An important anomalous behavior is evidence in the angular response of the polarization vector of second-harmonic radiation generated in layered rhombohedral III-VI semiconductors. We propose a general analysis which may be applied to other nonlinear systems of an arbitrarily high order of interaction. The method gives evidence of, at least, a sixth-order effect in our experiments.

A new resistance resonance effect based on the quantum-mechanical delocalization of electrons in a symmetric-double-well potential is presented. We show that changing the symmetry of the potential profile gives rise to a resistance peak if the transport properties of the two wells are different. The proposed effect is demonstrated experimentally in semiconductor heterostructures.

We present experimental as well as theoretical data for the linear-optical response of symmetrically strained ${\mathrm{Ge}}_4$${\mathrm{Si}}_6$ [001] superlattices. Ab initio calculations show that they have a direct gap. The complex dielectric function has been measured ellipsometrically. Agreement of the experimental second-derivative spectrum ${\mathit{d}}^2$${\mathrm{\epsilon }}_2$/d${\mathrm{\omega }}^2$ with the theory is obtained, both for the shape and position of bulklike transitions and for new superlatticelike transitions, after including lifetime effects in the calculated curves through Lorentzian convolution.

The line shape of the bulk Si 2p core-level photoemission peak is found to be strongly dependent on the thickness of ${\mathrm{SiO}}_2$ overlayers through which the electrons are transmitted. This effect is strongly energy dependent. We demonstrate that it arises from strong energy-dependent carrier relaxation in ${\mathrm{SiO}}_2$, and show how the effect may be used, in conjunction with Monte Carlo simulations, to extract energy-dependent scattering rates for electron-phonon and electron-electron scattering.

We report the infrared transmission of free-standing single crystals of the high-temperature superconductor ${\mathrm{Bi}}_2$${\mathrm{Sr}}_2$${\mathrm{Ca}}_1$${\mathrm{Cu}}_2$${\mathrm{O}}_{\mathit{x}}$, at temperatures between 25 and 300 K and at frequencies covering the range of 1.5${\mathit{k}}_{\mathit{B}}$${\mathit{T}}_{\mathit{c}}$〈ħω<12${\mathit{k}}_{\mathit{B}}$${\mathit{T}}_{\mathit{c}}$. The normal-state Drude relaxation rate follows a linear temperature dependence ħ/τ=3${\mathit{k}}_{\mathit{B}}$T. In the superconducting state there is no indication of a transmission peak, which characterizes a superconducting gap in the optical conductivity. We suggest that a strong pair-breaking interaction is responsible for this null result.

The antiferromagnetic (AFM) and superconducting (SC) phase-transition temperatures of ${\mathrm{Y}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Pr}}_{\mathit{x}}$${\mathrm{Ba}}_2$${\mathrm{Cu}}_{3\mathrm{-}\mathit{y}}$${\mathit{M}}_{\mathit{y}}$${\mathrm{O}}_{\mathit{z}}$, M=Fe,Co,Zn, were studied by magnetometry and ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ Mössbauer spectroscopy. For z∼7, substitutions at all sites except those in the ${\mathrm{CuO}}_2$ planes (Pr,Fe,Co) cause superconductivity to disappear at ${\mathit{x}}_{\mathit{c}}$=0.5 or ${\mathit{y}}_{\mathit{c}}$=0.4 and antiferromagnetism to appear above ${\mathit{x}}_{\mathit{c}}$ and ${\mathit{y}}_{\mathit{c}}$. For z∼6, antiferromagnetism persists for all x and y values. On the other hand, substitution in the Cu(2) planes (Zn) suppresses both superconductivity at ${\mathit{y}}_{\mathit{c}}$=0.24 for z∼7 and antiferromagnetism for z∼6. No antiferromagnetism is seen for z∼7.

The perturbation series for superconductors near $H_{c2\mathrm{}}$ are studied in the two- and three-dimensional Ginzburg-Landau model. The large-order behavior is discussed first on a theoretical basis by an instanton method of Lipatov type. The results are compared with an eleventh-order calculation in 2D and a sixth-order one in 3D and show good agreement with the theoretical prediction. The conjectures based upon an Abrikosov lattice configuration seem to be ruled out.

With and without bioconvective pattern formation, a theoretical model predicts growth in light-limited cultures of motile algae. At the critical density for pattern formation, the resulting doubly exponential population curves show an inflection. Such growth corresponds quantitatively to experiments in mechanically unstirred cultures. This attaches survival value to synchronized pattern formation.

Laser-induced desorption of NO from Si(111) has been investigated using state-specific detection techniques. Characterization of the internal-state population distributions with desorption-laser wavelengths in the range 1907–335 nm indicate that, at low initial NO coverages, desorption is driven by a common, nonthermal mechanism. The wavelength dependence of the yield and the effects of coadsorbates on the yield establish that photogenerated holes in a Si intrinsic surface state mediate the laser-adsorbate interaction.

For dynamical systems of large spatial extension giving rise to transport phenomena, like the Lorentz gas, we establish a relationship between the transport coefficient and the difference between the positive Lyapunov exponent and the Kolmogorov-Sinai entropy per unit time, characterizing the fractal and chaotic repeller of trapped trajectories. Consequences for nonequilibrium statistical mechanics are discussed.

For an arbitrary quantum evolution, it is shown that the integral of the uncertainty of energy with respect to time is independent of the particular Hamiltonian used to transport the quantum system along a given curve in the projective Hilbert space. It is the distance along this curve measured by the Fubini-Study metric. This gives a new time-energy uncertainty principle. New geometric meanings to time as measured by a clock and the transition probability during a quantum measurement are also obtained.

We analyze a large dynamical system of limit-cycle oscillators with mean-field coupling and randomly distributed natural frequencies. Depending on the choice of coupling strength and the spread of natural frequencies, the system exhibits frequency locking, amplitude death, and incoherence, as well as novel unsteady behavior characterized by periodic, quasiperiodic, or chaotic evolution of the system’s order parameter. The phase boundaries between several of these states are obtained analytically.

When cosmic strings cross and intercommute, four kinks are created. We calculate the linear density of these kinks, K(t), in an expanding universe. After a period of rapid initial growth, K(t) approaches the scaling K(t)∝${\mathit{t}}^{\mathrm{-}1}$. However, due to the slow decay of kinks, the kink density is orders of magnitude larger than one might expect. Thus, we predict that a single horizon-length segment should have ≊${10}^6$ kinks in the radiation-dominated era. This may explain the lack of scaling behavior in the formation of loops observed in numerical simulations.

We study the evolution of global monopoles by means of numerical simulations, and find that the monopoles obey a scaling solution in which there are a fixed number of monopoles in every horizon volume. Monopoles which form at the grand unification scale can serve as seeds for galaxy and large-scale structure formation.

The polarization of Ξ¯ ${}_{}{}^{+}{}_{}{}^{}$ hyperons produced by 800-GeV/c protons in the inclusive reaction p+Be→Ξ¯ ${}_{}{}^{+}{}_{}{}^{}$+X has been measured. The average polarization of the Ξ¯ ${}_{}{}^{+}{}_{}{}^{}$, at a mean ${\mathit{x}}_{\mathit{F}}$=0.39 and ${\mathit{p}}_{\mathit{t}}$=0.76 GeV/c, is -0.097±0.012±0.009. The magnetic moment of the Ξ¯ ${}_{}{}^{+}{}_{}{}^{}$ is 0.657±0.028±0.020 nuclear magneton.

We reexamine the determination of the pion form factor at large spacelike ${\mathit{Q}}^2$ via the reaction ep→en${\mathrm{\pi }}^{+}$ and find that, because of the magnitude of the pion-nucleon form factor and the existence of competing hitherto uncalculated processes in QCD, the pion electromagnetic form factor is not sufficiently well determined at higher ${\mathit{Q}}^2$ to compare with the expected scaling prediction of QCD. Instead, we conclude that the best way to get information about the pion electromagnetic form factor is to study ${\mathrm{\pi }}^0$ production.

We have used perturbative QCD to calculate the complete set of helicity amplitudes for the real and virtual Compton-scattering reactions ${\gamma }^{\left(\mathrm{*}\right)}$p→γp, using a variety of wave functions. A particularly interesting feature of these results is the existence of nontrivial phases in the amplitudes, and a great deal of structure in the amplitudes as a function of the virtuality of the initial photon. Results for ${\mathit{s}}^6$ dσ/dt(γp→γp) are compared to existing data.

Current data on deep-inelastic processes off nuclei are analyzed by using exact QCD sum rules for the total momentum and baryon charge of nuclei. Evidence for an overall enhancement of the gluon field in heavy nuclei (≥4%) is found which, combined with the calculation of nuclear shadowing, yields a substantial enhancement of valence-quark and gluon distributions at x≊0.1, as well as a suppression of the sea for x≤0.1. It is also shown that scaling violations lead to a strong decrease of shadowing for the sea at x≊0.05. Implications for disentangling the origin of internuclear forces are further discussed.

We have studied (${\mathit{K}}^{\mathrm{-}}$,${\mathit{K}}^{+}$) reactions from an emulsion target. The S=-2 H dibaryon has been searched for by the analysis of the ${\mathit{K}}^{+}$ momentum spectrum together with emulsion data. No evidence of H production was observed in the mass range of 1.90–2.16 GeV/${\mathit{c}}^2$. Upper limits for the production cross section of the H are (0.2–0.6)% of that for the quasifree ${\mathrm{\Xi }}^{\mathrm{-}}$ production at the 90% confidence level.

An internal-target technique was used to make the first measurements of the tensor analyzing power ${\mathit{T}}_{20}$ of electron-deuteron elastic scattering in the four-momentum-transfer range of 2–3 ${\mathrm{fm}}^{\mathrm{-}1}$. Polarized deuterium atoms were confined within a storage cell in the VEPP-3 electron storage ring in Novosibirsk to achieve a total target thickness of 3×${10}^{12}$ ${\mathrm{cm}}^{\mathrm{-}2}$, 15 times greater than was previously possible with an atomic-beam target alone. The results for ${\mathit{T}}_{20}$ are in agreement with reasonable models of the deuteron wave function.