Fluorescence microscopy with polarized excitation allows regions of uniform tilt to be seen within domains of the liquid-condensed phase in monolayers of esters at the air/water interface. Transitions between a tilted and an utilted phase have been observed. Tilt regions within domains form regular six-arm patterns that are analogous to the star defect in films of liquid crystals. It is shown that six-arm stars are to be expected in these monolayers. A second transition has also been observed at lower temperatures.

We discuss a possible mechanism of charge transport in hydrogen-bonded chains by protonic defects which can trap one excess electron or electron hole.

A model is proposed for the ‘‘first sharp diffraction peak’’ (FSDP) in glasses. The FSDP is a chemical-order prepeak due to interstitial volume around cation-centered structural units. Calculated FSDP positions of some covalent glasses agree well with experiment, and the anomalous temperature and pressure dependences of the FSDP can be understood in terms of density effects.

A minimum-energy path in strain space has been determined which takes cubic silicon into itself. Energies are computed using the Stillinger-Weber model potential and first-principles total-energy calculations. The energy along this path has an additional minimum corresponding to a crystal structure with a body-centered-tetragonal lattice and fivefold-coordinated atoms. Lattice-dynamics, molecular-dynamics, and elastic-constant calculations show the structure is stable.

The temperature-dependent resistivity of the two-dimensional quasicrystals ${\mathrm{Al}}_{65}$${\mathrm{Cu}}_{15}$${\mathrm{Co}}_{20}$ and ${\mathrm{Al}}_{70}$${\mathrm{Ni}}_{15}$${\mathrm{Co}}_{15}$ is studied along the periodic direction (${\mathrm{\rho }}_{\mathit{p}}$) and in the quasiperiodic plane (${\mathrm{\rho }}_{\mathit{q}}$) from 4.2 to 600 K. A transport anisotropy of 〈${\mathrm{\rho }}_{\mathit{q}}$/${\mathrm{\rho }}_{\mathit{p}}$〉≃8 is measured. In both materials ${\mathrm{\rho }}_{\mathit{p}}$ is metallic and can be described by a semiclassical electron-phonon scattering model. For ${\mathrm{\rho }}_{\mathit{q}}$ a nonmetallic behavior is found, suggesting a phonon-assisted tunneling mechanism.

The projectile K Auger electron emission observed during grazing collisions of 60-keV ${\mathrm{N}}^{6+}$ ions with Au(110) is characterized by two components with strikingly different dependences on perpendicular velocity. A ‘‘fast’’ component dominates and is ascribed to ‘‘subsurface’’ emission. This component was satisfactorily modeled using a Monte Carlo simulation of the projectile trajectories after surface penetration. A ‘‘slow’’ component appears at very small angles and has a time dependence characteristic of the neutralization-deexcitation cascade predicted to occur above the surface prior to bulk penetration.

The energetics and structure of multiple excess electrons in halogen-deficient ${\mathrm{Na}}_{\mathit{n}}$${\mathrm{F}}_{\mathit{m}}$ clusters are studied starting at the stoichiometric ionic lImit ${\mathrm{Na}}_{\mathit{n}}$${\mathrm{F}}_{\mathit{n}}$ and ending with pure metallic clusters ${\mathrm{Na}}_{\mathit{n}}$ (for n=4,3,2 and partially for n=14). The results exhibit structural transitions upon metallization, odd-even oscillations in n-m and possibly shell-closing effects portrayed in formation and ionization energies, and excess-metal face segregation for the larger system.

We present the first soft x-ray-emission spectra for solid Kr (4p-3d) and Xe (5p-4d) that are free of complicating satellite spectra. Monochromatic synchrotron-radiation excitation is used to suppress the satellites. The data are analyzed to determine the ${\mathit{P}}_{3/2}$ bandwidth for both elements; these results are compared with both photoemission data and available theoretical calculations. Bandwidths are found to be larger than those predicted by most electronic structure calculations.

The anomalous Hall effect of amorphous, high-resistance, Fe films (2–10 monolayers thick) is measured as a function of temperature. We find a logarithmic temperature dependence of the anomalous Hall resistance similar to the Coulomb anomaly of the resistance but twice its magnitude. The measurements are in excellent agreement with a recent theoretical calculation by Langenfeld and Wölfle and provide us with an independent confirmation of the influence of the enhanced Coulomb interaction in disordered electron systems on transport properties.

We discuss quantum corrections to the anomalous Hall conductivity in disordered metallic films containing magnetic moments. Within a model of skew scattering we show that Coulomb-anomaly terms vanish identically. The weak-localization contribution is cut off by the phase-breaking effect of skew scattering. In a dense system of magnetic moments, the internal magnetic field may cause a more rapid destruction of phase coherence. Our findings are in agreement with a recent experiment on ferromagnetic amorphous Fe films.

The effective magnetic moments of small iron and cobalt clusters have been calculated by assuming that the clusters undergo superparamagnetic relaxation. The effective moments per atom are found to be much below the bulk values, even at low temperatures (100 K). They increase with particle size and the applied magnetic field, and are in good agreement with recent beam experiments on ${\mathrm{Fe}}_{\mathit{N}}$ and ${\mathrm{Co}}_{\mathit{N}}$ clusters. We also provide the first realistic estimates of the true magnetic moments in small ${\mathrm{Co}}_{\mathit{N}}$ clusters. The present studies cast doubt on the recent theoretical interpretation of the observed reduced magnetic moments in small clusters compared to bulk as being due to melting of surface spins.

We discovered that an organic radical crystal, p-nitrophenyl nitronyl nitroxide (p-NPNN), is a quasi-1D ferromagnet induced by unpaired electrons on radicals. The magnetization and the susceptibility of the triclinic γ-phase crystal are very well represented by the Bethe-ansatz solution of the S=1/2 1D Heisenberg ferromagnet with nearest-neighbor coupling J≃4.3 K. Low-temperature specific heat and ac susceptibility measurements revealed that the crystal undergoes a ferromagnetic transition at 0.65 K. The interchain coupling ${\mathit{J}}^1$ was estimated to be about 0.1 K.

We have studied nonlocal electrical transport over macroscopic distances in the regime of the fractional quantum Hall effect (FQHE). Experiments clearly demonstrate dissipationless edge-state conduction associated with the FQHE. Surprisingly, our data imply that there is no edge-state conduction near filling factor ν=1/2 and on the low-ν side of the ν=1 QHE state, while edge-state conduction is observed near ν=3/2 and on the high-ν side of the ν=1 QHE state. We also observe that the electron-hole symmetry is broken for the edge states in a confined geometry.

We study theoretically the reproducible magnetoconductance fluctuations in macroscopic Anderson insulators where complex random interferences yield localization at a scale ξ larger than the elastic mean free path l. Based on the hypothesis of large ergodic quantum fluctuations of ξ when a flux quantum is applied through an area ${\xi }^2$, we show that the normalized magnetoconductance fluctuations δ${\mathit{G}}_{\mathrm{tot}}$/${\mathit{G}}_{\mathrm{tot}}$ is (${\xi }_{\mathit{p}}^{\mathit{D}}$/${\mathrm{\Omega }}_{\mathit{e}\mathit{f}\mathit{f}}$${)}^{1/2}$ for ergodic field changes ΔB∼${\mathrm{\phi }}_0$/${\xi }^2$, where ${\xi }_{\mathit{p}}$ is a percolation correlation length which approaches macroscopic length scales at very low temperatures, and ${\mathrm{\Omega }}_{\mathit{e}\mathit{f}\mathit{f}}$ is an effective volume for th classical self-averaging of the fluctuations.

The extended Hubbard model with on-site interaction U and nearest-neighbor interaction V/d is studied at half filling in high dimensions (d≫1). At small U and V the critical temperature and the order parameter are calculated including the 1/d corrections. The results differ from those obtained in the Hartree approximation by a factor of order unity.$-— At V/U=1/2 a transition is found from an antiferromagnetic to a charge-density-wave phase. A similar transition is found at large U and V, suggesting that the transition is present for all U and V satisfying V/U=1/2.

The low-temperature magnetoresistance (MR) in ${\mathrm{Bi}}_2$${\mathrm{Sr}}_2$Cu${\mathrm{O}}_6$ is highly anisotropic. By fitting the orbital MR with the weak-localization expression, we derive a carrier dephasing rate $\frac{1}{{\tau }_{\phi }}$ that varies as $T^{-\frac{1}{3}}$. This implies that the energy levels are greatly broadened at low temperatures. Both the energy scale derived from $\frac{1}{{\tau }_{\phi }}$ vs $T$ and the behavior of the longitudinal MR suggest a strong coupling between the holes and the Cu spins. We discuss implications of the large dephasing rate, and contrast the MR with that of conventional disordered metals.

Z-contrast electron microscopy demonstrates that interdiffusion is not affecting the resistive transitions observed in M×N ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}2}$/${\mathrm{PrBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathit{x}}$ superlattices. At moderate supersaturations, island growth is observed, the islands comprising one Ba-Y-Ba structural unit in height terminated at the Cu-chain plane, having sides 20–30 nm long along [100] and [010]. The associated gradual roughening of the growing surface has no apprent effect on critical currents for M≥2, the temperature and field dependence being comparable to that of a film.

We experimentally demonstrated the absence of the Zeeman effect on the Maki-Thompson fluctuation in the Aronov-Hikami-Larkin theory. Moreover, we fine that clean-limit analysis without the MTZ component closely fits the experimental data. Our analysis provides a quantitatively consistent picture of Y-Ba-Cu-O icluding transport and optical studies.

Thin tetrahedrally coordinated amorphous carbon (ta-C) films have been grown using a filtered vacuum arc. ta-C is a new allotrope of carbon whose existence was previously thought to be unlikely. A model is proposed which accounts for the formation and structure of these films on the basis of the compressive stress generated by the shallow implantation of carbon ions. An optimal range of beam energies between 15 and 70 eV, a high film stress, and a graphitic surface are predicted and confirmed by experimental evidence. Computer simulation of the growth confirms that high compressive stress is generated by impact energies in this range.

Low-energy spectral fluctuations are analyzed for higher-dimensional separable Hamiltonian systems including rectangular-well, harmonic-oscillator, and anharmonic spectra. Both nearest-neighbor spacing distribution and spectral rigidity via the ${\mathrm{\Delta }}_3$ statistics are studied. It is found that higher-dimensional statistics based on a few hundreds of states are very likely to reveal a level repulsion typical for chaotic systems. Especially critical in this sense are systems close to harmonic oscillators. Anharmonic effects tend to improve the convergence rate.