Scanning tunneling microscopy STM images of Si(100)-(2×1) surfaces bombarded by low-dose 3-keV ${\mathrm{Ar}}^{+}$ ions showed random defects which ordered into line defects perpendicular to the dimer rows upon annealing at elevated temperatures. Molecular-dynamics simulations were performed to explain the shapes and sizes of the observed random defects and also to examine the stability of ordered defects. Our simulations showed good agreement with STM observations.

Localization of bending waves is observed on a steel plate decorated with Lucite blocks. A significant experimental feature of the localized modes is an exponential decay of the mode intensity from their peaked centers, with a decay length that increases as (${\mathit{f}}_0$-f${)}^{\mathrm{-}1}$ when the mode frequency f approaches a quasi mobility edge ${\mathit{f}}_0$. Our experimental results, together with finite-element calculations, support the mechanism of strong bending wave scattering by the Lucite block resonances as the source of the localization phenomenon.

Thermally excited circular dislocation loops in a three-dimensional elastic solid renormalize the shear modulus μ to zero at a temperature of the same order of magnitude as the melting temperature of most solids. The vanishing is a universal power law as a function of reduced temperature t: μ∼${\mathit{t}}^{\gamma }$,γ∼0.5. In contrast to dislocation-mediated melting in two dimensions, this is achieved without a sudden proliferation of unbound dislocation loops. It should be possible to experimentally test this behavior with superheated solids.

Phase separation dynamics is studied in a density-matched liquid mixture in the presence of a weak linear concentration gradient. This novel situation enables nucleation and spinodal decomposition to be studied simultaneously. We observe at all quench depths (i) a central zone of nearly constant concentration width where interconnected domains grow linearly with time, surrounded by (ii) a zone of isolated droplets whose width increases with time, with the droplet growth compatible with a 1/3 law. These findings suggest generalized nucleation as the phase separation process.

We describe the observation of an extremely long-lived induction decay signal of the precession of the magnetization in superfluid ${}_{}{}^3{}_{}{}^{}\mathit{B}$. This is probably the first evidence of the formation of a coherent quantum magnetic state with deflected magnetization. This state can be excited at a frequency of 1 MHz at temperatures of about 0.1${\mathit{T}}_{\mathit{c}}$ and has been observed to persist for periods up to 25 s. The properties are entirely distinct from those of the well-known long-lived induction decay signal arising from a homogeneously precessing domain.

We report the first measurements of the longitudinal resonance frequency [${\nu }_{\mathrm{long}}$(A)] in ${}_{}{}^3{}_{}{}^{}\mathit{A}$ in the low-temperature limit, as well as new measurements near ${\mathit{T}}_{\mathit{c}}$. In the low-temperature limit, our data agree well with theoretically predicted behavior. The data allow us to make the first estimates of the BCS cutoff energy as a function of pressure and of the zero-temperature A-phase energy gap.

Evidence is presented, through high-resolution electron microscopy images, for the open-end growth of carbon nanotubes. Terminations of incomplete layers of carbon, seen on the tube surfaces and cone tips, suggest that the extension and thickening of the tubes occur by the island growth of graphite basal planes on existing tube surfaces. The nucleation of positive (pentagons) and negative (heptagons) disclinations on open tube ends results in changes of growth directions, producing different morphologies. A novel structure that shows complete ‘‘turn around growth,’’ involving pentagon-heptagon pairs, of the tubular assemblies is presented.

All-electron local-density-approximation electronic-structure calculations show how the ligand structure of a neutral halogen-bridged transition-metal linear-chain compound, ${\mathrm{Pt}}_2$${\mathrm{Br}}_6$${\left(\mathrm{N}{\mathrm{H}}_3\right)}_4$, modifies the electronic structure to reduce it to an effective one-dimensional system. The dimerization and opening of the band gap is then understood on the basis of a conventional two-band Su-Schrieffer-Heeger model for isolated chains. Despite the strong $\mathrm{pd}\sigma$ coupling between the $\mathrm{Pt} d_{{3z}^2-r^2}$ and $\mathrm{Br} p_z$ orbitals along the chains, the system will not dimerize in the absence of the ligand structure.

The diamond 1s core level absorption spectra measured with x-ray reflectance and partial photoelectron yield are compared. A steep rise and a feature around 290 eV in the partial yield are absent in the reflectance. This anomaly in the partial yield is due to the predominance of the Auger yield over the core exciton decay. A binding energy of 1.25 eV for a dipole forbidden core exciton is determined from these spectra. The spectral assignments of absorption features are revised, and discrepancies in diamond core exciton models are resolved.

We have observed Coulomb correlations between the two resonant tunneling conduction channels, one per spin orientation, associated with each localized site in the barrier of a metal-insulator-metal tunnel junction. Our data support the recent theory of Glazman and Matveev pertaining to correlated resonant tunneling. We also infer correlated inelastic hopping along chains consisting of two localized sites.

We report on high-resolution variable-temperature ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ magic-angle-spinning NMR spectra of the organic superconductor ${\mathrm{\beta }}_{\mathit{L}\mathrm{-}}$(ET${)}_2$${\mathrm{I}}_3$. Broadening of the resonances is observed when lowering the temperature, with onset near the incommensurate phase transition around 180 K inducing a static crystallographic disorder. The NMR line shape displays directly the spin distribution function in space. The results give evidence of weak Anderson localization. The theory of the Knight shift distribution in 2D disordered metal is presented. We determine the impurity scattering time of conduction electrons and use it to discuss the suppression of the superconducting transition temperature by the localization.

We have used neutron diffraction to observe the vortex lattice of ${\mathrm{UPt}}_3$. This is the first such measurement in a heavy-fermion system, a superconductor below 1 K, or in a system with such a long magnetic penetration depth (6000±75 Å). It also provides the first value for the pair coherence length, 111±2Å, to be obtained directly within the pairing state of ${\mathrm{UPt}}_3$. The lattice is oblique hexagonal with conventional quantization. Its anisotropy can be explained by considering a combination of gap and Fermi-surface anisotropies. The lattice does not appear to change near the transitions between the superconducting phases identified by other techniques.

Relaxation during multiple-pulse magnetic resonance experiments is treated by an average Liouvillian technique. The finite lattice temperature is taken into account by means of phenomenological correction terms. Both the transient and long-term response of the spin system are readily treated. We predict and verify a novel steady state of correlated spin polarizations in a spin-pair system under a periodic sequence of strong π pulses.

As is well known, operations on one particle of an Einstein-Podolsky-Rosen (EPR) pair cannot influence the marginal statistics of measurements on the other particle. We characterize the set of states accessible from an initial EPR state by one-particle operations and show that in a sense they allow two bits to be encoded reliably in one spin-1/2 particle: One party, ‘‘Alice,’’ prepares an EPR pair and sends one of the particles to another party, ‘‘Bob,’’ who applies one of four unitary operators to the particle, and then returns it to Alice. By measuring the two particles jointly, Alice can now reliably learn which operator Bob used.

We suggest that at an energy of ${10}^{16}$ eV, and possibly even up to ${10}^{19}$ eV, a substantial fraction of the observed cosmic rays may originate in the central regions of active galactic nuclei.

A chiral model based on a gauge group SU(3${)}_{\mathit{C}}$×SU(3${)}_{\mathit{L}}$×U(1${)}_{\mathit{X}}$ contains dilepton gauge bosons and new quarks with exotic charges-4/3 and +5/3. Although coincident at low energy with the standard model, in the extended theory the third quark family is treated differently from the first two, and anomaly cancellation requires that the number of families be equal to the number of quark colors.

We have searched for the doubly Cabibbo-suppressed decay ${\mathit{D}}^{\pm }$→φ ${\mathit{K}}^{\pm }$ and the singly Cabibbo-suppressed decay ${\mathit{D}}_{\mathit{s}}^{\pm }$→φ ${\mathit{K}}^{\pm }$ in data from the Fermilab photoproduction experiment E691. The ${\mathit{D}}^{\pm }$ decay mode is of particular interest because it cannot result from simple spectator decay. We observe a ${\mathit{D}}^{\pm }$ signal corresponding to a branching ratio of B(${\mathit{D}}^{\pm }$→φ${\mathit{K}}^{\pm }$)=(3.$3_{\mathrm{-}1.5}^{+1.8\mathrm{}}$±0.8)×${10}^{\mathrm{-}4}$. In the ${\mathit{D}}_{\mathit{s}}^{\pm }$ mode we measure an upper limit B(${\mathit{D}}_{\mathit{s}}^{\pm }$→φ${\mathit{K}}^{\pm }$)<0.2%.

The dijet angular distribution is measured in the Collider Detector at Fermilab. This measurement covers higher mass ranges and larger scattering angles than previously possible. Good agreement is observed between the data and both leading-order [O(${\mathrm{\alpha }}_{\mathit{s}}^2$)] and next-to-leading order [O(${\mathrm{\alpha }}_{\mathit{s}}^3$)] QCD calculations. A limit on quark compositeness of ${\mathrm{\Lambda }}_{\mathit{c}}$>1.0 TeV is obtained.

We consider the effect on baryon-baryon potentials and phase shifts of including quark delocalization and color screening in the nonrelativistic quark cluster model. We find that the inclusion of these additional effects allows a good qualitative description of both.

A comparison between the predictions of a theoretical model describing the giant dipole resonance in hot nuclei, which includes the coupling to time-dependent thermal fluctuations of the nuclear surface, and experimental data on the cross section and the angular distribution associated with the dipole decay of ${}_{}{}^{92}{}_{}{}^{}\mathrm{Mo}_{}^{\mathrm{*}}{}_{}{}^{}$ is presented. Effects of different time scales for fluctuuations in the deformation and orientation degrees of freedom are observed.