The electronic structure of ${\mathrm{CeRh}}_3$ was studied by photoemission and bremsstrahlung isochromate spectroscopy (BIS). An analysis of the spectra, taken at different temperatures, on the basis of the Anderson single-impurity model leads to considerable inconsistencies that mark the limits of applicability of the model. On the other hand, the BIS spectrum of ${\mathrm{CeRh}}_3$ can be well described by the results of a local-density-approximation band-structure calculation. These findings confirm a bandlike character of the 4f states in strongly hybridized Ce systems.

We have studied the photoemission spectra of perovskite-type ${\mathrm{Ti}}^{3+}$ and ${\mathrm{V}}^{4+}$ oxides, which have formally the ${\mathit{d}}^1$ configuration ranging from a Mott insulator to a paramagnetic metal. The results indicate that as the Mott-Hubbard gap closes, spectral weight is transferred from the upper and lower Hubbard bands to the region near the Fermi level with decreasing U/W (U,d-d Coulomb repulsion energy; W, one-electron d-band width), i.e., from the incoherent to the coherent part of the single-particle spectral function.

A family of resistivity curves, with different carrier concentrations, is obtained in a single sample of the dilute magnetic persistent photoconductor ${\mathrm{Cd}}_{0.91}$${\mathrm{Mn}}_{0.09}$Te:In. These curves exhibit a crossover from an exp(${\mathit{T}}_0$/T${)}^{1/2}$ form for variable-range hopping with interactions to an exp(${\mathit{E}}_{\mathit{H}}$/T) form, upon reducing temperature. All data scale onto a single curve. The energy ${\mathit{E}}_{\mathit{H}}$ is associated with a hard gap in the density of states which is magnetic in origin. The localization length is found to have the same critical behavior as the dielectric constant, on approaching the insulator-metal transition.

Activated conduction, ρ=${\mathrm{\rho }}_0$exp[(${\mathrm{T}}_0^{\mathrm{″}}$/T${)}^{\mathrm{x}}$], with x equal to or close eto 1 is observed for insulating Si:B at low temperatures, indicating the presence of a “hard” gap in the density of states. A magnetic field suppresses this unexpectedly strong temperature dependence, changing it to the variable-range-hopping form ρ(H)=${\mathrm{\rho }}_0$(H)exp{[${\mathrm{T}}_0^{\prime }$(H)/T${]}^{1/2}$}expected for a “soft” parabolic Coulomb gap. This suggests that the density of states is determined by electron correlations due to spin as well as charge. © 1992 The American Physical Society.

While the study of waves in disordered media, including effects such as Anderson localization, and the study of nonlinear systems, including effects such as soliton propagation, have each received considerable attention, the combined field, nonlinear wave propagation in disordered media, is relatively new. A fundamental question is: Does nonlinearity weaken Anderson localization? In this paper we report the results of an experiment, which can provide conditions filling a gap in the current theory, showing that states remain Anderson localized in the presence of nonlinearity.

We show that, in the absence of interlayer hopping, the ν=1/m quantum Hall states in double-layer systems contain a neutral gapless mode with linear dispersion, describing the relative fluctuations of the electron densities in the two layers. At finite temperature the system experiences a Kosterlitz-Thouless transition. In the presence of interlayer hopping an energy gap proportional to the square root of the hopping amplitude will be opened. In field theory this corresponds to a U(1) gauge field acquiring a mass due to the monopole-antimonopole plasma in the (2+1)-dimensional spacetime.

The annular Josephson junction allows for the study of undisturbed soliton (fluxon) motion in the absence of collisions. With new experimental methods and design we have realized for the first time a fully controllable way of introducing individual fluxons or antifluxons into such a system. This has allowed us to study multisoliton behavior and to make a comparison with existing soliton-chain perturbation theory. An unforeseen crossover in the dynamical behavior at high velocities is tentatively interpreted in terms of soliton bunching.

We study the normal-to-superconductor transition, within the two-dimensional gauge glass model, as a model of strongly disordered thin-film superconductors. The voltage-current characteristics are computed using dynamical simulation. At high temperature, we find the expected result that E∼${\mathit{J}}^{\mathit{a}\left(\mathit{T}\right)}$, with a(T)>1 for large current. It crosses over a linear resistivity at small current. Surprisingly, our results reveal a low-temperature regime in which E∼exp[-(${\mathit{J}}_{\mathit{T}}$/J${)}^{\mathrm{\mu }}$] with μ≃0.5. A possible finite-temperature glass transition is discussed.

Absorption spectra from 0.94–5.58 eV are obtained for gas-phase neutral silicon clusters ${\mathrm{Si}}_{18}$–${\mathrm{Si}}_{41}$ using resonant one- and two-color photodissociation spectroscopy. The spectra of all clusters are essentially identical. Above 3.0 eV, they exhibit six sharp absorption peaks with cross sections of 1–2 A${\mathrm{̊}}^2$. Multiple photon absorption peaks dominate the spectrum below 3.0 eV. Comparisons of the silicon cluster spectra to those of various forms of silicon show that they have much in common with the spectrum of bulk diamond-lattice crystalline silicon.

Grafted polymer layers are well known as stabilizing agents in colloidal dispersions. Here we show how these polymer ‘‘brushes’’ may also deeply modify wetting phenomena by favoring the formation of stable wetting layers of microscopic size. We discuss in particular the influence of a solvated polymer layer on the wetting properties of the substrate by a second minority solvent. In the case where the brush prefers the second solvent, this solvent may be drawn to the interface even if it would not ordinarily wet the substrate. On the contrary, a solvent that ordinarily forms a thick wetting layer may be partially inhibited from doing so (forming a thin trapped layer) if it is a worse solvent for the brush.

We note that the neutron spin must be treated as an intrinsically quantum variable when determining electromagnetically induced phase shifts in neutron interferometry by computing the otherwise-classical action over the classical orbit. We show that a putative acceleration of the neutron (γ/mc)E×(μ×B) recently suggested by Anandan, is essentially unobservable in such measurements over segments of the orbit where the electric and magnetic fields are constant (or vary slowly), within standard electroweak theory.

A forest-fire model is introduced which contains a lightning probability f. This leads to a self-organized critical state in the limit f→0 provided that the time scales of tree growth and burning down of forest clusters are separated. We derive scaling laws and calculate all critical exponents. The values of the critical exponents are confirmed by computer simulations. For a two-dimensional system, we show that the forest density in the critical state assumes its minimum possible value, i.e., that energy dissipation is maximum.

We report an ab initio calculation of the photoionization spectrum of He in the energy regime hitherto unexplored theoretically, namely, energies near the ${\mathrm{He}}^{+}$(N) states up to N=7. The recently reported experimental photoionization spectrum of He is fully reproduced by using our previously reported hyperspherical close-coupling method. We find clear evidence of an excited angular correction mode that was presumably overlooked in the analysis of the experimental data. We also present a calculated spectrum below ${\mathrm{He}}^{+}$ (N=7) as a reference for future experiments.

We show that light can be used as a lens to focus a collimated neutral atomic beam to submicron dimensions during deposition onto a substrate. We have used an optical standing wave at 589 nm as an array of cylindrical lenses to focus a perpendicular sodium beam into a grating on a substrate, with a periodicity of 294.3±0.3 nm. This result is the first direct evidence of submicron focusing of atoms by light, and represents a fundamentally new scheme for submicron lithography.

The classical-quantum correspondence is studied for the ‘‘wedge billard,’’ a system known to exhibit hard chaos. The Gutzwiller trace formula is recast as a damped sine or cosine transform, yielding peaks and zero crossings at the values of the actions of the periodic orbits. The lowest 190 energy eigenvalues of the quantum system are shown to contain a great deal of information about the shortest periodic orbits of the classical system.

A direct numerical study of a model of superflow, the nonlinear Schrödinger equation, and simple analytical arguments shows a very striking phenomenon: The flow around a disk creates a drag force beyond a well-defined threshold velocity, linked to the emission of vortices from the perimeter of the disk.

The Navier-Stokes equations are utilized to derive upper bounds on the turbulent energy dissipation rate for an incompressible Newtonian fluid confined between parallel comoving plates. These estimates provide a rigorous foundation for one of the basic scaling ideas of turbulence theory, namely, the independence of the dissipation rate and the viscosity at high Reynolds number. The bounds are compared to experiments on turbulence in the Couette-Taylor system.

Recent experimental studies have revealed for the first time some basic features of pulsed, relativistic (300–600 kV) backward-wave oscillators such as starting current, axial mode locking, and multifrequency operation. Above a critical beam current a gradual degradation of the spectrum purity of the electromagnetic radiation is observed, culminating in the onset of stochastic oscillations.

We analyze the effects of m≠0 tip states in scanning tunneling microscopy (STM). If near the Fermi level, an m≠0 tip state dominates, images with large but inverted atomic corrugation are expected. This provides an explanation of the STM images with inverted corrugations, and the sudden reversal of the STM corrugation from inverted to noninverted. An analysis of the effects of various combinations of m≠0 and m=0, d-type tip states is presented. We show that in most cases, a stable and large corrugation enhancement, either positive or negative, is expected, with predicted values in agreement with experimental observations.

The low-pressure phases in solid ${\mathrm{C}}_{70}$ have been explored using constant-pressure molecular dynamics and an empirical intermolecular potential extrapolated from one that gives an excellent account of the properties of ${\mathrm{C}}_{60}$. On cooling the high-temperature rotator phase, we find a transition to a partially ordered phase with trigonal symmetry and then a second transition to a monoclinic structure.