Desorption of NO molecules from a Pd(111) surface induced by femtosecond visible laser pulses has been investigated in real time. The measurements, accomplished by means of a two-pulse correlation scheme, reveal a subpicosecond response time. The findings indicate that the desorption arises from coupling to the nonequilibrium electronic excitation in the substrate.

The annealing behavior of the divacancy (${\mathit{V}}_2$) acceptor levels in silicon is investigated with the use of Schottky-barrier structures formed by the deposition of copper on n-type silicon irradiated with 2-MeV electrons. At temperatures below ∼150 °C an anomalously high annealing rate of the ${\mathit{V}}_2$ centers is observed, and we believe that the fast-diffusing interstitial ${\mathrm{Cu}}^{+}$ passivates their electrical activity and forms neutral complexes. In the temperature range 150–200 °C, where the metal-rich silicide η’-${\mathrm{Cu}}_3$Si forms, the concentration of ${\mathit{V}}_2$ remains almost constant, and we find no evidence for the injection of silicon self-interstitials during the formation of η’-${\mathrm{Cu}}_3$Si, in contrast to recent experiments.

The early stages of growth of highly strained ${\mathrm{In}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As on GaAs(100) have been investigated as a function of composition. The evolution of the film microstructure as determined by in situ STM and RHEED is from a two-dimensional rippled surface in the beginning stages of growth to a three-dimensional island morphology. A growth mode is proposed whereby strain relaxation is initially achieved through the kinetically limited evolution of surface morphology. In contrast to traditional critical-thickness theories, significant strain relief is accommodated by a coherent island morphology. This study represents a new view for both the growth mode and initial strain relaxation in thin films.

The first-principles generalized pseudopotential theory of bulk transition-metal interatomic potentials is extended to surfaces by transforming the total-energy functional to a local-environment representation in which both the volume term and the multiion potentials are modulated by local averages of the electron density or the density of states. The theory encompasses and goes beyond simple embedded-atom schemes by including the angular forces necessary to treat the central bcc metals. Applications to the vacancy-formation and free-surface energetics of Cu and Mo are discussed.

The domain structure in the nearly commensurate charge-density-wave phase of 1T-${\mathrm{TaS}}_2$ has been experimentally determined. Fourier-transformed scanning-tunneling-microscopy images display fine satellite structure in excellent agreement with that predicted by the amplitude- and phase-domain model of Nakanishi and Shiba. Earlier analyses of scanning-tunneling- and atomic-force-microscopy images of 1T-${\mathrm{TaS}}_2$ in the nearly commensurate phase are shown to be inadequate for the unambiguous identification and characterization of domain structure.

A novel nonlinear model is presented for the occurrence of current fluctuations at low temperatures in extrinsic semiconductors. It is based on impact ionization of shallow impurities and structure-forming processes leading to a current filament. Numerical investigations reproduce the current-voltage characteristics and reveal regular, quasiperiodic, and frequency-locked spontaneous current oscillations and a Ruelle-Takens-Newhouse transition to chaos in agreement with experimental observations in n-type GaAs.

The conductance through a quantum dot is calculated via an Anderson model of a site weakly coupled to ideal leads with an on-site Coulomb interaction. As the chemical potential is varied, peaks occur periodically in the conductance whenever an electron is added to the site. The participation of multiple electronic levels in each conductance peak explains the anomalous temperature dependence of peak heights observed in recent narrow-channel experiments.

We have studied the magnetic properties of cobalt clusters in a beam as functions of cluster size (N=20–200), magnetic field, and cluster temperature. The measured magnetic moments per atom increase with applied magnetic field and cluster size but decrease with increasing temperature, consistent with superparamagnetic behavior. Rapid orientation fluctuations of the true magnetic moments of these isolated particles yield the smaller, time-averaged, observed values. The true magnetic moments are (2.08±0.20)${\mathrm{\mu }}_{\mathit{B}}$ per atom and exceed the bulk value. Magnetically resolved isomers are seen for N=55–66.

It is shown theoretically that the critical current of a smooth and impurity-free superconducting constriction increases stepwise as a function of its width. The step height at zero temperature is e${\mathrm{\Delta }}_0$/ħ, dependent on the energy gap ${\mathrm{\Delta }}_0$ of the bulk superconductor but not on the junction parameters. This is the analog of the quantized conductance of a point contact in the normal state. It is essential that the constriction is short compared to the superconducting coherence length.

We present measurements at 4.2 K of the magnetoresistance (MR) measured with the current perpendicular to the layer planes (CPP) of equal and unequal thickness Ag/Co magnetic multilayers that display giant MR measured with the current in the layer planes (CIP). For Ag layer thicknesses from 2 to 60 nm, and Co thicknesses from 6 to 15 nm, the CPP MR extends up to nearly 50% and ranges from 3 times to more than 10 times as large as the CIP MR for the same samples.

A three-dimensional generalization of the wave function of Girvin et al. is constructed by taking the N→∞ limit of a solution of the two-dimensional massless Dirac equation with an SU(N) gauge field. The resulting wave function is closely related to instanton solutions of the self-dual Einstein quations, and can be used to construct a multiparticle wave function with remarkable holonomy properties and a ground-state wave function with off-diagonal long-range order.

We present a detailed investigation of the growth of the superconducting phase in a magnetic field. For type-I superconductors, the planar normal-superconductor interface is dynamically unstable. In the nucleation regime this feature leads to interface motion similar to that found in the solid-liquid transition. In the spinodal regime the spinodal growth proceeds by a sequence of phase-slip processes, unique to a system with a complex order parameter. In type-II superconductors, vortex absorption stabilizes a planar interface, despite the negative surface tension.

We study the time evolution of a superconductor, following a quench from the normal state, in two dimensions. For a type-I superconductor, quenched into a region where the normal state is metastable, the normal-superconductor phase boundary exhibits a dynamical instability similar to, but not identical with, that observed in solidification. In the case of a quench into the Meissner phase of a type-II superconductor, the average vortex spacing d as a function of time t is found to exhibit a crossover from d∼${\mathit{t}}^{1/2}$ to d∼lnt, the crossover time being an increasing function of the Ginzubrg-Landau parameter κ.

In the vortex-liquid state in ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$ there exist two distinct dissipative states separated by a field ${\mathit{H}}_{\mathit{k}}$. Below ${\mathit{H}}_{\mathit{k}}$, the resistivity is strongly field activated, with a prefactor that is anomalously enhanced over the normal-state resistivity ${\mathrm{\rho }}_{\mathit{N}}$ by ∼12 orders of magnitude. At ${\mathit{H}}_{\mathit{k}}$, the prefactor collapses to a temperature-independent value equal to ${\mathrm{\rho }}_{\mathit{N}}$, and the vortex motion becomes diffusive. The existence of the ${\mathit{H}}_{\mathit{k}}$ boundary is also reflected in the anomalous behavior of the Hall resistivity.

Magnetic-field-modulated microwave absorption and dc susceptibility measurements have detected evidence for superconductivity in As-rich GaAs layers grown by molecular-beam epitaxy at low temperatures (LT-GaAs). The transition temperature from the normal to the superconducting phase is 10 K. Electron microscopy of these layers found a new, As-rich layered structure in LT-GaAs that is most likely the origin of the superconductivity.

The catalytic oxidation of CO on Pt(110) exhibits, for certain sets of control parameters, oscillatory kinetics and spatiotemporal pattern formation which may be followed by photoemission electron microscopy. Within a very narrow range of conditions, these patterns consist of solitary waves with bell-shaped profiles which propagate with a constant velocity of about 3 μm/s along the crystallographic [001] axis of the surface. Collision of pulses traveling in opposite directions leads mostly to annihilation, but in some cases the two waves emerge again with unchanged shapes and velocities, as characteristic for solitons.

Geometric phases play an important role in the asymptotic behavior of multicomponent wave fields, such as electromagnetic waves in plasmas or quantum-mechanical spinors, particularly in the problem of Bohr-Sommerfeld quantization. The proper gauge independence of the eigenvalues and asymptotic wave functions can be understood in terms of gauge-invariant but noncanonical coordinates on the classical phase space.

Noise rise in the high-gain limit of a parametric magnetorestrictive amplifier is observed to occur close to the bifurcation point of the unperturbed strain dynamics. This work presents the first quantitative agreement between experimental results and the predicted universal scaling laws which relate the signal and noise gain to the bifurcation parameter. We also observe a scaling law, not predicted by the theory, in which the point of maximum signal gain shifts away from the bifurcation point as a function of the detuning with a critical exponent equal to -0.33 ±0.04.

We examine the constraints on the neutrino mass matrix consistent with the recent rediscovery of a 17-keV neutrino, the absence of neutrinoless double-β decay, and neutrino oscillation experiments. There are two cases consistent with the data, assuming only three Majorana neutrinos. One possibility is that the muon neutrino is heavier than 190 keV, and there is a lower bound on the probability ${\mathit{P}}_{\mathrm{\mu }\mathit{e}}$ of a muon neutrino oscillating into an electron neutrino, ${\mathit{P}}_{\mathrm{\mu }\mathit{e}}$>1.3×${10}^{\mathrm{-}3}$. The other possibility is that the muon neutrino is degenerate with the 17-keV neutrino to within an accuracy of ${10}^{\mathrm{-}11}$. In either case, there is a lower limit on the ${\nu }_{\mathit{e}}$ disappearance probability, ${\mathit{P}}_{\mathit{e}\to \mathit{e}}$≳0.02.

The QCD sum-rule approach for a nuclear medium is developed. The medium dependence of the neutron-proton mass difference calculated from this approach gives effects in nuclei which have direct relevance for the resolution of the Okamoto-Nolen-Schiffer anomaly.