Solid-on-solid models provide a comprehensive description of surface roughening, preroughening, and reconstruction. Au(110) deconstructs into a disordered flat phase. The (110) facets of Ag and Pd are candidates for realizations of preroughening. The preroughening transition is shown to be a line of continuously varying exponents using Coulomb-gas methods. Inside and outside corners of steps on the surface have different energy. The topological charge of this interaction is identified. It does not alter the roughening transition, but is relevant at the preroughening transition, and leads to generalized disordered flat phases.

A fluid confined between two parallel walls that exert different (competitive) surface fields may exhibit phase equilibria strikingly different from those found for equal fields. Macroscopic arguments and an explicit mean-field analysis predict that if the fields are such that the fluid wets one wall and dries the other (above a certain critical wetting transition temperature $T_w$) coexistence of two phases can only occur, for finite wall separation L, when T<$T_c$,L, where the critical temperature $T_c$,L lies below $T_w$. A scaling Ansatz suggests & where ${\beta }_s$ is the exponent that describes the growth of the wetting layer.

We report an ellipsometric coverage-vapor pressure isotherm study of multilayer oxygen films on graphite. Solid β oxygen is found to wet graphite at least from 37 to 43.8 K. The film thickness at melting is limited to four layers by intrusion of the nonwetting γ solid. Melting, except of the top layer, occurs in a single first-order transition, while there is evidence that the top layer of three-or-more-layer films melts continuously near 41 K.

We present high-q resolution low-energy electron diffraction results of the approach to thermal roughening of the Ni(110) surface. The process is found to occur in two reversible steps. At temperatures above 900 K vibrations become a significant fraction of the bond length and a large anharmonicity in the vibrational amplitude appears. A large asymmetry between in- and out-of-plane vibrations exists, causing the off-specular diffraction peaks to decay rapidly to zero. Finally, near 1200 K, a significant density of vacancies begins to form. Above 1300 K the surface roughens.

We have studied the Ni(111)5°[11¯0] vicinal surface using high-resolution x-ray diffraction. The resolved two-peak profile in the scans perpendicular to the step direction is explained by a two-phase model in which the surface consists of two types of region, one with large terraces and the other with small terraces. Additional measurements as a function of sample temperature show evidence that the step arrangement undergoes a phase transition aroung 570 K, with step clustering at low temperatures.

A microscopic theory for the long-wavelength dielectric dispersion [ε(ω)] in a strongly correlated dipolar liquid is presented. The calculated ε(ω) is stongly non-Debye if only the orientational mechanism of polarization relaxation is considered. However, simple Debye behavior is recovered when the translational contribution to polarization relaxation is significant. In addition, the present theory explains the computer simulation results of Pollock and Alder satisfactorily.

We have investigated the effects of pressure on the pinned and sliding charge-density-wave states of ${\mathrm{K}}_{0.3}$${\mathrm{MoO}}_3$ at 77 and 4.2 K. The application of hydrostatic pressure suppresses the threshold electric field both for the conventional charge-density-wave conduction and for the low-temperature, abrupt depinning. We show that the change in the pinning energy is due to the decrease of the charge-density-wave order parameter and that the pressure dependence of the threshold field favors weak-pinning theories.

We observe a photon-drag voltage along the optical path of photons propagating in the plane of an unbiased 2D electron gas in GaAs quantum wells. This voltage is induced by momentum transfer from 10-μm-wavelength photons to the electrons, resonantly matched in their intersubband energy to the photons by appropriate choice of the 3.2-nm well width. The voltage is reversed when the propagation direction of the photons is reversed. Moreover, the sign of the voltage also changes by sweeping the photon energy through the intersubband resonance condition in agreement with current theory.

We interpret an anomalous isotope shift in the vibrational spectrum of the deuterium-boron pair in silicon in terms of a Fermi resonance between the second harmonic of the transverse boron vibration and the fundamental longitudinal deuterium vibration. A simple quantum-mechanical treatment accounts for the reported observations and further predicts the oscillator strength and polarization of infrared absorption of the perturbed second harmonic of the boron vibration. We observe this second harmonic, now allowed due to its mixing with the deuterium mode, in agreement with the model.

Tunneling cyclotron resonance is used to measure the tunneling rate deep in the band gap of a pure AlAs barrier in a thin barrier GaAs/AlAs superlattice. The experimental results are analyzed in terms of a four-band k⋅P model which leads to a renormalized effective mass in the barrier. Excellent agreement with experiment is achieved and we are able to conclude that the mass in the AlAs barrier is strongly renormalized down to 0.09$m_e$ from the bulk-conduction-band value of 0.15$m_e$. .AE

It is shown that, for the t-J model, dilute holes in an antiferromagnet are unstable against phase separation into a hole-rich and a no-hole phase. When the spin-exchange interaction J exceeds a critical value $J_c$, the hole-rich phase has no electrons. It is proposed that for J slightly less than $J_c$ the hole-rich phase is a low-density superfluid of electron pairs. A brief discussion of phase separation in other related models is given.

The critical current density ${\mathrm{j}}_{\mathrm{c}}$(B,T,θ) of epitaxial, c-axis-oriented ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{\mathrm{x}}$ films was measured between 4.2 and 77 K in magnetic fields up to 8 T as a function of the field direction θ. Strongly enhanced critical currents are observed when the flux lines are aligned along the CuO planes, but there is also a maximum in ${\mathrm{j}}_{\mathrm{c}}$ when the magnetic field is adjusted parallel to the c axis. We relate these effects to an intrinsic pinning between CuO layers, an anisotropy of the shear modulus ${\mathrm{c}}_{66}$, and pinning effects of twin boundaries or stacking faults perpendicular to the film plane, respectively.

Magnetization measurements are reported on a nearly cubic single crystal ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{6+\mathrm{x}}$ which displays predominantly one variant of twin boundary. With this crystal, we were able to compare the effects of different vortex and twin-boundary orientations on magnetic behavior. The results demonstrate that there is a measurable effect due direct pinning of vortices by twin boundaries for applied fields perpendicular to the c axis. We also show that the large anisotropy in flux pinning for applied fields parallel and perpendicular to the c axis is not due to pinning by twin boundaries.

The formation of Al-Ni compounds by ball-milling of elemental powders has been investigated by means of in situ thermal analysis, x-ray diffraction, and scanning electron microscopy. The results show that AlNi forms in an explosive, exothermic reaction, driven by the large heat of compound formation. The mechanism discovered is suggested to explain the mechanical alloying of other systems.

We present a semiclassical theory for the two-point correlation function of the eigenphases of the S matrix for chaotic scattering. It is expressed as a sum of contributions from unstable periodic orbits of the classical scatttering mapping. Backed by numerical results and for correlation ranges $r^{\mathrm{*}}$(∼1/ħ) we obtain a universal function which is consistent with the result for Dyson’s circular ensemble. This result adds to the conjecture that universal fluctuations governed by random matrix theory are the quantum manifestation of classical chaos.

We sutdy a stochastic interacting particle system which displays a nonequilibrium transition in its relaxation dynamics in the infinite volume limit. The transition is destroyed by restriction to a finite volume, but its remnants remain until a crossover time $T_c$(L,ε), where L is the system size and ε is the control parameter measuring the distance from the bulk transition. We find that the crossover time $T_c$(L,ε) diverges where ε→0 in a fixed volume. Thus this finite volume system displays arbitrarily long time scales near the transition.

Intrinsic molecular fluctuations are associated with macrovariables whose time evolution is described by macrovariable equations. When the macrovariable equations describe chaotic trajectories, the covariance matrix for the molecular fluctuations diverges rapidly. This implies that the macrovariable equations are not stable and cannot be justified from an underlying molecluar description.

The properties of energy transport are numerically investigated with the use of a one-dimensional cellular-automaton model called 26R. The validity of Fourier’s law and the Green-Kubo formula for thermal conductivity κ is demonstrated for this model in the limit of large systems. Nonlinear correction to Fourier’s law and the recovery of left-right symmetry are also discussed.

Using fully quantal methods, we investigate various manifestations of the geometric phase in bound and free diatom systems. Adiabaticity and degeneracy are not invoked in the discussion.

It is shown that a large class of time-dependent solutions to Einstein’s equation are classical solutions to string theory. These include metrics with large curvature and some with spacetime singularities. Unlike the case of orbifold singularities, it is shown that string propagation through the singluar region is not well behaved.