Near-edge x-ray-absorption fine-structure spectroscopy studies are used to determine changes in the electronic, geometric, and magnetic structure of two sequential molecular precursors of ${\mathrm{O}}_2$ on Pt(111). Both molecules lie down on the surface. Physisorbed ${\mathrm{O}}_2$ is found to be van der Waals bonded, structurally unperturbed and paramagnetic, while chemisorbed ${\mathrm{O}}_2$ is π bonded, stretched by 0.16 Å, and exhibits a reduced or vanishing paramagnetic exchange splitting.

Using scanning tunneling microscopy, we have quantitatively characterized the configurations of steps on vicinal Si(111) surfaces misoriented by 1.2° and 2.3° towards the [1¯ 1¯ 2] direction. The measured terrace-width distributions are strongly peaked, consistent with predictions for thermally wandering steps. However, the distributions are much narrower than predicted for the simple terrace-step-kink model, indicating that the steps interact with energetic short-range repulsions. The magnitude of this energetic repulsion is gauged from a Gaussian fit to the data. The width of the distribution scales with step density as expected for repulsions which decay as the inverse square of step separation.

Motion of a substitutional impurity via a fast-diffusing intermediate species is discussed. An analytical solution is given for the case of low impurity concentration. For short times, few atoms migrate and the solution behaves exponentially. We observe this exponential signature in the diffusion of nanometer-scale B-doping profiles in Si. The migration frequency during oxidation-enhanced diffusion is consistent with diffusion-limited knockout of an interstitial-type-B species. This is the first direct experimental evidence for dopant diffusion in Si via an intermediate species.

Several experiments were performed in order to understand the creation and readout mechanisms of photostimulable (PS) centers in BaFBr:${\mathrm{Eu}}^{2+}$ single crystals. PS centers can be efficiently created starting from 6.7 eV, i.e., the minimal energy required to excite the first valence exciton. This exciton relaxes to an e-${\mathit{V}}_{\mathit{k}}$ (${\mathrm{Br}}_2^{\mathrm{-}}$) pair. The relaxation of such a defect in the neighborhood of ${\mathrm{Eu}}^{2+}$ yields a PS center, namely, an F-H (${\mathrm{Br}}_2^{\mathrm{-}}$) pair. An additional decay channel of the e-${\mathit{V}}_{\mathit{k}}$ pair results in ${\mathrm{Eu}}^{2+\mathrm{*}}$ emission due to the energy match between the emission of this pair and an absorption band of ${\mathrm{Eu}}^{2+}$.

We demonstrate the existence of resistance fluctuations in experimentally realizable ballistic conductors due to scattering from geometric features. The magnetic-field and energy correlation functions are calculated both semiclassically and exactly numerically, and are found to have a scale determined by the underlying chaotic classical scattering. These systems provide a test of the ‘‘random’’ quantum behavior of classically chaotic systems.

We calculate the rate of the elastic macroscopic quantum tunneling of the electric charge (q-MQT) in a system of two small-area, normal, tunnel junctions in the Coulomb blockade regime. Despite the fact that the intermediate electron state on the central electrode of the system during the tunneling is virtual, the rate of the q-MQT depends crucially on the character of real electron motion through this electrode. Typically this motion is diffusive, so that the tunneling rate is determined by the process of ‘‘virtual diffusion’’ of electrons on the time scale of the inverse Coulomb energy of the system, ħ/${\mathit{E}}_{\mathit{C}}$.

Spin-resolved photoemission data of the Fe-metal 3s core level show that the two structures known from spin-integrated photoemission are of minority- and majority-spin character, the minority-spin peak being located at lower binding energy. The line shapes and intensity ratio of the peaks differ considerably from previous results based on fits of conventional photoemission data. The observed intensity ratio (1.16±0.1) is similar to the value expected for delocalized d states (1.0).

The 1-K phase transition in ${\mathrm{UCu}}_5$, showing up in specific-heat data within the antiferromagnetic state below ${\mathit{T}}_{\mathit{N}}$≃15 K, was investigated. Neither the average internal fields seen by the ${\mathrm{\mu }}^{+}$ nor the magnetic and nuclear Bragg reflections in the neutron-diffraction data reflect the phase transition while the muon relaxation rates increase drastically below 1.2 K. These results are interpreted in terms of some additional small-moment magnetic order or spin-density-wave phenomenon, implying the coexistence of two rather independent electronic subsystems, one involving ‘‘heavy’’ electrons, associated with the weak magnetism, and the other associated with the ‘‘conventional’’ antiferromagnetic order.

We report the temperature and magnetic-field dependence of the thermopower of (TMTSF${)}_2$${\mathrm{ClO}}_4$ through the entire range of magnetic-field-induced spin-density-wave (FISDW) transitions. The activated behavior of the thermopower in the extremely stable FISDW state that resembles the 1/3 fractional quantized Hall effect provides strong evidence for a collective ground state. At high magnetic field above 25 T, we find a new phase with a true energy gap at the Fermi level.

The Hubbard model is investigated using functional integrals and a Hubbard-Stratonovich decomposition of the interaction term. Using a spin-space reference frame that fluctuates in time and space, the effective action both is spin-rotation invariant and exhibits the correct Hartree-Fock saddle point. For strong correlation the effective action for free carriers and spins coupled via a gauge field is obtained as a systematic expansion in t/U. The spiral state existing for small doping is discussed. The formalism allows straightforward generalization to intermediate and weak coupling.

Using a Fermi-liquid formalism in which the Cu d electrons are quasilocalized, we calculate the NMR relaxation for the Cu and O sites, the temperature-dependent magnetic susceptibility, and the neutron-scattering cross section. Our microscopic calculations of the dynamical susceptibility help to decouple narrow-band phenomena from spin-fluctuation effects. The former lead to a low (coherence) energy scale and considerable structure in the Lindhard function. The latter help to enhance these effects.

Silicon-oil-in-water emulsions stabilized with sodium dodecylsulfate (SDS), have been studied. They exhibit practically no coalescence, whereas for high surfactant concentrations a ‘‘creaming’’ of the emulsion is observed. We demonstrate that this behavior is related to a fluid-solid phase transition due to an attractive interaction induced by the depletion of SDS micelles. A simple model for the fluid-solid transition is proposed, in quantitative agreement with experiment.

We study the decay of classical systems with regular and chaotic dynamics by investigating the escape of a particle from a container with a small hole. For the case of ergodic motion, we find an exponential decay law, whereas the nonchaotic system decays according to a power law.

An experiment, analogous to that of Cimmino et al., is proposed to measure the phase shift induced by static electric fields on the passage of neutrons through an interferometer when the path-enclosed linear charge density is zero. A finite shift is predicted and discussed in light of the Aharonov-Casher result.

The flow under gravity of a granular material can exhibit either intermittent avalanches or a steady regime. The transition from the discrete to the steady regime is shown experimentally to display hysteresis. Next, a relationship between the current and the slope is established and interpreted.

Black holes may be produced from false-vacuum bubble implosions at the end of the quantum chromodynamics phase transition. Evaporation of these black holes during the keV era readjusts the abundances of light nuclei. An appropriate mass distribution of black holes gives nuclear abundances broadly consistent with observations even for ${\mathrm{\Omega }}_{\mathit{B}}$=1, reconciling a critical baryonic universe with standard-model particle physics.

We analyze the magnitude and angular pattern of distortions of the microwave background by collapsing spherical domain walls. We find a characteristic pattern of red-shift distortions of red or blue spikes surrounded by blue disks. The width and height of a spike is related to the diameter and magnitude of the disk. A measurement of the relations between these quantities thus can serve as an unambiguous indicator for a collapsing spherical domain wall. From the red-shift distortion in the blue disks we find an upper bound on the surface energy density of the walls σ≲8 ${\mathrm{MeV}}^3$.

Comparison of the results from the Kamiokande neutrino-electron scattering experiment with those from the chlorine experiment and with solar models shows that the explanation of the solar-neutrino problem probably requires physics beyond the standard electroweak model with zero neutrino masses. The experimental results, including the shape of the electron-recoil energy spectrum measured by Kamiokande, are in excellent agreement with a nonadiabatic solution of the Mikheyev-Smirnov-Wulfenstein effect, yielding a neutrino mass difference of Δ${\mathit{m}}^2$=1×${10}^{\mathrm{-}8}$ ${\sin }^{\mathrm{-}2}$${\mathrm{\Theta }}_{\mathit{V}}$ ${\mathrm{eV}}^2$.

We show that the scale-invariant curvature action for paths, the point-particle version of Polyakov’s extrinsic-curvature action for surfaces, does not couple consistently to gravity. The curvature action for paths yields a massless representation of the Poincaré group with fixed helicity and so potentially provides a description of single photons and gravitons. We present a physical interpretation of the inconsistency in terms of the nonlocalizability of the photon and point out a conceptual kinship with the local supersymmetry of a spinning particle.

We present a new method for including dynamical fermions in lattice gauge theories that can increase the efficiency of Monte Carlo simulations by significantly decreasing the amount of required computer time. The accuracy of the method is demonstrated by comparison with numerical results obtained with other methods in compact QED. New results on the phase transition of QED with massless fermions on $6^4$ and $8^4$ lattices are also presented.