The local atomic environment of Co atoms in a CoO crystal was imaged by hard x-ray holography. The complete three dimensional picture of the first two cobalt neighbor shells with nearly isotropic resolution was obtained, using a combination of normal and inverse, synchrotron and laboratory experiments. No a priori knowledge of the structure was used.

We report on both small angle neutron scattering and magnetization measurements in the cubic $(\mathrm{K},\mathrm{Ba}){\mathrm{BiO}}_3$ superconductor. We show that the flux lines are ordered into a hexagonal lattice at low field ( $B<\mathrm{}{B}_e\sim 0.6\mathrm{T}$) and that the diffracted intensity continuously drops to zero as the magnetic field is increased towards $B_e$. This intensity fall is attributed to a static Debye-Waller factor associated with disorder induced longitudinal fluctuations of the vortex lines. We show that $B_e$ lies close to the onset of the anomalous “peak effect” in magnetization measurements, suggesting that this peak is related to the change in the structure of the vortex solid.

We describe the operation of a laser cooled cesium fountain clock in the quantum limited regime. An ultrastable cryogenic sapphire oscillator is used to measure the short-term frequency stability of the fountain as a function of the number of detected atoms $N_{\mathrm{at}}$. For $N_{\mathrm{at}}$ varying from $4\times {10}^4$ to $6\times {10}^5$ the Allan standard deviation of the frequency fluctuations is in excellent agreement with the $N_{\mathrm{at}}^{-1/2\mathrm{}}$ law of atomic projection noise. With $6\times {10}^5$ atoms, the relative frequency stability is $4\times {10}^{-14\mathrm{}}{\tau }^{-1/2\mathrm{}}$, where τ is the integration time in seconds. This is the best short-term stability ever reported for primary frequency standards, a factor of 5 improvement over previous results.

We report on a novel approach to measure the phase relaxation length and femtosecond lifetime of hot quasiparticles on metal surfaces. A 4 K scanning tunneling microscope has been used to study the spatial decay of interference patterns in the local density of states for surface state electrons on Ag(111) and Cu(111). This decay is governed by inelastic electron-electron scattering. We find a $({E-E}_F{)}^{-2\mathrm{}}$ energy dependence of the lifetimes for both Ag and Cu, and our values are comparable to the corresponding bulk electron lifetimes. This indicates that electron-electron interaction of hot surface state electrons with the Fermi sea is dominated by the underlying bulk electrons.

We suggest that the transition to superconductivity in a single crystal of ${\mathrm{Ba}}_{0.6}{\mathrm{K}}_{0.4}{\mathrm{BiO}}_3$ with $T_c=32\mathrm{}\mathrm{K}$, and having critical fields with anomalous temperature dependencies and vanishing discontinuities in specific heat and magnetic susceptibility, may well be an example of a fourth order (in Ehrenfest's sense) phase transition. We have derived a free energy functional for a fourth order transition and calculated (for the temperature range $T_c/2<T\simeq T_c$) the temperature dependence of the critical fields. We find $H_{c1\mathrm{}}\left(T\right)\propto (1-T/T_c{)}^3$, $H_0\left(T\right)\propto (1-T/T_c{)}^2$, and $H_{c2\mathrm{}}\left(T\right)\propto (1-T/T_c{)}^1$ in general agreement with experiments.

We demonstrate an ultrastable ${\mathrm{CO}}_2$ laser trap that provides tight confinement of neutral atoms with negligible optical scattering and minimal laser-noise-induced heating. Using this method, fermionic ${}^6\mathrm{Li}$ atoms are stored in a 0.4 mK deep well with a $1/e$ trap lifetime of 300 sec, consistent with a background pressure of ${10}^{-11\mathrm{}}\mathrm{Torr}$. To our knowledge, this is the longest storage time ever achieved with an all-optical trap, comparable to the best reported magnetic traps.

The general theory of surface NMR imaging of large electromagnetically active systems is considered, motivated by geophysical applications. A general imaging equation is derived for the NMR voltage response, valid for arbitrary transmitter and receiver loop geometry and arbitrary conductivity structure of the sample. When the conductivity grows to the point where the electromagnetic skin depth becomes comparable to the sample size, significant diffusive retardation effects occur that strongly affect the signal. Accounting for these now allows more accurate imaging than previously possible. It is shown that the time constant $T_1$ may in principle be inferred directly from the diffusive tail of the signal.

A multiphoton microscopy based on coherent anti-Stokes Raman scattering is accomplished with near-infrared ultrashort laser pulses. We demonstrate vibrational imaging of chemical and biological samples with high sensitivity, high spatial resolution, noninvasiveness, and three-dimensional sectioning capability.

We have measured the velocity of a running crack in brittle single crystal silicon as a function of energy flow to the crack tip. The experiments are designed to permit direct comparison with molecular dynamics simulations; therefore the experiments provide an indirect but sensitive test of interatomic potentials. Performing molecular dynamics simulations of brittle crack motion at the atomic scale we find that experiments and simulations disagree showing that interatomic potentials are not yet well understood.

Ultrashort pulse laser techniques are applied to study optically induced modulation in exchange biased ferromagnetic/antiferromagnetic (FM/AF) thin bilayer films (NiFe/NiO). Photoexcitation of the FM/AF interface with subpicosecond laser pulses induces large modulation in the unidirectional exchange bias field ( $H_{\mathrm{ex}}$) on an ultrashort time scale. The “unpinning” of the exchange bias leads to coherent magnetization rotation in the permalloy film which is time resolved by the experiment and corresponds to a large modulation in the magnetization component ( $\Delta M_Z{/M}_S\sim 0.5$), on a time scale of 100 psec.

Strong infrared fields can be used for controlled spinning of molecules to very high angular momentum states. The angular momentum acquired can be sufficient to break molecular bonds. The approach is suitable for all anisotropic molecules, and we illustrate it by dissociating a homonuclear diatomic ${\mathrm{Cl}}_2$, with optical centrifuge efficiently separating ${\mathrm{Cl}}^{35}$ and ${\mathrm{Cl}}^{37}$ isotopes and thus demonstrating high sensitivity to the moment of inertia.

The analysis of small- and ultra-small-angle neutron scattering data for sedimentary rocks shows that the pore-rock fabric interface is a surface fractal $(D_s=2.82\mathrm{})$ over 3 orders of magnitude of the length scale and 10 orders of magnitude in intensity. The fractal dimension and scatterer size obtained from scanning electron microscopy image processing are consistent with neutron scattering data.

A fourth-order Young interference experiment was done to demonstrate a practical way to measure the de Broglie wavelength of a two-photon wave packet. A two-photon collinear beam is generated by type-II spontaneous parametric down-conversion. By modifying the transverse field profile of the pump laser beam that generates the two-photon beam we demonstrate that it is possible to measure the de Broglie wavelength of the single-photon constituents of the two-photon wave packet, the de Broglie wavelength of the two-photon wave packet as a whole and an ill defined intermediate de Broglie wavelength between the two cases.

The dynamics of atomic steps and the interactions between them were observed by in situ scanning electron microscopy for the sublimation of a Si(111) surface which was atomically flat on a large $(\sim 100\mu \mathrm{m}\times 50\mu \mathrm{m})$ scale. Newly nucleated widely spaced steps moved at a constant velocity. For more narrowly spaced steps, diffusion mediated step-step interactions reduced the step velocity. To further probe these interactions, steps were made to collide. In destructive collisions, steps decelerated and flattened. In constructive collisions double atomic steps were produced.

The effect of impurities on the surface and interfacial melting of ice is investigated in the context of the Derjaguin-Landau-Verwey-Overbeek theory by calculating van der Waals and Coulombic interactions within interfacial solution films. At high temperatures, the classical solute effect dominates the melting behavior. However, depending on the amount of impurity, as temperature decreases the slope of the film-thickness versus temperature curve changes in a manner that depends on the relative strengths of van der Waals and Coulombic interactions. The results explain the wide range of experimental discrepancies and hence impact a host of environmental phenomena.

Recently, Arkani-Hamed, Dimopoulos, and Dvali have proposed that there are extra compact dimensions of space, accessible to gravity but not to ordinary matter, which could be macroscopically large. In this Letter, we argue that high-energy collider processes in which gravitons are radiated into these new dimensions place significant, model-independent constraints on this picture. We present the constraints from anomalous single photon production at $e^{+}{e}^{-}$ colliders and from monojet production at hadron colliders.

We report the direct observation of internal layering in thin ( $\sim 45–90Å$) liquid films of nearly spherical, nonpolar molecules, tetrakis(2-ethylhexoxy)silane, using synchrotron x-ray reflectivity. The Patterson functions have secondary maxima indicating layer formation, and model-independent fitting to the reflectivity data shows that there are three electron density oscillations near the solid-liquid interface, with a period of $\sim 10Å$ (consistent with the molecular dimensions). The oscillation amplitude has a strong inverse dependence on the substrate surface roughness.

The combination of semiconductor quantum well structures and strongly piezoelectric crystals leads to a system in which surface acoustic waves with very large amplitudes can interact with charge carriers in the well. The surface acoustic wave induces a dynamic lateral superlattice potential in the plane of the quantum well which is strong enough to spatially break up a two-dimensional electron system into moving wires of trapped charge. This transition is manifested in an increase of the electron transport velocity with sound amplitude, eventually reaching the sound velocity. The sound absorption by the electron system then becomes governed by nonlinearities and is strongly reduced. We study the transition from the linear towards the strongly nonlinear regime of interaction and present a theoretical description of such phenomena in a 2D system.

Experimental observations of pulsed ultrasonic transmission through granular glass beads under oedometric loading are presented. We observe in the transmitted signals the coexistence of a coherent ballistic pulse traveling through an “effective contact medium” and a specklelike multiply scattered signal. The relative amplitudes of these signals strongly depend on the ratios of the bead size to the wavelength and to the detector size. Experimental data support recent descriptions of the inhomogeneous stress field within granular media.