via collective beam-plasma interactions. The propagation of the beam front is measured with temporal and axial resolution via beam excitation light. A broadened light front can result that propagates much slower than the injected beam particle speed.

We have measured the electric-field dependence of the reflectivity of the blue phase III (BP III) of cholesteric liquid crystals when the dielectric anisotropy ${\mathrm{\epsilon }}_{\mathit{a}}$<0. We propose a model which assumes that the boundary aligns the sample to a depth L and in which L is increased by the applied field. The free energy is proportional to ${\mathit{E}}^{\mathit{n}}$, where n depends on the structure of BP III. The data are fitted well by a Lorentzian line shape, and the peak intensity and linewidth agree well with the theory for n=2.1. This value is consistent with the double-twist model of BP III, but not with cubic and quasicrystal models, since the energies of these latter structures depend on higher powers of E.

The electric-field dependence of the correlation region induced by a surface potential in cholestric liquid-crystal phases is considered theoretically. Based upon arguments given for the helicoidal and cubic blue phases I and II, it is argued that recent experimental results on blue phase III rule out a cubic or icosahedral structure for this state but are consistent with one composed of cylindrical elements, in each of which the order is characterized by a curling or double-twist configuration. In the bulk, these flexible cylinders interlace and form a three-dimensional mesh. Near a boundary, however, they lie preferentially in the bounding plane as a consequence of the surface potential.

Crystals also admit a non-Euclidean space-group symmetry. This is shown to be the case for the hexagonal and the cubic-close-packed structures and (slightly broken) for α-${\mathrm{Na}}_2$${\mathrm{Co}}_3$. Accordingly, quasicrystals embedded in the superspace and normal crystals in space share the same type of crystallographic symmetries.

The adsorption of Na on Al(111) at room temperature has been studied by surface extended x-ray-absorption fine-structure (SEXAFS) experiments as well as by parameter-free calculations. For coverages of ${\mathrm{\Theta }}_{\mathrm{Na}}$=0.16–0.33, the SEXAFS analysis shows that Na atoms occupy an unusual six-fold-coordinated substitutional site. The Na-Al bond length is determined as 3.31 Å, consistent with metallic bonding. Ab initio density-functional-theory calculations for several adsorbate geometries show that the substitutional site has the lowest total energy.

X-ray scattering from a tetragonal single crystal of ${\mathrm{YBa}}_2$(${\mathrm{Cu}}_{0.955}$${\mathrm{Al}}_{0.045}$${)}_3$${\mathrm{O}}_7$ shows diffuse streaking in [110] directions about the Bragg peaks. Through a quantitative calculation using a coupled concentration wave, static displacement wave approach, we show that this is essentially attributable to the shear displacement field produced by a disordered oxygen array on the Cu(1)-O ‘‘chain’’ plane. We observe pronounced short-range chain order (local orthorhombic fluctuations) whose correlation range is considerably greater than the superconducting coherence length. This suggests that on a scale relevant for superconductivity the (local) orthorhombicity remains important in this tetragonal structure.

We report on the first measurements by high-resolution electron-energy-loss spectroscopy of the elementary excitations of ${\mathrm{C}}_{60}$ thin films deposited on Si(100). By varying the primary electron energy, the spectrum extending from the far ir to the far vuv has been investigated. Many spectral features are comparable to earlier observations by photon, photoelectron, and neutron spectroscopies. New molecular excitations are revealed including the lowest electronic excitation at 1.5 eV and collective excitations at 6.3 and 28 eV.

The first experimental studies of pulsed electrohydrodynamics ion emission from molten lithium are reported. Ions are produced at the apices of cusps formed on the surface of liquid lithium by applying a pulsed electric field of nanosecond duration. The ion species are dominated ${\mathrm{by}}^7$${\mathrm{Li}}^{+}$ and have a turn-on time of less than 10 ns as measured by time-of-flight mass spectroscopy. Current densities of ∼300 A/${\mathrm{cm}}^2$ have been observed. Implications for the use of this ion source in light-ion inertial-confinement-fusion reactors are discussed.

Ab initio local-orbital quantum molecular dynamics is used to study the finite-temperature properties of amorphous silicon. Using two structural models of a-Si with 63 and 216 atoms, we examine the structure and temperature dependence of conduction and valence band tails. An explanation is suggested for the recent experimental observations of an asymmetry in the temperature dependence of the band-tail widths of the conduction and valence bands in a-Si. Finally, we conect these simulations to other theoretical descriptions of band tailing.

Angular variations in the kinetic energy of scattered species are found to provide a useful probe of the transition between gas-surface scattering regimes, complementing angular flux distributions. As incidence energies exceed a few eV, these change from being consistent with scattering from an extended target to being more typical of scattering from individual atoms. Results are presented for the Xe/Pt(111) system and are supported by detailed trajectory calculations.

The charge asymmetry between the up and down atoms of an asymmetric dimer on Si(100)-(2×1) or Ge(100)-(2×1) is tied to the core-level energy splitting. Previous studies of the surface components in the core-level photoemission spectra disagreed on the assignments of the atomic origins, resulting in a disagreement on the charge asymmetry. The present core-level study of the growth of Ge on Si(100) shows clearly that the dimers are essentially covalent.

The electronic structure of potassium-covered single-domain Si(100)2×1 surfaces has been studied with angle-resolved direct (ultraviolet) and inverse photoemission at room temperature. At saturation coverage, the surface is metallic due to the filling of the minimum of a strongly dispersive empty surface state of mainly K 4${\mathit{p}}_{\mathit{z}}$ character. Parabolic-like dispersions are observed for this state in the Γ¯-J¯ ’ and the Γ¯-J¯ directions (i.e., both along and perpendicular to the dimer rows), showing the metallic bonding in the overlayer and a strong K-K interaction in both directions.

A scanning tunneling microscope has been used to study ${\mathrm{Bi}}_2$${\mathrm{Sr}}_2$${\mathrm{CaCu}}_2$${\mathrm{O}}_{\mathit{x}}$ single crystals with transition temperatures of 85 K. Images of atoms and topographical features were obtained at low temperatures and spectra were acquired in the vacuum tunneling mode. Interpretations of the conductance data suggest that 2Δ/${\mathit{k}}_{\mathit{B}}$${\mathit{T}}_{\mathit{c}}$≊8.2. Most significantly, an additional conductance peak at 90 meV, suggesting a localized state, is observed. The latter would appear to support the marginal-Fermi-liquid picture.

The electric admittance of a two-dimensional electron gas on liquid helium measured at audio frequencies ω is observed to oscillate as a function of magnetic field at strong magnetic fields. The oscillations can be attributed to the propagation of very-low-frequency (ωτ∼${10}^{\mathrm{-}6}$, τ scattering time; ω/${\mathrm{\omega }}_{\mathit{c}}$∼${10}^{\mathrm{-}8}$, ${\mathrm{\omega }}_{\mathit{c}}$ cyclotron frequency) edge magnetoplasmons. The directly determined dispersion relation agrees with theory and quantitatively with measurements in the collisionless regime (ωτ≫1). The attenuation, theoretically obtained by incorporating the screening in a simple local-capacitance model, agrees well with experiments.

We report Monte Carlo simulations for the T=0 phase diagram of a mesoscopic metallic junction. We present some evidences as a T=0 phase transition induced by the dispersion strength α. In the strong-coupling region the predictions of the spin-wave theory turn out to be correct and the algebraic decay of correlations implies quasi-long-range order, corresponding to the absence of a Coulomb-blockade voltage threshold. The critical junction resistance is estimated to be ${\mathit{R}}_{\mathit{t}}$≊0.6 kΩ.

Using spin-resonance techniques, we measure the energy gap in the excitation spectrum of ${\mathrm{CsNiF}}_3$, a quasi-1D ferromagnet, in a magnetic field H transverse to the chain axis. The strong depression of the gap observed at low field is due to the quantum and thermal fluctuations and is well described by the exactly solvable quantum sine-Grodon field theory. In longitudinal response, the observed line shape cannot be described by spin-wave theory. This is indirect evidence for breather modes in the excitation spectrum.

The ground state of the Kondo-lattice model with one conduction electron is analyzed. A rigorous proof is given that this system forms an incomplete ferromagnetic order with ${\mathit{S}}_{\mathrm{tot}}$=(N-1)/2 for antiferromagnetic exchange coupling. The wave function of the ground state is derived and some of its properties are discussed.

We present full potential linear-muffin-tin-orbital calculations based on the local-density approximation, which reproduce the T=0 phase diagram of cerium (Ce), including the volumes and transition pressures for both the α→α’, and the α’→bct transitions. The α→α’ transition is largely determined by a balance of two competing terms: a Madelung term and a 4f one-electron term. The α’→bct transition is driven by both 4f and 5d partial-wave contributions. This is the first successful, ab initio calculation of a crystallographic (T=0) phase diagram of an f-electron system.

The complex ac penetration depth, surface impedance, and susceptibility are calculated for a superconducting half space and film containing a vortex lattice of arbitrary orientation with respect to the surface. Within linear response theory, full account is taken of the correct boundary conditions (image vortices), diffuse driving force and nonlocal elasticity of the vortex lattice, collective and individual elastic pinning, flux flow (viscous drag), and thermally activated depinning (creep).

The kinetics of ordering with a reduction of a crystal lattice point symmetry and related transformation-induced elastic strain is considered for the first time. Ordering in ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ is specifically discussed. A computer simulation predicts a temporal development of the microstructure through the tweed to the (110) microtwin structure driven by the elastic strain accommodation. The results obtained are quite general in the sense that predicted morphologies are typical for other systems with the point-symmetry reduction where the elastic strain accommodation plays an important role.