(N-1)! coexisting antiphase states are predicted to appear in an N-mode laser when the pump power drops below the threshold during part of the modulation cycle. The total output exhibits the so-called spiking mode pulsations at a frequency ${\mathrm{\omega }}_{\mathit{s}}$. However, each longitudinal-mode output shows pulses at a frequency ${\mathrm{\omega }}_{\mathit{s}}$/N, with each oscillator shifted by 2π/${\mathrm{\omega }}_{\mathit{s}}$ from its neighbor, resulting from a ‘‘winner-takes-all’’ dynamics. The assignment to antiphase states embedded in a high-dimensional phase space by injection seeding is shown. Applicability to a rewritable memory of (N-1)! different ‘‘dynamical patterns’’ is demonstrated on the basis of numerical simulations.

We describe several one-dimensional sub-Doppler laser-cooling experiments that cool Rb to finite and zero velocities in a magnetic field and polarization gradients. We then present a physical picture that unifies these measurements in terms of coherent two-photon velocity-selective resonances between atomic ground-state sublevels (including Raman resonances). We propose several sub-Doppler cooling schemes without fields or without polarization gradients, based on VSR between nondegenerate ground states.

Strongly anisotropic, polarized Cl K-V x-ray emission from gas-phase ${\mathrm{CF}}_3$Cl has been observed following resonant excitation with a linearly polarized x-ray beam. Distinctively different angular distributions are observed for x-ray emission involving molecular orbitals of different symmetries. A classical model of the x-ray absorption-emission process accurately describes the observed radiation patterns.

We report the discovery of a novel, magnetic-field-driven first-order phase transition in nematic liquid crystals. The transition is between a spatially periodic distortion, stable at intermediate field strengths, and a uniform distortion which is the ground state at high fields. From studies of dynamics we show that the transition is first order. We also find a spinodal point, below which the transition from the uniform to the periodic state occurs continuously. We discuss the utility of thickness gradient samples and determine the equilibrium wavelength of the periodic phase as a function of magnetic-field strength.

We observe the homogeneous 2D nucleation of solid anisotropic domains from a liquid phase in an amphiphilic nitrobenzoxadiazole stearic acid monolayer. The nucleation rate decreases exponentially with the inverse of the excess surface pressure. We measure the line energy λ between the two phases. Its value, averaged over the contour of a seed, is (5±0.5)×${10}^{\mathrm{-}7}$ erg/cm at 20 °C. It decreases with temperature and when stearic acid impurities are added to the monolayer. We also discuss the anisotropy of λ in the frame of a model based on dipolar electric interactions between molecules.

We have developed a novel computational scheme that allows direct numerical simulation of polymer-colloid mixtures at constant osmotic pressure. Using this technique, we have studied the entropic attraction that is caused by ideal polymers dissolved in a simple (hard-sphere) colloidal dispersion. In particular, we studied the nonpairwise additivity of the polymer-induced entropic interaction. The present simulations show that the nonpairwise additivity has a pronounced effect on the structure of a polymer-colloid mixture.

The potential at which conducting polymers can be electrochemically doped to the conducting state shifts slowly then the material is maintained in the insulating state. A logarithmic law for the shift as a function of the wait time in the insulating state has been observed over the range ${10}^{\mathrm{-}4}$–${10}^5$ s. The influence of temperature, pressure, and nature of the electrolyte has been studied. A logarithmic shift is also observed as a function of the scan rate, which indicates that the relaxation process concerns kinetic parameters of the reaction rather than the thermodynamical redox potential. The kinetics of the doping process is shown to obey a universal law, which resembles the aging process of glassy materials.

We have measured both adsorption isotherms and third-sound resonance of atomically thin ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ films on solid hydrogen. We find helium more weakly bound to a hydrogen surface than to other rare-gas surfaces, with a van der Waals cofficient of 4.6±0.4 K (layers${)}^3$. We have also measured third sound, at 0.18 K, down to a total helium coverage of 0.45±0.01 atomic layer, indicating an inert coverage at T=0 K of 0.29 atomic layer or less. In common with other weak-binding substrates we also see depressions in third-sound velocity near half-layer intervals.

A self-organized mechanism is used as a growth model to study the scaling properties of the growth of a 1D surface. It is found that the surface width w(t,L) at time t, for small system size L, obeys the scaling ansatz w(t,L)∼${\mathit{L}}^{\mathrm{\alpha }}$f(t/${\mathit{L}}^{\mathit{z}}$). Values of the exponents z and α show that the usual continuum description of growth is not applicable here. Moreover, it might be possible that the 1D surfaces grown by this model are not well defined for large L.

Metastable ${\mathrm{Zr}}_{100\mathrm{-}\mathit{x}}$${\mathrm{Al}}_{\mathit{x}}$ alloys have been formed by ball milling of elemental Zr and Al powders: supersaturated hcp solid solution for x≤15, and an amorphous phase for x≥17.5. Enthalpy-composition curves for both phases were determined by measurements of the enthalpy of transformation to equilibrium. A cusp indicating the crossover of these two curves is observed near the critical composition for amorphization. Our results indicate that phase formation by ball milling in Zr-Al is determined by polymorphous constraints and not by nucleation and growth under metastable two-phase equilibrium.

Islanding and misfit relaxation are obstacles for growth of heteroepitaxial films. Surfactants not only inhibit islanding, but also control defect structure. Growth of Ge on Si(111) was mediated by a monolayer of Sb floating on the surface. Upon exceeding the critical thickness, Shockley partial dislocations initially thread to the surface and then act as nucleation sites for complementary partial dislocations which glide down to the interface, leaving behind a fully relaxed, defect-free, epitaxial Ge film. Thus, the seemingly incompatible goals of strain relief and defect-free growth can be met by a surfactant-modified growth front.

The surface structure of the epitaxial ${\mathrm{NiSi}}_2$/Si(111) system has been determined applying a new ion-scattering method. Detecting backscattered ions with ultrahigh energy resolution we resolve the signals from successive atomic layers. From both their intensity and energy, which depends on the specific ion trajectories, we directly deduce the (sub)surface atom coordinates. Applying this new approach, we find that the ${\mathrm{NiSi}}_2$(111) surface has a bulklike topology, i.e., it is terminated by a Si-Ni-Si triple layer. The outermost Ni-Si and Ni-Ni interlayer distances are relaxed from their bulk values.

The onset of metallization in highly compressed solid hydrogen and a corresponding discontinuity in molecular vibrations have been linked in the literature to band-gap closure in an ordered hcp structure. We performed extensive first-principles calculations on the energetics and the electronic properties of solid hydrogen, and explored in detail variations in molecular orientations, bond lengths, and the c/a ratio, within an hcp lattice. We find that the commonly assumed structure is energetically unfavorable, and that lower-energy structures have wider band gaps to much higher density. Implications for the onset of metallization are discussed.

To determine the size dependence of the bonding in divalent-metal clusters we use a many-electron Hamiltonian describing the interplay between van der Waals (vdW) and covalent interactions. Using a saddle-point slave-boson method and taking into account the size-dependent screening of charge fluctuations, we obtain for ${\mathrm{Hg}}_{\mathit{n}}$ a sharp transition with vdW to covalent bonding for increasing n. We show also, by solving the model Hamiltonian exactly, that for divalent metals vdW and covalent bonding coexist already in the dimers.

A new line spectrum in gold-doped silicon with a prominent zero-phonon line at 6120 ${\mathrm{cm}}^{\mathrm{-}1}$ is discussed. Several phonon replicas are observed with a phonon energy of about 57.4 ${\mathrm{cm}}^{\mathrm{-}1}$. The phonon replicas are split due to a weak Jahn-Teller interaction of E⊗E type. The center, which is suggested to have trigonal symmetry, is likely to involve two substitutional gold atoms and an iron atom on a tetrahedral interstitial site.

Detailed information on the electronic structure of the neutral substitutional gold center in silicon (${\mathrm{Au}}^0$) has been revealed from Zeeman studies of the donor and acceptor excitation spectra at 793 and 611 meV, respectively. The center is paramagnetic, S=1/2, with ${\mathit{g}}_{\mathrm{\parallel }}$≊2.8 and ${\mathit{g}}_{\mathrm{\perp }}$≊0, and has a static 〈100〉 tetragonal distortion. Reorientation between different equivalent distortions is observed even at 1.9 K which establishes the single substitutional nature for this gold center. The fact that ${\mathit{g}}_{\mathrm{\perp }}$≊0 explains the failure to detect ${\mathrm{Au}}^0$ by EPR.

Using angle-resolved laser photoemission we have studied the ultrafast electron relaxation processes on the Ge(111) π-bonded 2×1 surface with subpicosecond time resolution. Photoexcitation of the bulk bands and subsequent bulk-surface coupling results in a transient population of the normally unoccupied ${\mathrm{\pi }}^{\mathrm{*}}$-antibonding surface band. Our studies permit the direct observation of a unique process, that of the recombination of surface electrons with bulk holes mediated by phonons at the surface, which we find to be the primary mechanism involved in the ultrafast decay of the transient surface electron population.

A simple, yet physically reasonable, model is presented which describes an arbitrary number of interacting particles in a quantum dot. Exact analytic expressions are obtained for the energy spectrum as a function of particle number and magnetic field.

We have fabricated and investigated submicron-size (0.01 and 0.04 μ${\mathrm{m}}^2$) Pb-alloy single Josephson junctions attached to high-resistance thin-film NiCr or Cr leads which provide the necessary conditions for a strong charging effect. When the Josephson coupling energy is less than the charging energy, we find a novel shape of the current-voltage curves, with a Coulomb gap at small voltages, and a current peak at larger voltages. A theory based on the concept of incoherent Cooper-pair tunneling has explained the data well.

A low-frequency torsional oscillator has been used to search for flux-lattice melting in an untwinned single crystal of ${\mathrm{Y}}_1$${\mathrm{Ba}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$. The damping of the oscillator was measured as a function of temperature, for applied magnetic fields in the range 0.1≤H≤2.3 T. A remarkably sharp damping peak has been located. It is suggested that the temperature of the peak corresponds to the melting point of the Abrikosov flux lattice.