We describe Z-pinch experiments imploding an aluminum-plasma jet onto a coaxial, micron-diameter wire. Spatially resolved x-ray pinhole images and time resolved x-ray data indicate that energy is supplied initially to the aluminum-jet plasma and subsequently transferred to the wire. The resultant pinch appears more uniform (stable) than a wire-only or jet-only pinch and demonstrates that an imploding-plasma liner will couple energy from a pulsed-power generator to a micron-diameter-sized plasma channel.

The paper reports on the observation of the electron paramagnetic resonance spectrum of the isolated substitutional gold impurity in silicon. The spectrum has orthorhombic I (${\mathit{C}}_{2\mathit{v}}$) symmetry and an effective spin S=1/2. It has been detected in silver-doped samples with gold being introduced as contamination of the isotope used for diffusion. Parameters of the spectrum are given and an electronic model is proposed. With the results of the current study the puzzling question concerning paramagnetism of the isolated gold impurity in silicon appears to be clarified.

We discuss localized excitations on the incipient infinite percolation cluster. Assuming a simple exponential decay of the amplitudes ${\mathrm{\psi }}_{\mathit{i}}$ in terms of the chemical (minimal) path, we show theoretically that the ψ’s are characterized by a logarithmically broad distribution, and display multifractal features as a function of the Euclidean distance. The moments of ${\mathrm{\psi }}_{\mathit{i}}$ exhibit novel crossover phenomena. Our numerical simulations of fractons exhibit a nontrivial distribution of localization lengths, even when the chemical distance is fixed. These results are explained via a generalization of the theory.

We propose a stochastic differential equation for the growth of interfaces that is invariant under reparametrization and thus incorporates the chaange in local time scales resulting from nonlinear distortions. In its most general form, the equation accommodates overhanging configurations and in the nearly planar limit it reduces to previously proposed interface evolution models. The new features are relevant and lead to qualitatively new behavior at long times.

By using the chemical shift in core-level photoemission from adsorbed species, we apply the technique of energy scan photoelectron diffraction to molecules containing nonequivalent atoms of the same element. As an example, we demonstrate the complete structural characterization of the surface acetate species on Cu{110} incuding independent determination of the sites of the two inequivalent carbon atoms.

The epitaxial growth of Au on Ag(110) has been studied by scanning tunneling microscopy up to 2.5 ML. In the submonolayer range the results show that gold atoms are intermixed with the silver atoms in the top two layers. Above 1 ML, a two-dimensional fingerlike growth gives rise to anisotropic three-dimensional islands of gold. This ‘‘intermixed Stranski-Krastanov’’ growth mode is in quantitative agreement with ion channeling data which were previously interpreted as a bilayer growth mode [Fenter and Gustafsson, Phys. Rev. Lett. 64, 1142 (1990)].

Vacuum ultraviolet photoelectron spectra are reported for mercury clusters with up to 109 atoms. These spectra yield quantitative information about the evolution of ionization potentials and bandwidths. Further results about partial photoionization cross sections are obtained by varying the photon energy. The photon energy dependence provides direct experimental evidence that large mercury clusters ${\mathrm{Hg}}_{\mathit{x}}$ (x≥60) possess already a high density of p states near ${\mathit{E}}_{\mathit{F}}$.

We have advanced a new optical-absorption technique for the study of molecular-beam isolated clusters. For ${\mathrm{Hg}}_{\mathit{x}}$ clusters 2<x<200), the optical-absorption cross sections have been measured directly between 4.3 and 6.2 eV. With increasing cluster sizes a gradual enhancement of the absorption cross section at 5.93 eV is observed and discussed in terms of a surface plasmon resonance. The spectra of large clusters can be fitted quantitatively either by using the complex dielectric function of the metallic bulk material or by using the Mie-Drude imaginary part of the dynamic polarizability.

Optical absorption spectra for mass-selected ${\mathrm{Hg}}_{\mathit{n}}^{+}$ and ${\mathrm{Hg}}_{\mathit{n}}^{++}$ clusters show an abrupt transition to a collective, plasmonlike absorption as a function of increasing cluster size. The position of the single observed plasmon maximum is independent of the charge state and nearly independent of cluster size. The peak positions agree well with those of the classical Mie plasmon calculated from the experimental dielectric function. The width of the plasmon resonance is discussed and a strong temperature effect is conjectured.

Isolated single quantum dots of different size have been fabricated by laser-induced local interdiffusion of a GaAs/AlGaAs quantum-well structure. Microscopic photoluminescence (PL) reveals a splitting and a blueshift, which depend systematically on dot size. The distinct PL peaks separated in energy by up to 10 meV are attributed to recombination between zero-dimensional (0D) electron and hole states. Complete quantization and inherent exclusion of inhomogeneous broadening in a single dot structure cause PL linewidths below 0.5 meV. The strength of the higher-energy transitions indicates the slowed energy relaxation theoretically predicted for 0D systems.

We have studied the magnetotransport properties of a new metallic granular Co-Ag system. The spin-dependent electron scattering is revealed in the forms of a giant magnetoresistance and an extraordinary Hall effect, both of which are found to be strongly dependent on the Co particle size and the electron mean free path. The experimental correlation ${\mathrm{\rho }}_{\mathit{x}\mathit{y}}$∝${\mathrm{\rho }}_{\mathit{x}\mathit{x}}^{3.7}$ uncovered is unexpected from existing theories. Interfacial scatterings of intermediate range are required in order to account for the anomalous magnetotransport in this magnetic granular system.

The inelastic scattering effect on electron tunneling through a double-barrier resonant tunneling device has been studied with a cumulant expansion on the electron transmission probability and the I-V characteristics using the Fröhlich Hamiltonian which allows electron recoil. The low-order expansion formula used for numerical calculation satisfies a sum rule; its analytical derivation is given here for the first time. As the Fermi energy in the emitting lead is increased, electron recoil enhances the incoherence process and so broadens the phonon replica, which is also shifted towards the main peak. When the Fermi energy reaches the LO-phonon energy, the phonon replica and the main peak merge into one.

Diagonal and Hall resistivities (${\mathrm{\rho }}_{\mathrm{\infty }}$ and ${\mathrm{\rho }}_{\mathit{x}\mathit{y}}$) in the normal and superconducting states are studied in one-unit-cell-thick ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ artificial materials. A number of transport properties in bulk ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ are shown to be inherent properties of the individual conducting ${\mathrm{CuO}}_2$ bilayer. Evidence of Kosterlitz-Thouless resistive transition as well as the excitation of free vortex and antivortex are presented.

Within a wide class of ferromagnetic and antiferromagnetic systems, quantum tunneling of magnetization direction is spin-parity dependent: it vanishes for magnetic particles with half-integer spin, but is allowed for integer spin. A coherent-state path-integral calculation shows that this topological effect results from interference between tunneling paths.

In some spin tunneling problems there are several different but symmetry-related tunneling paths that connect the same initial and final configurations. The topological phase factors of the corresponding tunneling amplitudes can lead to destructive interference between the different paths, so that the total tunneling amplitude is zero. In the study of tunneling between different ground-state configurations of the Kagomé-lattice quantum Heisenberg antiferromagnet, this occurs when the spin s is half odd integer.

Previous polarized electron experiments and recent ab initio calculations suggest that the surface layer magnetic moments of Gd(0001) are antiferromagnetically coupled to the bulk magnetic moments. Spin-polarized photoemission data are presented which show that the spin polarization of the magnetic surface state and the surface 4f states of Gd(0001) are coupled ferromagnetically to the bulk magnetic moment.

The magnetic metal ions in the cubic pyrochlore ${\mathrm{Tb}}_2$${\mathrm{Mo}}_2$${\mathrm{O}}_7$ form an infinite three-dimensional network of corner-sharing tetrahedra with a very high potential for frustration in the presence of antiferromagnetism. We have performed neutron scattering measurements which show short-range spatial correlations that develop continuously with decreasing temperature, while the characteristic time scale for the fluctuating moments decreases dramatically below ${\mathit{T}}_{\mathit{f}}$∼25 K. Therefore, this pure material, which possess frustration that is purely geometrical in origin, displays a spin-glass state at low temperatures.

Coherent optical phonons are generated impulsively in Ge by irradiation with femtosecond laser pulses. They are detected via reflectivity modulations in the time domain in a pump-probe configuration. The deformation potential of the optical phonon is responsible both for the generation and for the detection process. The excitation of the coherent optical phonons is explained by anisotropic weakening of bonding valence orbitals.

We demonstrate for the first time that a porous silicon layer (PSL), which has a bright light-emission band in the range of 500–700 nm, exhibits a strong visible-range luminescence under the illumination of an infrared ultrashort pulsed laser. The dependence of integrated luminescence intensity on pump power shows that this is a third-order nonlinear optical effect. By comparing with UV-light-excited spectra of PSL and samples with low porosity which have inefficient luminescence, a possible explanation is proposed whereby the large nonlinear optical response is due to the quantum confinement effect.

It has been claimed that the kinetics of reactions of the form A+B→0 can be well described using the Kirkwood superposition principle to decouple n-body correlations into products of pair correlations. The strength of this approximation is assessed through its predictions for the nearest available neighbor recombination scheme, for which analytic and Monte Carlo results are available. It is shown that it is much more successful than classical kinetics because of the inclusion of spatially nonuniform pair correlations, but fails asymptotically at large pair separations or long times because of the neglect of higher correlations.