We present measurements of the magnetohydrodynamic ‘‘dynamo’’ due to correlated fluctuations of velocity and magnetic field in the SPHEX spheromak. We show that there are both single-mode and turbulent dynamo processes present, although the single-mode process is in this case an ‘‘antidynamo’’ opposing the externally applied electric field. The size of the turbulent dynamo at the magnetic axis is close to that required to drive the toroidal current there.

Self-consistent equilibria are obtained for high beta plasma where almost all of the ions are energetic with a gyroradius of the order of the plasma scale length. Magnetohydrodynamics would not apply to such a plasma. Recent experiments with tokamaks suggest that it would be insensitive to microinstabilities. Several methods are described for creating the plasma with intense neutralized ion beams.

Inelastic electron scattering using a two-beam channeling condition is used for the first time to create excitations having selectable even or odd symmetry relative to an atom column. The method is first established using plasmon and interband scattering in diamond. Next, for the carbon 1s absorption edge, scattering to modes having odd symmetry gives a strong exciton peak. Scattering to modes having even symmetry results in a depressed edge having no exciton peak in evidence.

We have used x-ray reflectivity and transmission electron microscopy to study the ${\mathrm{CaF}}_2$/Si(111) interface. The results are consistent with a reconstructed two-layer CaF interface which can be irreversibly transformed to a different structure simply by increasing the thickness of the ${\mathrm{CaF}}_2$ overlayer. We are able to reconcile previous measurements of the interface structure and gain insight into the rich variety of phenomena that may be observed at heteroepitaxial interfaces.

Optical reflectance and light scattering measurements are used to study bubble nucleation of various liquids and subsequent explosive vaporization at the surface of a thin chromium film heated by a 248-nm KrF excimer laser. Liquids studied include water, ethanol, methanol, isopropanol, and different mixtures of water and isopropanol. The reflectance and scattering signals show distinct transients when the excimer laser fluence exceeds a certain liquid-dependent threshold. The reflectance signals are analyzed to provide bubble growth kinetics and explosive vaporization thresholds of the liquids.

Temporal director fluctuations in nematic ordering were studied by computer simulation on the Lebwohl-Lasher model as well as by neutron-scattering experiments on the nematogen d-PAA. The time-series data have been analyzed by the rescaled-range method and in terms of the power spectrum in order to determine the Hurst exponent H. Theory and experiment are in good agreement. A value of H≃1 was found for the nematic phase, characterizing fractional Brownian motion, whereas H≃0.5, reflecting ordinary Brownian motion, applies in the isotropic phase. Field-induced crossover from fractional to ordinary Brownian motion was observed in the nematic phase.

Deuterium magnetic resonance of cylindrically confined liquid crystals reveal a structural transition driven by a homeotropic-to-planar anchoring transition in the nematic phase and an orientational wetting (quasicomplete-to-partial) transition in the isotropic phase as the molecular length of the surface coupling agent is decreased. A simple phenomenological description reveals a weak positive surface order parameter in the homeotropic case and a negative one in the planar case. The absence of a symmetry breaking transition in the planar case is attributed to weak interfacial coupling.

Free-standing films of a smectic liquid crystal possessing the bulk phase sequence smectic A, ferroelectric smectic C, antiferroelectric smectic ${\mathit{C}}_{\mathit{A}}$ are studied. Using ellipsometric measurements, we show that the bulk phases still exist in films consisting of only four, three, and even two smectic layers, i.e., the phase transition from the ferroelectric smectic-C phase to the antiferroelectric smectic-${\mathit{C}}_{\mathit{A}}$ phase in the three- and two-layer films is characterized by the inversion of the tilt and polarization direction in a single smectic layer.

We describe the first direct measurement of the Andreev reflection of a beam of quasiparticle excitations in the B phase of superfluid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ in the ballistic regime (T/${\mathit{T}}_{\mathit{c}}$≤0.2). The beam is generated by a blackbody radiator. The changing effective excitation gap which gives rise to the Andreev reflection is provided by a superflow gradient along the direction of the beam induced by a moving paddle. The component of the beam reflected by Andreev processes is observed via the retroreflective nature of the process which returns the reflected excitations to the blackbody and thereby increases its temperature over the value observed with no superflow.

We have grown fcc crystalline islands of ${\mathrm{C}}_{60}$ on a clean Si(111)7×7 surface. Scanning tunneling microscopy reveals that the islands are oriented primarily in two distinct directions independent of the island height and size. We show that this is a result of the pinning of ${\mathrm{C}}_{60}$ molecules at the corner holes associated with a disorder-to-order transition at the interface. Interlayer molecular interactions play a vital role in the process. The presence of two distinct island orientations is a manifestation of the formation of double domain solid ${\mathrm{C}}_{60}$ on the Si(111)7×7 surface.

Calculations are presented in the wetting properties of liquid hydrogen films on various substrates. The well depth D for the adsorption potential is even smaller for alkali metal substrates than for noble gas surfaces. A simple model calculation leads to the prediction that wetting transitions should then occur at a temperature ${\mathit{T}}_{\mathit{w}}$ about 20 K. Quartz microbalance data obtained for ${\mathrm{H}}_2$ on Rb are consistent with this result. Specifically, ${\mathit{T}}_{\mathit{w}}$ is found to be 17.89±0.04 K. The wetting phase diagram is found to be in good agreement with thermodynamic expectations.

We study the structure of nested multilayered systems composed of two infinite carbon tubules via density functional theory. The calculated intertubule distance is 3.39 Å, comparable to the recent measurement of 3.4 Å. In such a system, the energy gained by adding a new cylindrical layer around a central one is estimted to be 80% of the graphite dilayer binding energy. Low translation and rotation barriers suggest that carbon tubules of limited length could easily slide into or out of each other and rotate along the cylindrical axis. Comparison with graphite an hyperfullerenes is proposed.

We have measured at low temperatures the current through a submicrometer superconducting island connected to two normal metal leads by ultrasmall tunnel junctions. As the bias voltage is lowered well below twice the superconducting energy gap, the current changes from being e periodic with gate charge to 2e periodic. This behavior is clear evidence that there is a difference in the total energy between the ground states of an even and odd number of electrons on the island. The 2e-periodic current peaks are the first observation of the Coulomb blockade of Andreev reflection.

We report on a collective low temperature metal-insulator transition which develops in a dilute 2D electron system in Si at zero magnetic field, below a critical carrier density ${\mathit{n}}_{\mathit{s}\mathit{c}}$≊${10}^{11}$ ${\mathrm{cm}}^{\mathrm{-}2}$. In the insulator phase, the dc conduction is thermally activated and exhibits a sharp threshold as a function of electric field. The collective insulator state at zero field shows many of the features attributed to the pinned Wigner solid. We have also observed a trend from a collective to a single-particle insulator state with decreasing electron density and/or increasing disorder.

The fluctuations of vortices in Josephson-coupled layered superconductors are shown to have a profound effect on values of the temperature-dependent penetration depth, Ginzburg-Landau parameter, and upper critical field extracted from reversible magnetization data below the critical temperature.

The temperature-concentration phase diagram of doped bismuthate superconductors is described using a coarse grained anisotropic Heisenberg model. In contrast to previous treatments, we find a robust region of coexistence between the charge density wave (CDW) and the superconducting phases. Random fields break the CDW phase into metastable domains, which may explain various recent experiments. A partial Meissner effect without bulk superconductivity is predicted at low doping concentrations and at low temperatures.

Neutron diffraction measurements confirm the presence of long-range antiferromagnetic order in superlattices of cobalt oxide and nickel oxide. A single transition temperature between the values for bulk CoO and NiO is evident for two samples with 36 Å periods as previously reported, but the separate Ni and Co order parameters in a 72 Å period superlattice approximate bulk behavior. In the latter sample the magnetic order remains coherent across ostensibly paramagnetic CoO interlayers above 400 K. Mean field analysis accounts for the layer thickness dependence of the ordering temperature.

We report low field proton NMR measurements in the spin density wave (SDW) state of (TMTSF${)}_2$${\mathrm{PF}}_6$ that show a narrowing of the linewidth when the SDW is depinned by an electric field. The NMR absorption amplitude affirms that sample heating is negligible. A shortening of the spin-phase memory time corresponding to the line narrowing is also observed. Low field measurements of the spin-lattice relaxation rate show a fluctuation enhancement just below the spin density wave transition and a rapid drop below 3 K that lack a quantitative understanding.

Monte Carlo simulation is used to study the gas flow of particles laser desorbed from a binary target into a vacuum. Pulsed desorption off of a finite area is modeled by using a three-dimensional simulation algorithm. Our results show the formation of a desorption jet. For a thermal desorption mechanism, the light species is desorbed with a higher velocity than the heavy species, but accelerates the latter and focuses it toward the jet axis. These phenomena influence the composition of the desorption jet, and the angle and energy distribution of the desorbed particles.

We study the kinetics of ballistic annihilation, A+A→0, with continuous initial particle velocity distributions. The concentration and the rms velocity are found to decay as c∼${\mathit{t}}^{\mathrm{-}\mathrm{\alpha }}$ and ${\mathit{v}}_{\mathrm{rms}}$∼${\mathit{t}}^{\mathrm{-}\mathrm{\beta }}$, respectively, with the relation α+β=1 holding in any spatial dimension. A ‘‘mean-field’’ Boltzmann equation for the evolution of the velocity distribution predicts that α and β depend strongly on the initial condition, a behavior which is confirmed numerically in one and two dimensions.