A microscopic theory for the ubiquitous phenomenon of static friction is presented. Interactions between two surfaces are modeled by an energy penalty that increases exponentially with the degree of surface overlap. The resulting static friction is proportional to load, in accordance with Amontons's laws. However, the friction coefficient between bare surfaces vanishes as the area of individual contacts grows, except in the rare case of commensurate surfaces. An area independent friction coefficient is obtained for any surface geometry when an adsorbed layer of mobile atoms is introduced between the surfaces. The predictions from our simple analytic model are confirmed by detailed molecular dynamics simulations.

New sideband partners of the yrast bands built on the $\pi h_{11/2}\nu h_{11/2}$ configuration were identified in ${}_{55}\mathrm{Cs}$, ${}_{57}\mathrm{La}$, and ${}_{61}\mathrm{Pm}$ $N=75\mathrm{}$ isotones of ${}^{134}\mathrm{Pr}$. These bands form with ${}^{134}\mathrm{Pr}$ unique doublet-band systematics suggesting a common basis. Aplanar solutions of 3D tilted axis cranking calculations for triaxial shapes define left- and right-handed chiral systems out of the three angular momenta provided by the valence particles and the core rotation, which leads to spontaneous chiral symmetry breaking and the doublet bands. Small energy differences between the doublet bands suggest collective chiral vibrations.

An ultracold narrow atomic beam of metastable neon in the ${1s}_3\left[\right(2s{)}^{5}3p:{}_{}{}^1{}_{}{}^{}P_0^{}{}_{}{}^{}]$ state is used to study specular reflection of atoms from a solid surface at extremely slow incident velocity. The reflectivity on a silicon (1,0,0) surface and a BK7 glass surface is measured at the normal incident velocity between $1\mathrm{mm}/\mathrm{s}$ and $3\mathrm{cm}/\mathrm{s}$. The reflectivity above $30\%$ is observed at about $1\mathrm{mm}/\mathrm{s}$. The observed velocity dependence is explained semiquantitatively by the quantum reflection that is caused by the attractive Casimir–van der Waals potential of the atom-surface interaction.

We report the first observation of a striking history dependence of the structure function of vortex matter in the peak effect regime in a Nb single crystal by using small angle neutron scattering combined with in situ magnetic susceptibility measurements. Metastable phases of vortex matter, supercooled vortex liquid and superheated vortex solid, have been identified. We interpret our results as direct structural evidence for a first-order vortex solid-liquid transition at the peak effect.

Spatiotemporal magnetization reversal dynamics in a ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}$ microstructure is studied using ps time scale scanning Kerr microscopy. Time domain images reveal a striking change in the reversal associated with the reduction in switching time when a transverse bias field is applied. Magnetization oscillations subsequent to reversal are observed at two resonance frequencies, which sensitively depend on the bias field strength. The oscillation at $f=2\mathrm{}$ GHz is caused by the damped precession of $\mathbf{M}$, while the lower frequency $\sim 0.8$ GHz mode is interpreted in terms of domain wall oscillation.

We report conduction measurements on the clean, free surface of transparent insulating $\mathrm{BaTiO}{}_3$ single crystals in high vacuum. We find that the insulating $\mathrm{BaTiO}{}_3$ crystals exhibit surface conductance that is dependent on the spontaneous polarization, whereas no conduction perpendicular to the surface is observed. The surface conduction shows semimetallic temperature dependence and persists down to at least 100 K. The observations suggest a two-dimensional electron on a clean, free ferroelectric surface that may be regarded as a ferroelectric metal. The results have important implications for understandings of the fundamental properties of ferroelectrics, the size effect, and ferroelectric devices.

We study experimentally the jamming phenomenon of granular flow of monodisperse disks of $D=5\mathrm{}\mathrm{mm}$ diameter in a two-dimensional hopper with opening $R$. The jamming probability $J\left(d\right)$ is measured where $d\equiv R/D$. We found that $J\left(d\right)$ decreases from 1 to zero when $d$ increases from 2 to 5. From observing the disk configurations of the arch in the jamming events, the jamming probability can be explained quantitatively by treating the arch as the trajectory of a restricted random walker.

We propose a model for stochastic formation of opinion clusters, modeled by an evolving network, and herd behavior to account for the observed fat-tail distribution in returns of financial-price data. The only parameter of the model is $h$, the rate of information dispersion per trade, which is a measure of herding behavior. For $h$ below a critical $h^{*}$ the system displays a power-law distribution of the returns with exponential cutoff. However, for $h>\mathrm{}{h}^{*}$ an increase in the probability of large returns is found and may be associated with the occurrence of large crashes.

Electron microscope imaging for gadolinium metallofullerenes encapsulating in single-wall carbon nanotubes $\left[\right(\mathrm{Gd}@\mathrm{C}{}_{82}{)}_n@\mathrm{SWNTs}]$ identifies the single Gd atom encaged in each. The intermolecular distance between $\mathrm{Gd}@\mathrm{C}{}_{82}$ is extremely regular, regarding the chains of $\mathrm{Gd}@\mathrm{C}{}_{82}$ as novel one-dimensional crystals. Chemical state analysis of Gd atoms suggests evidence for charge transfer from Gd to either a fullerene cage or a nanotube. The slopes of the temperature dependence of electric resistance for the matlike films of $(\mathrm{Gd}@\mathrm{C}{}_{82}{)}_n@\mathrm{SWNTs}$ and $(\mathrm{C}{}_{60}{)}_n@\mathrm{SWNTs}$ are much steeper than that for empty SWNTs, suggesting the electron scattering due to the electrostatic potential from inside fullerenes playing an important role.

We calculate the shadow image in far field below a thin crystal when a coherent electron source is placed at micrometer distances above the specimen, and note that the presence of a planar fault results in very strong oscillatory contrast. We realize these predictions experimentally using a field-emission electron source in a microscope. With this technique, we determine displacement vectors at planar faults with an accuracy down to 1 pm in studies of the ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{CaCu}}_2{\mathrm{O}}_8$ superconductor containing thin intercalated layers.

We demonstrate that the attractive interaction measured between like-charged colloidal spheres near a wall can be accounted for by a nonequilibrium hydrodynamic effect. We present both analytical results and Brownian dynamics simulations which quantitatively capture the one-wall experiments of Larsen and Grier [Nature (London) 385, 230 (1997)], using a single unmeasured parameter.

We have studied experimentally the rheological behavior of concentrated suspensions of soft deformable microgels below the yield point. We have found history-dependent effects which are interpreted in terms of aging and rejuvenation phenomena, analogous to those existing in glassy systems. The stress amplitude controls the long-time memory and determines the slow evolution of the suspensions.

Cosmological data suggest that we live in an interesting period in the history of the universe when ${\rho }_{\Lambda }\sim {\rho }_M\sim {\rho }_R$. The occurrence of any epoch with such a “triple coincidence” is puzzling, while the question of why we happen to live during this special epoch is the “Why now?” problem. We introduce a framework which makes the triple coincidence inevitable; furthermore, the “Why now?” problem is transformed and greatly ameliorated. The framework assumes that the only relevant mass scales are the electroweak scale $M_{\mathrm{EW}}$, and the Planck scale $M_{\mathrm{Pl}}$ and requires ${\rho }_{\Lambda }^{1/4}\sim M_{\mathrm{EW}}^2/M_{\mathrm{Pl}}$ parametrically. Assuming that the true vacuum energy vanishes, we present a simple model, where a false vacuum energy yields a cosmological constant of this form.

We have observed the spontaneous evolution of a dense sample of Rydberg atoms into an ultracold plasma, in spite of the fact that each of the atoms may initially be bound by up to $100{\mathrm{cm}}^{-1\mathrm{}}$. When the atoms are initially bound by $70{\mathrm{cm}}^{-1\mathrm{}}$, this evolution occurs when most of the atoms are translationally cold, $<1\mathrm{mK}$, but a small fraction, $\sim 1\%$, is at room temperature. Ionizing collisions between hot and cold Rydberg atoms and blackbody photoionization produce an essentially stationary cloud of cold ions, which traps electrons produced later. The trapped electrons rapidly collisionally ionize the remaining cold Rydberg atoms to form a cold plasma.

We show that the crystal growth rate of a very long-chain $n$-alkane $\mathrm{C}{}_{198}\mathrm{H}{}_{398}$ from solution can decrease with increasing supersaturation and follow strongly negative order kinetics. The experimental behavior can be well represented by a theoretical model which allows the molecule to attach and detach as either extended or folded in two. The obstruction of extended-chain growth by unstable folded depositions increases disproportionately with increasing concentration. As a consequence of this abnormal kinetics, a “dilution wave” can propagate and trigger a folded-to-extended-chain transformation on its way.

We present a scheme for creating quantum entangled atomic states through the coherent spin-exchange collision of a spinor Bose-Einstein condensate. The state generated possesses macroscopic Einstein-Podolsky-Rosen correlation and the fluctuation in one of its quasispin components vanishes. We show that an elongated condensate with large aspect ratio is most suitable for creating such a state.

We propose and analyze a scheme for generating entangled atomic beams out of a Bose-Einstein condensate using spin-exchanging collisions. In particular, we show how to create both atomic squeezed states and entangled states of pairs of atoms.

We describe a simple experimental technique which allows us to store a small and deterministic number of neutral atoms in an optical dipole trap. The desired atom number is prepared in a magneto-optical trap overlapped with a single focused Nd:YAG laser beam. Dipole trap loading efficiency of $100\%$ and storage times of about one minute have been achieved. We have also prepared atoms in a certain hyperfine state and demonstrated the feasibility of a state-selective detection via resonance fluorescence at the level of a few neutral atoms. A spin relaxation time of the polarized sample of $4.2\pm 0.7\mathrm{s}$ has been measured. Possible applications are briefly discussed.

Exploiting the energetic interaction of intense femtosecond laser pulses with deuterium clusters, it is possible to create conditions in which nuclear fusion results from explosions of these clusters. We have conducted high-resolution neutron time-of-flight spectroscopy on these plasmas and show that they yield fast bursts of nearly monochromatic fusion neutrons with temporal duration as short as a few hundred picoseconds. Such a short, nearly pointlike source now opens up the unique possibility of using these bright neutron pulses, either as a pump or a probe, to conduct ultrafast studies with neutrons.

We have measured the spectrum of velocity fluctuations in a granular system confined to a vertical plane and driven into a homogeneous, steady state by strong vertical vibration. The distribution of horizontal velocities is not Maxwell-Boltzmann and is given by $P\left(v\right)=C\exp [-\beta (|v|/\sigma {)}^{\alpha }]$ where $\alpha =1.55\mathrm{}\pm 0.1$ at all frequencies and amplitudes investigated, and also for varying boundary conditions. The deviation from Maxwell-Boltzmann statistics occurs in the absence of spatial clustering and does not result from an inhomogeneous average over regions of varying local density. Surprisingly, $P\left(v\right)$ has the same shape over a wide range of densities.