Normally unoccupied adsorbate-induced states within the GaAs band gap were studied by measurement of ultraviolet-photoemission spectra from pulsed-laser-excited surfaces. Strikingly similar discrete structures within the gap were observed for submonolayer coverages of both chemisorbed oxygen and gold. The implications of these results for the understanding of Fermi-level pinning at interfaces are discussed.

Energetic positive muons were injected into the backs of thin moderators (lithium fluoride, quartz, and copper), and the transmitted beam energy analyzed. The ${\mu }^{+}$ time-of-flight spectra for lithium fluoride and quartz were observed to have two components: a narrow distribution of slow (10 eV) ${\mu }^{+}$ rate ≅ (1.6±0.35) × ${10}^{-7\mathrm{}}$ per incident ${\mu }^{+}$ for lithium fluoride] and a broad fast component (0-2 keV), while the data for copper indicated only a fast contribution. Slow (<10 eV) negative muonium ions (${\mu }^{+}{e}^{-}{e}^{-}$) were also observed for the first time in vacuum.

The measurement of current transport due to ballistic, quasimonoenergetic, hot electrons injected into thin layers of GaAs indicates that some electrons transfer into the first satellite valleys (L valleys). Applying hydrostatic pressure, which changes the relative energies of the valleys, results in a corresponding shift of the electron energy for which transfer is evident. Transfer of ≃25% at atmospheric pressure was estimated for a transit time of 0.03 ps. We have also measured the conduction-band discontinuity between GaAs and AlGaAs and find it to be insensitive to hydrostatic pressure.

The infrared reflectivity of CsI has been measured in a diamond-anvil cell up to a pressure of 1.7 Mbar. An analysis of the data indicates that the metallization pressure lies in the range of 1.1±0.1 Mbar.

Evolution of heavy-fermion behavior in ${\mathrm{CeCu}}_2$${\mathrm{Si}}_2$ from strong mixed valence in ${\mathrm{CeNi}}_2$${\mathrm{Si}}_2$ is demonstrated in the ${\mathrm{CeCu}}_{2\mathrm{-}\mathrm{x}}$${\mathrm{Ni}}_{\mathrm{x}}$${\mathrm{Si}}_2$ system. Heavy-fermion behavior, as probed by the low-temperature susceptibility, χ(O), is destroyed at xapeq20.65. There is an anomalous increase in the Ce-ligand distances, whithout any anomaly in the Ce-Ce separation, for x<0.65, tracking the x dependence of χ(O). This observation shows explicitly for the first time that the tendency for dehybridization of the ligand valence orbitals with the Ce 4f orbital is essential to attain the heavy-fermion ground state.

We measure the conductance variations of submicrometer inversion-layer segments in silicon devices, systematically changing the length, width, inelastic diffusion length, gate voltage, magnetic field, and temperature. Results agree with the theory of universal conductance fluctuations, demonstrating that random quantum interference causes rms conductance changes ΔG=$e^2$/h in each phase-coherent subunit of each segment. The random quantum interference is extremely sensitive to change of a single scatterer.

The magnetic ordering of very thin Gd layers on Fe(100) has been characterized with use of the element-specific magnetic resolving power of spin-polarized Auger spectroscopy. We find antiparallel coupling of Gd to the Fe substrate, and identify surface-specific temperature dependence of the Gd and Fe sublattice magnetizations. The magnetic correlation length in Gd above its ordering temperature is obtained.

In the framework of the simplest Einstein-Cartan generalization of the standard cosmological model, it is shown that an inflationary phase may occur at a sufficiently early epoch, during which the dominant contributions to the effective energy-momentum tensor are represented by the spin density of the matter sources. The general features of this inflationary scenario are briefly discussed, and in particular the possibility of obtaining an expansion rate different from that of the standard exponential inflation is stressed.

We present first results obtained from a simulation of lattice OCD with staggered fermions by a Monte Carlo algorithm that incorporates the effect of the fermion determinant exactly. The chiral condensate $\overline{\chi }\chi$ and various Wilson-loop expectation values are measured on a $4^4$ space-time lattice and the results are compared with the same quantities measured on the same-size lattice with the pseudofermion method. A quantitatively good agreement is found.

The equation of motion of the tachyon field is obtained by requiring conformal invariance of the closed bosonic string propagator in a tachyon background. The cubic tachyon coupling is also obtained in this way. These equations are generalizations of the Kosterlitz-Thouless flow equations and involve nonperturbative contributions to the $\beta$ functions.

The low-energy effective theory arising from compactification of the $E_8\otimes E_8^{\prime }$ heterotic superstring on $M_4\times K_6$ is discussed. Symmetry between the observed and shadow world will occur only for manifolds (of which no examples are yet known) with special values of $Tr\left(R\wedge R\right)$. Other scenarios are described in which no new gauge bosons or chiral fermions appear.

Evidence for the possible production, and rapid decay into $e^{+}{e}^{-}$ pairs, of a new, light particle in heavy-ion collisions motivates the reexamination of searches for light particles in upsilon decays. We have searched for the decay $\Upsilon \mathrm{}\left(1S\right)\mathrm{}\to \gamma +\alpha$, where $\alpha$ subsequently decays into an $e^{+}{e}^{-}$ pair in the detector. We observe no evidence for this decay, and obtain an upper limit for the branching ratio. We also show that our limit excludes the possibility of short-lived axions within the original axion model.

We have searched for the exclusive decay of the $\Upsilon \mathrm{}\left(1S\right)\mathrm{}$ into a photon and a short-lived spin-0 particle, $a$, decaying into $e^{+}{e}^{-}$, using the CLEO detector at the Cornell Electron Storage Ring. Upper limits for the product branching ratio $B\left(\Upsilon \mathrm{}\right(1S)\mathrm{}\to \gamma a)B(a\to e^{+}{e}^{-})$ are established for a range of masses, $2m_e<m_a<2\mathrm{}{m}_{\mu }$.

A rotational band with a constant moment of inertia ${\mathcal{I}}^{\mathrm{}\left(2\right)\mathrm{}}={58\hslash }^2$ ${\mathrm{MeV}}^{-1\mathrm{}}$ has been observed in ${}_{}{}^{152}{}_{}{}^{}\mathrm{Dy}$ extending from spin ${18}^{+}$ to ${40}^{+}$. The band coexists with the known oblate yrast states although it is up to 1.5 MeV higher in excitation energy. It carries 4% of the decay strength and it is proposed to be a four-quasiparticle aligned structure. It is conjectured that the superdeformed states at the highest spins may decay via this band rather than via the yrast oblate states.

The linear dispersion relation for axisymmetric TM modes in a cylindrical waveguide lined with a dielectric material and enclosing a thin annular electron beam is derived and solved. Approximate analytic solutions are obtained for both weak and moderate beam regimes. A model of nonlinear saturation is developed. This model, combined with the linear theory in the moderate beam regime, defines the most efficient and compact Cherenkov maser.

Experimental observations on the reflection and refraction of a planar ion-acoustic soliton from a metallic mesh electrode are performed in a uniform double-plasma device. Reflection and refraction angles are observed to depend on the incident wave amplitude, showing a nonlinear Snell's law.

Interface melting in various tilt boundaries between crystals of Lennard-Jones particles is predicted by a harmonic analysis of the ground-state configurations. Interface excess free energies obtained in this way are extrapolated to the triple point, and these values are compared with the crystal-melt excess free energy. The validity of the method is confirmed by direct comparisons with high-temperature structures obtained by molecular-dynamics techniques, and with excess free energies obtained from the same simulations. Systems containing boundaries that exhibit interface melting experience disorder at the melting point, whereas the others can be superheated.

Deviations in a $d$-dimensional Euclidean connected lattice of the spectral number (cumulative) of vibrational states from the frequently generalized formula $N\left(\omega \right)\propto {\omega }^d$, i.e., density $\rho \left(\omega \right)\propto {\omega }^{d-1\mathrm{}}$, are common at very low frequency in many materials (e.g., crystalline), and are not related to disorder or fractal connectivity. These anomalies have been shown to be due to strong anisotropy, or to noncentral molecular-type forces, or both. The apparent spectral densities seen in globular and sheet proteins are compatible with conventional theoretical models dominated by molecular bond-bending or torsional forces.

A microscopic magnetic antiphase domain structure has been observed in a single-crystal Gd-Y superlattice by neutron diffraction. Furthermore, this long-range antiferromagnetic correlation is found to occur in a multibilayer, in which each bilayer consists of $N_{\mathrm{Gd}}$ ferromagnetic atomic planes of Gd followed by $N_{\mathrm{Y}}$ planes of nonmagnetic Y, for $N_{\mathrm{Y}}=N_{\mathrm{Gd}}=10\mathrm{}$ but not for $N_{\mathrm{Y}}=6\mathrm{} or 20$. This oscillatory behavior is consistent with recent theoretical speculation that the Gd moments are coupled through the intervening Y via the Ruderman-Kittel-Kasuya-Yosida interaction.

X-ray scattering measurements of the critical fluctuations in RbCa${\mathrm{F}}_3$ above $T_c$ have revealed two different length scales. The shorter one arises from the usual critical fluctuations and does not diverge at the transition, which is of first order. The longer one is associated with the presence of defects and appears to diverge at $T_c$. We suggest that this new feature can be interpreted in terms of large-scale fluctuations into the low-temperature phase, mediated by extended defects such as dislocations.