A dynamic-scaling approach is developed for the description of the droplet-size distribution in vapor-deposited thin films and processes where droplets are formed by nucleation, growth, and coalescence of the droplets. The exponent describing the scaling of the droplet-size distribution and the growth law for the mean droplet size are calculated exactly. A realistic, yet simple, droplet-growth model is developed. The simulation data are found to be consistent with the experiments on vapor-deposited tin and with the theoretical predictions in $d=1, 2, \mathrm{and} 3$.

Elastic and quasielastic neutron-scattering results for the melting of submonolayer ethylene films on graphite are described and microscopic evidence is presented for a continuous melting transition. Comparisons are made with data for equivalent methane films and with molecular-dynamics simulations. Differences in melting behavior are attributed to different vacancy creation mechanisms in the films.

The in-plane phonons of the commensurate monolayer of deuterium adsorbed on graphite have been measured. They show evidence for dispersion rather than completely localized mode character. In addition to the phonon gap a transverse and a longitudinal zone-boundary phonon could be measured. The coupling constants between the adsorbed molecules themselves and between molecules and the substrate have been deduced. It is found that the in-plane coupling to the substrate is nearly 10 times stronger than the coupling to neighboring molecules.

We report on a molecular-dynamics simulation of an Al(110) surface using the effective-medium theory to describe the interatomic interactions. The surface region is found to start melting ≅200 K below the bulk melting temperature with a gradual increase in the thickness of the disordered layer as the temperature approaches the bulk melting point. The more close-packed Al(111) surface shows a much weaker disordering below the melting temperature.

Permanent Si $E^{\prime }$ centers with concentrations as high as ${10}^{17}$ spins/g induced in high-purity Si${\mathrm{O}}_2$ by sub-band-gap (6.4 eV) light were studied by electron-spin resonance. Although an electron-trap nitrogen center has been reported as the dominant defect induced by 7.9-eV photons in Suprasil 1 silica, its absence in the present experiment is evidence that free carriers are not produced by 6.4-eV photons. The $E^{\prime }$-center concentration increased as the square of 6.4-eV laser power, confirming the efficacy of two-photon processes for producing point defects in silica with sub-band-gap light. Our evidence supports the view that $E^{\prime }$ centers are generated by nonradiative decay of neutral excitons.

Antimony overlayers on the GaAs(110) surface have been studied by scanning tunneling microscopy and spectroscopy. On ordered Sb terraces, a characteristic spectrum of surface states is observed. Near the edges of Sb islands, additional states are found within the band-gap region. These band-gap states comprise two separate bands of filled and empty states, with the surface Fermi level pinned between the two bands.

The conductance of a dilute 2D electron gas on hydrogen is measured as a function of ambient ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ gas density. At densities below ≅ ${10}^{20}$ ${\mathrm{cm}}^{-3\mathrm{}}$ the electron scattering rate is the sum of a classical term linear in ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ density plus a ${}_{}{}^4{}_{}{}^{}\mathrm{He}$-adsorbate-scattering term. Towards higher densities, however, the conductivity decreases exponentially which we attribute to strong localization of electrons below a threshold energy $E_c\gtrsim k_{\mathrm{B}}T$. We present an estimate of $E_c$ based on weak-localization theory and find good agreement with both our 2D data and the 3D mobility measurements in the literature. In 3D, the Ioffe-Regel criterion for localization is found to be $k{l}_0=2.5\mathrm{}\pm 0.5$.

We report on numerical studies of impurity states in quasiperiodic Fibonacci lattices. The binding energies of these states are used to define an effective mass which depends on the position of the impurity. The mass shows quasiperiodic behavior in a scale that is much larger than that of the lattice and which depends on the size of the impurity. Heavier electrons are associated with larger impurity sizes.

Recently, a macroscopic theory of $N$-channel disordered conductors treated the evolution (with the length $L$) of the probability distribution of the transfer matrix for the full conductor and allowed a theoretical description of the universal conductance fluctuations. Those results are used here to calculate the correlation function between transmission as well as reflection coefficients: In the case $L\gg W$ (width of the sample), the former essentially coincides with the one obtained from microscopic perturbative calculations. The latter, on the other hand, is a prediction of the present model.

A simple real-space renormalization method yields the ground-state energy of the Heisenberg antiferromagnet. We find the ground-state energy per spin for $s=\frac{1}{2}$ (-0.4438 in 1D, -0.6723 in 2D) and $s=1\mathrm{}$ (-1.388 in 1D and -1.907 in 2D) to three-figure accuracy, using properties of relatively small odd-numbered clusters. Our results provide reasonable proof for long-range order in the ground state of the $s=\frac{1}{2}$ Heisenberg antiferromagnet in 2D.

The ground state of a quantum vacancy in a 2D antiferromagnet is found to involve a long-range dipolar distortion of the staggered magnetization. An effective Hamiltonian of vacancies interacting with long-wavelength spin waves is derived. The implications for the anitferromagnetic long-range order are discussed.

It is shown by a brief calculation that the method of anisotropy measurement of $\gamma$-ray emission from spin-polarized nuclei is a useful tool to investigate multiple-spin-modulation waves which have been suggested to exist in several kinds of materials but have not yet been proven by definitive experimental evidence. An application of this method is made for a fcc antiferromagnetic Mn-Ni alloy and the first direct experimental evidence for a triple-Q spin-density wave is given.

Ultrathin films (10 to 17 monolayers) of fcc Fe(100) grown epitaxially on Cu(100) are unambiguously found to be paramagnetic at 295 K by ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ conversion-electron Mössbauer spectroscopy in UHV. Below $T_{\mathrm{N}}=65\mathrm{}\pm 5$ K, fcc-Fe films are magnetically ordered and show a small average hyperfine field, e.g., 1.1 T at 29 K for 10 monolayers, indicating a small atomic magnetic moment. This demonstrates that fcc Fe(100) stabilized at a lattice constant close to that of Cu has an antiferromagnetic ground state.

The quantum mechanics of noninteracting electrons is studied in a nonintegrable elliptic billiard with a uniform magnetic field applied perpendicularly. We make an attempt to establish a connection between chaotic dynamics and macroscopic quantum observables. For small two-dimensional systems, a remarkable reduction and large fluctuations of the diamagnetic susceptibility are found in the corresponding classically chaotic region.

A new non-Markovian, correlated-jump model for phase fluctuations of an electromagnetic field is introduced. The phase-diffusion, generalized telegraph, Burshtein, and Brownian-motion-like models are all obtained from this model in the proper limits. The spectrum and correlation functions of the stochastic field are predicted, and detailed line shapes of the Mollow triplet of resonance fluorescence are given and shown to depend on the field intensity, a purely non-Markovian effect. Two different experimental procedures are proposed for the determination of the stochastic parameters of a laser field.

Phase transitions of trapped particles and ions, observed initially in 1959 by collisional cooling and recently by laser cooling, are explained as order-chaos transitions. Here, two trapped ${\mathrm{Ba}}^{+}$ ions are examined experimentally and by computer solution of the equations of motion. The ordered state, quasiperiodic with two frequencies, becomes chaotic when a bifurcation introduces a third frequency at a critical value of a control parameter. This route evolves from the nonlinear Coulomb coupling of the ion pair's axial and radial motions, displaying frequency locking and hysteresis, which is observed.

A continuous-time dynamic model of a network of $N$ nonlinear elements interacting via random asymmetric couplings is studied. A self-consistent mean-field theory, exact in the $N\to \infty$ limit, predicts a transition from a stationary phase to a chaotic phase occurring at a critical value of the gain parameter. The autocorrelations of the chaotic flow as well as the maximal Lyapunov exponent are calculated.

The quantum theory of a complex scalar field coupled to gravity is considered. A formalism for the semiclassical approach in Euclidean time is developed and used to study wormhole physics. The conserved global charge plays an essential role. Wormhole physics turns on only after the symmetry is spontaneously broken. An effective self-interaction for Goldstone bosons due to wormholes is shown to be a cosine potential, whose vacuum energy will be reduced by the cosmic expansion. Some implications and questions are discussed.

Asymptotic expressions are derived for the mean up-crossing rate, size, and number density of excursions above a high level by a stationary, non-Gaussian, random field in $D$ dimensions. These formulas are relevant in the analysis of the large-scale matter distribution in the Universe.

It is shown that present-day resonant-bar gravitational-wave detectors are sensitive to nuclearites of strange matter. The published data from a short test run of the Stanford gravitational-wave detector are used to obtain a flux limit for nuclearites.