Based on our theoretical results of dynamical behaviors of light transmission in optical superlattices, we show that there is a new type of optical bistable mechanism, i.e., the index-modulation mechanism, existing in a two-dimensional superlattice that contains dielectric nonlinearity of the Kerr form. This bistable mechanism is not exhibited in one-dimensional superlattices.

Experiments were conducted on TFTR to study the radiation of krypton which will be important for future tokamaks, such as ITER, for the diagnostic of the central ion temperature and for the control of the energy release from the plasma by radiative cooling. The total krypton radiation was monitored, and satellite spectra of Kr xxxv were recorded with a high-resolution crystal spectrometer. Radiative cooling and reduced particle recycling at the plasma edge region were observed, in reasonable agreement with modeling calculations which included radial transport.

For the tokamak magnetic confinement concept, theory has predicted a distinct relationship between the plasma shape, the internal magnetic structure, and the presence or absence of fast ion losses in the presence of plasma instabilities. We have, for the first time, carried out measurements of the magnetic safety factor profile, q(r), in plasmas unstable to a specific instability, the so-called ‘‘fishbone’’ mode. The experimental equilibria reconstructed from these data have been used to demonstrate that when the plasma is unstable to fishbones, the fast ion confinement properties depend strongly on the radius of the magnetic surface where q(r)=1.

Polystyrene (PS)-polyisoprene (PI) diblock copolymers dissolved in n-decane aggregate into spherical micelles with a PS core and a corona of tethered PI chains. The PI corona may be considered as a brush on the surface of a sphere or as the outer part of a many-armed polymer star. The thermal density fluctuations of the PI corona have been observed by neutron spin-echo spectroscopy. The peculiar multi-decay time relaxation behavior can be described remarkably well by a model based on an idea of de Gennes for treating the corona as a semidilute polymer solution with varying concentration profile.

We propose, and verify in the case of a Ge-doped-silica-core optical fiber, a general explanation for the power-law dependencies on dose frequently observed for the concentrations of radiation-induced defect centers in insulating glasses. This insight permits detailed prediction of the postirradiation recovery curves given just the empirical exponent of the power law, 0<f<1, and the experimental irradiation time ${\mathit{t}}_{\mathrm{irrad}}$. The time constant of the recovery is given by ${\mathit{t}}_{\mathrm{irrad}}$/(1-f), independent of the order of kinetics. We establish a microscopic model (radiolytic oxygen molecules) for the γ-ray-induced absorption at 1.3 μm in our test fibers and we infer a diffusion-limited bimolecular recombination process.

Dynamics of superheating, melting, and annealing processes at Cu(111) and Cu(110) surfaces, induced by laser-pulse irradiation, are investigated using molecular dynamics simulations, incorporating energy transfer from the electronic to the ionic degrees of freedom. Superheating occurs at Cu(111) for conditions that lead to melting of the Cu(110) surface. Highly damaged Cu(111) surfaces structurally anneal under the influence of a superheating pulse.

An exact renormalization group describes extremely slow, logarithmic diffusion in the presence of a biasing field on ramified fractal structures. Recursion equations are singular at the fixed point and the standard analysis to extract asymptotic behaviors has to be reconsidered. The model reproduces mechanisms working for biased diffusion on percolation clusters. For 1-d structures, logarithmic diffusions generalizing that discussed by Sinai [Theory Probab. Its Appl. 27, 256 (1982)] are obtained by the same methods.

Molecular-dynamics simulations for hydrogen diffusion in Nb are performed at high temperatures (T=450 K and T=580 K). Two key experimental observations are reproduced by our model; the strong deviations from simple jump diffusion behavior and the ‘‘anomalous Debye-Walker’’ factor. The simulation reveals a rapid local-diffusion motion, predominantly confined to the so-called 4T configuration. The time scale for this motion is found to be of the order 100–200 fs.

We report on the first laser spectroscopy of alkali atoms (Cs and Rb) and molecules (${\mathrm{Na}}_2$ and ${\mathrm{Li}}_2$) in superfluid helium. General features of the observed spectra can be explained in terms of the spherical atomic bubble model. The excitation and emission spectra for the ${\mathit{D}}_2$- lines, however, have double peaked profiles, indicating the importance of the nonspherical density distribution of surrounding helium atoms. The emission spectra for the molecules show well-resolved vibrational structures in the electronic ground states.

We have developed a new method for producing a high density of neutral atoms in liquid helium; laser sputtering within liquid helium. When we irradiate samples immersed in liquid helium with a pulsed laser, a large number of clusters are introduced into the liquid. When we further irradiate these clusters with an additional pulse laser, the clusters are sputtered and decomposed, which results in the creation of a high density of isolated atoms in the liquid. For alkaline earth atoms this method is demonstrated, and the results of laser spectroscopy are given.

We calculate the entropy of a two-dimensional Fermi liquid using a model with a contact interaction between fermions. We find that there are ${\mathit{T}}^2$ contributions to the entropy from interactions separate from those due to the collective modes. These ${\mathit{T}}^2$ contributions arise fron nonanalytic corrections to the real part of the self-energy which may be calculated from the leading-log dependence of the imaginary part of the self-energy through the Kramers-Kronig relation. We find no evidence of a breakdown in Fermi liquid theory in 2D and conclude that Fermi liquids in 2D are similar to 3D Fermi liquids.

Co(101¯0) with close-packed rows separated by the c-axis distance in a hcp analog to fcc (110). In contrast to the (2×1) missing-row (MR) structures formed upon oxygen adsorption on several fcc (110) surfaces, a novel type of MR reconstruction is revealed by scanning tunnel microscopy and low energy electron diffraction on Co(101¯0): The low coverage (2×1) O phase constitutes a double-layer MR structure with (2×1) MR configurations in the two topmost Co layers; it develops locally by moving every other atom at the topmost close-packed Co rows into respective short bridge sites of the layer underneath. Results on the c(2×4) and the high coverage (2×1) oxygen phases support this conclusion.

Ab initio studies of the reconstruction mechanism of (001) fcc transition metal surfaces are presented, showing that a close-packed quasihexagonal reconstruction is possible for the late 5d metals Ir, Pt, and Au, while it is disfavored in the isovalent 4d metals Rh, Pd, and Ag. The driving mechanism is identified in the tensile excess stress of the unreconstructed surfaces. The stress overcomes the substrate resistance to reconstruction only in 5d metals, where it is much larger than in 4d metals because of the stronger relativistic effects. The origin of surface stress is a d charge depletion from the surface layer.

Ordered phases of O on W(110) entail compressive surface stress, the manifestations of which are directly observed for different coverages using scanning tunneling microscopy. Low coverage adsorption results in a gas phase with disordered persistent structures. At higher coverage, ordered phases condense with disordered domains. O adsorption in the two distinct triply coordinated sites of the W(110) unit cell leads to separate domains with the adsorption site exchanged. Annealing relieves compression within high coverage phases by the formation of site-exchange domain superstructures.

We show that systematic differences occur in the corrugations of the systems Ni(110)c(2×4)H, Rh(110)(1×3)H, and (1×2)H, when determined from He and Ne diffraction: Whereas the hills along the H-free close-packed metal rows correspond to underlying metal atoms in all corrugations deduced from Ne diffraction, they are shifted to short bridge sites in all He-derived corrugations. This assignment is possible, as the H adatoms mark threefold hollow sites on both (110) substrates. These observations provide strong experimental support for anticorrugating effects in He-metal surface interactions as proposed by Annett and Haydock [Phys. Rev. Lett. 53, 838 (1984)].

The low frequency vibrations of benzene molecules adsorbed on Rh(111) have been investigated with inelastic He atom scattering. Well resolved energy losses of 13.1, 12.9, and 12.7 meV were observed for the pure benzene (2 √3 ×3) structure, the CO+${\mathrm{C}}_6$${\mathrm{H}}_6$ c(2 √3 ×4) rect and (3×3) structures, respectively. As these are the first experimental data for vibrations of a large adsorbed molecule in this energy regime extended Hueckel calculations were used to identify the observed mode as the frustrated translation of the benzene molecule parallel to the surface.

Magnetic polarons in magnetically disordered systems (for brevity, spin-glass polarons) are in one respect very unlike other polarons: Usual polaron hopping at low T proceeds via tunneling, and these polarons do not affect the T dependence of the hopping rate, while the spin-glass polaron tunneling is suppressed by the disorder, and their hopping proceeds via activation for all T. It gives rise to the reentrance of the simple activated T dependence of variable range hopping conductivity at very low T. Recent experiments in CdMnTe are discussed.

Using scanning tunneling microscopy and spectroscopy, we have observed the formation of standing waves by the scattering of surface state electrons at steps and defects on the Au(111) surface. From the periods, peak positions, and intensities of the standing waves, the energy dispersion of the surface states, the scattering phase shifts as a function of energy and crystallographic direction, and coherence lengths could be determined.

Transport properties of two-dimensional charged bosons in the normal and superconducting state are derived. The Wiedemann-Franz law and the Lorentz number are obtained for the normal state. A strong suppression of the quasiparticle scattering rate and a strong enhancement of the thermal conductivity in the superconducting state are found. Temperature dependence of the in-plane thermal conductivity of YBCO crystals is explained.

The chain oxygen dynamics of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathit{x}}$ have been investigated using a Monte Carlo simulation of the asymmetric next-nearest-neighbor Ising model for the oxygen atoms in the basal plane. The effect of an electric field is to change the basal plane coordination of Cu ions, resulting in a change in the carrier doping of the ${\mathrm{CuO}}_2$ planes. The ratio of magnitudes of the changes in the doping under potentials of +10 V and -10 V is in good agreement in magnitude and sign with that observed in field effect experiments, as are also the time constants for the resistance changes.