Magnetic supercurrents are observed in superfluid ${}_{}{}^3{}_{}{}^{}\mathit{B}$. These supercurrents transport the longitudinal magnetization from one experimental cell to another through a narrow channel, driven by gradients of the order parameter. In both cells NMR is induced by separate signal generators at the same frequency. The supercurrent arises if a phase difference of the magnetization precession is established across the narrow channel. A critical spin supercurrent is measured at which precession phase slippage takes place. Experimental values of the critical spin supercurrent are in agreement with theoretical predictions.

The low-field NMR spectra of ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ boundary layers on exfoliated graphite show collective modes for T<1 mK. We measure the amplitude and frequency for these modes with the static $H_0$ field applied parallel to the graphite planes and varying continuously between 0 and 15 G. One of the modes extrapolates to a nonzero frequency and amplitude as the field is dropped to zero. We interpret these nonzero intercepts as an indication of zero-field magnetic order in the ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ boundary layers.

We report measurements on the spin-density relaxation in the superfluid ${}_{}{}^3{}_{}{}^{}{A}_1$ phase as a function of temperature, pressure (3–28 bars), and magnetic field (0.75–14 kOe). The temperature dependence of the relaxation time shows an unexpected discontinuity near the middle of the phase and very close to $T_c$ (the zero-field transition temperature). The relaxation time changes only by about 30% over the pressure range measured. In the higher-temperature side of the phase the relaxation time is proportional to the applied field.

We have used time-resolved digital imaging of uniform, charged polystyrene spheres in colloidal suspension confined between smooth glass plates to study in detail the nature of particle motions in equilibrated two-dimensional dense fluid, hexatic, and crystalline phases. We observe dynamic ordered regions in the fluid and hexatic phases, with strongly correlated particle hopping near their borders associated with motions and rearrangements of overlapping elementary dislocation pairs.

Phase diagrams and all three independent structure functions of oil, water, and amphiphile mixtures have been calculated from a three-component lattice model introduced previously. Both two- and three-dimensional systems were studied, by transfer-matrix methods and mean-field theory, respectively. With increasing amphiphile concentration, the phase diagram shows the commonly observed progression from three-phase coexistence through a microemulsion to two-phase coexistence with a lamellar phase. All three structure functions of the microemulsion are in qualitative agreement with experiment.

Interatomic potentials consisting of two-body and three-body covalent forces are proposed for ${\mathrm{GeSe}}_2$. Using these in molecular-dynamics simulations, the nature of intermediate-range order is investigated. All the features in S(q), including the first sharp diffraction peak (FSDP), are in agreement with experiments. The FSDP arises from Ge-Ge and Ge-Se correlations between 4–8 Å, and the anomalous decrease in its height on cooling is due to frustration enhanced by increased density. The statistics of edge-sharing tetrahedra and rings are also discussed.

Evidence for a new optically driven nonequilibrium phonon state has been observed experimentally. Among the properties which differentiate this state is that the nonequilibrium state has two decay rates in the picosecond regime, rather than the single decay rate observed under thermal equilibrium. The magnitudes of the two decay rates depend strongly on the phonon occupation numbers. For the most part, the observed properties of the new state correspond well to theoretical predictions. The new state appears as a precursor to laser damage under the present experimental conditions.

A new systematics of the ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ isomer shifts (δ) in various elemental hosts is presented. δ values measured for ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ impurities, amorphous alloys, and crystalline intermetallics were used. The volume-corrected δ values are found to have the same or very close values to that of the corresponding intermetallics and amorphous phases. Contrary to earlier systematics, it is shown that no drastic downturn of the δ values in the region of metalloid hosts can be justified. The new systematics facilitate the interpretation of the great number of experimentally determined values.

We study the influence of conduction electrons on spectral and dynamical properties of the biased two-level system using path-integral methods. The structure factor for inelastic neutron scattering is calculated in the case of weak coupling (K≪1) and for a special value of the coupling strength (K=1/2). The effect of interbounce interactions is systematically taken into account at low temperatures, thus removing shortcomings of the dilute-bounce-gas approximation. The method and results are relevant also for the ‘‘macroscopic-quantum-coherence’’ problem.

We have observed ordering of dilute dispersions of spherical and cylindrical macromolecules in magnetized ferrofluids. The order results from structural correlations between macromolecular and ferrofluid particles rather than from macroscopic magnetostatic effects. We have aligned elongated macromolecules by this technique and have obtained anisotropic neutron-diffraction patterns, which reflect the internal structure of the macromolecules. The method provides a tool for orienting suspended macromolecular assemblies which are not amenable to conventional alignment techniques.

Resonant enhancement of the magnetic x-ray scattering cross section in UAs has been investigated by tuning the incident x-ray energy through the uranium ${\mathrm{M}}_{\mathrm{IV}}$ and ${\mathrm{M}}_{\mathrm{V}}$ absorption edges. At the ${\mathrm{M}}_{\mathrm{IV}}$ edge the intensity for the (0,0,(5/2) magnetic reflection is enhanced by ${10}^7$ relative to the nonresonant component far above the edge, and is a remarkable 1% of the intensity of the (0,0,2) charge peak. At the ${\mathrm{M}}_{\mathrm{V}}$ edge the enhancement is ${10}^5$. The dramatic enhancement at M edges has been predicted by Hannon et al., and arises from strong electric multipole transitions between atomic core states and the exchange-split Fermi edge states.

As with amorphous solids, the absence of periodic order makes it difficult to calculate the electronic structure of liquids. However, unlike the solid case, techniques for handling correlated topological disorder are standard in liquid theory. We show how recasting tight-binding models into random-matrix problems makes the band-structure-in-a-liquid problem rigorously equivalent to a simple equilibrium liquid calculation—enabling us to make use of these well developed techniques. An exact mean-spherical-approximation solution is provided as an example.

We have directly monitored population changes in surface states as photoexcited bulk carriers recombine at a semiconductor surface. By observing the time dependence of the photoexcited carriers in the conduction band, as well as the transient population in the ${\mathrm{\pi }}^{\mathrm{*}}$ surface state, a detailed, microscopic model of transient surface recombination is constructed for the Si(111)2×1 surface which includes transient surface-charging effects on the bulk transport self-consistently.

We obtain the solution for an electron tunneling through a thin potential barrier with local Einstein phonons, by means of a continued fraction expansion. Our results demonstrate the strong feedback between inelastic and elastic scattering, the associated singularities, an increase in low-energy transmission with a nonmonotonic temperature dependence, and a crossover from quantum to adiabatic behavior with increasing temperature and electron velocity.

We predict that in semiconductor superlattices with electron tunneling between different quantum wells, the energy of the plasmon associated with the motion of electrons in the superlattice direction should exhibit strong oscillations as a function of magnetic field. This collective phenomenon is the first of its kind. It can be used to measure the carrier density in the superlattice and also to probe the Landau-level broadening and many-body enhancement of the electron g factor.

The sharp peak in the tunneling conductance at a vortex core, reported by Hess et al. in ${\mathrm{NbSe}}_2$, is attributed to self-energy corrections of the normal electrons (in the core) caused by their coupling to excitations of the superconducting region (outside the core). The shape of the zero-bias anomaly is reproduced without benefit from adjustable parameters, though the predicted size is a little too large. If the critical currents in the superconducting region (outside the core) are recognized by letting the excitation density (at zero energy) be finite, then a perfect fit can be obtained.

The large-N limit of a nearest-neighbor SU(N) antiferromagnet on a bipartite lattice exhibits in dimensions d≥2 a zero-temperature phase transition between a Néel ordered state and a resonating-valence-bond state. Here it is shown in d=1,2 that topological effects produce spin-Peierls or valence-bond-solid order in the non-Néel phase with a ground-state degeneracy which varies periodically with ‘‘spin’’ for fixed N with periodicity given by the coordination number of the lattice. Thus a non-Néel phase of the spin-(1/2 Heisenberg model on a square lattice would be a spin-Peierls state with a fourfold degeneracy due to broken lattice rotational symmetry.

We use the exact renormalization procedure, introduced by Machta [Phys. Rev. B 24, 5260 (1981)], to evaluate the waiting time density for a walker to jump to one of its nearest neighbors on a decimated lattice, in terms of the original waiting time densities on the nondecimated lattice. We explicitly identify all the fixed points and their corresponding domain of attraction for the one-dimensional case and for the Sierpinsky gasket.

We report analysis of data from the South Pole Air Shower Experiment taken in January and February 1988 while the array was being commissioned. These first results are already of interest because they lead to a limit on an air-shower signal from SN 1987A comparable to the best existing limit and also because the supernova produced a high x-ray flux and a possible TeV signal during that period.

The strong CP problem is solved by use of quantum gravity. It is argued that the coherent-state parameters ${\alpha }_i$ describing the effect of wormholes (baby universes) adjust themselves so as to make the strong interactions CP invariant. There remains though a small CP breaking so that θ¯ is not exactly zero. The main prediction is that we do not need the axion proposed by Peccei and Quinn.