The channeling of electrons along or between atomic rows in a crystal is used as the basis of a powerful lattice-location technique capable of analyzing small quantities of crystal impurities with high spatial resolution. We demonstrate the technique by locating Sb dopant in Si and compare the results with ion-channeling and planar-electron-channeling analysis. Delocalization corrections are required with the electron-channeling analyses.

A theoretical investigation of an ordered $p(1\mathrm{}\times 1)$ H overlayer on Ni(001) shows a marked reduction of the surface Ni moment to ∼0.2${\mathrm{\mu }}_{\mathrm{B}}$ (which at room temperature gives the impression of a "dead" layer) and the formation of a covalent-metallic bond between H and Ni. These results, along with the calculated equilibrium properties and single-particle spectrum, are discussed and compared to experiment.

Density-functional total-energy calculations of H/Ni(100) show that the equilibrium H position is in the center site, $0.6a_0$ above the plane of the surface Ni atoms (with a Ni-H bond length of 1.8 Å). The bridge-site minimum lies only 0.1 eV higher than the center-site minimum, whereas the top-site minimum lies about 0.3 eV higher. This is consistent with a high hydrogen surface mobility.

Epitaxial Gd(0001) has been investigated with spin-polarized low-energy-electron diffraction and the magneto-optic Kerr effect. The ferromagnetic critical temperature of the surface layer is found to lie up to 22 K above the bulk Curie point, demonstrating the existence of surface-enhanced magnetic order. Furthermore, spin-resolved photoemission spectroscopy reveals that the $4f$ spins of the surface are not ferromagnetically coupled to the bulk moments.

We show explicitly that in a certain frequency range a surface plasmon polariton (SPP) is localized parallel to the metal surface by the presence of random roughness. By use of a diagrammatic method developed earlier, a self-consistent equation is derived for the renormalized diffusion coefficient of the SPP. We interpret surface-enhanced phenomena in terms of localized SPP and obtain an expression for the enhanced intensity near the metal surface. We find important differences in the enhancement results due to localization; these are consistent with experiments.

We have observed an oscillatory conductance in electrical transport through In-InGaAs contacts, corresponding to a series of dips in the $I-V$ characteristic for both bias polarities at $\mathrm{eV}\sim n\hslash {\omega }_0$, where $n$ are integers and $\hslash {\omega }_0$ is the LO-phonon energy of InGaAs. We explain the data by successive LO-phonon emission in high-field transport of ballistic electrons through microchannels of In-GaAs and point out that the experiment is a solid-state analog of the Franck-Hertz experiment.

The temperature variation of the dielectric constant has been measured in Rb${\mathrm{H}}_3$ ${\left(\mathrm{S}\mathrm{e}{\mathrm{O}}_3\right)}_2$ at various bias electric fields. The results show a nonlinear variation of the transition temperature between the incommensurate and the commensurate phase with the applied electric field; this is consistent with the existence of a Lifshitz point at the critical field $E_{\mathrm{L}}\approx 49$ kV/cm.

We report a new technique that enabled us to measure nonequilibrium carrier transport in GaAs. Hot electrons were injected into $n^{+}$-GaAs with an excess energy of 0.25 eV above the conduction-band edge. The effect of scattering on the injected electrons was observed by use of a planar doped barrier as a "hot-electron spectrometer." The measured spectra indicated that significant scattering occurred and that mean free paths were on the order of a few hundred angstroms.

Conduction-band surface-plasmon excitations are seen to contribute to the quasielastic scattering of low-energy electrons from clean Si(111)7×7 surfaces. We have analyzed these observations by means of a multiple-scattering theory and show that these excitations are localized below the surface space-charge layer. A comparison of the deduced surface-charge-density profile is in good agreement with the Fermi-level pinning at this surface.

We have made extensive studies of the temperature, gate voltage, and electric field dependences of the conductance peaks in small silicon inversion layers in order to distinguish between resonant-tunneling models and a hopping model. We find that many of the peaks are consistent only with a hopping model, whereas some could be consistent with an early resonant-tunneling model. None of our structure is consistent with resonant tunneling if the recent formulation of Stone and Lee is correct.

We develop a fully relativistic theory of the process of photoemission from paramagnetic metals and illustrate it by explicit calculations of the photocurrent and the spin polarization of electrons photoemitted from a single-crystal platinum sample. Our results are in good agreement with the available experimental data and indicate that energy-, angle-, and spin-resolved photoemission spectroscopy is a powerful new probe of the electronic structure even in the case of nonmagnetic metals.

The low-temperature magnetoresistance of quench-condensed Li films of varying widths is studied in order to observe the one-dimensional localization effects first predicted by Thouless. The localization effects are dominant and clearly differentiated from other contributions to the resistivity. The roles of the various scattering mechanisms controlling the localization contribution are determined.

We discuss two results for the Anderson model of random quantum Hamiltonians: (1) smoothness of the density of states in the one-dimensional model, even in many cases where the potential distribution is not smooth; and (2) a criterion for localization which, among other consequences, implies that certain estimates of Fröhlich and Spencer yield a dense point spectrum for the multidimensional model at large randomness or large energies.

The quantum behavior of two identical point vortices (e.g., in a superfluid ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ thin film) is studied. It is argued that this system obeys neither Bose nor Fermi statistics, but intermediate or $\theta$ statistics: We find that a single vortex in this system possesses quarter-fractional statistics (i.e., $\theta =\frac{\pi }{2} or 3\frac{\pi }{2}$). The source of the $\theta$ statistics is identified in the relative zero-point motion of the vortices.

Several statistical properties of the energy levels of a two-level atom interacting with one mode of quantized electromagnetic field are investigated in connection with possible "quantum-chaotic" behavior of the system.

We study an aggregation process which gives rise to compact clusters with no loops. A generalization of the node-counting theorem, applicable to such branched graphs (trees), is proved. This is used to determine the spectral dimension of these clusters on square and cubic embedding lattices by Monte Carlo simulations. The results are explained in terms of the geometric structure of these trees.

Using a simple example we show that the distribution for the energy levels for integrable systems is not the uncorrelated Poisson distribution as is commonly believed. In particular, the spectrum was found to be rather rigid. We conjecture that these are typical properties of the integrable quantum systems.

It is shown that very general features of the critical theory of the Yang-Lee edge singularity in two dimensions completely determine the way in which the theory realizes conformal invariance. This leads to the value $\sigma =-\frac{1}{6}$ for the edge exponent, and makes possible the calculation of the correlation functions.

A new formulation of the Dirac impulse approximation is discussed which connects the $p$-nucleus optical potential to a dynamical description of the relativistic $\mathrm{NN}$ amplitude. Use of pseudovector $\pi N$ coupling eliminates rapid energy dependence found in the original impulse approximation. First calculations demonstrate success for 181 MeV with no loss of effectiveness at 500 and 800 MeV.

Quantitative measurements have been made of correlations in the $\gamma$-ray continuum emitted by rotational nuclei populated in heavy-ion compound-nucleus reactions. The experimentally deduced intensity of the "ridge" structure in the correlation spectrum implies an average probability for inband stretched $E2\mathrm{}$ decay of < 20% at spins above $30\hslash$ in contrast to traditional expectations.