The four-wave-mixing interactions produced by pumping at two well-separated frequencies can couple four different radiation modes to generate a new kind of squeezed state of light. A dual-frequency homodyne detection scheme is described and is used to observe this type of nonclassical correlation. Initial experimental results in an optical fiber show a noise level 20% below the vacuum noise level for the output of the dual-frequency detector, even though the noise at each individual detector remains above the vacuum level.

We report on the dependence of enhanced backscattering of light in a random medium on sample thickness, mean free path, and size of scattering centers. Introduction of a new difference technique allows for independent observation of contributions from long and short light paths in a suspension of polystyrene spheres. A new anisotropy effect, which has been found to be most prominent for the smallest particles studied, could be classified as a lower-order multiple-scattering phenomenon.

It is proposed that a molten alloy may contain a 104-atom cluster with icosahedral symmetry and largely icosahedral packing. The cluster may be described as involving twenty interpenetrating Friauf polyhedra. On rapid freezing these clusters form cubic crystals related to the β-W structure. The structure is compatible with x-ray and neutron powder diffraction patterns, the single-crystal precession x-ray patterns of ${\mathrm{CuLi}}_3$${\mathrm{Al}}_6$, the electron diffraction photographs, and the high-resolution electron micrographs.

We present the first real-space images, obtained by scanning tunneling microscopy, which show the ordered atomic structures of the Ag/Si(111) surface for several submonolayer coverages. The (√3 × √3 )R30° surface is shown to be of the honeycomb structure, and the room-temperature coverage is determined to be theta=(2/3). The (1×3) overlayer consists predominantly of rows of Ag atoms separated by two empty rows. At low coverage the surface shows long-range 7×7 order, but patches occur within the 7×7 cells whree Si adatoms are absent.

Scanning tunneling microscopy and current-imaging spectroscopy are used to determine the local structural arrangement and stoichiometry of √3 × √3 Ag on Si(111). The nature of the local electronic structure and the spatial character of the wave functions observed on an atomic scale lead to a structure consisting of Ag trimers embedded in a Si honeycomb formed by threefold-coordinated Si atoms.

We report experimental results for the thermal boundary resistance ${\mathrm{R}}_{\mathrm{K}}$ between gold and superfluid ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ which were obtaiend by the use of thermometry with 3-nK resolution. The data imply that ${\mathrm{R}}_{\mathrm{K}}$ is singular at the superfluid transition temperature ${\mathrm{T}}_{\lambda }$. Comparison with theory suggests that the singularity results from a hydrodynamic effect proposed by Landau, and that it is associated with the vanishing of the superfluid and normal-fluid currents at the boundaries.

The static nuclear magnetization of bcc solid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ has been measured for molar volumes ranging from 23.91 down to 21.20 ${\mathrm{cm}}^3$/mol, at temperatures between 10 mK and 70 μK. ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ order antiferromagnetically at all the molar volumes studied. The precise scaling of the magnetization with its maximum value $M_{\max }$ and the ordering temperature $T_{\mathrm{N}}$ is found to fail, unlike the case of a previous experiment for a much narrower range of molar volumes. The values of the Weiss temperature CTHETA are compared with those obtained by other workers.

Specific-heat measurements on amorphous ${\mathrm{Fe}}_{\mathrm{x}}$${\mathrm{Zr}}_{100\mathrm{-}\mathrm{x}}$ (x=90 and 92) by a thermal relaxation method reveal a temperature decay of the form T(t)=${\mathrm{T}}_0$+ΔT exp[-(t/τ${)}^{\mathrm{\beta }}$] below 20 K, where the alloys are asperomagnetically ordered. β≃0.5 when ${\mathrm{T}}_0$→0. The stretched exponential is a manifestation of nonergodic behavior, because of the inability of the spin system to explore the available random magnetic configurations on the 100-ms times scale of the experiment.

A two-dimensional model is proposed to describe systems with phase transitions which take place in terms of crystalline as well as internal degrees of freedom. Computer simulation of the model shows that the interplay between the two sets of degrees of freedom permits observation of grain-boundary formation and interfacial melting, a nonequilibrium process by which the system melts at the boundaries of a polycrystalline domain structure. Lipid membranes are candidates for systems with pronounced interfacial melting behavior.

We show that, in contrast to normal polymers, a backbone nematic polymer, with dipoles along the chain axis, yields a dielectric susceptibility increased by a factor of the order of the degree of polymerization. We find (i) a purely exponential variation of susceptibility with temperature, partly reflecting the activiation of hairpin defects of chain conformations and (ii) nonlocality in the response, unlike isotropic polymers. The unusual form of these results suggests (macroscopic) dielectric experiments for finally observing hairpins and studying zero-field chain statistics.

We define the concept of multifractality for linear growth models. This is done on the ensemble of all trajectories and it allows us to partition this set into equivalence classes characterized by singularity strengths α and growth rates z(α). To extract information on the embedding properties of these subsets in the physical lattice we define a mean-square displacement exponent ν(α). The formalism is illustrated for the indefinitely growing self-avoiding walk on the square lattice with a twenty-step exact enumeration. For each of the quantities z(α) and ν(α) we find a continuous spectrum of values.

Ion shadowing and blocking measurements indicate that the thermal expansion coefficient of a Pb crystal is substantially enhanced at its (110) surface. This is evidenced by a decrease in surface contraction with temperature. The first atomic layer is shifted with respect to its truncated-bulk location by -15.4±2.5% of a bulk spacing at 29 K, but by only -3±5% at 485 K.

An apparent superconducting transition with an onset temperature above 40 K has been detected under pressures in the La-Ba-Cu-O compound system synthesized directly from a solid-state reaction of ${\mathrm{La}}_2$${\mathrm{O}}_3$, CuO, and ${\mathrm{BaCO}}_3$ followed by a decomposition of the mixture in a reduced atmosphere. The experiment is described and the results of effects of magnetic field and pressure are discussed.

We report the results of resistivity and magnetic susceptibility measurements in ${\mathrm{La}}_{2\mathrm{-}\mathrm{x}}$${\mathrm{Sr}}_{\mathrm{x}}$${\mathrm{CuO}}_4$ for x≤0.3. The x=0.2 sample shows a superconducting transition at 36.2 K with a width of 1.4 K. The associated dc diamagnetic susceptibility (Meissner effect) is a large fraction (60%–70%) of the ideal value. We estimate the density of states from critical-field and resistivity data and suggest, by analogy to ${\mathrm{BaPb}}_{1\mathrm{-}\mathrm{x}}$${\mathrm{Bi}}_{\mathrm{x}}$${\mathrm{O}}_3$, that conventional phonon-mediated superconductivity can account for the high ${\mathrm{T}}_{\mathrm{c}}$ in this class of materials.

The ground-state energy, hybridization matrix element, local moment, and spin-density correlations of a one-dimensional, finite-chain, periodic, symmetric Anderson model are obtained by numerical simulations and compared with perturbation theory and strong-coupling results. We find that the local f-electron spins are compensated by correlation with other f electrons as well as band electrons leading to a nonmagnetic ground state.

Cohn’s theorem is extended to the case of circuit elements with the nonlinear I-V characteristic V=${\mathrm{rI}}^{\mathrm{\alpha }}$. This simplifies the study of resistance noise in nonlinear resistor networks. Exact exponent inequalities are derived. Fractal and percolating structures are considered. The infinite number of exponents necessary to characterize completely the electrical properties of linear and nonlinear percolating networks are calculated within the Migdal-Kadanoff approximation.

We have investigated the band-gap renormalization due to many-body effects in electron-hole plasmas in 2D GaAS-GaAlAs multiple quantum-well structures. A comparison of these data with corresponding 3D data and calculations for both dimensionalities shows that the band-gap shift increases absolutely but decreases in effective Rydberg units with decreasing dimensionality. The dimensionality dependence of the band-gap shift is traced to different screening efficiencies in 3D and 2D systems.

Kadanoff transformations are discussed in terms of a metric in the space of Gibbs measures. Direct Monte Carlo computation of this metric is illustrated by trial calculations for small Ising systems. Applications to gauge-field quantization are suggested.

Limits are set on $B^0$B${¯}^0$ mixing by use of dilepton events from Υ(4S) decay. On the assumption that the charged- and neutral-B semileptonic branching ratios are equal and that 41% of the B mesons from the Υ(4S) are neutral, a 90%-confidence-level upper limit of 24% is set on $B^0$B${¯}^0$ mixing. Limits are also given for the ratio of the lifetimes of neutral and charged B mesons. The 90%-confidence-level limits are &<2.05.

It is shown that in a wide class of models that give an interestingly large electric dipole moment for the electron, $d_e$ can be bounded from $d_n$ or B(μ→eγ) provided that certain assumptions are made about the pattern of flavor mixing. Types of models not satisfying these assumptions are also discussed.