We use the wavelet transform microscope to explore the intricate fractal geometry of Witten and Sander’s diffusion-limited aggregates. We report on the discovery of Fibonacci sequences in the internal hierarchical structure of these clusters. We discuss the relevance of the golden mean arithmetic to the numerically well established statistical self-similarity of these aggregates.

Calculations on finite-size systems are carried out to examine the hierarchy theory of the fractional quantum Hall effect. The concept of quasiparticle and quasihole is justified to remain valid at high densities. Numerical results reveal a hard-core boundary constraint on the anyonic quasiparticles so that their wave function must vanish as two of them get close in space. The dynamics of this contraint originates from a strong short-range repulsion between the quasiparticles. The observed quasiparticle-quasihole asymmetry in the hierarchy is understood through the hard-core anyon theory.

A serpentine superlattice quantum-wire array avoids the tilt sensitivity of a tilted superlattice and promises significant 1D confinement at the 10 nm scale. Transmission electron micrographs confirm the intended geometry. Three independent polarization measurements, an energy shift, and the light-hole–heavy-hole splitting at 1.4 K, when compared with theory demonstrate 1D valence band states and 2D conduction band states. All five measurements are explained by lateral ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As wells and barriers of x=0.12 and 0.21, respectively, thus characterizing the step-flow growth.

We develop a statistical theory of the amplitude of Coulomb blockade oscillations in semiconductor quantum dots based on the hypothesis that chaotic dynamics in the dot potential leads to behavior described by random-matrix theory. Breaking time-reversal symmetry is predicted to cause an experimentally observable change in the distribution of amplitudes. The theory is tested numerically and good agreement is found.

The existence of spontaneous polar Kerr rotation in ${\mathrm{Bi}}_2$${\mathrm{Sr}}_2$${\mathrm{CaCu}}_2$${\mathrm{O}}_8$ single crystals and ${\mathrm{YBa}}_2$${\mathrm{Cu}}_2$${\mathrm{O}}_7$ thin films was tested using a Sagnac interferometer. Observation of this effect would be strong evidence that the superconductivity in the cuprates is described by a theory that predicts broken time-reversal symmetry. The Kerr effect was analyzed for both a spatially fluctuating component (anticipating domains) and absolute offset. Neither effect was observed within the sensitivity of the apparatus. The drift of the apparatus sets an upper limit for the offset component at 10 μrad. The noise places an upper limit of 3 μrad on the standard deviation of the spatial fluctuation of the effect.

The underscreened Kondo impurity problem provides an idealized model where Fermi-liquid excitations coexist with magnetic degrees of freedom, completely decoupling from them at low frequency. We show that a simple two-fluid approach works properly in this simple case and discuss the extent to which this kind of decoupling can be used to understand the coexistence of quasiparticle excitations and low-energy magnetic fluctuations in heavy-fermion compounds.

By means of a Schwinger-boson approach we show that the staggered magnetization M in the quasi-two-dimensional quantum Heisenberg antiferromagnet is for temperatures T close to the Néel temperature ${\mathit{T}}_{\mathit{N}}$ proportional to (1-T/${\mathit{T}}_{\mathit{N}}$${)}^{1/2}$, in agreement with experiments on ${\mathrm{La}}_2$${\mathrm{CuO}}_4$. We calculate M for all T and show that the recently proposed lnT law breaks down as soon as M becomes small. We also show that the interplane spin-wave velocity vanishes slightly above ${\mathit{T}}_{\mathit{N}}$, while spin waves propagating within the planes extrapolate smoothly across ${\mathit{T}}_{\mathit{N}}$.

We show that mixed states can produce maximal violations in the Bell inequality due to Clauser, Horne, Shimony, and Holt (CHSH). This follows from the degeneracy of the operator which is naturally associated with the Bell inequality (here called the Bell operator). We have calculated the form of all the eigenvalues for the generic CHSH Bell operator. Finally, we consider several examples which demonstrate the utility of studying the eigenvalues and eigenvectors of the Bell operator.

We discuss new strict upper limits on the T-odd, P-even electron-electron, electron-nucleon, and nucleon-nucleon interactions which follow from the limits on the electron and neutron electric dipole moments. We also consider searches for T-odd, P-even interactions with atomic radiative transitions in positronium (electron-electron) and other atoms (electron-nucleon).

The ratio of cross sections for inelastic muon scattering on xenon and deuterium nuclei was measured at very low Bjorken x (0.000 02<${\mathit{x}}_{\mathrm{Bj}}$<0.25). The data were taken at Fermilab experiment E-665 with a 490 GeV/c muon beam incident on liquid deuterium and gaseous xenon targets. Two largely independent analysis techniques gave statistically consistent results. The xenon-to-deterium per-nucleon cross-section ratio is constant at approximately 0.7 for ${\mathit{x}}_{\mathrm{Bj}}$ below 0.003.

Using the (lowest-order) perturbative QCD, we argue that high energy heavy-ion collisions proceed via two stages: equilibration of gluons takes time ${\mathrm{\tau }}_{\mathit{g}}$∼1/2 fm/c, while production and equilibration of quarks needs time at least ${\mathrm{\tau }}_{\mathit{q}}$∼2 fm/c. If so, the initial gluon plasma is much hotter than usually estimated, ${\mathit{T}}_{\mathit{g}}$∼400 MeV, which leads to enhanced charm production and significant modifications of other proposed signals.

Spin correlation effects are often observed in inelastic neutron scattering and nuclear magnetic resonance (NMR) when tunneling is important. In studies of proton-proton exchange couplings observed in the ${}_{}{}^1{}_{}{}^{}\mathrm{H}$ NMR of transition-metal polyhydrides, we have had to deal with exchange degeneracies in large collections of identical spins. This Letter presents a method that easily handles such problems with low symmetry, eliminates ad hoc assumptions with respect to the feasibility of any particular permutation of particles, and is readily implemented in computer calculations.

State-selective single-electron capture in slow (0.5–3 keV/amu) collisions of ${\mathrm{He}}^{2+}$ with laser-excited ${\mathrm{Na}}^{\mathrm{*}}$(3p) atoms has been studied experimentally by means of translational energy spectroscopy, and theoretically by 38-state atomic orbital (AO) close-coupling calculations. The initial orbital alignment of the ${\mathrm{Na}}^{\mathrm{*}}$(3p) state has been controlled via polarization of the exciting laser light. Electron capture into the dominant ${\mathrm{He}}^{+}$(n=4) state is strongly favored for linear light polarization perpendicular to the ${\mathrm{He}}^{2+}$ beam. The impact energy dependence of the observed alignment behavior can be quantitatively explained by the AO calculations.

The binding energy of positronium chloride is calculated using a model potential for the ten core electrons and the quantum Monte Carlo method for the eight valence electrons and the positron. The result is 1.91±0.16 eV. Except for three- and four-particle systems, this is the first accurate calculation of the binding energy of a compound containing a positron.

We give the quantum-mechanical formulation of a model which predicts the onset of a spatial dissipative structure in a nonlinear optical system. In the case of roll patterns, we show that the two signal beams which constitute the pattern are correlated twin beams, i.e., their intensity difference exhibits fluctuations below the standard quantum limit.

We consider the reflection of de Broglie waves for a three-level atom from an atomic mirror using the evanescent wave at a vacuum dielectric interface. We show that in addition to state-selective reflection the atomic mirror in the near-field region can reflect the atom in a coherent superposition of different internal states entangled with different center-of-mass motion.

We report on the first successful measurements of the spectral width of an x-ray laser line. The experiments observed the 206.38-Å laser in Ne-like Se and indicate an unamplified width of 50 mÅ, show gain narrowing to 10 mÅ in intermediate length amplifiers, and show no significant rebroadening in saturated amplifiers. The unamplified width is 1.4 times the expected Doppler width, and the lack of rebroadening leads to speculation that collisional effects may play a significant role in determining the line profiles.

Toroidal electron clouds with a low aspect ratio (as small as 1.3) and lasting for thousands of poloidal rotation periods have been formed in the laboratory. Characteristic toroidal effects like a large inward shift of the minor axis of equipotential contours, elliptical and triangular deformations, etc., have been observed experimentally for the first time. The results of new analytic and numerical investigations of low-aspect-ratio electron cloud equilibria, which reproduce many of the observed features, are also presented.

We present measurements of stimulated electromagnetic emission (SEE) excited in the ionosphere by a powerful high-frequency ordinary mode radio wave vertically injected from a ground-based transmitter, at frequencies ${\mathit{f}}_0$ near high harmonics of the ionospheric electron cyclotron frequency ${\mathit{f}}_{\mathit{c}}$. A prominent lower-sideband SEE feature was found to be absent in an extremely narrow ${\mathit{f}}_0$ range of Δ${\mathit{f}}_0$/${\mathit{f}}_0$≊2×${10}^{\mathrm{-}5}$. This absorption resonance width allows an estimate of ${\mathit{f}}_{\mathit{c}}$ with an accuracy of a few tens of Hz, corresponding to a magnetic field magnitude accuracy of about 1 nT.

A novel mechanism for strong ion heating inside magnetized sheaths, formed at plasma-wall interfaces in radio-frequency-driven plasmas, is studied. The ion gyration frequency is modulated by the oscillating charge density inside the sheath, resulting in a Hill-type parametric equation of motion. The gyration velocity is unstable when the time-averaged gyrofrequency Ω^ is near a subharmonic nω/2 of the rf frequency. Large energy absorption occurs within only a few gyrations because of the initial exponential growth. Nonlinear saturation occurs at kinetic energies higher than the time-averaged potential difference across the sheath.