The motion of a single hole in the one-band t-t’-J model that is constrained to move over only one plaquette is shown to lead to a ground state with a three-dimensional spin texture whose topology is that of a singly charged Skyrmion. This geometry mimics the weakly doped 214 superconductors where the Sr or Ce ions locally pin the otherwise mobile holes with a pinning potential that has fourfold symmetry. The competition between t and J that leads to the novel chiral-symmetry-breaking ground states is shown to be describable via a semiclassical theory that accounts for a coupling of the hole’s spin current to the magnetization current of the antiferromagnetic background.

We have investigated the microscopic ordering of the flux lattice in the mixed state of ${\mathrm{Bi}}_{2.1}$${\mathrm{Sr}}_{1.9}$${\mathrm{Ca}}_{0.9}$${\mathrm{Cu}}_2$${\mathrm{O}}_{8+\mathrm{\delta }}$ near ${\mathit{H}}_{\mathit{c}1}$ by image analysis of Bitter-decorated samples. We observe a dramatic transition from strong isotropic disorder to hexatic order with increasing magnetic field. This transition occurs at a lower applied magnetic field for samples which are annealed in oxygen.

We demonstrate that for a large class of excitable media the minimum excitability required for spiral wave propagation follows the universal scaling law ${\mathrm{\Delta }}_{\min }$=const×${\mathrm{\varepsilon }}^{1/3}$, where ɛ is the usual small parameter associated with the abruptness of excitation. The prefactor of the scaling law is obtained by solving the free-boundary problem of wave propagation. The quantitative validity of the free-boundary formulation is tested for the first time by direct comparison with the results of numerical simulation of a specific two-variable model of excitable kinetics.

We show that after integrating over the zero mode in Liouville correlation functions, the remaining functional integral resembles a free theory and may be evaluated by formally continuing the central charge. We apply this technique to the unitary minimal models coupled to gravity on the sphere, computing a number of three-point functions. After taking into account the normalizations of operators and the functional integral, we find exact agreement between the Liouville three-point functions and the results from matrix models.

Generalized quasicoherent states for the Weyl-Heisenberg quantum group have been defined by Biedenharn and MacFarlane. In this Letter other quantum Weyl-Heisenberg coherent states are defined for complex q in the usual Fock space. Such states are shown to exhibit interesting squeezing properties, in particular when ‖q‖≊1, for the q analog to the harmonic oscillator.

A rich spectrum composed of hundreds of sharp features (HWHM≲20 MHz) has been observed in the fundamental Q branch of solid ${\mathrm{H}}_2$, representing the first case of solid phase linear spectroscopy in which the high-resolution capabilities of laser spectroscopy have been fully exploited. These features are interpreted as splittings of o-${\mathrm{H}}_2$ pairs based on the work by Hardy, Berlinsky, and Harris.

The diffusion and absorption coefficients of microwave radiation in random mixtures of metallic and dielectric spheres are determined from measurements of the intensity correlation function with frequency shift and of the scale dependence of transmission. We find a narrow window of localization in frequency and metallic concentration. The transition is rounded by the presence of absorption.

Observations of periodic intensity bursts during the start-up phase of a free-electron-laser oscillator operating in the microwave regime are reported. The bursts are composed of radiation micropulses several nanoseconds wide and separated by the resonant-cavity round-trip time (∼35 ns). The occurrence of the bursts is correlated to random current spikes superposed on the continuous electron-beam current density. The observations are compared with theoretical results from an impulse response model of a free-electron laser.

A single-particle computation, simple analysis, and a particle simulation show that energy gain of an electron in a vacuum is possible using a laser and with a weak perpendicular static electric field (${\mathit{E}}_{\mathrm{app}}$). This simple system does not need any structure to accelerate the electron. If ${\mathit{E}}_{\mathrm{app}}$=0 an electron will just oscillate, with no net acceleration because of the symmetry of the laser’s electromagnetic wave in space and time. The static electric field breaks the symmetry of the wave so that the a electron is accelerated in both half wavelengths of the wave.

The normal modes of a magnetized spheroidally shaped pure ion plasma have recently been measured. Here the theory of these modes is presented. Although one might expect that a numerical solution is required (because the plasma dielectric is anisotropic and the plasma is inhomogeneous), the problem is actually separable in an unusual coordinate system. The result is a simple electrostatic fluid dispersion relation for modes in a cloud of any spheroidal shape.

We study rotational equilibria and low-order electrostatic modes of a magnetically confined, non-neutral ion plasma. The plasma rotation rate is controlled with radiation pressure from a laser beam and is continuously varied over the entire allowed range, including Brillouin flow. Excitation of an asymmetric plasma mode by a static field asymmetry is observed. The symmetric quadrupole mode is also studied; its behavior is characteristic of a strongly magnetized plasma at low density, and of an unmagnetized plasma at Brillouin flow.

We have studied the adsorption of cyclohexane and water on molecularly smooth mica using an angle-averaging, refractive-index-matching ellipsometric technique. The isotherms are linear for submonolayer coverages, showing the importance of entropy effects, and give finite thicknesses (≊2 nm) at saturation. The similarity of the two isotherms suggests that the adsorption is governed by nonspecific interactions. There is no evidence of layering but the isotherms do not agree with the Lifshitz theory of van der Waals forces.

We present a study on the temperature dependence of the microscopic entanglement distance, the chain dimension, and the plateau modulus of poly(ethylene propylene) alternating copolymer. The results provide insight into the microscopic origin of entanglement constraints and favor packing and scaling models over the topological approach. Furthermore, these results are at variance with one of the basic relations of the Doi-Edwards theory of viscoelasticity which unites the elastic response of a polymer melt with the entanglement distance.

Spectral hole burning is observed for the OH stretching mode of HDO dissolved in ${\mathrm{D}}_2$O at 298 K after intense infrared excitation. Three spectral components are inferred from the transient band shapes and related to an icelike molecular environment and other hydrogen-bonding configurations. A population lifetime of ${\mathit{T}}_1$=8±2 ps and an anharmonic frequency shift of 270±20 ${\mathrm{cm}}^{\mathrm{-}1}$ are measured.

A molecular monolayer adsorbed at the interface between the basal plane of graphite and an organic solution of didodecylbenzene has been observed in situ by scanning tunneling microscopy at a resolution of 0.2 nm. The monolayer forms a 2D polycrystal with crystallite sizes in the range of a few nanometers. The predominant domain boundary is described by a glide plane. Fast image recording allowed, for the first time, direct observation of the molecular dynamics on the time scale of 100 ms. In particular, the motion of domain boundaries could be associated with diffusing ‘‘free volume.’’

We carry out Monte Carlo simulations of the two-dimensional netural Coulomb gas of integer charges on a triangular lattice, as a function of temperature and chemical potential, and find rich critical behavior. We find transitions which do not seem to follow the expectations of a symmetry analysis, and nonuniversal jumps in the inverse dielectric constant.

We study driven interface dynamics in a model with nonlocal shadowing in two spatial dimensions using a nonequilibrium solid-on-solid model. In a wide temperature range, the system forms columnar structures which coarsen with a measured exponent of 0.56±0.02. The power spectrum of the interface shape exhibits a dynamic scaling. At low temperatures the system is described by the Kardar-Parisi-Zhang equation. We discuss the dynamic universality, and present evidence for a nonequilibrium phase transition between a rough and columnar phase.

The evolution of the surface structure of a wetting film on a rough surface as a function of the film thickness has been studied by x-ray specular reflection and surface diffusion scattering. For thin films (≲60 Å) the liquid surface is characterized by static undulations induced by the roughness of the substrate; however, with increasing film thickness the structure is dominated by thermally induced capillary waves. The data are quantitatively described by a model with exclusively van der Waals liquid-substrate interactions.

A precursor of the strong first-order structural phase transition in a resorcinol [${\mathrm{C}}_6$${\mathrm{H}}_6$(OH${)}_2$] crystal was detected by measuring the lifetime of the fluorescence. A critical decrease in the lifetime and an increase in the intensity of the impurity-induced fluorescence were found to occur starting from 30 K below ${\mathit{T}}_{\mathit{c}}$. Large-amplitude and short-lived vibrational fluctuations associated with the phase transition are suggested as a possible origin of the precursor.

${\mathrm{Si}}_{\mathit{x}}$${\mathrm{Ge}}_{1\mathrm{-}\mathit{x}}$ alloys are studied with a new method based on density-functional theory and Monte Carlo sampling. Using perturbation theory with respect to the virtual crystal, we are able to map the alloy onto a lattice gas with long-range interactions, which are determined from first principles. Monte Carlo simulations show that ${\mathrm{Si}}_{\mathit{x}}$${\mathrm{Ge}}_{1\mathrm{-}\mathit{x}}$ is a model random alloy with a miscibility gap below ≊170 K. The bond-length distribution displays three well-defined peaks whose positions depend on composition, but not on temperature. The resulting lattice parameter follows Vegard’s law very closely.