The surface- and bulk-derived components of the Si 2p core levels, acquired by photoemission from Si(111)-(7×7), show strong and different oscillations caused by extended fine structure above the 2p edge. An analysis of these oscillations yields the bulk and surface bond lengths which agree well with the known structure. The heretofore controversial issues of the photoemission escape depth and the atomic origin of the surface core levels are resolved.

The structure of ${\mathrm{C}}_{60}$ molecules adsorbed on the Cu(111)-(1×1) surface has been investigated by scanning tunneling microscopy (STM). Bias voltage dependent STM images of individual ${\mathrm{C}}_{60}$ molecules in the monolayer film showed unique intramolecular structures with a threefold symmetry. The observed images agree well with those calculated using the local density approximation. With charge transfer from the Cu(111) substrate to the monolayer film, the ${\mathrm{C}}_{60}$ molecule ratchets to threefold hollow sites.

A missing-row reconstruction of an fcc (111) metal surface has been observed for the first time. Direct observation of many small islands formed at the surface during S adsorption on Ni(111) indicates that a long-range mass transport takes place and that the surface undergoes a reconstruction. We present evidence that this reconstruction corresponds to a model in which every fifth Ni 〈110〉 surface row is missing, with a total of 0.4 monolayer of S atoms adsorbed in threefold hollow positions on the surface and in the created troughs. The driving force for this novel missing-row reconstruction is proposed to be adsorption-induced surface stress.

By using energy calculations and kinetic Monte Carlo simulations we find a kinetic mechanism that appears to control the shape of the islands formed by the aggregation of Pt atoms adsorbed on Pt(111).

On the basis of an extensive set of vapor pressure isotherm and diffraction measurements and computer simulations, we present a microscopic description of the mechanism responsible for the observations of Youn and Hess, Phys. Rev. Lett. 64, 918 (1990), relating to the (reentrant) layering properties of argon-on-graphite films. In the neighborhood of 67 K (and for films more than one layer thick) a transition region exists where the outermost solid layer becomes liquid by a coverage driven process involving layer promotion. Once formed, the liquid layer can be ‘‘re’’ solidified by further increases in argon coverage. This advancing solid-liquid interface results in (re)appearance of vertical steps in the isotherms.

We report the first observation of well defined minibands and minigaps between them, at energies above the barriers in multi-quantum-well structures. Using intersubband absorption spectroscopy, we have observed the optical transitions between confined electronic states of isolated quantum wells to minibands in the continuum of the periodic structure. By comparison with a theoretical model we spectroscopically identify all the observed transitions and explain their strength and spectral shape. In addition, we estimate the coherence length of the electronic wave function in these minibands comparing the absorption spectrum with that of a finite array of quantum wells.

The charge relaxation in an electron capture process on the continuously distributed gap states in a-Si:H has been analyzed. It is shown that a process of charge redistribution among the gap states occurs during a filling pulse, causing the thermal emission energy of the trapped electrons shift deeper into the mobility gap. For an exponential distribution of gap states, an electron’s thermal emission time is proportional to the filling pulse width. These results provide a natural explanation for the recently reported results on a junction capacitance transient experiment, which were attributed to a novel defect relaxation process.

We report fully relativistic band structure and total energy studies of ${\mathrm{UPt}}_3$ in the different magnetic states. We find that the ground state of ${\mathrm{Upt}}_3$ is nonmagentic, even though stable ferromagnetic and antiferromagnetic solutions are also found. We find that the total energy calculations predict the direction of the ordered moment correctly and for the first time the ‘‘metamagnetic transition’’ is found from a first principles total energy calculation for heavy fermion compounds.

The possibility of current-carrying ground states due to the Aharonov-Casher effect in mesoscopic and macroscopic systems is discussed. In mesoscopic metal rings, the resulting spontaneous spin currents are dominated by the charge currents due to the Aharonov-Bohm effect. In an annulus-shaped Josephson-junction array, the corresponding vortex current generates a spontaneous voltage across the annulus, which appears to be observable.

Correlation effects in the transport properties of a single quantum level coupled to electron reservoirs are discussed theoretically using nonequilibrium Green functions approach. Our method is based on the introduction of a second-order self-energy associated with the Coulomb interaction that consistently eliminates the pathologies of previous perturbative calculations. We present results for the current-voltage characteristic illustrating the different correlation effects that may be found in the system, including the Kondo anomaly and Coulomb blockage. We discuss the experimental conditions for the simultaneous observation of these effects in an ultrasmall quantum dot.

The response of the Luttinger liquid to a local potential is studied at zero temperature. It exhibits a crossover behavior. On the largest time scale and in the case of repulsive electron-electron interaction, the backscattering from the potential contributes to the core-hole Green’s function G(t) the factor (${\mathit{t}}_0$/t${)}^{1/8}$—a universal (potential independent) decay law. The orthogonality catastrophe remains of the same analytical type as for the simple metals.

Ballistic electron emission microscopy studies of the Au/Si(100) interface have been performed at temperatures below 77 K for the first time. Spectra below 10 K show collector charging due to the high semiconductor resistivity. Results above 10 K demonstrate unambiguously that both quantum-mechanical phase and amplitude effects are required to describe electron transmission across a metal-semiconductor interface. Furthermore, the ballistic (collisionless) model of electron transmission across this interface is shown to be valid for a wide energy range.

We consider a channel of an incompressible fractional-quantum-Hall-effect (FQHE) liquid containing an island of another FQHE liquid. It is predicted that the resistance of this channel will be periodic in the flux through the island, with the period equal to an odd integer multiple of the fundamental flux quantum, ${\mathrm{\phi }}_0$=hc/e. The multiplicity depends on the quasiparticle charges of the two FQHE liquids.

We report direct observations of vortices in a square superconducting wire grid imaged using scanning Hall probe microscopy. Real space images of vortex configurations are obtained as a function of the flux per unit cell f by measuring the local magnetic field just above the sample. At f=1/2 we observe domains of the checkerboard ground state. As f is reduced from 1/2 to 1/3 vacancies first penerate the grain boundaries and then the checkerboard domains. Near f=1/3 we observe domains of the 1/3 staircase ground state. Heating the sample close to ${\mathit{T}}_{\mathit{c}}$ produces correlated vortex hopping.

A new NMR approach was devised to investigate thermal motion of vortices based on the observation of dephasing effects of the transverse nuclear magnetization below ${\mathit{T}}_{\mathit{c}}$. The effect was observed in ${}_{}{}^{89}{}_{}{}^{}\mathrm{Y}$ spin-spin relaxation time ${\mathit{T}}_2$ measurements of ${\mathrm{TBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$ for two crystal orientations with respect to the applied magnetic field. The data were fitted with a simple model of diffusion of ${}_{}{}^{89}{}_{}{}^{}\mathrm{Y}$ nuclei with respect to the local magnetic field gradient generated by the moving vortices. Small values of a thermally activated effective diffusion constant of the vortices’ motion well below ${\mathit{T}}_{\mathit{c}}$ with reasonable activation energies were derived.

Recent measurements show that the two low-temperature superconducting phases of ${\mathrm{UPt}}_3$ have very different responses to applied pressure, and suggest that there are three distinct superconducting phases when pressure and temperature are varied. It is shown that these features follow from the two-component theory of unconventional superconductivity, in which the superconducting order parameter couples to the antiferromagnetic order parameter. Within this picture a full theory for the phase diagram of ${\mathrm{UPt}}_3$ in three-dimensional magnetic-field–pressure–temperature space is obtained that agrees quantitatively with measurements. Predictions for future experiments are presented.

We report on small angle neutron scattering observations of the flux line lattice (FLL) in a single crystal of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$. To probe the mass anisotropy ratio, ${\mathit{m}}_3$/${\mathit{m}}_1$, measurements were made as a function of angle, Θ, between the 8 kOe applied field and the crystallographic (001) axis for 0°≤Θ≤80°. With the rotation about an a/b (or y) axis, two symmetry-related distorted hexagonal FLL domains formed. Contrary to theoretical prediction, the lattices formed are consistent with a rotation of the short basis vector, ${\mathbf{a}}_1$, from the x axis by 15°, after the effects of anisotropy are removed. The mass ratio is 20±2, which is slightly lower than published values. The temperature dependence of the intensity is not conventional.

The first direct evidence of oscillatory coupling in Co/Au(111)/Co trilayers grown in ultrahigh vacuum is reported. For samples with identical cobalt layer thicknesses, up to three peakjs of magnetoresistance, corresponding to antiferromagnetic coupling between the cobalt layers, are observed with increasing gold spacer layer thickness, ${\mathit{t}}_{\mathrm{Au}}$. By growing trilayers with different cobalt coercive fields, a direct measurement of both ferromagnetic and antiferromagnetic coupling as a function of ${\mathit{t}}_{\mathrm{Au}}$ was possible. The experimental data are in good agreement with theoretical predictions.

We report the experimental proof of the self-induced birefringence of infrared light in many-valley cubic semiconductors. The effect is connected with the redistribution of free electrons between the equivalent valleys on account of heating by the infrared wave. The agreement of the obtained data with the theoretical prediction is very good.

Optical dephasing and specific heat measurements were performed on two rare-earth-doped silicate glasses. The effective homogeneous linewidth of the optical transition, ${\mathrm{\Gamma }}_{\mathrm{hom}}$ was compared to the two-level-system (TLS) contribution to the specific heat, ${\mathit{C}}_{\mathit{v}}^{\mathrm{TLS}}$, between 0.4 and 12 K. Both ${\mathrm{\Gamma }}_{\mathrm{hom}}$ and ${\mathit{C}}_{\mathit{v}}^{\mathrm{TLS}}$ vary as ${\mathit{T}}^{\mathrm{\alpha }}$ with the same value of α for a given rare-earth/glass sample, but with different α for the two samples (α=1.3 for the ${\mathrm{Pr}}^{3+}$/glass, α=1.0 for ${\mathrm{Eu}}^{3+}$/glass). From the ratio of ${\mathrm{\Gamma }}_{\mathrm{hom}}$ to ${\mathit{C}}_{\mathit{v}}^{\mathrm{TLS}}$ for each glass, it appears that the coupling strengths to the TLS for each rare-earth optical transition are similar, but that the density of TLS differ due to their different compositions.