The predicted 4s4${\mathrm{p}}^2$ ${}_{}{}^4{}_{}{}^{}\mathrm{P}$ metastable state of the negative calcium ion has been observed. Measured autodetachment rates yield a lifetime of (2.9±1.0)×${10}^{\mathrm{-}4}$ s, which is concluded to pertain to the J=(5/2 state. By means of laser photodetachment near the Ca ${}_{}{}^3{}_{}{}^{}\mathrm{S}_1^{}{}_{}{}^{}$ threshold, the electron affinity of the Ca 4s4p ${}_{}{}^3{}_{}{}^{}\mathrm{P}$ parent state is found to be 0.562±0.005 eV.

A new three-photon separated-oscillatory-field microwave-resonance technique has been employed to measure the $4^2$${\mathrm{S}}_{1/2}$-$4^2$${\mathrm{F}}_{5/2}$ fine-structure interval in ${\mathrm{He}}^{+}$ with an accuracy of 4 ppm. The indirect result for the ${\mathrm{He}}^{+}$ (n=4) Lamb shift is scrL=1768.732(124) MHz. This 70-ppm measurement provides the most precise Lamb-shift determination in any hydrogenic ion or atom outside of the n=2 manifold. This experimental result is in excellent agreement with the theoretical value based on Mohr’s calculation of the (n=2) binding correction.

Structural and dynamical properties of nonlinear traveling-wave states in binary fluid layers heated from below are determined by numerical integration of the proper hydrodynamic field equations with experimental horizontal boundary conditions. The fluid separates into traveling rolls of alternating high and low concentration. Phase differences drive lateral currents and Reynolds stresses generate lateral mean flow.

The phase shift predicted by Aharonov and Casher for a magnetic dipole diffracting around a charged electrode has been observed for the case of thermal neutrons, using a neutron interferometer containing a 30-kV/mm vacuum electrode system. The judicious use of the Earth’s gravitational field introduces a spin-independent phase shift which enables unpolarized neutrons to be used. A supplementary magnetic bias field of the correct magnitude allows first-order sensitivity to be achieved; even so, the theoretically predicted phase shift is only 1.50 mrad for the geometry and conditions of the experiment. We observe a phase shift of 2.19±0.52 mrad.

Flat, cylindrical, and spherical soliton solutions to various model equations are known. Many of these exact solutions have been seen in numerical simulations. However, there are few simulations that actually show that exact flat solitons can break up into an array of exact cylindrical or spherical solitons and follow this on a step by step basis. This Letter presents the first of these two kinds of transition for the Zakharov-Kuznetsov equation governing ion acoustic solitons in strongly magnetized plasmas.

The process of oxygen chemisorption on a Cu(110) surface has been observed dynamically using scanning tunneling microscopy. Nucleation and growth of the chemisorbed oxide layer occur preferentially along the 〈001〉, forming long isolated chains. The buckled-row model is established as the correct description of the Cu(110)-O(2×1) superstructure with alternate 〈001〉 copper rows displaced outward by 0.8±0.2 Å from the first layer.

We present experimental results and their interpretation on the propagation of surface acoustic waves on a quasiperiodically corrugated solid. The surface is made of a thousand grooves engraved according to a Fibonacci sequence. For the first time, we observe the spatial structure of the critical proper modes obtained from an optical diffraction experiment. These special modes are characteristic of quasiperiodic systems and exhibit remarkable scaling features.

Measurements of abundances and electronic properties of neutral sodium halide clusters, ${\mathrm{Na}}_{\mathrm{n}}$${\mathrm{X}}_{\mathrm{n}\mathrm{-}1}$ (n<100), demonstrate a remarkable range of excess-electron-dominated behavior. Clusters which can form a cubic lattice containing a single anion vacancy have the electron localized in the vacancy, stabilizing the cluster against fragmentation. For the singular values of n which correspond to a filled cubic lattice, the electron is very weakly bound. A simple quantitative model of electron localization is proposed to account for the observed patterns of abundances and electron binding energies.

In situ high-pressure x-ray-absorption spectra have been performed on amorphous and crystalline ${\mathrm{GeO}}_2$ using a diamond-anvil cell adapted to ane energy-dispersive spectrometer. The coordination of Ge changes from fourfold to sixfold at pressures between 7 and 9 GPa. The progressive evolution of the measured Ge-O distances as well as the modification in the x-ray-absorption near-edge structure indicate two different sites rather than a progressive site modification. The phase transition observed in the amorphous phase is reversible in contrast to that observed in the crystalline form.

It is demonstrated that analysis of the shape of diffracted beams in LEED can be used to determine the size and separation distribution functions of structurally incoherent regions growing on a crystalline substrate. The method has been used to investigate the growth of In clusters on cleaved GaAs(110). An exponent of x=0.5±0.15 is obtained for the change in mean island size with dose. The data imply that coalescence is important in the growth process.

We consider the problem of elastic (e.g., polymerized) membranes whose undulations are constrained by the presence of other membranes, or by a wall. Monte Carlo simulation shows that in the low-temperature, ordered phase the fluctuation-driven ‘‘steric’’ potential decreases as a power of the mean distance between membranes, 1/$l^{\tau }$, with the exponent τ=3.1±0.2. This result, very different from that predicted and measured for the case of fluid membranes (τ=2), suggests possible experiments on the swelling of polymerized lamellar phases which would demonstrate the existence of an ordered phase below a crumpling transition.

We report measurements of the superfluid density of ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ confined between two Si wafers. These are the first measurements of helium confined in a sufficiently well-defined planar geometry to show a crossover from three-dimensional-like to finite-size to two-dimensional behavior. Data for confinement in 0.106, 0.509, 2.8, and 3.9-μm-thickness cells are analyzed for scaling with the exponent of the bulk correlation length, ν. We find that this scaling does not work: An exponent different from ν is required. We discuss these results in light of finite-size scaling predictions and earlier measurements.

We present both calculations and a physical interpretation of the observed suppression (quenching) of the low-field Hall resistance in quasi-one-dimensional ballistic microstructures. We find that quenching is due to a property of the contact geometry and is not intrinsic to the quasi-one-dimensional limit. Generic quenching, as observed experimentally, is found only when the width of the wires is gradually increased near the junction to the Hall probes. The resulting collimation of the electrons in the forward direction reduces the sensitivity to a magnetic field.

We propose an approach to study one-dimensional electron tunneling in an arbitrarily shaped barrier in the presence of electron-optical phonon scattering. An independent-boson model is used for the electron-phonon interaction. Our result for a double-barrier structure shows the occurrence of phonon-assisted resonant tunneling.

Infrared reflectivity measurements of crystalline ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$ (${\mathrm{T}}_{\mathrm{c}}$≃92 K) are performed with the electric field both parallel and perpendicular to the Cu-O planes. We find evidence for an unusually large in-plane energy gap (∼8${\mathrm{kT}}_{\mathrm{c}}$), while a much smaller energy scale (∼3${\mathrm{kT}}_{\mathrm{c}}$) is obtained with the field perpendicular to the planes suggesting substantial gap anisotropy. Temperature-dependent measurements near ${\mathrm{T}}_{\mathrm{c}}$ demonstrate a clear relationship between the development of the ∼8${\mathrm{kT}}_{\mathrm{c}}$ feature and the superconducting transition.

We present a generalization of small-polaron band theory based on methods used in the study of Davydov solitons. The eigenstates of the small-polaron band are found to be stationary solutions of our equations of motion; however, among the nonstationary solutions can be found a family of soliton states. The soliton solutions we obtain differ from Davydov solitons in fundamental ways, but are fully consistent with the theory of small polarons.

We report the first observation of stimulated emission in quasi-one-dimensional semiconductor quantum wires. Amplified spontaneous emission and stimulated emission spectra of the GaAs/AlGaAs quantum wires exhibit fine structure arising from transitions between lateral, one-dimensional electron and hole subbands. The observed subband separations, ∼10 meV, are consistent with the calculated ones.

The local susceptibilities and the 3d spin dynamics of isolated nickel ions in various alkali-element hosts have been measured, utilizing the perturbed γ-ray distribution method after recoil implantation. In the heavy alkali-metal hosts, Cs, Rb, and K, the local susceptibilities of the isolated Ni ions irrespectively show the temperature behavior of a fully localized spin-orbit-coupled 3${\mathrm{d}}^9$ configuration. Clear host dependence of the magnetic behavior is seen in the spin-fluctuation rates which increase with decreasing host volume. In Na, the magnetic behavior drastically deviates from that of the purely ionic configuration, and Ni ions in Li as well as in Ca and Ba hosts are nonmagnetic.

Resonant tunneling of electrons in GaAs-AlGaAs quantum wells is resolved by picosecond pump-and-probe electroabsorption measurements. The temperature-independent tunneling escape times are dramatically affected by the applied electric field, with a pronounced minimum at the field corresponding to the resonance between the n=1 electron level in one quantum well, and the n=2 electron level in the adjacent one. The calculated field dependence of the tunneling times is in qualitative agreement with the data.

A spin-dependent electron-phonon coupling is investigated. In particular, an electron-hole correlation induces a new itinerant phase in metals which presents several interesting features.