Since Berry introduced topological phases to describe the adiabatic transport of the spin of particles in parameter space, they have become a practical and descriptive concept for understanding interference phenomena in many quantum mechanical systems. For the photon two different applications of this concept were found in crystal optics: (1) the optical activity of helically wound optical fibers and (2) the development of the state of polarization on the Poincaré sphere. We present a remarkable optical ‘‘nonlinearity’’ of certain polarizing interferometers, which we discovered by using the concept of the topological phase on the Poincaré sphere and we demonstrate it with a simple experiment.

Coherent transfer of energy (CTE) gives rise to a new peak and dip in the probe gain spectrum that move proportionally with the intracavity injected power showing that stimulated emission and absorption significantly speed up the semiconductor response. Gain modification is seen in two nondegenerate, cross-polarized modes of a microcavity laser when light is injected into only one mode, giving strong evidence for the CTE origin of the gain asymmetry.

Turing patterns involve regions of different chemical compositions which lead to density gradients that, in liquids, are potentially unstable hydrodynamically. Nonlinear hydrodynamics coupled with a model of Turing pattern formation show that convection modifies and coexists with some Turing patterns and excludes others, and thereby plays a significant role in pattern selection.

The Swift-Hohenberg equation is studied in the presence of a multiplicative noise. This stochastic equation could describe a situation in which a noise has been superimposed on the temperature gradient between the two plates of a Rayleigh-Bénard cell. A linear stability analysis and numerical simulations show that, in constrast to the additive-noise case, convective structures appear in a regime in which a deterministic analysis predicts a homogeneous solution.

Evidence of intermittency in the interplanetary space plasma has been recently pointed out. We present a magnetohydrodynamic (MHD) cascade model, derived from a binomial process, whose results fit the observed scaling law for the qth power of the structure functions. Using this model we modify the oldest Kraichnan theory showing, for the first time, the multifractal structure of fully developed MHD turbulence.

Coating of the walls of TEXTOR with silicon has led to improved tokamak plasma performance. Very low concentrations of C, B, and O are measured. Radiation from silicon is located at the plasma periphery at r/a≥0.75 and decreases with increasing plasma density. Density limits are enhanced by 30% as compared to boronized conditions; large density gradients and low electron temperatures at the edge (<10 eV) are obtained. The improved confinement regimes observed earlier at low densities [${\mathrm{\tau }}_{\mathit{E}}$=1.7×ITER L 89-P International Thermonuclear Experimental Reactor)] were extended to significantly higher densities in spite of a high radiative power fraction.

The momentum distribution of the proton in liquid and solid hydrogen has been measured by neutron Compton scattering (NCS), at energy transfers between 3 and 50 eV. The data display features due to interference between the proton and neutron wave functions and are accurately described by a simple quantum mechanical model, incorporating previous spectroscopic data. The excellent agreement between calculation and data in this simple system demonstrates that the NCS technique can provide accurate information about the behavior of the proton in condensed matter. There are many applications of NCS to more complex physical systems of fundamental interest in physics, chemistry, and biology.

We study microphase separation in melts of diblock copolymers consisting of a main chain liquid crystalline block and an isotropic block. In the nematic phase the nematic block is easily stretched due to the presence of hairpins. This effect dominates splay and thus favors spherical micelles and cylinders with a nematic cores. The phase diagram is thus qualitatively different from that of an isotropic diblock and shows multiply reentrant sequences. The mesophases of nematic-isotropic diblocks afford opportunities for studying finite size effects on the nematic transition.

We present the first low frequency (0.1–50 Hz) measurements of the complex elastic constant on ${\mathrm{C}}_{60}$ single crystals. We have measured a negative dip anomaly of 25% at ${\mathit{T}}_{\mathrm{I}}$=261 K, which did not show up in previous elastic studies at ${10}^4$ Hz. The slow relaxation observed near ${\mathit{T}}_{\mathrm{I}}$ is supposed to be due to the very slow dynamics of the order parameter fluctuations. In addition it is shown that the elastic anomalies observed at ${10}^4$ Hz and 160 K originate from the same physical process as the ‘‘glass’’ transition at 80 K observed in thermal expansivity.

A wide variety of lecithins exhibit a “rippled” intermediate phase—the ${\mathrm{P}}_{\mathrm{\beta }\prime }$ phase, in addition to the common ${\mathrm{L}}_{\mathrm{\alpha }}$ and ${\mathrm{L}}_{\mathrm{\beta }\prime }$ phases of hydraged phospholipids. We describe a continuum Landau theory that can account for all of the observed phases, including the asymmetric ripple phase observed in chiral bilayers. We predict the possible existence of more than one distinct ripple phase made possible by the two-dimensional nature of the tilt order parameter. Furthermore, we show that chiral bilayers can exhibit phase transitions from symmetric to asymmetric ripples as, for example, the temperature is lowered. © 1993 The American Physical Society

Novel methods were used to generate and analyze new 15 term high temperature series for both the (connected) susceptibility χ and the structure factor (disconnected susceptibility) ${\mathrm{\chi }}_{\mathit{d}}$ for the random field Ising model with dimensionless coupling K=J/kT, in general dimension d. For both the bimodal and the Gaussian field distributions, with mean square field ${\mathit{J}}^2$g, we find that (${\mathrm{\chi }}_{\mathit{d}}$-χ)/${\mathit{K}}^2$g${\mathrm{\chi }}^2$=1 as T→${\mathit{T}}_{\mathit{c}}$(g), for a range of [${\mathit{h}}^2$]=${\mathit{J}}^2$g and d=3,4,5. This confirms the exponent relation γ¯=2γ (where ${\mathrm{\chi }}_{\mathit{d}}$∼${\mathit{t}}^{\mathrm{-}\gamma \mathrm{¯}}$, χ∼${\mathit{t}}^{\mathrm{-}\gamma }$, t=T-${\mathit{T}}_{\mathit{c}}$) providing that random field exponents are determined by two (and not three) independent exponents. We also present new accurate values for γ.

We discuss early-stage spinodal decomposition in a near-critical binary fluid for a situation in which the system is quenched abruptly by changing the pressure and in which the subsequent phase separation occurs adiabatically. The resulting nonequilibrium situation has features that do not fit conventional theoretical assumptions. We find that changes in the effective temperature during the transition can account for the lack of agreement between earlier theories and recent experimental results of Bailey and Cannell.

Circularly polarized third-sound resonances are used to drive up and drive down persistent flow states in the superfluid ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ film inside the resonator, analogous to swirling a classical fluid by agitation. The induced flow states involve vortex densities pinned by the roughness of the substrate which can include left and right circulating vortices present simultaneously within the resonator. Densities are measured to be on the order of ${10}^5$/${\mathrm{cm}}^2$. The peak flow speed of the wave oscillations necessary to swirl the film are near the critical velocity for dc flow dissipation.

The effects of the ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ interfacial layer on the average superfluid fraction (ρ${\mathrm{^}}_{\mathit{s}}$/ρ) and the specularity (S) of quasiparticle scattering of superfluid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ were measured as a function of temperature, pressure, and pore size by means of fourth sound propagation. Up to a pore size dependent threshold ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ coverage, both ρ${\mathrm{^}}_{\mathit{s}}$/ρ and S remain equal to those for pure ${}_{}{}^3{}_{}{}^{}\mathrm{He}$. Beyond the threshold, both rapidly increase as ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ coverage is increased. The enhancements vanish at pressures greater than some critical pressures depending on ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ thickness and pore size.

We present results obtained by in situ scannning tunneling microscopy which show the morphological details of the transition from layer by layer growth to three-dimensional island growth during electrodeposition. Two epitaxial layers of Ag are sequentially formed prior to the heterogeneous nucleation of three-dimensional Ag crystallites which preferentially develop on steps. The 3D growth initiates when 2D protrusions growing on the completed second adlayer achieve a critical dimension of order 20–50 nm. Our observations and analysis indicate that the growth transition may be kinetically determined by adatom migration over descending steps.

Measurements of the sticking probability s(T) for H on bulk liquid ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ reveal the onset of the universal √T dependence expected at very low atom temperatures. Studies of s(T) as a function of film thickness clearly demonstrate the influence of the van der Waals–Casimir force due to the substrate, in agreement with recent theories.

The surface of an elastically stressed solid is shown to undergo an instability in which deep, cracklike grooves form by surface diffusion. These grooves sharpen and accelerate as they deepen. The resultant morphology is in excellent agreement with recent experimental observation in several disparate materials systems.

We have made the first dynamic measurement of the (1×1)-CO island growth rate and the simultaneous CO coverage on the quasihexagonal reconstructed (hex-R) phase during the CO-induced hex-R→(1×1) phase transformation on Pt{100}. The island growth rate is described by a strongly nonlinear power law with respect to the local CO coverage on the hex-R phase at surface temperatures between 380 and 410 K, with an apparent reaction order of 4.5±0.4. These kinetics manifest themselves as a strongly flux dependent net sticking probability.

X-ray reflectivity measurements were used to determine the structure of the Pt(001)/solution interface as a function of the applied potential in alkaline and acid electrolytes. Unlike the Pt(001)/vacuum interface, the electrolyte interface was found to be unreconstructed at all potentials. The lattice spacing between the first and second layer was found to be a funciton of potential in the region where approximately a monolayer of H was adsorbed. The expansion was up to 2.5% of a lattice spacing (0.05 Å) in alkaline electrolyte, and up to 1% of a lattice spacing in acid electrolytes.

We present the first implementation of a unified approach to the study of alloys, using the atomic-sphere approximation formulation of the Korringa-Kohn-Rostoker coherent potential approximation method [P. P. Singh and A. Gonis, Phys. Rev. B 48, 1989 (1993)], which allows the treatment of the disordered alloy and of the ordered alloys on an equal footing. We apply this method to the study of the phase stability of the Ni-Pt alloy and resolve a number of discrepancies that have arisen in recent studies of this system.