For coverages up to one monolayer, Cu adsorbs in a pseudomorphic structure on the Ru(0001) surface with a 5% tensile strain. Angle-resolved photoemission near the K point in the surface Brillouin zone reveals a state -1.5 eV below the Fermi level which appears localized in the Cu and outermost Ru layers. This state is confirmed by surface linearized, augmented plane-wave calculations to be the antibonding partner of a pair of Cu(3d)-Ru*4d)–derived interface states.

Experimental evidence from studies of the onset of superconductivity in ultrathin Sn films is presented which implies that the sheet resistance is the only relevant variable in determining the onset of global phase coherence. This result is found by a theoretical argument involving both the phase-number and energy-time uncertainty relations.

The magnetic-field–induced Wigner condensation was studied as a function of the electron temperature. Evaluating energy relaxation time and transport measurements we have determined the heat capacity of electrons in n-${\mathrm{Hg}}_{0.8}$${\mathrm{Cd}}_{0.2}$Te. As far as we know, this procedure yields the first experimental data of the heat capacity of a condensed, low-density electron system (n≊${10}^{14}$ electrons/${\mathrm{cm}}^3$). The data revealed a transition of the electron gas to a liquidlike state and eventually to a solidlike state with decreasing temperature.

Aharonov-Bohm magnetoconductance oscillations have been measured in series arrays of 1, 3, 10, and 30 submicron-diameter Ag loops. At constant temperature, the amplitude of the h/e oscillations is observed to decrease as the square root of number of loops, while the amplitude of h/2e conductance oscillations, measured in the same samples, is independent of the number of series loops. This is direct confirmation of the ensemble averaging properties of h/e oscillations in multiloop systems. The amplitude of the h/e oscillations is in good agreement with recent calculations.

The specific heat (C) of ${\mathrm{CeAl}}_3$ has been measured between 0.35 and 20 K at pressures to 8.2 kbar. A very strong and nonlinear dependence on pressure is observed. In particular, the maximum in C/T, a prominent feature at zero pressure which is apparently closely related to the other unusual properties characteristic of the low-temperature behavior, disappears at even very low pressures. There is no transition to a superconducting or magnetically ordered state under pressure. Measurements at zero pressure to 50 mK show a quadratic term in C in addition to the linear term.

A method based on the effective-medium approximation is developed for calculation of the low-frequency density of vibrational states, g(ω), in proteins. The calculated values of fractal exponent γ [g(ω)∼${\mathrm{\omega }}^{\gamma }$] are anomalously low (0<γ<1) in accord with estimates from measurements of the electron-spin relaxation time in low-spin ferric proteins. The essential element leading to the low γ value is the limited cross-chain connectivity in proteins, rather than the geometric arrangement of the polypeptide chain.

The cross section for the production of ${\pi }^{+}$${\pi }^{\mathrm{-}}$ or $K^{+}$$K^{\mathrm{-}}$ pairs in γγ interactions is measured for $m_{\pi \pi }$ between 1.7 and 3.5 GeV/$c^2$ and for two intervals of γγ center-of-mass scattering angle. Results are compared with predictions of a QCD model.

Inclusive charged-pion spectra from p¯d annihilations at rest have been measured in a high-statistics experiment in search of broad states. Analysis of these spectra reveals an enhancement of the ${\pi }^{\mathrm{-}}$ spectrum at 315 MeV/c. This may be interpreted as a production of a new state of mass 1485 MeV/$c^2$ and width at most 200 MeV/$c^2$ recoiling against the ${\pi }^{\mathrm{-}}$. This quasi two-body final state accounts for a large fraction of the p¯n annihilations.

A novel method of analysis which eliminates the combinatorial background in searches for states produced in p¯n annihilations and in association with a recoil ${\pi }^{\mathrm{-}}$ is presented. The difference between ${\pi }^{\mathrm{-}}$ and ${\pi }^{+}$ spectra on p¯n annihilations is the spectrum of the recoiling ${\pi }^{\mathrm{-}}$ or difference spectrum. We applied this analysis to the exclusive channels p¯n→2${\pi }^{\mathrm{-}}$${\pi }^{+}$, 2${\pi }^{\mathrm{-}}$${\pi }^{+}$${\pi }^0$, 3${\pi }^{\mathrm{-}}$2${\pi }^{+}$. A new prominent state of mass and width ≃1480 and 100 MeV/$c^2$ is present in the first and dominates the third channel. These three channels are interpreted in terms of two-body intermediate states only. The suppression or absence of ‘‘direct’’ annihilation is consistent with theoretical models which view the annihilation as a short-range (0.1 fm) phenomenon.

We discuss the central rapidity region of high-energy proton-nucleus collisions in the context of a flux-tube model. This model supposes the creation of a color flux tube by a random-walk color-charging process and its subsequent decay by qq¯ and gluon-pair creation. The observed dependence of particle multiplicity on the number ν of projectile interactions is explained. Some further implications of the model for high-energy proton-nucleus and nucleus-nucleus collisions, including A dependence in the latter case, are discussed.

We propose a criterion that tests the existence of isolated quarks in QCD.

By directly applying light-front boosts to model wave functions, we calculate the soft parts as well as the hard parts of exclusive processes. In the model used by Isgur and Llewellyn Smith, the asymptotic terms begin to dominate for ${\mathrm{Q}}_{\mathrm{c}}^2$≊3.5 (GeV/c${)}^2$ for the pion charge form factor, a much smaller value than previously reported.

From results of a scanning-tunneling-microscopy study we show that, on Pt(100), (i) boundaries between different rotational domains of the hexagonal reconstruction only occur at steps and (ii) neither the step direction nor (iii) the orientation of the respective neighbored domain dictates the direction of the reconstructed domain. The domain-domain and domain-step interactions decrease in the same order; their magnitude and the activation energy for reorientation of domains is related to a structural transition of this surface at 1100 K.

The lowest multiplet component ${}_{}{}^3{}_{}{}^{}\mathrm{H}_4^{}{}_{}{}^{}$ of 4${\mathrm{f}}^2$ in ${\mathrm{PrF}}_3$ has been investigated spectroscopically. An interaction between the ${\mathrm{Pr}}^{3+}$ ions exists, which results in a Davydov splitting of electronic excitations. The system of optical phonons also displays anomalous behavior: Magnetic phonon splitting of an ${\mathrm{E}}_{\mathrm{g}}$ mode and a temperature-dependent frequency renormalization of another mode have been observed. The electronic and the lattice effects can be interpreted simultaneously on the assumption of a 4f-electron–phonon interaction of the Jahn-Teller type as the prevailing interaction mechanism.

Distinct differences have been found in the response of LVV and KLL Auger yields from 7×7 and 1×1 Si(111) surfaces probed with x-ray standing-wave excitations. By the taking into account of the shorter mean free path of the LVV electrons, the differences can be explained by a contraction of the top two (111) atom planes by approximately 0.5 Å. This agrees well with earlier analyses of ion-scattering measurements, but such a contraction has not been detected in other surface measurements or predicted by pseudopotential calculations. Current stacking-fault models of the 7×7 reconstruction may require modification in order to be consistent with these standing-wave measurements.

The dispersion curves of both the optical and acoustical surface phonons in the superconducting compounds NbC(100) and TaC(100) have been determined over the entire Brillouin zone of the Γ¯-M¯ symmetry axis by use of angle-resolved high-resolution electron-energy-loss spectroscopy. In contrast to the bulk phonon, no anomalies (dip) due to the electron-phonon coupling in the dispersion curves of the longitudinal phonon have been found at these surfaces. Conversely, the in-plane force constant between carbon and metal atoms is strongly enhanced there.

Commensurate monolayers of a mixture of 70% carbon monoxide and 30% argon on graphite are studied by neutron and low-energy-electron diffraction. A 2×2 superstructure due to 3:1 compositional ordering is observed below 25 K. The compositional ordering is most likely due to molecular-axis ordering of carbon monoxide molecules into a pinwheel pattern with argon atoms at the central sites of each pinwheel. Such a pinwheel structure has been predicted by Harris, Mouritsen, and Berlinsky for planar rotors with anisotropic interactions on a triangular lattice with vacancies.

We report measurements of the temperature dependence of the ultrasonic attenuation in normal-state ${\mathrm{UPt}}_3$. At about 12 K a pronounced longitudinal absorption peak is observed. Such a peak does not appear for transverse-acoustic waves. Our experimental results can be well explained by a narrow resonance in the quasiparticle excitation spectrum near the Fermi energy and are consistent with the enhanced specific-heat coefficient.

We show that the first-principles local-density–functional Xα method reliably predicts proton Fermi-contact coupling constants for planar, neutral, organic π radicals. Results for the radical soliton in polyacetylene yield -0.39 for the ratio of the two observed proton Fermi-contact constants, close to the experimental value of -0.33. These studies also justify use of McConnell’s relation to analyze the polyacetylene proton ENDOR spectrum. Our theoretical value of McConnell’s constant for polyacetylene is -26 G, in good agreement with classical estimates of this quantity.

We analyze infrared-optical measurements on gas-evaporated gold blacks, performed by Harris many years ago. The data agree quantitatively with recent theories for anomalous conduction on fractal structures. The frequency-dependent conductivity obeys σ∝${\mathrm{\omega }}^{0.7}$ below the relaxation frequency for electrons in a single particle. This is consistent with the conductivity exponents for percolation clusters and for diffusion-limited aggregates.