The first full partial-structure-factor analysis of molten ${\mathrm{GeSe}}_2$ is made using the method of isotopic substitution in neutron diffraction. It is shown that the melt comprises roughly equal numbers of edge- and corner-sharing tetrahedra which give rise to a highly connected or network liquid. Concentration fluctuations extend over distances characteristic of the intermediate-range order, contrary to the results obtained from recently developed effective potentials for covalently bonded glass-forming melts. The problem as to whether or not ${\mathrm{GeSe}}_2$ forms a chemically ordered continuous random network is examined.

We propose a new method to compute Lyapunov exponents from limited experimental data. The method is tested on a variety of known model systems, and it is found that the algorithm can be used to obtain a reasonable Lyapunov-exponent spectrum from only 5000 data points with a precision of ${10}^{\mathrm{-}1}$ or ${10}^{\mathrm{-}2}$ in three- or four-dimensional phase space, or 10 000 data points in five-dimensional phase space. We also apply our algorithm to the daily-averaged data of surface temperature observed at two locations in the United States to quantitatively evaluate atmospheric predictability.

We construct the ultraviolet limit of the massive Gross-Neveu model in three dimensions and with a large number of flavor components N.

Some peculiarities of the energy diagram of Rydberg atoms in parallel electric and magnetic fields are interpreted by making use of a supersymmetric approach to these systems. The expression of the supercharge operator is given as a function of the generators of the SO(4) symmetry group. Some applications to analytical determinations of the spectrum and eigenfunctions are discussed and agree with previous experimental observations.

We present a quantitative theory of ionization and above-threshold ionization of He by short (subpicosecond), intense laser pulses. The calculations include the effect of bound states shifting through resonance during the pulse as well as the switching of the process from six to seven photons due to the shift of the ionization threshold. The results are in good agreement with and add further insight into recent experimental data.

Probe-wave amplification and absorption spectra are reported for cesium atoms cooled and confined in a Zeeman-shift spontaneous-force optical trap. Novel spectral features are observed with narrow frequency widths and with single-pass gain of 20% in some cases. Negative radiation pressure is demonstrated as the mechanical consequence of optical gain and is investigated as a possible means for optical implosion of a trapped sample.

In this paper we report both experimental and theoretical results on a Rayleigh-Bénard convection experiment with a static spatially periodic forcing. For reduced Rayleigh number of order 100, the system undergoes a secondary Hopf bifurcation involving novel and surprising spatially inhomogeneous temporally periodic states. We give a description of these various inhomogeneous states, and develop a simple phenomenological model based on symmetry considerations which seems to capture all the essential qualitative features.

We reconsider the conceptual foundations of the renormalization-group (RG) formalism. We show that the RG map, defined on a suitable space of interactions, is always single valued and Lipschitz continuous on its domain of definition. This rules out a recently proposed scenario for the RG description of first-order phase transitions. On the other hand, we prove in several cases that near a first-order phase transition the renormalized measure is not a Gibbs measure for any reasonable interaction. It follows that the conventional RG description of first-order transitions is not universally valid.

The formation of disordered regions is observed on the Ga(111)c2×8 surface, at temperatures in the range 150–350 °C. The disorder occurs by the diffusion of surface adatoms in the 〈011¯〉 directions. The disordered regions form at domain boundaries, and grow continuously with temperature until the entire surface becomes disordered at 300 °C. We argue that this phase transition is an example of premelting in two dimensions, i.e., ‘‘edge melting.’’

Neutron-inelastic-scattering measurements have been made on a sample of highly purified solid ${\mathrm{C}}_{60}$. New features in the spectrum of intramolecular modes not obtainable by optical spectroscopy have been identified. Available theoretical calculations show trends in accord with the experimental results but disagree in important details, and improved calculations are desirable.

We prove that for any system, and within the framework of any reasonable local approximation to the Hohenberg-Kohn-Sham exchange-correlation energy functional, the Harris energy functional posseses either a saddle point or a local minimum at a self-consistent ground-state charge density. This invalidates the common suggestion that this functional has a local maximum at this charge density. Some numerical results in support of our arguments are presented.

Electron-stimulated desorption of ${\mathrm{Ar}}^{+}$, ${\mathrm{Ar}}_2^{+}$, ${\mathrm{Ar}}^{2+}$, and ${\mathrm{Kr}}^{+}$ ions from solid Ar and Kr was studied for the electron energy range from 10 to 120 eV. For ${\mathrm{Ar}}^{+}$ and ${\mathrm{Ar}}_2^{+}$ excitation resonances with onsets at 24.2, 25.4, 34, and 50 eV have been found. The two lowest thresholds cannot be explained by excitations of single Ar atoms. They are interpreted as pairs of interacting surface and bulk excitions, respectively, on neighboring atoms. The bulk species can diffuse over more than 100 layers. Novel conclusions about the desorption mechanism can be derived.

The most outstanding feature observed for dopants in hydrogenated amorphous silicon—a shift in the Fermi level accompanied by an increase in the charged-defect density—has previously been postulated to stem from the formation of substitutional-dopant–dangling-bond complexes. Using first-principles self-consistent pseudopotential calculations in conjunction with a supercell model for the amorphous network and the ability of network relaxation from the first-principles results, we have studied the electronic and structural properties of substitutional fourfold-coordinated phosphorus and boron at the second-neighbor position to a dangling-bond defect. We demonstrate that such impurity-defect complexes can account for the general features observed experimentally.

Bloch equation conductivity perpendicular to the layers of a superlattice (period d) is evaluated using an extension of the balance-equation approach [X. L. Lei and C. S. Ting, Phys. Rev. B 32, 1112 (1985)] to narrow-band transport. The perpendicular peak drift velocity ${\mathit{v}}_{\mathit{p}}$ and the critical field ${\mathit{E}}_{\mathit{c}}$, at which the drift velocity peaks, are analyzed as functions of miniband width. Our theoretical prediction that ${\mathit{E}}_{\mathit{c}}$d increases with decreasing miniband width agrees well with the data of Sibille et al. [Phys. Rev. Lett. 64, 52 (1990)], even for the samples of narrowest miniband width in their experiment.

We report both synchrotron-x-ray and neutron-diffraction studies of the magnetic ordering in a crystal of ${\mathrm{Mn}}_{0.75}$${\mathrm{Zn}}_{0.25}$${\mathrm{F}}_2$ in a magnetic field. The neutron experiments reproduce previous results showing the establishment of a short-range domain state on cooling in a field. Remarkably, the magnetic x-ray scattering shows that within a few microns of the surface there is a second-order transition to true long-range order on field cooling. Implications of these results are discussed.

The 2D quantum system of electrons at a GaAs/GaAlAs heterojunction in high magnetic field at low temperature is shown to exhibit conduction typical of pinned charge-density waves. Crossover from Ohmic conduction occurs on the same boundary at which radio-frequency resonances signal the onset of transverse elasticity. A further small non-Ohmic region is isolated from the main area by a v=1/5 quantum-Hall-effect phase. The relationship found between the threshold conduction field and the resonance frequency is well accounted for by a model of pinned electron crystallites.

We have measured specific heat, magnetic susceptibility, and resistivity on the cerium-intermetallic compound ${\mathrm{CePt}}_2$${\mathrm{Sn}}_2$. The heat capacity shows a strong increase below a few kelvin, typical of a large many-body enhancement of the density of states or equivalently of the effective electronic mass. Just before the material orders antiferromagnetically at ${\mathit{T}}_{\mathit{N}}$=0.88 K, the linear temperature coefficient of the specific heat γ is approximately 3.5 J/mol ${\mathrm{K}}^2$, making this material one of the heaviest electron systems known. The low Néel temperature and huge specific heat imply similarly low-energy scales for competing RKKY and Kondo-like interactions.

To explain the field-independent phase diagrams observed in ${\mathrm{UPt}}_3$ a scenario based on a superconducting (SC) class belonging to the one-dimensional representation (1D-rep) with odd parity is proposed. The antiferromagnetic (AF) order lifts the spin-space degeneracy of the pairing function to split ${\mathit{T}}_{\mathit{c}}$. A nontrivial coupling of the two orderings, SC and AF, is derived and a Ginzburg-Landau theory is developed to examine the successive phase transitions. It is demonstrated that the present 1D-rep scenario is more consistent with various experiments on ${\mathrm{UPt}}_3$ than the previous 2D-rep scenario.

We study the phenomenon of quantum creep in bulk superconductors within the framework of weak-collective-pinning theory. Single-vortex pinning at moderate magnetic fields as well as creep of vortex bundles at high fields are discussed for the case of current densities near critical. In the limit of strong dissipation and for moderate fields the basic parameter determining the tunneling rate is the ratio ${\mathrm{\rho }}_{\mathit{n}}$/ξ (${\mathrm{\rho }}_{\mathit{n}}$=normal-state resistivity, ξ=coherent length), with strong tunneling realized for ${\mathrm{\rho }}_{\mathit{h}}$/ξ≳1 kΩ.

We have carried out a Monte Carlo study of anisotropic 3D uniformly frustrated XY models, as a model for the type-II high-${\mathit{T}}_{\mathit{c}}$ superconductors. Vortex-line-lattice melting, vortex-line cutting, and entanglement have been studied in relation to the superconducting phase transition.