We have investigated the spectral and temporal dynamics associated with the interaction between monochromatic and thermal phonon distributions in YAG:${\mathrm{Pr}}^{3+}$. Using defect-induced one-phonon absorption to generate a monochromatic phonon distribution at 43.3 ${\mathrm{cm}}^{\mathrm{-}1}$, we measure a ${\mathit{T}}^{\mathrm{-}3}$ dependence of the monochromatic phonon lifetime in the temperature range 9 to 25 K. We observe the evolution of additional broadband phonon distributions which do not occur at low temperatures.

This work is the first report of the use of nonlinear optics techniques to probe the pressure dependence of electronic energy levels in a solid. An advantage which may be significant is that for the multiphoton processes involved, relatively low-energy photons that are not absorbed by the cell windows can probe states having energies which would be strongly absorbed by the windows in a one-photon excitation. The measurements follow the pressure dependence of the energetically lowest polariton in KI using the three-photon-spectroscopy method.

We have studied the optical second-harmonic reflectance of Ag(111) as a function of the incident photon energy and the interfacial potential in an electrochemical environment. The behavior of the anisotropic contribution is consistent with a potential-induced surface reconstruction from ${\mathit{C}}_{3\mathit{v}}$ to ${\mathit{C}}_3$ under conditions of positive surface charge.

We used anomalous x-ray-diffraction methods to measure the contribution of an epitaxial copper overlayer on silicon to the crystal truncation rods (CTR’s). The intensities of the CTR’s are analyzed to determine interface structure; the epitaxy of a large-misfit system, Cu on Si(111), can be described in relationship to this structure. Anomalous scattering observed at the Cu K edge along a Si CTR demonstrates copper atoms to be in registry with the Si(111) surface. The copper-atom registry at the interface can be modeled based on the known bulk η-${\mathrm{Cu}}_3$Si structure and observed epitaxy.

The bonding energies of the Pd 3d and the C 1s core levels have been studied for the p(2 √2 × √2 )R45°, p(3 √2 × √2 )R45°, and p(4 √2 × √2 )R45° structures of CO on Pd(100). Adsorption of CO shifts the Pd 3d surface emission to higher binding energies with the magnitude of the shift depending almost linearly on the number of Pd to CO bonds; the measured shift per bond is close to 0.5 eV. A direct relation is established between the detailed geometry of the CO overlayer and the changes in the Pd 3d spectra.

Very-low-energy (≊28 eV), high-flux (≊0.4 mA/${\mathrm{cm}}^2$) Ar-ion irradiation during molecular-beam epitaxy changed the nucleation of GaAs on Si(100) from Stranski-Krastanov to a mechanism approaching layer-by-layer growth. While three-dimensional island nucleation was eliminated, the growth surface exhibited low-amplitude undulations. The results are explained by ion-induced removal of atoms from stable 3D islands, which suppressed 3D island nucleation.

We have measured the evolution with temperature of the structure of vicinal Si(001) from double- to single-atomic-height steps using high-resolution low-energy electron diffraction. The observed temperature dependence is qualitatively explained with a model that describes this system in analogy with mixing equilibrium between two states, of which one is n-fold degenerate.

We have proposed a new model for this Sb-stabilized InSb(111)B-(2×2) reconstructed surface prepared by molecular beam epitaxy. Adsorption of Sb trimers at a fourfold atop site of the outermost Sb layers is confirmed by intensity analysis of transmission electron diffraction patterns obtained from the reconstructed surface. Also, Auger electron spectroscopy measurements provided a satisfactory surface composition for the InSb(111)B-(2×2) surface.

We present results of direct measurements of polymer depletion layers at the liquid/air interface using neutron reflectivity. The systems studied are semidilute solutions of polystyrene in toluene using polymers of different molecular weights. The thickness of the depletion layer d is found to be of the order of the correlation length ξ of the polymer in the bulk solution. We show, for the first time, the existence of a depletion layer at the free surface of a polymer solution when ${\gamma }_{\mathit{p}}$>${\gamma }_{\mathit{s}}$, where ${\gamma }_{\mathit{p}}$ and ${\gamma }_{\mathit{s}}$ are surface tensions of pure polymer and pure solvent, respectively. We show also that the thickness of the depletion layer scales with the bulk concentration ${\mathrm{\phi }}_{\mathit{b}}$ as d∼${\mathrm{\phi }}_{\mathit{b}}^{\mathrm{-}0.75}$.

The first sputtering measurements of the most volatile solid hydrogenic targets are reported. Bombardment of these targets by hydrogen and deuterium ions leads to erosion predominantly via electronic transitions. The magnitude of the yield depends strongly on the particular isotope. No existing theory for this electronic sputtering can explain the large yields that range from about 100 ${\mathrm{D}}_2$/H for solid deuterium up to 800 ${\mathrm{H}}_2$/H for solid hydrogen.

This Letter reports the first measurements of Poincaré sections of charge-density-wave (CDW) dynamics. High-quality crystals of ${\mathrm{NbSe}}_3$ were excited by combined dc and ac currents. Mode-locked and -unlocked behavior are identified by Poincaré sections consisting of points and closed curves, respectively. We analyze our results in terms of a dynamical phase transition. We argue that multiply degenerate attractors exist in subharmonic mode-locked phases. Dynamics of such phases are dominated by domain walls separating sections of the CDW with different attractors.

A novel method to measure x-ray-absorption spectra without the inner-shell lifetime broadening is presented. It is based on a high-resolution spectrometer which can be used to analyze the fluorescence photon energy with better resolution than the natural linewidth. The dramatic improvement in resolution and detailed structure for the x-ray-absorption near-edge structure (XANES) at the Dy ${\mathit{L}}_{\mathrm{III}}$ edge is presented. This new technique reveals structure which is totally invisible using conventional XANES.

The spectrum of electronic excitations of Na and K overlayers adsorbed on Al(111) has been studied by means of electron-energy-loss-spectroscopy experiments, and self-consistent, dynamical-response calculations. Losses are observed in two distinct energy and coverage domains. The loss observed during the formation of the second atomic layer shows novel features, which are traced to the intrinsic quantum-mechanical nature of the excitations being probed, and their spatial confinement by the overlayer.

A new concept for the electronic excitations in adsorbed alkali-metal layers is presented. It explains how these excitations evolve with coverage from below one monolayer to thick multilayers, and it establishes a direct relation of these overlayer collective modes to those of clean alkali-metal surfaces.

We present measurements of the transport properties of 0.75-μm-long, narrow, insulating indium oxide wires and rings. These devices have no apparent tunnel barriers, yet they exhibit effects similar to those found in series arrays of very small-capacitance tunnel junctions: highly nonlinear I-V characteristics and a zero-bias conductance which is periodic in a voltage applied by means of a lateral gate. These effects are due to the influence of single-electron charging on transport through localized states in the insulating regime.

The excess low-frequency 1/f noise and discrete two-level resistance fluctuations (TLFs) were studied in small-area NbN-MgO-NbN tunnel junctions with a high, low-temperature density of active defects. Strong and evolving interactions between large TLFs indicate that these fluctuations result from the self-organization of interacting defect elements. In the low-T tunneling regime, an unusual slowing down of the rates and a decrease in amplitude with increasing T is sometimes observed, indicative of a thermally induced change in the self-organized two-level state.

We report measurements of the temperature and length dependence of the conductance of a wide two-dimensional electron gas in a strongly localized regime. Our results indicate that the conduction occurs via resonant tunneling below about 0.1 K and, at higher temperatures, via hopping through channels that contain more than one localized state. A dramatic increase of the average logarithm of conductance 〈lnG〉 with the increasing sample length is observed in the tunneling regime, for which there is no satisfactory theoretical explanation yet. This effect persists even up to ≳4.2 K.

A general study of electron linear transport in systems with open boundary conditions is presented. It is shown that a consistent treatment of bulk and boundary contributions is only achieved in a strictly gauge-invariant formulation of the electomagnetic linear response. Invariance under large gauge transformations requires the use of a generalized version of the continuity equation in which current sources at infinity are explicitly included. These sources are described by delta functions located at the points of infinity and they guarantee global charge conservation. The formulations of steady-state transport in terms of global conductance coefficients and nonlocal conductivity tensors are shown to be strictly equivalent for interacting electron systems in the presence of a magnetic field. As a corollary, the reciprocity theorem for a four-lead resistance is proved in its full generality for systems with arbitrary many-body interactions.

We report on the first experiments showing the influence of surface magnetization on optical second harmonic generation in reflection at a Fe(110) surface. The magneto-optical Kerr effect modifies the hyperpolarizability of the surface in the optical field, leading to a dependence of the second harmonic yield on the direction of magnetization relative to the light fields. For the clean surface an effect of 25% was determined, which decays exponentially with surface contamination by the residual gas, thus demonstrating the high surface sensitivity of this technique.

We present measurements of electrical resitivity ρ(T), specific heat C(T), entropy S(T), and magnetic susceptibility χ(T) as functions of temperature T for the alloy system ${\mathrm{Y}}_{1\mathrm{-}\mathit{x}}$${\mathrm{U}}_{\mathit{x}}$${\mathrm{Pd}}_3$. For x=0.2, ρ(T)/ρ(0) is almost linear in T for 0.2≤T≤20 K, and C(T)/T∼-ln(αT) for 0.6<T<16 K. Also, the added molar entropy per U, ΔS(T)-ΔS(0) appears to saturate to (R/2)ln(2), suggesting that ΔS(0)≊(R/2)ln(2). We argue that our data provide comprehensive evidence in a dilute alloy for the two-channel quadrupolar Kondo effect (${\mathit{T}}_{\mathit{K}}$≊42 K) with concomitant ‘‘marginal Fermi liquid’’ phenomenology.