The Kramers-Kronig (KK) dispersion relation has been proved to hold between independently measured spectra of the phase shift φ(ω) and the modulus ‖χ${\mathrm{̃}}^{\mathrm{}\left(3\right)\mathrm{}}$/(ω)‖ of third-order electric susceptibility χ${\mathrm{̃}}^{\mathrm{}\left(3\right)\mathrm{}}$ (=‖χ${\mathrm{̃}}^{\mathrm{}\left(3\right)\mathrm{}}$‖${\mathit{e}}^{\mathit{i}\mathrm{\phi }}$) for the third-order harmonic generation in silicon-based polymer, poly(dihexylsilane) (PDHS) films, providing a direct experimental substantiation of the reciprocal KK relations in the nonlinear optical solids. The reciprocal dispersion relations have been also found to hold for the real and imaginary parts of χ${\mathrm{̃}}^{\mathrm{}\left(3\right)\mathrm{}}$ in PDHS films.

We have investigated the rise of a single large glass bead through a vibrated cylindrical column of smaller particles and found that vibration-induced size separation in this geometry arises from convective processes rather than from local rearrangements as had been proposed previously. A convection cycle, rising in the middle and dropping in a thin stream along the walls of the cell, is responsible for all particle movement. Particles larger than the width of the thin downward convection zone are carried to the top of the column and then trapped, resulting in size segregation. For a variety of accelerations the position of the rising particle can be scaled onto a single curve.

We report results showing that spatially periodic Bernstein-Greene-Kruskal (BGK) waves, which are exact nonlinear traveling wave solutions of the Vlasov-Maxwell equations for collisionless plasmas, satisfy a nonlinear principle of superposition in the small amplitude limit. The analysis explicates the notion of superimposed BGK waves which, as recent numerical calculations suggest, is crucial in the proper description of the time-asymptotic state of a plasma when a large amplitude electrostatic wave undergoes nonlinear Landau damping.

Long-wavelength (${\mathit{k}}_{\mathrm{\perp }}$${\mathrm{\rho }}_{\mathit{i}}$<1) density turbulence has been measured with good spatial localization in the core region of a high temperature tokamak plasma with auxiliary heating. Density fluctuations of ñ/n>0.5% exist for ${\mathit{k}}_{\mathrm{\perp }}$<2 ${\mathrm{cm}}^{\mathrm{-}1}$ with radial and poloidal correlation lengths typically 1–2.5 cm in the confinement region, corresponding to ${\mathit{k}}_{\mathrm{\perp }}$${\mathrm{\rho }}_{\mathit{i}}$≊0.1–0.3. An anisotropic wave-number spectrum is observed, and estimates of the turbulence-driven transport are comparable to the anomalous transport observed in tokamaks.

The scanning tunneling microscope has been used to distinguish among a series of related molecules on Pt(111) by details of their observed structures. The electronic isomers naphthalene and azulene can be recognized, as can three structural isomers of monomethylazulene, as well as dimethyl- and trimethylazulene. The number and position of substituents affect the diffusion rates, sticking coefficients, and orientations. A simple methodology based on extended Hückel theory, including the substrate, generates electron and hole density plots which show very good agreement with the data.

The simplest model of entangling polymers, a semidilute solution of hard infinitely thin rods that perform only translational Brownian motion, is studied. Reptationlike scaling theory for the transversal diffusion constant is presented. It is shown that the scaling predictions can also be derived from a microscopic dynamic theory in which the interaction of the pair of rods with the surrounding medium is described in a mean-field-like approximation.

A model pair potential is calculated for Mn-Mn pairs in Al using a Green’s function method. The pair potential has a preferred spacing of 4.7 Å. The energy resulting from these Mn-Mn interactions strongly favors the ${\mathrm{Al}}_6$Mn, α-AlMnSi, and icosahedral quasicrystal structures relative to competing simple structures, providing a possible mechanism for stabilizing the complex structures.

The generalized stacking fault energy and entropy have been calculated from first principles for two {111} planar cuts in Si separating widely spaced (shuffle plane) and narrowly spaced (glide plane) atomic layers. Energy considerations predict that the preferred fault is the shuffle plane. When the entropy is taken into account, it is found that for tensile stresses there is a critical temperature above which the preferred mode changes from shuffle to glide. We suggest that this change in preferred fault mode may be related to the brittle-ductile transition.

We have elucidated the mechanisms of defect production and annealing in ion-implanted amorphous silicon using in situ conductivity measurements as a probe of the defect structure. The defect evolution is shown to depend strongly on the substrate temperature and slightly on the irradiating ion and dose rate. It is demonstrated that two different defect structures exist, one of which, never observed before, is stable at 77 K and anneals out upon heating to 300 K. These results are explained on the basis of a new model of defect evolution in amorphous silicon.

We report new phenomena associated with the infrared-active vibrons in hydrogen at megabar pressures. We find a striking 3 order of magnitude increase in vibron absorbance at the 150 GPa phase transition at 85 K. A discontinuity in the frequency of the infrared vibron is observed which is identical to that measured by Raman spectroscopy at the same temperature. The results indicate there is a significant change in electronic properties at the transition. In addition, the infrared measurements provide evidence for a phase transition at 110 GPa at low temperature.

We present new experimental results on the thermal conductivity of isotopically enriched ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ diamond crystals at low temperatures. To our knowledge, the measured value for a 99.9% ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ crystal at 104 K, 410 W/cm K, is the highest measured thermal conducitivity for a solid above liquid nitrogen temperature. Our measured temperature dependent conductivities for the isotopically enriched diamond and natural abundance diamond specimens are well described by Callaway’s theoretical model. We predict that the thermal conductivity of a 99.999% ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ diamond crystal should exceed 2000 W/cm K at ∼80 K.

Synchrotron radiation photoemission spectroscopy suggests that the room temperature grown Au/Si(111) interface is an abrupt interface with the contact made by metallic Au and bulk Si. Si 2p core level spectra show no sign of an interface component, but only the surface reacted and bulk Si components during the growth of the interface. A surface Au-Si alloy film is first formed for Au coverages below 3 monolayers. The alloy is then stabilized into an ${\mathrm{Au}}_3$Si-like film and detached from the Si substrate when metallic Au starts nucleation in between.

We report the first determination of the Fermi surface for a quasi-one-dimensional oxide conductor, ${\mathrm{Li}}_{0.9}$${\mathrm{Mo}}_6$${\mathrm{O}}_{17}$. The Fermi surface has been measured within the cleavage plane of the crystal using high-resolution angle-resolved photoemission spectroscopy. The Fermi surface consists of two parallel straight lines, separated by a nesting vector of approximately 0.7±0.05 A${\mathrm{̊}}^{\mathrm{-}1}$. A large density of states at ${\mathit{E}}_{\mathit{F}}$ is observed from the measured band dispersion, despite a low photoemission spectral intensity at ${\mathit{E}}_{\mathit{F}}$. The measured Fermi surface allows the prediction of the magnitude of the displacement vector associated with soft phonons and a postulated Peierls transition in ${\mathrm{Li}}_{0.9}$${\mathrm{Mo}}_6$${\mathrm{O}}_{17}$.

The critical behavior in the ${\mathit{Z}}_{\mathit{N}}$ model with θ parameter is considered in the Coulomb gas representation. We focus our attention on the dependence of the critical exponents of correlation functions of ${\mathit{Z}}_{\mathit{N}}$ theory with θ=2π/N on the rank of the group, N.

A model for interacting spinless fermions in one dimension is presented and solved exactly. The solution is shown to be a Luttinger liquid with charge density wave instabilities for well characterized filling factors. Under very plausible assumptions, the exact solution is extended to the spin case with the usual charge-spin separation into two different Luttinger liquids. Required technicalities are almost trivial but the solution is very rich: Periodicity of instabilities and correlation exponents can be chosen at will.

A striking evolution of the I-V curves is observed in a single sample (i.e., for a given realization of quenched disorder) of the charge density wave conductor ${\mathrm{NbSe}}_3$ in the presence of an external rf field of varying amplitude. This yields qualitatively different ‘‘depinning transitions’’ from the pinned and the mode-locked states. In some regimes the transition is apparently continuous and shows scaling behavior in agreement with some recent theoretical results. In other regimes the transition turns first order at both harmonic and subharmonic steps, but with a marked asymmetry.

A novel carrier-acoustic instability is predicted for quasi-one-dimensional plasmas in semiconductor quantum wires with nonequilibrium carrier distributions. The complete collective excitation spectrum of the one-dimensional quantum plasma is obtained solving the complex dispersion relation in the random-phase approximation.

We have measured the current-voltage (I-V) characteristic of semiconductor superlattices in the presence of intense terahertz electric fields produced by free-electron lasers. The nonlinear I-V curves exhibit new structure that we attribute to photon-mediated sequential resonant tunneling. This tunneling process consists of well to well sequential tunneling into photon sidebands induced by the terahertz electric fields.

We argue that it is the hopping transport that is responsible for broadening of the ${\mathrm{\sigma }}_{\mathit{x}\mathit{x}}$ peaks. An explicit expression for the width Δν of the peak as a function of the temperature T is found. A close relation between the characteristic temperature in the dependence Δν on T and that in the variable-range-hopping exponent at an integer ν is established. Broadening of the peak with increasing current is also explained. The current J is shown to act like the effective temperature ${\mathit{T}}_{\mathit{e}\mathit{f}\mathit{f}}$∝${\mathit{J}}^{1/2}$ if ${\mathit{T}}_{\mathit{e}\mathit{f}\mathit{f}}$≫T. The anomalous behavior of two peaks which are close to each other (spin split, e.g.) is considered.

We report on transport measurements in fields up to 16 T in clean, untwinned single crystals of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$ which indicate that there is a critical end point for first-order melting in the H-T phase diagram in the mixed state of that system. Our data show that at a well defined value of the magnetic field, the phase boundary sharply changes slope where the first-order melting transition gives way to a second-order vortex-glass transition. These data suggest that the recently observed first-order transition is robust in the presence of a finite amount of disorder and that the vortex-glass transition only occurs for disorder beyond a certain critical amount.