Optically detected magnetic resonance has been employed for the first time on photoluminescence from a Si/${\mathrm{Si}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Ge}}_{\mathit{x}}$ strained-layer superlattice. Emission bands occur at 0.87 and 0.8 eV. One of the resonances is anisotropic with ${\mathit{g}}_{\mathrm{?}}$=4.46±0.05 and ${\mathit{g}}_{\mathrm{\perp }}$<0.4 and is assigned to holes of the ${\mathit{J}}_{\mathit{z}}$=±3/2 valence band in the SiGe layers. This result demonstrates that at least part of the emission must originate from the superlattice region of these structures.

We consider the evolution of an electronic system initially in equilibrium with a semiconductor crystal lattice upon a sudden rise in the lattice temperature. On a short time scale (∼1 ps), electrons equilibrate with the optical phonons and establish a peculiar quasiperiodic energy distribution. Time evolution toward this distribution is discussed on the basis of an exact solution of the Boltzmann transport equation. While the quasiequilibrium regime persists (longer than ∼1 ns), the electronic system possesses a number of unusual thermodynamic and transport properties. The specific heat is suppressed as if some of the electronic degrees of freedom of were frozen out; the low-field electron mobility is substantially enhanced.

We report high-resolution nonlinear-laser-spectroscopy measurements of relaxation of lowest-energy heavy-hole excitons in GaAs multiple-quantum-well structures. We show that excitons below the absorption line center are spatially localized, and migrate among localization sites with a time scale of order 100 ps. The measurements give the resultant quasiequilibrium energy distribution of the scattered excitons and, based on the temperature dependence of the migration rate, confirm the theoretical model for phonon-assisted migration.

We describe a first-principles theory for compositional and magnetic correlations in alloys and compare the results of the theory with recent diffuse, unpolarized, neutron-scattering measurements on a single crystal of ferromagnetic ${\mathrm{Fe}}_{0.865}$${\mathrm{V}}_{0.135}$. The nuclear cross section is described very well by the theory and we are able to connect the q-dependent structure to the underlying electronic structure of the alloy. The magnetocompositional and magnetic correlations also may be obtained for comparison to polarized measurements.

We observe that the retrapping current of high-resistance, small-capacitance, superconducting tunnel junctions decreases sharply with decreasing temperature, and then has a puzzling, flat, nonzero minimum at low T, rather than continuing to decrease as quasiparticle damping freezes out. We explain the crossover by considering the combined admittance of the leads and of the junction (including the onset of pair-breaking tunneling at the gap voltage) at both dc and the Josephson frequency. Our analog simulations and analytic approximations both agree well with the data.

The zero-temperature superconducting transition in a Josephson-junction array with half of a flux quantum per plaquette is considered. Its critical behavior is described by an effective free energy in three dimensions with a transition in a new universality class. From this we infer the critical behavior and the value of the universal resistance at the transition. Relevance of these results to recent experiments on very-small-capacitance arrays is discussed.

The temperature dependence of the magnetic-field penetration depth λ of the organic superconductor κ-[bis(ethylenedithio)-tetrathiafulvalene${]}_2$Cu(NCS${)}_2$ has been determined by means of complex susceptibility measurements for single crystals. λ was found to follow a power law, λ(T)/λ(0)-1∝(T/${\mathit{T}}_{\mathit{c}}$${)}^2$, at low temperatures instead of the exponential behavior expected from BCS theory. This result is considered as the first evidence for anisotropic superconductivity with nodes of the gap parameter on the Fermi surface in this material.

We study P,T-breaking physical properties of anyons. Concerning static properties, we find no magnetic field in the anyon superconductor and very small magnetic field in the normal state. Concerning optical properties, we have derived the Wen-Zee–type effective Lagrangian. Therefore anyons exhibit P,T-breaking optical properties without suppression. We conclude that anyon models can be experimentally tested through their P,T-breaking optical properties.

We predict a glass transition in the recently discovered flux-fluid state of high-${\mathit{T}}_{\mathit{c}}$ superconductors due to topological entanglements. Two possible relaxation mechanisms are considered—single-flux-line motion with relaxation time ${\mathrm{\tau }}_1$∼exp{exp[(Λ/d${)}^2$]}, and collective motion of many flux lines with relaxation time ${\mathrm{\tau }}_{\mathrm{col}\mathrm{\sim }}$exp[(Λ/d${)}^6$], where Λ is the magnitude of transverse fluctuations of flux lines and d is the intervortex spacing. This extremely slow relaxation enables the system of entangled flux lines to support supercurrents in the presence of only a few strong pinning centers.

One-dimensional reductions of the self-dual Yang-Mills equations yield various classical systems depending on the choice of the Lie algebra associated with the self-dual fields. Included are the Euler-Arnold equations for rigid bodies in n dimensions, the Kovalevskaya top, and a generalization of the Nahm equation which is related to a classical third-order differential equation possessing a movable natural boundary in the complex plane.

Models of random surfaces defined by integrals over self-dual unitary quaternion matrices are solved exactly in a double-scaling limit. There are contributions to the specific heat from surfaces with odd Euler characteristic, indicating that these are theories of unoriented strings. For the k=1 model, these contributions are determined from the quantum mechanics of a particle moving in a potential given by the specific heat of the k=1 unitary model, up to a linear term. A by-product of this analysis is a new solution of unitary-matrix models, formulated in terms of matrix differential operators.

We point out a problem with a recent lattice calculation of the neutron electric dipole moment induced by a θ term in QCD, and explain how a correct calculation should be done.

An energy-dependent one-dimensional potential barrier for heavy-ion fusion reactions is shown to be consistent with the full dynamical coupled-channel calculation, provided the potential is written in terms of the kinetic energy ɛ in the relative-separation coordinate at the fusion barrier. It is also shown that earlier conclusions about the inadequacy of the energy-dependent barrier-penetration model is a direct consequence of expressing the energy dependence as a function of the center-of-mass bombarding energy ${\mathit{E}}_{\mathrm{c}.\mathrm{m}.\mathrm{}}$.

We present a method for calculating quantum spectra of arbitrary highly excited atoms in strong magnetic fields at fixed scaled energy ɛ=E/${\mathit{B}}^{2/3}$. Since classical dynamics depends exclusively on ɛ, this approach is most suited to analyzing the quantum manifestations of classical chaos. We find that modulations of the spectra associated with classical periodic orbits depend strongly on the quantum defect μ. In particular, the spectra at given ɛ are most (least) modulated for integer (half-integer) values of μ. We also find that the energy-level statistics tend more closely towards the Wigner (‘‘chaotic’’) limit for half-integer μ.

Instabilities due to a cross-field ion flow are reexamined by including the electromagnetic response of the ions, which has been ignored in existing discussions. It is found that this effect can lead to significant enhancement of the growth rates. Among the new results, we find a purely growing, electromagnetic unstable mode with a wave vector k parallel to the ambient magnetic field. The plasma configuration under consideration is similar to that used in the discussion of the well-known modified-two-stream instability. This instability has a growth rate faster than the ion cyclotron frequency, and is not susceptible to high-plasma-β stabilization.

We have measured the dielectric susceptibility of several glass-forming liquids over 13 decades of frequency. The primary relaxation for all the liquids, over the entire frequency and temperature range studied, can be collapsed onto a single scaling curve with only two parameters, peak position and width. This curve is different from any of the theoretical forms suggested in the literature. The relaxation evolves smoothly from Debye behavior at high temperature.

Two scaling regimes, D∼${\mathit{N}}^{\mathrm{\delta }}$ with δ=0.49±0.02 and 0.80±0.04, have been identified in a model set of nearly symmetric diblock copolymer melts, where D and N are the system peridocity and degree of polymerization, respectively. The crossover from δ=0.49 to 0.80 is identified as the Gaussian to stretched-coil transition (GST). Contrary to current theory, the GST occurs well below the order-disorder transition (ODT), ${\mathit{N}}_{\mathrm{GST}}$=0.57${\mathit{N}}_{\mathrm{ODT}}$. We associate δ=0.80 with the crossover from weak-segregation (δ=1/2) to strong-segregation (δ=2/3) behavior.

Using a Ginzburg-Landau free energy, we show that the failure of an oil/water interface to be wetted by a microemulsion is directly related to its structure. At the disorder line where the fluid loses this structure, an unusual wetting transition can occur. We calculate the elastic constant of mean curvature for both oil/water and oil/microemulsion interfaces. Employing a lattice model, we show that an incipient lamellar phase instability leads to ultralow interfacial tensions between oil and water when coexisting with a microemulsion.

We have carried out an experiment in which sandpiles are built up to a critical size and then perturbed by the dropping of individual grains of sand onto the pile. After each grain is added, the size of the resulting avalanche, if any, is recorded. For sufficiently small sandpiles, the observed mass fluctuations are scale invariant and the probability distribution of avalanches shows finite-size scaling. This demonstrates that real, finite-size sandpiles may be described by models of self-organized criticality. However, we also find that this description breaks down in the limit of large sandpiles.

We report high-resolution infrared–reflection-absorption measurements of an unreconstructed, ideally H-terminated Si(111) surface. The marked width and frequency variations of the Si-H stretching vibration with temperature are completely accounted for by a weak anharmonic coupling of this mode to a Si surface phonon band centered at 210±25 ${\mathrm{cm}}^{\mathrm{-}1}$. A decrease in Si-H stretch intensity, observed as the temperature is increased above 300 K, suggests a strong anharmonic coupling between the Si-H stretching and bending modes.