A strong electromagnetic impulse (Δt≃0.2 μs) with central frequency in the whistler-wave regime is applied to a large laboratory plasma dominated by Coulomb collisions (${\nu }_{\mathit{e}\mathit{i}}$≃ω≪${\mathrm{\omega }}_{\mathit{c}\mathit{e}}$≪${\mathrm{\omega }}_{\mathit{p}\mathit{e}}$). Local electron heating at the antenna and transport along ${\mathit{B}}_0$ create a channel of high conductivity along which the whistler pulse penetrates with little damping. Because of its rapid temporal evolution, this new form of modulational instability does not involve ducting by density gradients which require ion time scales to develop.

Path-integral Monte Carlo calculations have been used to study small clusters of ${\mathrm{H}}_2$ molecules at low temperatures. Below about 2 K, clusters of 13 and 18 molecules exhibit manifestations of superfluid behavior. However, exchange permutation of molecules is greatly suppressed in a cluster of 33 molecules, even at 1 K.

Asymptotic kinetics for random sequential addition of unoriented nonspherical objects is characterized by an algebraic time dependence. By studying 1D systems, we show that the exponents describing the random sequential addition of objects with and without proper area are not simply related: Whereas the asymptotic behavior for rectangles follows the expected ${\mathit{t}}^{\mathrm{-}1/2}$ law, the long-time kinetics for infinitely thin line segments is governed by a nontrivial, irrational, exponent (${\mathit{t}}^{\mathrm{\surd }2\mathrm{-}1}$) which results from a competition between creation and destruction of targets in the asymptotic regime.

Phase diagrams at constant temperature and pressure for multicomponent mixtures contain a large amount of information on the composition fluctuations in coexisting phases. For three coexisting phases all the composition fluctuations in the three phases can be determined from the phase diagram up to a scale factor. New geometric constraints on phase diagrams are also obtained.

Steady states of driven lattice gases with open boundaries are investigated. Particles are fed into the system at one edge, travel under the action of an external field, and leave the system at the opposite edge. Two types of phase transitions involving nonanalytic changes in the density profiles and the particle number fluctuation spectra are encountered upon varying the feeding rate and the particle interactions, and associated diverging length scales are identified. The principle governing the transitions is the tendency of the system to maximize the transported current.

We characterize the molecular reorientational dynamics in two phases of solid ${\mathrm{C}}_{60}$ with ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ NMR measurements. A change in the nature of the dynamics, indicated by a change in kinetic parameters extracted from spin-lattice relaxation data, occurs at the phase transition at 260 K. Above the transition, the molecules appear to execute continuous rotational diffusion; below the transition, they appear to jump between symmetry-equivalent orientations. This interpretation is consistent with the x-ray-diffraction results of Heiney et al. as well as our NMR relaxation and spectral data.

We have investigated the thermal roughening of the Ag(110) surface using synchrotron x-ray diffraction. The data taken out of plane (nonzero perpendicular momentum transfer) show a clear two-component line shape below the roughening transition at ${\mathit{T}}_{\mathit{R}}$=790 K. We interpret this as coexistence of flat (110)-oriented regions and slightly inclined, rough regions on the surface below ${\mathit{T}}_{\mathit{R}}$. The temperature dependence of the angle between the components and their relative amplitudes implies that roughening takes place by the gradual replacement of the (110) faceted regions by the rough phase.

A synergistic high-resolution electron microscopy (HREM) and theoretical analysis of the structure of a grain boundary in copper containing bismuth is presented. The calculation of the structure of the boundary were carried out using N-body empirical potentials constructed using results of ab initio full-potential linear-muffin-tin-orbital calculations. Excellent agreement between the calculated and observed structures is shown by comparing a through-focal series of observed and calculated images. It is shown for the first time that HREM combined with computer modeling employing realistic empirical potentials can decipher with a great accuracy the structure of boundaries containing multiple atomic species.

${\mathrm{N}}_2$ physisorbed on top of a Xe spacer layer on Ag(111) and Pd(111) has been studied by angle-resolved and polarization-dependent UV photoemission. The ${\mathrm{N}}_2$ 1${\mathrm{\pi }}_{\mathit{u}}$ valence level exhibits a vibrational fine structure due to two multiplets corresponding to the ionic (${\mathrm{N}}_2^{+}$) and neutral (${\mathrm{N}}_2$) states. The neutral-state multiplet is explained through hopping of the photohole during photoemission. We show that its intensity is stronger for emission from the in-plane component of 1${\mathrm{\pi }}_{\mathit{u}}$, than for the perpendicular one. This is due to a larger lateral overlap in the former case, as concluded by the observed band formation.

We present a study of energy relaxation in two representative charge-density-wave compounds: ${\mathrm{TaS}}_3$ and ${\mathrm{NbSe}}_3$ below T=0.5 K. The evolution of the relaxation indicates a crossover between a nonequilibrium state and the thermodynamical equilibrium state when the system has been allowed to age. In the equilibrium state the relaxation is thermally activated with an activation energy of ∼1 K. We interpret these results as long-time dynamics in the network of charge-density-wave dislocations with a critical temperature close to 0 K.

Fully angular-resolved kinetic-energy distributions of alkali and halogen atoms emitted due to electron-stimulated desorption have been measured for (100) and (110) alkali-halide surfaces. An unexpected strong directional emission of nonthermal halogen atoms along the 〈100〉 axis of the investigated crystals has been found which is in contradiction to the predictions of the previously proposed ‘‘Pooley model.’’ We propose a new model involving diffusion of hot holes to the surface, and sudden localization of the excited hole at the surface of the crystal.

We have studied the uniaxial magnetic anisotropy of Co/Pd superlattices grown under identical conditions by molecular-beam epitaxy along the three crystal axes: [001], [110], and [111]. Our measurements unambiguously demonstrate that the large systematic variations of the anisotropy energy with crystal orientation result solely from differences in the volume contribution to the anisotropy. We find the perpendicular interface anisotropy to be independent of the epitaxial orientation (0.63±0.05 erg/${\mathrm{cm}}^2$), and hence to be an intrinsic property of the Co/Pd interface.

We present direct observations on the alternating roles of a defect level in trapping and recombination processes of nonequilibrium charge carriers in silicon, by combined photoluminescence and magnetic-resonance techniques, where the microscopic signature of the defect can be monitored unambiguously. Intercenter charge-transfer processes are shown to be efficient and important in the trapping and recombination processes of the carriers, beyond the framework of the established Shockley-Read-Hall model.

Numerical results for the density of states to remove or add electrons to a finite Hubbard cluster are presented for both positive and negative on-site interactions. The behavior of the filling versus the chemical potential is discussed. At half filling there is a gap in the density of states. When the repulsive-U Hubbard model is doped spectral weight is transferred into the gap, and the chemical potential is found to move across the gap as one goes from electron to hole doping. We discuss the relationship of these results to experiment. For the negative-U Hubbard model, the chemical potential shifts continuously and lies in the middle of the superconducting gap.

We identify a new global topological self-interaction of anyons represented by a self-induced Aharonov-Bohm phase measuring the oriented self-interaction number of a closed particle trajectory in the plane.

Using a variational argument, we show that a two-dimensional (2D) crystal becomes defective in the presence of a random potential. The threshold pinning force and flow properties of a plastically deformed crystal are studied using a perturbation theory valid for weak pinning potential and strong driving force. In the case of a 2D flux-line lattice, it is shown that dislocations introduce extra dissipation in the system, thus increasing the total pinning force, and resulting in nonlinear I-V characteristics.

We have measured the static and dynamic spin fluctuations in a crystal of ${\mathrm{La}}_{2-x}{\mathrm{Sr}}_x\mathrm{Cu}{\mathrm{O}}_{4+y}$ in the spin-glass doping regime. The static spin correlations are well described by a simple model in which the inverse correlation length $\kappa (x, T)=\kappa (x, 0)+\kappa (0, T)$. The dynamic spin fluctuations exhibit a simple scaling behavior in $\frac{\omega }{T}$ for temperatures $10 \mathrm{K}\le T\le 500 \mathrm{K}$ for the measured energies $4.5\le \omega \le 12$ meV.

We report here on the first successful construction and operation of a Michelson interferometer for x rays. Its decisive strategem is the mixing of Laue- and Bragg-case beams diffracted by only one set of Bragg planes throughout the instrument. We illustrate the operability of the new interferometer by measuring the copper K${\mathrm{\alpha }}_1$K${\mathrm{\alpha }}_2$ doublet in Fourier-spectrometric mode. A total of more than 750 orders were scanned.

We consider random sequential adsorption on a lattice. We use analytical results on the Bethe lattice and cactus as references to develop systematic perturbationlike expansions which are very rapidly convergent. The latter produces the jamming density of a square lattice with an accuracy within ${10}^{\mathrm{-}5}$. This expansion is based on both physical and mathematical considerations and is not restricted to random sequential adsorption.

The effective conformal field theory governing the long-distance dynamics of string solitions in four dimensions, such as the Nielsen-Olesen vortex or QCD strings, is described. It is an interacting Poincaré-invariant conformal field theory with four bosons and c=26. The compatibility of these naively contradictory features is explicitly demonstrated through second order in a perturbation expansion about the long-string vacuum.