The magnetic hyperfine field was measured at ${}_{}{}^{111}{}_{}{}^{}\mathrm{In}$${(}^{111}$Cd) probes on Ni(111) surfaces utilizing the perturbed γγ-angular-correlation method. Over the entire temperature range up to the Curie temperature the magnetic hyperfine field at probes in the topmost monolayer was found to be reduced as compared to the field for probes in the 3.5th monolayer and in bulk. The probe lattice location was inferred from the structural information derived through simultaneous measurement of the electric-field-gradient tensor acting at probe nuclei.

The electrodynamical properties of the edge excitations in the fractional quantum Hall (FQH) states are studied. We show how to experimentally measure the (optical) charges of the edge excitations. The interactions between the edge excitations are studied. We also discuss in detail the edge excitations of the ν=1±1/n FQH states. Measuring the dynamical properties of the edge excitations is a practical way to probe the topological orders in the FQH states.

It is shown that fractional statistics on a torus are consistent only with multicomponent wave functions. This is expected to be generally true for all 2D, closed, multiply connected, orientable manifolds. The fractional quantum Hall effect with periodic boundary conditions is seen to fit into this new picture, where the quasiholes may be interpreted as a kind of generalized anyons.

Recoil-γ coincidences have been measured in the reaction ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$${+}^{159}$Tb at beam energies of 300 and 400 MeV. In the γ-ray spectra corresponding to excitation energies above 140 MeV a split giant dipole resonance is observed with widths substantially smaller than found at lower excitation energy. The possible influence of excitation energy and angular momentum on this effect is discussed. The intensity ratio of the two dipole resonance components is found to change with excitation energy, indicating a transition of the nuclear shape from prolate towards oblate.

We present results of Floquet calculations of rates for ionization of H by high-intensity light with wavelengths up to 1064 nm. If the frequency ω is well below the atomic-orbital frequency ${\mathrm{\omega }}_{\mathrm{at}}$ the rates approximately obey a law similar to that given by the Keldysh tunneling theory, and they approach the dc rate as the intensity increases. If ω>${\mathrm{\omega }}_{\mathrm{at}}$ there is no tunneling regime and the rates eventually decrease toward zero as the intensity increases.

We report an observation of the long-term evolution of a radially localized electronic wave packet formed by the coherent superposition of Rydberg states of atomic potassium. Initially, the wave packet can be described classically. Subsequent dephasing of the discrete states in the superposition leads to a loss of spatial localization so that the evolution can no longer be described classically. However, the wave packet revives at a later time. Theory and experiment show good agreement including an accurate measurement of the phase shift of the wave packet on revival.

A nonlinear theory of intense laser-plasma interactions is developed and used to describe relativistic optical guiding, coherent harmonic radiation production, and nonlinear plasma wakefield generation. Relativistic optical guiding is found to be ineffective in preventing the leading portion (≤ a plasma wavelength) of a laser pulse from diffracting. Coherent harmonic generation is found to be most efficient for short laser pulses. Optical guiding and harmonic generation may be enhanced by the presence of large amplitude plasma wakefields. These phenomena may be important in laser-driven plasma accelerators, x-ray sources, and fusion schemes.

The nonlinear evolution and spectral properties of ion temperature gradient-driven modes in a three-dimensional sheared magnetic field with multiple rational surfaces have been investigated using gyrokinetic plasma simulation techniques. A detailed study of the electrostatic potential fluctuation spectra shows that it is dominated by the modes with moderate poloidal wavelength (0.1≤${\mathit{k}}_{\mathit{y}}$${\mathrm{\rho }}_{\mathit{s}}$≤0.5). The measured thermal flux in the steady state, which is lower than the quasilinear value at saturation, is found to decrease weakly with an increase in the magnetic shear strength.

An exact formula relating second moment of the density relaxation spectrum and static structure factor of simple liquids at arbitrary temperatures is used to derive the long-wavelength excitation frequencies of a liquid at low (but finite) temperatures, thus generalizing Feynman’s (T=0) result on quantum liquids. At very low temperatures anomalous dispersion is expected while a purely linear frequency-wave-number relationship is estimated to apply for q≪2 √6 (${\mathit{k}}_{\mathit{B}}$T)/(ħc) only. The static structure factor is shown to have a classical and a quantum contribution determining its long-wavelength properties at high (near ${\mathit{T}}_{\mathit{c}}$) and low temperatures, respectively.

We perturbatively calculate the partition function and the two-point squared distance for a self-avoiding tethered manifold. By directly summing the leading divergences of the perturbation series, we show that they can be organized to yield scaling forms. The manifolds are indeed one-loop renormalizable to all orders.

We have studied the irreversible aggregation of colloidal polystyrene spheres during two limiting regimes of growth: diffusion-limited aggregation and reaction-limited aggregation. For each growth regime, the time-dependent cluster-size distribution exhibits a scaling form which reveals intrinsic features of these growth processes.

The direct consequences of the phased excitation (Bragg scattering) by neutrons of an ordered array of resonant nuclei are observed experimentally for ${}_{}{}^{115}{}_{}{}^{}\mathrm{In}$ in a nearly perfect single crystal of InSb. The energy width of the peak in the integrated intensity of the (640) Bragg reflection at the 1.457-eV resonance is more than 3 times greater than that for an isolated nucleus. Anomalous transmission of neutrons at the (642) Bragg reflection is observed for a crystal with μt=44, consistent with the predicted suppression of the inelastic (n,γ) decay channel.

We show that finite-range matching rules and growth rules exist for an infinite set of 2D pentagonal tilings other than the original Penrose tilings. There is a natural ordering of these tilings based on the range required for the rules. The results have implications for the determination of the atomic structure of icosahedral alloys.

Ordering in epitaxial Si/Ge alloys grown by molecular-beam epitaxy has been observed by several authors. Attempts to explain this unusual phenomenon on the basis of the bulk thermodynamic properties of the alloy have failed. In this Letter we show that the observed ordering is not an equilibrium bulk property, but rather the result of surface growth kinetics. We attribute the ordering to atomic-scale stresses present in the reconstructed Si(001) surface during growth, leading to double-layer segregation of Ge and Si along one of the four equivalent 〈111〉 directions. This near-surface ordering is then quenched-in as the crystal grows.

Diffusion studies of Cu+Re and Re+CU films on silicon show that the formation of ${\mathrm{Cu}}_3$Si precursor lowers the formation temperature of ${\mathrm{ReSi}}_2$ from over 900 to 550 °C. The results are explained and generalized to all metal-rich silicides by the specific volume of silicon being much larger in these compounds than in elementary silicon. In forming metal-rich silicides, silicon atoms are forced out of their original planes and are free to form silicon-rich silicides with adjacent metals, or to form silicon self-interstitials at the metal-rich-silicide–silicon interface.

Exciton annihilation processes involving biexcitonic interactions are known to efficiently ionize molecular and semiconductor crystals and large molecular clusters. We present the first spectroscopic evidence for biexcitonic two-photon ionization of small molecular clusters. In this case the process resembles resonant multiphoton autoionization of two-electron atoms.

A model of hopping diffusion, with tunneling as the hopping mechanism, is studied. In the presence of photons, the size of the barrier, hence the hopping rate, are time dependent. A closed expression for the diffusion coefficient in the single photon case is obtained. It is found that for systems with low conductivity, a properly chosen phonon can increase the conductivity by a large factor. Such a phonon can be forced upon the system externally. The analytical results are supplemented by numerical calculations.

We report calorimetric measurements of the organic conductor (TMTSF${)}_2$${\mathrm{ClO}}_4$ in the quantum limit. In addition to the field-induced spin-density-wave (FISDW) phases, we have measured the magnetic-field-dependent specific heat associated with the recently discovered reentrant phase. In terms of a semiempirical model, we find that the reentrant transition is second order, but that the electronic density of states is greatly reduced in the reentrant phase. We also observe a specific-heat signal corresponding to the anomalous ‘‘fast oscillations’’ which are known to coexist with the FISDW phases

We have measured the thermopower of small ${\mathit{n}}^{+}$-GaAs wires using a novel electron heating technique. The results show very large fluctuations which are in good agreement with existing theories. We believe this to be the first observation of universal thermopower fluctuations.

We present measurements showing dramatic nonlocal behavior in the four-terminal resistances of a high-mobility quantum Hall conductor. These measurements illustrate that the standard definition of the resistivity tensor is inappropriate, but they are in excellent agreement with a new model of the conductor that treats the edge and bulk conducting pathways independently. This model uses a single intensive parameter, analogous to a local resistivity for the bulk channel only, to characterize the system.