The novel application of a surface-temperature-modulation technique to the important class of bimolecular surface reactions is shown to lead to detailed dynamical information in a direct fashion. Knowledge of the adlayer composition or structure is not required for an evaluation of the activation energy. The activation barrier for the reaction CO(a) +O(a) → C${\mathrm{O}}_2$(g) on the Pt(110) surface is found to decrease precipitously from a value of 22 kcal-${\mathrm{mol}}^{-1\mathrm{}}$ at low coverages to a value of approximately 8 kcal-${\mathrm{mol}}^{-1\mathrm{}}$ in the presence of high coverages of oxygen adatoms.

We report the first direct measurements of the thermal boundary conductance between superfluid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$-$B$ and sintered silver in the temperature region well below $T_c$. The conductance is highly temperature dependent, being dominated by an $\exp (-\frac{\Delta }{\mathrm{kT}})$ dependence in the region $T<\mathrm{}0.3\mathrm{}{T}_c$. Measurements made at the three pressures 0, 4, and 12 bars also demonstrate the variation of the conductance with the energy gap, $\Delta$.

The fact that a kinetic self-avoiding walk can only meet topologically connected lines of occupied sites (instead of isolated points) is shown to have important consequences for the asymptotic behavior. The exponent of the kinetic-growth walk (a model for polymer growth) is in fact $\nu =\frac{3}{\mathrm{}(2+d)\mathrm{}}$ instead of the recently proposed value $\nu =\frac{2}{\mathrm{}(d+1\mathrm{})\mathrm{}}$. Especially for $d=3\mathrm{}$, however, the asymptotic behavior is reached only for very long walks ($N\gg {10}^6$). This explains why numerical data seem to indicate lower values for $\nu$.

Tunneling images of single atomic steps on Si(111) have been obtained with a tunneling microscope. The 7×7 reconstruction is observed to persist essentially undistorted right up to the steps. The position of each step coincides with a 7×7 unit-mesh edge in both the upper and lower terraces adjacent to it. Asymmetry within the 7×7 unit mesh is observed and correlated with faulting of terraces adjacent to the step. The results are described by an extension of the dimer adatom stacking-fault model of Takayanagi et al.

We have observed surface states indigenous to the Si(111) 7×7 superlattice with the tunneling microscope. The data show the states' energies and strengths to be strongly dependent on position in the unit mesh. Implications of this for structural models of the 7×7 superlattice are discussed.

The glass transition, structure, and dynamics of a ${\mathrm{Ca}}_{67}$${\mathrm{Mg}}_{33}$ metallic glass are studied via a new molecular-dynamics method incorporating the density dependence of the potentials. Results are in agreement with neutron-scattering data. The accessible configurational energy of the glass is found to possess several nearly degenerate potential minima.

X-ray-diffraction studies of the structures and phase transitions of the tilted hexatic phases (smectic $F$ and smectic $I$ in thin liquid-crystal films of 4-$n$-heptyloxybenzylidene-4-n-$n$-heptylaniline (70.7) are reported. The measured correlation lengths were strongly anisotropic in both phases. The smectic-$I$ to smectic-$F$ transition is first order as expected from the symmetry change. The smectic-$F$ to smectic-$G$ transition is first order with strong pretransition effects and becomes nearly second order as the film thickness is decreased.

The low-temperature phase of the dilute Ising antiferromagnet ${\mathrm{Fe}}_{0.55}$${\mathrm{Mg}}_{0.45}$${\mathrm{Cl}}_2$ in zero field is studied by specific-heat, ac-susceptibility, and neutron-scattering experiments. We find that in this phase, spin-glass behavior and antiferromagnetic long-range order coexist. Such a mixed-order phase is predicted by the mean-field theory of reentrant spin-glasses, but has never been observed before.

The response of thermally activated free vortices in superconducting thin films to a crossed electric field and temperature gradient is shown to produce a static magnetic field perpendicular to the plane of the film. The magnetization, which results from an induced imbalance between the free vortex and antivortex densities, is proportional to the logarithmic derivative of the free-vortex density and to a vortex-nonequilibrium relaxation time.

Measurements are reported of a new thermoelectric effect in thin indium-indium-oxide superconducting films. In the temperature regime between the Kosterlitz-Thouless vortex dissociation temperature $T_c$ and the BCS transition temperature $T_{c0\mathrm{}}$, a simultaneous electric field and temperature gradient cause the film to become weakly magnetized with a magnetization normal to the plane of the film. The magnetization rises to a maximum between $T_c$ and $T_{c0\mathrm{}}$ and is linear in both the temperature gradient and electric field.

We show that the binding energy of surface states is a multibranch function of the image-plane position. The states of the Rydberg series (including the conventional crystal-derived states) have a unique labeling in terms of the number of extrema in the wave function beyond the crystal edge, and the spatial extent of the image states is determined by their binding energy. In addition, we find that the image plane is further from the crystal edge on more loosely packed surfaces and that dynamical corrections to the image potential account for increases in the effective mass of <5%.

We have observed for the first time a single sine-Gordon soliton trapped in an annular Josephson junction. This system offers a unique possibility to study undisturbed soliton motion. In the context of perturbation theory, the soliton may be viewed as a relativistic particle moving under a uniform force with damping. Accordingly our experimental results are displayed directly in a force-versus-momentum plane, where they may be described by a theoretically derived universal curve.

The conventional classical treatment of the field emitted by a Mössbauer nucleus predicts an enhanced counting rate in a two-detector coincidence scheme, whereas quantum electrodynamics does not. Our experiment agrees with QED.

The nature of the ground-state broken symmetry in a one-dimensional half-filled band with arbitrarily long-range Coulomb interactions between electrons is shown to be precisely given by two simple inequalities involving the Coulomb parameters. It is further shown that non-$2k_{\mathrm{F}}$ periodicity may occur if the first of these inequalities is violated.

Using the new experimental technique of hot-electron spectroscopy we have, for the first time, observed electrons in extreme nonequilibrium. When the transit-region width is comparable to the calculated hot-electron mean free path, two peaks are observed in the measured spectrum. The high-energy peak corresponds to quasiballistic electrons suffering few, if any, collisions in the transit region. The low-energy peak is due to excitation of the Fermi sea by the injected hot electrons.

Subpicosecond infrared pulses were used to study in GaAs at 15 K the spectral dependence of the absorption saturation around the excitation-pulse wavelength. The nonthermal part of the carrier energy distribution is found to peak at the excitation frequency. A line-shape analysis allows the determination of the electron-hole-pair dephasing time.

Under perpendicular magnetic field, the spin susceptibility of a noninteracting two-dimensional electron gas with open Fermi surface shows a novel behavior due to the orbital effect. It exhibits a series of peaks at wave vectors which obey a quantized nesting condition. When the field increases, each of these peaks becomes in turn the absolute maximum. Their magnitude diverges logarithmically at low temperature. We discuss some experimental consequences in actual anisotropic metals.

A new, very sensitive method was used to study the existence of magnetic moments of Fe and Ni when deposited on a nonmagnetic metal. Evidence is presented that isolated Ni atoms possess a magnetic moment on the surface of Pb, contrary to previous results. At greater coverage of Ni and Fe the onset of ferromagnetism was found at the thickness observed in other experiments. The technique is sensitive to ${10}^{-6\mathrm{}}$ of an atomic layer of Fe and can detect the existence of localized moments of magnetic materials on any metal substrate.

A theory is presented which predicts an anomalously large magnetic dichroism in the $M_{4,5}$ x-ray absorption-edge structure of rare earths in magnetically ordered materials. Polarized synchrotron radiation can therefore be used to determine accurately the magnitude, the orientation, and the temperature and magnetic field dependence of the local rare-earth magnetic moment in a large variety of magnetically ordered materials and thin films.

Higher-order corrections to the Korteweg-de Vries equation are examined by Hamiltonian methods. Starting from the underlying Hamiltonian systems (e.g., the two-fluid equations in the case of ion-acoustic waves), one finds that the corrected equations have the same Poisson bracket as the Korteweg-de Vries equation at every order. One also finds that the underlying equations become nonlocal at sufficiently high order.