We predict, on the basis of a model calculation, that Fano interference effects may be observed in type-II quantum-well structures resulting in pronounced nonreciprocal absorption and emission profiles and interference narrowing due to overlapping resonances.

The transport of fluid particles on three-dimensional standing surface waves is studied by the inviscid irrotational theory. When two internally resonant modes are excited simultaneously, a second-order vortical drift velocity emerges on the surface proportional to the angular momentum. Particles can move periodically, quasiperiodically, or chaotically over a wide distance, depending on the size of the container. The theory presented is applied to the smallest system, having a transport effect that has been discovered in capillary-wave experiments.

The evolution and radiation of strongly heated and ionized solid density material is calculated for conditions which are produced by an intense, femtosecond laser pulse. It is found that the spectrally integrated radiation emitted in the frequency range hν>${\mathit{kT}}_{\mathit{e}}$, where ${\mathit{T}}_{\mathit{e}}$ is the initial peak plasma temperature, can be as short in duration as ∼100 fs if ${\mathit{kT}}_{\mathit{e}}$ is in an optimum range, set by the target material chosen. For temperatures in this range, the radiation pulse duration is controlled primarily by hydrodynamic expansion. Low x-ray yields can be attributed to suppression of high-ion-stage populations by the high rate of three-body recombination in solid density plasma.

The first experiment simulating helium ash exhaust in a DT fusion reactor has been performed in the JT-60 tokamak with L-mode divertor discharges. He was injected with a 30-keV neutral beam to realize core fueling. Divertor neutral pressures of hydrogen and He increased in proportion to the cube of the electron density of the main plasma. The He enrichment factor was 0.5 at n${\mathrm{¯}}_{\mathit{e}}$=6×${10}^{19}$ ${\mathrm{m}}^{\mathrm{-}3}$ and increased in proportion to ${\mathit{n}}_{\mathit{e}}$. In an L-mode plasma of a fusion reactor, thermalized α particles (He ash) generated in the core plasma can be easily exhausted with a pumping speed of several tens ${\mathrm{m}}^3$/s.

The stabilization of both the (m=2, n=1) tearing mode and a detached plasma has been obtained with the use of the ergodic divertor in Tore Supra Ohmically heated discharges at the density limit and for low plasma pressure. This has allowed us, for the first time, to define and to check a discharge piloting strategy to prevent density-limit disruptions and to create a stable edge-radiating layer that dissipates 100% of the input power.

Collective molecular-reorientation phenomena in the nematic liquid crystal 5CB are investigated in dynamic-grating experiments using picosecond excitation pulses. Grating buildup and decay is monitored by diffraction of a cw laser beam. It is shown that molecular reorientation still increases after the excitation pulse but relaxes exponentially later. The observed dynamics can be explained by a flow-alignment theory considering photoelastic stresses leading to additional forces besides the optical torques, which are well known from previous experiments.

We compute the asymptotic structure factor ${\mathit{S}}_{\mathbf{k}}$(t) [=L(t${)}^{\mathit{d}}$g(kL(t)), where L(t) is a time-dependent characteristic length scale and d is the dimensionality] for a system with a nonconserved n-component vector order parameter quenched into the ordered phase. The well-known Ohta-Jasnow-Kawasaki-Yalabik-Gunton result is recovered for n=1. The scaling function g(x) has the large-x behavior g(x)∼${\mathit{x}}^{\mathrm{-}(\mathit{d}+\mathit{n})}$, which includes Porod’s law (for n=1) as a special case.

For a mixture of hard-sphere dipoles and neutral hard spheres we calculate the correlation functions from integral equations and evaluate the concentration structure factor ${\mathit{S}}_{\mathit{c}\mathit{c}}$(k). For large enough dipolar interaction, this structure factor becomes infinite, indicating a demixing phase transition. This instability is also found for charged hard spheres in a dipolar solvent and is the reason for the problems faced previously in investigations of hard-sphere model electrolytes.

We report for the first time a study of the specular reflectivity of neutrons by an oil-water interface. We have overcome the problem of neutron absorption in the upper oil phase by using thin oil layers of well-controlled thickness. The study is performed on an oil-water interface covered by a surfactant layer previously studied by light scattering and ellipsometry. The neutron study allows us to determine the thickness of the surfactant layer and the oil-water interfacial roughness, which is large due to the ultralow interfacial tension.

We present the first evidence by acoustic measurements of H tunneling and trapping by O atoms in a rare-earth–hydride system. The ${\mathrm{YO}}_{0.0027}$${\mathrm{H}}_{0.016}$ alloy presents three new elastic-energy-loss peaks most likely due to H trapped by O between 1.4 and 330 K. The peak at the lowest temperature is due to tunneling of the trapped H; its relaxation rate strongly depends on temperature indicating a dominant contribution of multiphonon processes already at a few degrees kelvin. The other two peaks, with activation energies of 0.14 and 0.22 eV, can be attributed to jumps of H in the distorted environment of the O atom.

We report the first direct observation of light-enhanced hydrogen motion in hydrogenated amorphous silicon. Diffusion enhancement increases with illumination intensity in undoped material and is suppressed in doped and in compensated material. The enhancement is attributed to an increased release rate of hydrogen from silicon-hydrogen bonds in the presence of photogenerated carriers. The implications of the effect for metastable defect formation are discussed.

The electromagnetic response function of a ${\mathrm{C}}_{60}$ cluster is calculated using linear-response theory. We find that the valence electrons are quite delocalized and show collective excitations. In the low-energy part of the excitation spectrum, the lowest allowed transition at ħω≊3 eV is strongly screened, and the other transitions below 6 eV are moderately screened, in agreement with experiment. We also predict a giant collective resonance at an unusually high energy of ≊20 eV.

The optical properties of the stable icosahedral quasicrystal ${\mathrm{Al}}_{63.5}$${\mathrm{Cu}}_{24.5}$${\mathrm{Fe}}_{12}$ have been measured from 40 to 25 000 ${\mathrm{cm}}^{\mathrm{-}1}$ at 300 and 80 K. Unlike metallic glasses with a Drude spectrum with strong elastic scattering by disorder, or semiconductors with a conductivity gap, the optical conductivity of this quasicrystal is distinctive: Starting from the very low dc value, it increases linearly with frequency well into the near infrared. A prominent peak in the conductivity is observed at 245 ${\mathrm{cm}}^{\mathrm{-}1}$; its position and strength suggest that it arises from a direct excitation of phonons.

We have made direct experimental observation of a new mechanism for Fermi-level pinning in Si-doped (001) GaAs. Scanning-tunneklng-microscope images show that high levels of Si doping cause the GaAs(001)-(2×4) unit cells to reorder by the formation of kinks in the dimer vacancy rows. We are able to show that these kinks are surface acceptors, which form in the required numbers fo compensate exactly the GaAs surface region. We find that in the depleted surface layer all the incorporated Si atoms are donors up to Si concentrations of at least 1×${10}^{19}$ ${\mathrm{cm}}^{\mathrm{-}3}$.

Optical-absorption change following photoexcitation of the lowest triplet self-trapped exciton (STE) in NaCl has been measured in the femtosecond time regime. It is found that a short-lived intermediate state is generated within 1 ps and decays accompanied by restoration of the lowest STE. An oscillation in the population of the lowest STE and the intermediate state with a period of 1.1 ps was observed. Formation of Frenkel pairs has been found to occur not at the initial stage of relaxation but as a result of the relaxation leading to the lowest STE.

Dimensional crossovers of nonclassical conductivity have been observed going from 1D to 2D and from 2D to 3D in bulk n-${\mathrm{Hg}}_{0.8}$${\mathrm{Cd}}_{0.2}$Te for the first time. Various samples of micron dimensions were studied at relative high temperatures between 1.4 and 30 K. Dimensional crossovers were provoked by changing the sample temperature. In this narrow-gap semiconductor, with an extremely small effective mass, the nonclassical conductivity is related to electron-electron interaction.

We have observed terahertz radiation induced by subband-gap femtosecond optical excitation from GaAs. We belive this is due to screening of the surface depletion field by virtual photocarriers (the inverse Franz-Keldysh effect).

We have measured the nonlinear transport in the spin-density-wave (SDW) state of (TMTSF${)}_2$${\mathrm{PF}}_6$. Besides the typical sliding SDW conduction, at temperatures close to ${\mathit{T}}_{\mathrm{SDW}}$, we find a new type of collective electron transport below T≃1 K, with temperature-independent conductivity which follows a Zener-type expression. We discuss the relevant energy scales of the ground-state excitations, both for single-particle tunneling and for coherent SDW processes.

We measured the Hall constant, resistivity, and magnetoresistance of the narrow-band-gap semiconductor ${\mathrm{TmSe}}_{0.45}$${\mathrm{Te}}_{0.55}$ at pressures up to 17 kbar and down to 4 K. As the band gap can be closed with pressure, a semiconductor-metal transition occurs. Above 5 kbar, when the gap is partially closed, a transition to a more insulating phase is detected. The Hall effect at low temperature and high pressure reveals that the resistivity increase is caused by a condensation of free carriers, which strongly supports this as the first observation of the excitonic insulator ground state of condensed matter.

Glassy behavior (including hysteresis, irreversibility, a peak in the zero-field-cooled magnetization, and nonexponential relaxation) is observed in a quenched ferrofluid system consisting of 50-Å magnetite particles. An Arrott plot, ${\mathit{M}}^2$ versus H/M, shows clear features of random anisotropy similar to what is found in amorphous ferromagnets. We discuss the glassy behavior in terms of both the random anisotropy and the dipole interactions, and we constrast the unusual response of our system with canonical spin glasses.