Working on the ${}_{}{}^7{}_{}{}^{}\mathrm{F}_0^{}{}_{}{}^{}$${\mathrm{-}}^5$${\mathrm{D}}_0$ transition of ${\mathrm{Eu}}^{3+}$ in ${\mathrm{Y}}_2$${\mathrm{O}}_3$, we provide the first detailed characterization of excitation-induced shifts in optical transition frequencies and demonstrate their exaggeration of nominally homogeneous dephasing rates. The shifts (found to vary in rough proportion to the number of ${\mathrm{Eu}}^{3+}$ ions excited and to be as small as one part in ${10}^{12}$) were identified through their unique signature in specially designed photon-echo experiments. The effects reported may constitute a rather general complication in optical measurements of homogeneous relaxation rates in solids.

We present a simple new effective-field theory for the metallic state of a disordered interacting Fermi liquid, taking into account its instability towards the formation of local-moment states. We find a generalization of the compensation theorem of the single-impurity Anderson model, namely that strongly localized magnetic instabilities occur even when the mean-field single-quasiparticle states are extended. The theory clarifies the understanding of recent thermodynamic and spin-resonance measurements in phosphorus-doped silicon.

Magnetization measurements in strong pulsed magnetic fields on single-crystal samples of the S=1 linear-chain Heisenberg antiferromagnet Ni(${\mathrm{C}}_2$${\mathrm{H}}_8$${\mathrm{H}}_2$${)}_2$${\mathrm{NO}}_2$(${\mathrm{ClO}}_4$) are reported. The magnetization is very small at the low-field region and begins to increase sharply at a finite field for all of the three principal axes. This is evidence for the existence of the Haldane gap in this compound.

An expansion in powers of 1/z is used to study the effect of phase fluctuations on the transition temperature of a granular superconductor, modeled as an array of Josephson junctions. The lowest-order correction to $T_c$/zJ diverges to negative infinity at the grain diameter α=zJ/U=2 and reaches the value -1/2z when α=∞, which corresponds to the classical XY model. The lowest-order correction to the critical grain diameter is also calculated.

We present a simple recursive iteration of the leapfrog discretization of Newton’s equations which leads to a removal of the finite-step-size error to any desired order. This is done in a manner that preserves phase-space areas and reversibility, as required for use in the hybrid Monte Carlo method for simulating fermionic fields. The resulting asymptotic volume dependence is exp[(lnV${)}^{1/2}$]. We test the scheme on the (2+1)-dimensional Hubbard model.

We report on detailed measurements of the specific heat of ${\mathrm{UPt}}_3$, performed on a high-quality single crystal in a magnetic field perpendicular to the c axis, at temperatures down to 100 mK. Two distinct phase transitions at zero field are seen to converge at a critical point, near H=5 kOe, which coincides with the sharp break in the ${\mathrm{H}}_{\mathrm{c}2}$ curve. Beyond that point, there is evidence for only one phase. Combining these thermodynamic results with ultrasonic attenuation and ${\mathrm{H}}_{\mathrm{c}2}$ data, an H-T diagram is constructed which consists of a ‘‘polycritical’’ point and several superconducting phases.

Magnetic hysteresis of single crystals of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{x}}$ was measured in pulsed high magnetic fields above 100 T. The data were analyzed taking into account the temperature increase due to the application of pulsed fields. It is argued that values of magnetic fields at which the magnetic hysteresis disappears can be reasonably interpreted as ${\mathrm{B}}_{\mathrm{c}2}$ at low temperatures. The estimated upper critical fields at absolute zero were ${\mathit{B}}_{\mathit{c}}$$2^{\mathrm{\parallel }}$(0)=40±5 T and ${\mathrm{B}}_{\mathrm{c}2}^{\mathrm{\perp }}$(0)=110±10 T, which leads to the anisotropy ratio of about 3.

New models of rotating neutron stars show that only a surprisingly narrow range of possible equations of state (EOS’s) can simultaneously allow a rotating neutron star with frequency as large as 1968 Hz and a spherical (nonrotating) neutron star with mass as large as 1.44${\mathrm{M}}_{\mathrm{\odot }}$. The mass and baryon mass for the 1968-Hz models exceed 1.5${\mathrm{M}}_{\mathrm{\odot }}$ and 1.7${\mathrm{M}}_{\mathrm{\odot }}$, implying a progenitor mass >1.7${\mathrm{M}}_{\mathrm{\odot }}$. Those EOS’s that allowed 1968-Hz models have, for spherical stars, a stringent upper mass limit <1.7${\mathrm{M}}_{\mathrm{\odot }}$. Each model at 1968 Hz has mass above the spherical upper mass limit for its EOS, implying collapse upon spin down.

We have measured dijet angular distributions at √s =1.8 TeV with the Collider Detector at Fermilab and the Tevatron p¯p Collider and find agreement with leading-order QCD. By comparing the distribution for the highest dijet invariant masses with the prediction of a model of quark compositeness, we set a lower limit on the associated scale parameter ${\Lambda }_c$ at 330 GeV (95% C.L.).

QED in 2+1 dimensions, analyzed to lowest order in the 1/N expansion, has been shown to exhibit dynamical chiral-symmetry breaking when the number N of fermions is less than 32/${\mathrm{\pi }}^2$. This analysis is extended by considering higher-order corrections to the gap equation. It is shown that while these corrections modify the form of the gap equation, the nature of the symmetry breaking remains the same. It is also shown that the critical number of fermions is a gauge-invariant quantity.

It is shown that one-nucleon-loop calculations of the vacuum contributions to the effective potential for hadronic field theories with point nucleon fields are not compatible with large-${\mathrm{N}}_{\mathrm{c}}$ QCD. One expects that nucleon substructure will lead to a suppression of such effects of at least order ${\mathrm{N}}_{\mathrm{c}}^{1\mathrm{-}\mathrm{d}}$, where d is the dimension of space-time. Issues of the self-consistency of the large-${\mathrm{N}}_{\mathrm{c}}$ QCD are discussed.

In this Letter a new technique for measuring ultrafast vibrational dephasing is introduced that depends on the measurement of the decay of Raman interference fringes. The technique has been applied to the 524-${\mathrm{cm}}^{\mathrm{-}1}$ mode of liquid ${\mathrm{CH}}_3$I and the 656-${\mathrm{cm}}^{\mathrm{-}1}$ mode of liquid ${\mathrm{CS}}_2$, and the results are found to be in excellent agreement with previous experimental studies and with theory.

Quasielastic light scattering from Brownian particles in the rarefied environment of a glow discharge exhibits Gaussianlike intensity correlation functions owing to the long mean free paths of the particles. The shape of the correlation function depends on the particles’ average thermal velocity and friction coefficient, which can be related to aggregate mass and structure, and indicates a crossover from kinetic to hydrodynamic behavior.

Up to five arrays of soft-x-ray detectors are used with the Fourier-Bessel harmonic reconstruction method to generate 2D images of sawtooth collapses during ohmic plasma discharges on the Tokamak de Varennes. For low-harmonic reconstructions (M≤2), a quasi-interchange behavior (Wesson model) is observed during the sawtooth crash, but a reconnectionlike behavior (Kadomtsev model) is recovered using higher harmonics (M≥3) on the same data. This indicates that the Kadomtsev model is a better description for the sawtooth collapse, although the collapse time remains shorter than predicted.

The resistance to motion of a wire in superfluid ${}_{}{}^3{}_{}{}^{}\mathit{B}$ has three contributions: that due to the internal friction of the resonator; that due to pair breaking; and that due to the quasiparticle gas. We have been able to separate quasiparticle contribution and find that it is highly nonlinear with velocity on the scale of the Landau velocity, Δ/${\mathrm{p}}_{\mathrm{F}}$, and falls with increasing velocity. This indicates that the quasiparticle resistance is also governed by the condensate, almost certainly through Andreev reflection in the flow field around the wire.

We report the first observation of the slowing down of molecular rotation around the long axis in the smectic-A phase of a ferroelectric liquid crystal. This effect, evidenced by degenerate four-wave mixing, is interpreted in terms of cooperative orientation of the transverse molecular axes, due to a coupling between the fluctuating ferroelectric order and the transient biaxial mode induced by the laser fields.

We report the first explicit measurements on the profile of a spreading edge of nonvolatile liquid, in support of the theory of Hervet and de Gennes on a one-dimensional thin spreading edge. From the laser light interference patterns, the meniscus shape of the edge was reconstructed and the advancing dynamic contact angle was measured. The meniscus shape and the contact angle are in good agreement with their theory. The meniscus shape obtained at several different capillary numbers can be collapsed into one dimensionless curve, using their scaling laws.

It is shown that previously defined clusters, which give a geometrical description of the fluctuations in the q-state Potts model, at criticality have a fractal structure made of links and blobs as in percolation. Using the mapping from the Potts model to the Coulomb gas it is found that the fractal dimension of the links or red bonds $D_R$ is given by 5/4, 3/4, 13/24, 7/20, 0, while the fractal dimension of the external hull ${\mathit{D}}_{\mathit{h}}$ is given by 2, 7/4, 5/3, 8/5, 3/2, for q=0,1,2,3,4. A model originally introduced by Mandelbrot and Given for percolation clusters is found to correctly describe the fractal structure of the Potts clusters.

Electronic spectra of mass-selected, supersonically cooled carbazole ${\mathrm{Ar}}_{\mathrm{n}}$ clusters undergo abrupt size-dependent changes of band positions, widths, and shapes between n=6–14. Monte Carlo simulations indicate that these effects are due to size- and temperature-dependent structural transitions between monolayer-type wetting to dropletlike nonwetting clusters.

We describe a new method for calculating the surface tension along a surface separating two coexisting phases. It is based on a Monte Carlo simulation where one-half of the lattice is adiabatically brought from one phase to the other. The surface free energy is obtained as a difference between the total free energies of the homogeneous and mixed phases. We present the results from a numerical simulation of the two-dimensional seven-state Potts model. Application to lattice quantum chromodynamics is also discussed.