In birefringent nonlinear optical media, it is shown that phase-matched wave-mixing processes occur naturally among the extraordinary and ordinary wave components of a strong pump and a weak probe beam. The necessary and sufficient conditions that these parametric processes may lead to amplification and or polarization switching of the probe beam are quantitatively analyzed.

We report strong narrow-band stimulated far-infrared cyclotron-resonance emission from the light holes in germanium in crossed electric and magnetic fields. The emission spectrum consists of a single line which is linearly tunable with magnetic field. The gain of the cyclotron-resonance laser is determined to be 0.05±0.02 ${\mathrm{cm}}^{\mathrm{-}1}$. For the first time we have identified the lasing transition to be the n=2 to n=1 Landau-level transition of the b-set light holes by a comparison of absorption and emission spectra with calculations of the band structure including nonparabolicity corrections.

The k-ω spectra of low-frequency waves which exist in a tandem-mirror plasma are observed by using the Fraunhofer-diffraction method. The observed dispersion relations are in good agreement with those of drift waves including a Doppler shift due to E×B rotation velocity. The fluctuation level is observed to depend sensitively on the radial profile of a plasma potential. It has a maximum value when a slightly negative electric field is formed, and decreases with increase in an electric field regardless of its sign.

The kinetics of microphase separation and ordering of a diblock copolymer onto a lattice has been studied using time-resolved high-resolution small-angle x-ray scattering. The measurements show rapid formation of spherical domains after quenching and a subsequent ordering of the spheres. The results are discussed within the framework of simple models for nucleation and crystalli- zation.

A realistic model of a two-dimensional molecular crystal of methane adsorbed on MgO(100) has been studied by molecular dynamics. The low-temperature phase has quasi-long-range order in the molecular orientations, in which there proliferates a dilute gas of vortex-antivortex pairs. Finite-size scaling calculations indicate that an unbinding transition takes place at ${\mathit{T}}_{\mathit{c}}$≊27 K. In addition, the specific heat exhibits a marked anomaly at T≊32 K, in good agreement with the Kosterlitz-Thouless theory.

The current-voltage characteristics of indium-oxide films in the activationless-hopping regime exhibit an inflection point at a thickness-dependent electric field. It is argued that this electric field reflects a 2D-3D dimensionality crossover expected of a variable-range-hopping system.

The theory of depinning of charge-density waves by quantum tunneling that has been applied successfully to bulk specimens (3D) is extended to specimens where one or more of the transverse dimensions becomes less than bulk transverse phase-coherence distance. Results for threshold fields, ${\mathit{E}}_{\mathit{T}}$, derived by McCarten et al. for 2D weak pinning are extended to 1D. The square of the pinning frequency should be proportional to ${\mathit{E}}_{\mathit{T}}$. The reversible threshold polarization, ε(0)${\mathit{E}}_{\mathit{T}}$, should be essentially independent of dimensions.

Magnetoresistance at 0 K is theoretically examined. Because Kondo temperatures must be very sensitive to local disorder of ligands around f ions as implied by their large Grüneisen constant, they can be random in the neighborhood of defects and dislocations. The disorder of Kondo temperatures gives positive magnetoresistance at low fields, but negative magnetoresistance at high fields; the magnetoresistance has a peak, when the magnetization is about a half of its saturated value. If Kondo temperatures are distributed down to the zero energy, the magnetoresistance can be positively linear to fields at low fields.

We report the discovery of antiferromagnetic interlayer exchange coupling and enhanced saturation magnetoresistance in two new metallic superlattice systems, Co/Cr and Co/Ru. In these systems and in Fe/Cr superlattices both the magnitude of the interlayer magnetic exchange coupling and the saturation magnetoresistance are found to oscillate with the Cr or Ru spacer layer thickness with a period ranging from 12 Å in Co/Ru to ≃18–21 Å in the Fe/Cr and Co/Cr systems.

We have carried out angle-resolved photoemission spectroscopy on single crystals of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{6.9}$. The crystals were cleaved in situ, under ultrahigh vacuum while the sample stage was cooled to 8 K. By observing the dispersion of the electron energy bands as they cross the Fermi energy, we have mapped the Fermi surfaces. There is reasonable agreement between the experimental results and the predictions of band-structure calculations using the local-density approximation, as well as with positron annihilation experiments. Rather than δ holes, these results indicate that the Fermi surface of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{6.9}$ encloses 1+δ holes, where δ is the doping level.

We report observation of hexatic order in Abrikosov flux lattices in very clean crystals of the high-${\mathit{T}}_{\mathit{c}}$ superconductor ${\mathrm{Bi}}_{2.1}$${\mathrm{Sr}}_{1.9}$${\mathrm{Ca}}_{0.9}$${\mathrm{Cu}}_2$${\mathrm{O}}_{8+\mathrm{\delta }}$. Our experiments consist of in situ magnetic decoration of the flux lattice at 4.2 K. Analysis of the decoration images shows that the positional order decays exponentially with a correlation length of a few lattice constants while the orientational order persists for hundreds of lattice constants and decays algebraically with an exponent ${\mathrm{\eta }}_6$=0.06±0.01. Our results confirm recent theoretical speculation that the positional order should be far more sensitive to disorder than the orientational order and that the low-temperature ordered phase of the flux lines in these systems might be a hexatic glass.

Apply neutron spin-echo spectroscopy, we investigate low-energy vibrational excitations in a series of silica aerogels of varying connectivity. Connectivity is adjusted both by precursor solution chemistry and by heat treatment. Polymeric aerogels show fractonlike densities of states, whereas colloidal materials exhibit a peak in the μev regime. On sintering, the low-frequency excitations disappear. We conclude that neutron spin-echo spectroscopy provides a measure of the topological aspects of disordered materials.

We show that the intense space charge of a high-current beam may increase the gap capacitance by a factor of 2 to 3 over the vacuum value. The limiting current under an ac gap voltage is computed and compared with the steady-state value. The implications of these findings on operation efficiency and frequency stability of high-power microwave devices are discussed.

We study polymer pulsed-field gel electrophoresis by an off-lattice computer simulation. The effects of 90° rotations of the field on the chains’ conformations are analyzed. We find that 90° pulsed fields can be used to increase significantly the resolution of the chains’ separation according to size.

We study by means of a Monte Carlo simulation the rates of interconversion of metastable RNA secondary structures as the thermodynamic limit is approached. The sequences are random and uncorrelated and the refolding events are kinetically controlled and occur as the chain grows by sequential random incorporation of nucleotides. The scaling law connecting the size of the barriers with the length of the chain exhibits a striking similarity with the related kinetics of spin glasses and other disordered systems.

We show that the time evolution of a space curve is associated with a geometric phase. This phase arises from the path dependence of the rotation of the natural Frenet-Serret triad with respect to a nonrotating (Fermi-Walker) frame. We derive a general expression in 1+1 dimension for the phase and the associated gauge potential, and discuss the application of this formalism to the classical, continuous, antiferromagnetic Heisenberg spin chain.

A Maxwell demon gathers and uses information to extract work from heat. Limits derived here suggest that a Maxwell demon can extract work only by waiting for rare thermal fluctuations.

A null result was obtained for the weight change of a right-spinning gyroscope, contradicting the results recently reported by Hayasaka and Takeuchi. No weight change could be observed under a variety of spin directions for rotational frequencies between 0 and 2.2×${10}^4$ rpm. Our limit of -0.025±0.07 mg is more than 2 orders of magnitude smaller than the effect reported by Hayasaka and Takeuchi.

We have studied the production of ${\mathit{D}}_{\mathit{s}}$ mesons in the decays of B mesons at the Υ(4S) resonance. We report on the first observation of exclusive B-meson decays B->${\mathit{D}}_{\mathit{s}}^{\mathrm{-}}$${\mathit{D}}^{\mathrm{*}+}$, B→${\mathit{D}}_{\mathit{s}}^{\mathrm{-}}$${\mathit{D}}^{+}$, and B→${\mathit{D}}_{\mathit{s}}^{\mathrm{-}}$${\mathit{D}}^0$. We also present a new measurement of the branching ratio and the momentum spectrum for the inclusive decay B→${\mathit{D}}_{\mathit{s}}$X.

The next-to-leading order inclusive jet cross section is calculated including both quarks and gluons. The general structure of the dependence of the cross section on the explicit jet definition and on the choice of the renormalization scale ${\mathrm{\mu }}^2$ is found to be very similar to the case of gluons only, calculated earlier. The resulting cross section is shown to involve a much reduced theoretical uncertainty compared to the lowest-order result. First comparisons with experimental data are also exhibited.