I show that a dilute, sterically stabilized lyotropic smectic liquid crystal, subjected to a sufficiently large velocity gradient in the plane of the layers, will undergo a phase separation, with regions of reduced layer spacing coexisting with regions devoid of any layer material. The critical shear rate for this transition should go as (layer spacing${)}^{\mathrm{-}3}$.

We report long-range interstitial migration of B in Si at low temperature, initiated by kick-out reactions with self-interstitials (I) created by Si implantation. At 450°C, migration path lengths ∼100 nm are measured within a time frame of 15 min. Observations of the number and spatial distribution of displaced B atoms in relation to the distributions of I and vacancies (V) computed from ion transport theory allow us to deduce the reaction kinetics. The reactions I+${\mathrm{B}}_{\mathit{s}}$→${\mathrm{B}}_{\mathit{i}}$, V+${\mathrm{B}}_{\mathit{i}}$→${\mathrm{B}}_{\mathit{s}}$, and I+V→0 are essentially diffusion limited, with capture radii of atomic dimensions.

We report the first studies of the A-B transition in superfluid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ confined by microscopically smooth surfaces. The transition exhibited dramatic supercooling, down to 0.15${\mathit{T}}_{\mathit{c}}$. The lifetime τ of the metastable A phase has a temperature dependence consistent with Leggett’s ‘‘baked Alaska’’ model based on nucleation by ionizing radiation. Radiation sources near the cryostat strongly reduce the lifetime, but do not alter its temperature dependence, and τ increases with increasing magnetic field in accord with Leggett’s model.

The spreading of a microscopic nonvolatile liquid drop on a homogeneous solid substrate has been studied by molecular dynamics simulations of Lennard-Jones systems. The substrate is assumed to be continuous without atomic structure and exerting a long-range Lennard-Jones potential on liquid particles in the drop. A molecular precursor film is observed to spread initially with nearly constant speed, crossing over later to diffusive spreading. These results are compared with recent molecular dynamics results of a volatile liquid on a structured substrate.

Leaky tori are two-dimensional surfaces with g handles and r horns (punctures) that extend to infinity. They model certain features of mesoscopic systems with multiple Aharonov-Bohm-type geometries connected to infinitely long leads. For a large class of leaky tori with finite area, in the presence of a constant magnetic field and threading fluxes, we calculate exactly the persistent currents, adiabatic charge transport, and the (appropriately defined) Hall conductances.

Damage spreading in the nearest-neighbor Ising model on a triangular lattice, for ferro- and antiferromagnetic interactions, is investigated using Glauber dynamics. Two procedures for updating spins are employed, the sequential and parallel ones. (a) The sequential algorithm leads to a dynamic transition at a temperature very close to the usual static critical temperature ${\mathit{T}}_{\mathit{c}}$ in the ferromagnetic case, whereas in the antiferromagnetic problem, no transition is found, suggesting that the equilibrium phase transition and the frozen-chaotic one are strongly correlated. (b) The parallel recipe is not able to distinguish the two interactions, giving a similar dynamic transition for both, at a temperature which is considerably different from the ferromagnetic Curie temperature.

A notion of mutual fractional statistics is introduced, and a field-theoretical construction to implement it is given. Realizations in layered Hall systems are suggested. A generalization of anyon superconductivity, arising from mutual statistics, is proposed.

A local-density-functional cluster method is used to calculate the structure and vibrational modes of substitutional oxygen, ${\mathrm{O}}_{\mathrm{As}}$, in gallium arsenide. We find the defect can exist in a surprisingly large number of five charge states: ${\mathrm{O}}^{\mathit{n}\mathrm{-}}$ with n=-1, 0, 1, 2, and 3. The structures of the first two of these are very different from the last three. Their calculated modes are in fair agreement with observations on O in GaP and GaAs. The first pair of defects have a midgap level, and the third has an empty upper-gap level which can become occupied in photoillumination experiments. The consequent structural change causes a lowering in vibrational mode frequency as is observed.

A mechanically controllable break junction is used to study quantum size effects on conduction in metallic constrictions. When changing the constriction radius, we observe reproducible jumps in the conductance which are of the order of 2${\mathit{e}}^2$/h. For contacts adjusted at a jump the conductance switches in time between two values, which we interpret as ‘‘two-level fluctuations’’ in the site of a single atom in the constriction. For superconducting point contacts we observe concomitant jumps in the supercurrent of order eΔ/ħ, which is consistent with a recent prediction.

Unusual effects noticed in previous force microscopy data are explained by a model based on work-function anisotropies and their associated patch charges. Measurable forces between macroscopic bodies can be due to the interaction of patch charges, with important consequences in the fields of surface forces, contact mechanics, adhesion, Schottky barriers, and the surface properties of insulators.

We have measured the cotunneling current below the Coulomb blockade threshold in a circuit of two ultra-small metallic tunnel junctions. The thermal enhancement of cotunneling, as well as the island-charge dependence, is in excellent agreement with theory. Circuit parameters were measured enabling theoretical and experimental values for the cotunneling current to be compared without adjustable parameters. This comparison yielded agreement within the 15% uncertainty of the experiment. Data showing the cotunneling current near the threshold voltage are also presented.

A far-infrared resonance has been observed in superconducting ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$ thin films in the presence of high magnetic fields. It corresponds to the quasiparticle pair creation process inside the vortex core. The resonance frequency is ${\mathrm{\omega }}_0$=1.3${\mathit{kT}}_{\mathit{c}}$/ħ with a linewidth 1/τ≃0.6ω. This value for ${\mathrm{\omega }}_0$ implies, within BCS theory, a large energy gap in ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$.

We have used the magneto-oscillatory behavior of the quasi-two-dimensional orbits in the charge-transfer organic salt (BEDT-TTF${)}_2$KHg(SCN${)}_4$ to probe its underlying magnetic ground states, which arise from the coexisting quasi-one-dimensional nature of the material. The complex nature of the oscillations results from the field dependence of these states. Our results allow comparison between several competing models which have attempted to describe the unusual properties of this material.

Low-frequency magnetic noise and mutual inductance measurements indicate that the electromagnetic response of very thin ${\mathrm{Bi}}_2$ ${\mathrm{Sr}}_2$${\mathrm{CaCu}}_2$${\mathrm{O}}_8$ films is dominated by Arrhenius law diffusion of thermally created vortices and antivortices. We explain the measured diffusion coefficient via pinning of the vortex cores on a single type of line defect. The observed superfluid response differs from simple Kosterlitz-Thouless predictions as it is predominantly controlled by vortex-pin rather than vortex-antivortex interactions.

We exhibit a factorization of the exactly solvable discrete 1/${\mathit{r}}^2$ exchange Heisenberg model. We express the Hamiltonian of the model on a lattice of L sites, as a sum over the squares of L operators in eight distinct ways, using the eight generators of the SU(3) group, and demonstrate that each of the 8 L operators annihilate the Gutzwiller wave function. The wave function is thus proven to be the exact ground state of the 1/${\mathit{r}}^2$ model, and we also provide a scheme for the construction of an infinite number of Hamiltonians for which it is the ground state.

An essentially exact solution of the infinite-dimensional Hubbard model is made possible by a new self-consistent Monte Carlo procedure. Near half filling antiferromagnetism and a pseudogap in the single-particle density of states are found for sufficiently large values of the intrasite Coulomb interaction. At half filling the antiferromagnetic transition temperature obtains its largest value when the intrasite Coulomb interaction U≊3.

We show that the Chern-Simons theory coupled to complex scalars can be consistently quantized in the Hamiltonian formalism without gauge constraints. A new structure of the anyon operator displaying fractional spin and statistics follows logically from our analysis without any ad hoc assumptions.

The electronic and elastic properties of large fullerene molecules are studied. The low-lying electronic levels are described by the Dirac equations in (2+1) dimensions, and the intramolecular modes are given by the theory of elasticity. Coupling between electrons and phonons can also be written in a simple way. The quantum dynamics of the ions is modified by the appearance of nontrivial Berry’s phases. The qualitative features of fullerenes with elliptical and cylindrical geometries, and minimal surfaces with negative curvature are also studied.

The Heisenberg antiferromagnet, which arises from the large-U Hubbard model, is investigated on the ${\mathrm{C}}_{60}$ molecule and other fullerenes. The connectivity of ${\mathrm{C}}_{60}$ leads to an exotic classical ground state with nontrivial topology. We argue that there is no phase transition in the Hubbard model as a function of U/t, and thus the large-U solution is relevant for the physical case of intermediate coupling. The system undergoes a first-order metamagnetic phase transition. We also consider the S=1/2 case using perturbation theory. Experimental tests are suggested.

A photoinduced magnetic moment has been observed in Cu and Al samples exposed to unpolarized visible light at low temperatures. It is shown that the light refected from a metal surface transfers some of its quasimomentum to conduction electrons. This mechanism creates surface currents which, for an appropriate geometry, bring about the photomagnetic effect.