Fragmentation channels of metal clusters are studied as functions of their size and charge state by the use of ab initio self-consistent theories. Results for geometry-optimized microclusters agree quite well with the jellium model and lend credibility to the latter for the study of Coulomb explosion in multiply charged metal clusters.

We report the first voltage-dependent scanning tunneling microscope images of a compound semiconductor surface, GaAs(110). Images show either only Ga atoms, or only As atoms, depending on the bias voltage. By combining voltage-dependent images with theoretical calculations, we quantitatively determine surface structural parameters which cannot be inferred from the images alone.

We report on absolute measurements of the orientation dependence of the ${\mathrm{e}}^{+}$-${\mathrm{e}}^{\mathrm{-}}$ pair production by 20–150-GeV photons aligned or nearly aligned with the 〈110〉 axial direction of a thin Ge crystal. The observed effects are very large, and are well described by theoretical predictions based on the existence of strong macroscopic fields in aligned crystals.

We have observed a two-stage melting transition in a two-dimensional (2D) colloidal suspension of highly charged, submicron-sized spheres in water using optical microscopy and digital imaging. Our system is confined between two flat glass plates, has a lateral extent of at least 1000 spheres, and has equilibrated for over ${10}^5$ time steps. Direct observation of topological defects and computed correlation functions from real-space images gives insight into the nature of the 2D melting process.

The most significant feature in the transition from the quasicrystalline to the amorphous state is the loss of long-range bond-orientational order. Disclinations are candidates for elementary excitations which destroy angular correlations. Generalizing the topological defect classification, we investigate point singularities in two-dimensional pentagonal quasicrystals and construct disclinations, dislocations, and disclination dipoles.

Time-of-flight studies of monatomic and diatomic gases scattered from long-chain, amphiphilic monolayers are reported. The extent of energy transfer can be correlated with the rigidity of the chains and the gas/surface mass ratio. Surface vibrational modes responsible for the energy transfer are suggested.

Amplified 150–300-fs laser pulses are applied to monitor the thermal modulation of the transmissivity of thin copper films. Non- equilibrium electron-lattice temperatures are observed. The process of electron-phonon energy transfer was time resolved and was observed to be 1–4 ps increasing with the laser fluence.

Using Brillouin scattering we have succeeded in observing the normal modes of vibration of unsupported films in a region where the dispersion relationship is quadratic. Extremely low-lying excitations were observed in thin films with thicknesses as small as 200 Å. Contrary to what has been found in work on supported films, we are able to extract information on a number of the elastic moduli because the measured velocities in very thin films do not depend on the properties of the substrate. This technique should be a valuable addition to the tools which can be used in the study of materials in thin-film form.

The crossover from mean-field to nonclassical (model I) criticality for 3D critical wetting with short-range forces is derived via an appropriately formulated Ginzburg criterion. Subsequent crossovers to models II and III are also discussed. Although the domain of classical behavior is found to be small, we suggest that recent numerical simulations have failed to venture outside this regime. Pure, asymptotic nonuniversal critical behavior may be inaccessible to presently available experimental systems.

The ultrasonic attenuation of the heavy-fermion superconductor ${\mathrm{UPt}}_3$ is investigated as a function of temperature, magnetic field strength, and frequency. It is shown that in the presence of a dc magnetic field at least one metastable and two stable phases exist in the superconducting state.

A neutron elastic- and inelastic-scattering study of single-crystal bcc lithium was performed above and below the martensitic phase transformation in the vicinity of 75 K. The transformation is abrupt and the bcc lattice partially transforms to a 9R-related (Sm-type) structure. The 9R ${\mathrm{c}}^{\mathrm{*}}$ and ${\mathrm{a}}^{\mathrm{*}}$ axes of this variant are nearly along the [110] and [11¯0] bcc directions, respectively. The (10L) and (20L) 9R reflections were broadened and shifted from their ideal positions compared to the (00L) 9R reflections, indicative of numerous stacking faults. On warming, the sample reverts back to a single crystal with the same bcc orientation.

Measurements of the temperature and concentration dependence of the specific heat, magnetic susceptibility, and electrical resistivity for ${\mathrm{Ce}}_{1\mathrm{-}\mathrm{x}}$${\mathrm{La}}_{\mathrm{x}}$${\mathrm{Pb}}_3$ are presented. The data scale with the concentration of Ce ions over surprisingly large intervals of x and T. The low-temperature specific heat per Ce ion agrees quantitatively with that of an S=(1/2) Kondo impurity of $T_K$apeq23.3 K. These results strongly suggest that intersite correlations do not play the expected important role and that the high specific heat γ reported for ${\mathrm{CePb}}_3$ is mainly a manifestation of the single-ion Kondo resonance.

The magnetic scattering rate of Fe in Mg is measured as a function of temperature by means of weak localization. It shows a strong temperature dependence which is attributed to the Kondo effect. At low temperatures Nozières predicted a Fermi-liquid behavior for the electron system plus the Kondo impurity with no magnetic scattering. Weak localization allows a check of the applicability of the Fermi-liquid theory.

We have observed fluctuations in the low-temperature resistance of small-diameter Bi wires, and Bi films. These fluctuations appear most clearly as a function of time. They become larger as the sample is made shorter, and as the temperature is reduced. Their magnitude and temperature dependence are in reasonable agreement with the recently developed theory of ‘‘universal’’ resistance fluctuations in one- and two-dimensional conductors. According to the theory, the fluctuations we have observed are due to the motion of single (or a small number of) scattering centers.

We have used near-critical-angle reflection of polarized neutrons to probe for ferromagnetism in fcc Fe and Co epitaxial films (7 to 20 Å thick). fcc Co on Cu(001) exhibits a strong ferromagnetic response with a magnetic moment per atom μ=(1.8±.25)${\mathrm{\mu }}_{\mathrm{B}}$. fcc Fe epitaxied to Cu(001) and Rh(001) shows no in-plane ferromagnetism in contrast to a polycrystalline bcc Fe film of similar thickness. The results are compared with the calculated magnitudes of local moments in these metastable magnetic phases.

We report results from a first-principles total-energy study of primitive (1×1) O chemisorbed on magnetic Fe(001). The adsorption-induced relaxation is found to be a factor of three larger than was inferred earlier from an analysis of LEED intensity data, reflecting strong covalent O—Fe bonding. The resulting arrangement of surface Fe and O atoms already closely resembles a rock-salt FeO monolayer which is comparatively weakly bound to the substrate. The surface bands are compared with angle-resolved photoemission data of Panzner, Mueller and Rhodin.

We demonstrate the existence of a novel type of off-diagonal long-range order in the fractional-quantum-Hall-effect (FQHE) ground state. This is revealed for the case of fractional filling factor ν=1/m by application of Wilczek’s ‘‘anyon’’ gauge transformation to attach m quantized flux tubes to each particle. The binding of the zeros of the wave function to the particles in the FQHE is a (2+1)-dimensional analog of oblique confinement in which a condensation occurs, not of ordinary particles, but rather of composite objects consisting of particles and gauge flux tubes.

A simple quantum system, the semiconductor-based double-barrier resonant-tunneling structure, exhibits intrinsic bistability which we attribute to the feedback dependence of the energy of the electronic states in the well on the tunneling current density.

Chemical trends of barrier heights reported for metal- and silicide-silicon contacts are analyzed. The data are easily explained when both virtual gap states of the complex band structure of the semiconductor and electronic levels of defects created in the semiconductor close to the interface during its formation are considered. The virtual gap states determine the barrier heights when either the defect density is low or the defects are completely charged or all neutral.

We show that large piezoelectrically induced electric fields strongly modify the optical properties of [111] growth axis strained-layer superlattices with growth axis along [111]. These internal fields reduce the superlattice band gap, change optical matrix elements, and cause a spatial separation of photoexcited electrons and holes so as to screen the fields. Very large (${\mathrm{\chi }}^3$∼${10}^{\mathrm{-}1}$ esu) optical nonlinearities occur because of the free-carrier screening of the strain-generated internal electric fields.