X-ray data were collected on films of ${\mathrm{Al}}_{0.72}$${\mathrm{Mn}}_{0.22}$${\mathrm{Si}}_{0.06}$ sputtered on NaCl at 45, 150, and 230 °C. The 45 °C films show a typical metallic-glass structure factor, $S\left(Q\right)\mathrm{}$, while at 230 °C the structure is quasicrystalline plus Al. A combined particle-size and phason strain broadening was applied to the normalized and reduced $S\left(Q\right)\mathrm{}$ for the 230 °C film to bring it essentially into coincidence with the amorphous (45 °C) $S\left(Q\right)\mathrm{}$ leading us to conclude that the glass, or amorphous, phase represents a defect limit of the quasicrystal.

First-principles total-energy calculations have been performed for the Mo(001) surface. Subsequent tight-binding calculations of the surface-phonon dispersion curves for the unreconstructed surface show that Fermi-surface nesting of surface states leads to a softening of surface modes near $\overline{M}$, with the maximum instability very close to the wave vector of the observed incommensurate reconstruction. Our results disagree strongly with the prevailing short-ranged force models for the incommensurate reconstruction on Mo(001).

Theoretical predictions for inverse photoemission from free-electron-like materials are tested by measurement of the energy and angle dependence of the emitted photon intensity from Al. The predicted cross-section minimum at the plasma frequency ${\omega }_p$ is observed as well as a characteristic increase below ${\omega }_p$ due to the inverse of the surface photoelectric effect. Above ${\omega }_p$ there is an additional bulklike contribution from the radiative decay of bulk plasmons. Other materials with a well-defined plasma resonance, e.g., Ge and Si, exhibit a similar cross-section behavior.

It is shown, by use of a Landauer-type formulation of the quantum Hall transport, that in small and narrow two-dimensional rings, the Hall quantization of ${\rho }_{\mathrm{xy}}$ is accompanied by a finite, but small, ${\rho }_{\mathrm{xx}}$ which exhibits periodic Aharonov-Bohm oscillations. These oscillations arise as a subtle consequence of the possible elastic backscattering of the current-carrying electrons in narrow channels.

The electronic and magnetic structures of ${\mathrm{Nd}}_2$${\mathrm{Fe}}_{14}$B and related compounds have been studied with photoemission spectroscopy and self-consistent spin-polarized electronic structure calculations. The positions of the exchange-split $\mathrm{Fe}3d$ bands and the localized $4f$ levels were determined. The densities of states in the ferromagnetic and paramagnetic states are essentially identical which provides strong evidence for considerable magnetic short-range order above $T_c$, as in the fluctuating-band model of itinerant-electron magnetism.

We have measured the four-terminal magnetoresistance of an electron waveguide, i.e., a high-mobility wire fabricated in GaAs-AlGaAs heterostructure in which only a few transverse one-dimensional subbands carry the current, and simulated the measurement numerically. We observe that the average resistance increases when the current path bends through a junction at or beyond the voltage terminals because of a change (due to the bend) in the relative transmittance of the few subbands. Our observations reveal that the average resistance is predominantly associated with scattering from the leads used for the measurement.

The steady-state density of electrons accumulated in the well of a GaAs/AlGaAs double-barrier resonant tunneling structure is optically determined as a function of applied voltage by monitoring of the integrated area under the photoluminescence signal from the confined GaAs well. The characteristic time, ≥ 350 ps, obtained as the quotient of the areal charge and current densities, is consistent with calculations of the intrinsic lifetime of the resonant state, independent of intrasubband scattering processes.

We show that for a one-dimensional electron gas with strong repulsive electron-electron interactions and a weak retarded attractive interaction, superconducting fluctuations can occur at high temperatures. The dominant driving force for these fluctuations is the repulsive interactions! Although the results are for a one-dimensional model, a strong analogy exists between our results and the short-ranged resonating-valence-bond picture of superconductivity.

Group-theoretical concepts are used to define a generalized transfer matrix for a substitutionally disordered material. The matrix can easily be constructed and averaged. Diagonalizing of the generalized transfer matrix truncated to finite dimensions enables averaged densities of states to be calculated for infinite systems. The method is checked against direct simulation and appears to be an accurate and reliable way of finding the density of states in systems with arbitrarily strong disorder.

A computer simulation of a representative continuum system, the inverted random-void model in three and six dimensions, is reported. It is the first such simulation where the local geometry of the conducting particles is taken into account. The results show that the critical behaviors of both the electrical resistivity and the resistance noise, near the percolation threshold, are well described by the recently suggested models of links in the nodes-links-blobs picture.

A dilute nonsymmetric ferromagnet and a version of the Hopfield model are solved in the limit where the average number of inputs per spin is finite. The solution is based on the fact that the magnetization of each site is a function of the number and the type of inputs and their connection strengths. Extension of this solution to the symmetric case is discussed. The solution can also be extended to any other distribution of interactions.

The average eigenvalue distribution $\rho \left(\lambda \right)$ of $N\times N$ real random asymmetric matrices $J_{\mathrm{ij}} \left(J_{\mathrm{ji}}\ne J_{\mathrm{ij}}\right)$ is calculated in the limit of $N\to \infty$. It is found that $\rho \left(\lambda \right)$ is uniform in an ellipse, in the complex plane, whose real and imaginary axes are $1+\tau$ and $1-\tau$, respectively. The parameter $\tau$ is given by $\tau =N{\left[J_{\mathrm{ij}}{J}_{\mathrm{ji}}\right]}_J$ and $N{\left[J_{\mathrm{ij}}^2\right]}_J$ is normalized to 1. In the $\tau =1\mathrm{}$ limit, Wigner's semicircle law is recovered. The results are extended to complex asymmetric matrices.

An era of inflation in the hot big bang can lead to a dilution of axions. Such a dilution removes the upper bound on $f_A$, the symmetry-breaking scale at which axions are produced. The dilution may occur during or just after inflation, but in either case there is a restriction on the reheat temperature of the Universe after inflation. Hence, such a scenario for an invisible axion requires baryogenesis to occur at a low temperature.

A variational Ansatz for a solution of the Euclidean time-dependent Weinberg-Salam field equations which connects topologically distinct vacua is presented. The Ansatz allows a unified description of real-time transitions involving baryon-number nonconservation from the zero-temperature (instanton) limit up to the electroweak transition temperature.

A novel action-variational approach based on certain natural criteria is proposed. Its accuracy and advantages are demonstrated for U(1) gauge theory in four dimensions.

By use of general principles (Kubo-Martin-Schwinger condition, breakdown of Lorentz invariance, triviality arguments), the nature of diagrammatic perturbation theory in relativistic field theory at nonzero temperature is investigated. By operator-algebraic techniques it is found that the conventional method is inconsistent, and an essentially unique alternative is given.

We show that the Dirac-bracket quantization of a single self-dual field leads naturally to the bosonization formulas. We find a numerical parameter describing the soliton charge and unveiling hidden soliton sectors.

It is argued that the interactions between solitons are well approximated by a finite-dimensional dynamical system, provided that the static forces between the solitons are relatively weak. The application to skyrmion dynamics and the nucleon-nucleon interaction is described.

The possible patterns into which global flavor symmetry and parity conservation can break in three-dimensional Abelian gauge theories are derived. It is found that the two symmetries are incompatible: If one does not break, the other breaks maximally. For an odd number of flavors, in particular, parity conservation is always broken. A simple derivation of the quantum numbers of the vacuum in such theories, is also presented.

The strikingly large spin-spin correlation $A_{\mathrm{NN}}$ observed in $\mathrm{pp}$ elastic scattering at $p_{\mathrm{lab}}=2.5\mathrm{} \mathrm{and} 11.75$ GeV/c and the unexpected energy dependence of absorptive corrections to quasielastic proton-proton scattering in a nuclear target can be interpreted in terms of two $J=L=S=1\mathrm{}$, $B=2\mathrm{}$ resonance structures associated with the strange- and charmed-particle production thresholds, interfering with a perturbative QCD background. The results provide support for the "color-transparency" phenomenon predicted in perturbative QCD away from resonances or heavy-quark thresholds.