We present a three-dimensional statistical field theory of density fluctuations motivated by the Ginzburg-Landau theory of superconductivity. The free-field theory yields Yukawa-type two-particle cumulant correlations and no higher-order ones, in agreement with high-energy heavy-ion data. We mention the extension of our model to describe hadronic reactions and indicate how it may be related to QCD. We predict the multiplicity distribution of particles produced in heavy-ion collisions.

An asymptotic expansion for the electronic energy of ${\mathrm{H}}_2^{+}$ is developed in inverse powers of D, the spatial dimension, and the singularity structure in the D→∞ limit is elucidated by analysis of the coefficients at large order (∼30 to 45). For the ground state and several excited states, Padé-Borel summation yields an accuracy of eight or more significant figures.

We report the observation of the splitting of an atomic beam by the optical Stern-Gerlach effect. A beam of metastable He atoms interacts with a nearly or exactly resonant laser field with a well-defined intensity gradient perpendicular to the atomic beam. The coherent splitting of the atomic beam is produced in the case of exact resonance. For the nonresonant case, a deflection of the atomic beam is observed. We have studied the splitting and deflection of the atomic beam as a function of laser detuning from resonance. Our results are in good agreement with theoretical predictions.

We show experimentally, here for Na vapor, and theoretically that picosecond frequency-swept laser pulses create in multilevel systems an inversion profile that is far narrower than the pulse spectrum. This selectivity persists even when the Rabi frequency is substantially larger than the spacing between pumped and suppressed transitions.

For the first time we calculate ab initio values of the asymmetry parameter β for double photoionization and obtain agreement with experiment. The suggestion that the measurements do not agree with the Wannier predictions of Greene and Huetz et al. is shown not to be substantiated by our calculations.

We observed phase transitions and ordered structures of laser-cooled ${\mathrm{Mg}}^{+}$ ions stored in a radio-frequency quadrupole storage ring with a diameter of 115 mm. The ions are confined two dimensionally by a quadrupole field and can move freely along the ring circumference. By cooling the ions with tangentially intersecting laser beams, we observed a linear string of ions aligned along the center line of the quadrupole field. For higher ion densities the linear structure changes into a helical structure. The dynamics of the stored ions was studied.

The R-matrix method has been used to study the scattering of electrons by oxygen molecules for impact energies in the range from threshold to 15 eV. Electronic excitation cross sections for transitions to the ${\mathit{a}}^1$${\mathrm{\Delta }}_{\mathit{g}}$, ${\mathit{b}}^1$${\mathrm{\Sigma }}_{\mathit{g}}^{+}$, and ‘‘6 eV’’ states of oxygen are presented. Important contributions from a ${}_{}{}^2{}_{}{}^{}\mathrm{\Pi }_{\mathit{u}}^{}{}_{}{}^{}$ resonance, in addition to the well-known ${}_{}{}^2{}_{}{}^{}\mathrm{\Pi }_{\mathit{g}}^{}{}_{}{}^{}$ resonance, are found to significantly modify previous theoretical predictions. Integral elastic-scattering cross sections are also obtained for the first time for a complicated open-shell system using an ab initio method.

We have developed a light-force technique for measuring polarizabilities. This new method uses the polarizaton forces experienced by an atom in the intense, inhomogeneous electric field of a standing-wave laser to deduce the polarizability. Using a Nd:YAG laser at ${\lambda }_{\mathrm{SW}}$=1.064 μm for the light force, we measured the polarizability of rubidium at this wavelength to be α(${\mathrm{\omega }}_{\mathrm{SW}}$)=114±9 A${\mathrm{̊}}^3$ (σ). Conversion of this ac polarizability to a static value using a semiempirical formula gives a value of ${\mathrm{\alpha }}_{\mathrm{dc}}$=52 A${\mathrm{̊}}^3$, within 10% of the best published experimental results.

Besides the usual single-monomer evaporation, the (${\mathrm{C}}_3$${\mathrm{H}}_8$${)}_{\mathit{n}}$(${\mathrm{C}}_3$${\mathrm{H}}_7^{+}$) cluster ions produced by electron-impact ionization of neutral propane clusters have been observed to decay by an additional channel leading to evaporation of up to four ${\mathrm{C}}_3$${\mathrm{H}}_8$ monomers. It is shown that this additional fragmentation channel is initiated by a new decay mechanism, i.e., the isomerization of an n-propyl ion to a more stable sec-propyl ion within the cluster.

The photonic band structure in a two-dimensional dielectric array is investigated using the coherent microwave transient spectroscopy (COMITS) technique. The array consists of alumina-ceramic rods arranged in a regular square lattice. The dispersion relation for electromagnetic waves in this photonic crystal is determined directly using the phase sensitivity of COMITS. The experimental results are compared to theoretical predictions obtained using the plane-wave expansion technique. Configurations with the electric field parallel and perpendicular to the axis of the rods are investigated.

We present Monte Carlo results for the deposition of particles on a line, in a two-dimensional semi-infinite flow simulated by a lattice gas automation. Instead of straight inclined needles, as observed for diffusion-limited deposition with a drift, we obtain a distribution of clusters which are inclined with an angle increasing linearly with the distance to the baseline. The kinetics is different than in diffusion-limited deposition, whereas the static properties of the clusters are similar.

Depolarized Rayleigh scattering on a columnar discotic liquid crystal is described. Column undulations and mode quantization allows the scattering to be visible only for two directions of reciprocal space, and for well-defined light propagation angles. The observed constant angular extension of the scattering shows that column undulations are not controlled by curvature elasticity, but by an anisotropic 3D solidlike elasticity. This behavior is probably associated with column entanglement, as recently discussed by Prost.

A model for surface growth with some of the features of molecular-beam epitaxy is proposed and investigated. Particles are deposited randomly on a one-dimensional substrate and the surface relaxes through diffusion processes, which obey detailed balance. The model undergoes a phase transition from a rough phase to a grooved phase. Both phases display scaling in space and time, with equal exponents. We also propose a Langevin equation, which should describe this growth process and show that this equation contains an infinite number of relevant terms.

We present a Landau theory derived from an alloy Hamiltonian based on a quantum-mechanical description of cohesion in metallic systems. This Landau theory, obtained by making a mean-field approximation, provides an excellent description of the ordering transitions in CuAu, ${\mathrm{Cu}}_3$Au, and ${\mathrm{CuAu}}_3$, including the sequence of transitions from the disordered to the modulated CuAu II phase to the low-temperature CuAu I phase.

Molecular-dynamics simulations are used to show that strongly interacting dipolar spheres can form a ferroelectric nematic phase. This is the first demonstration that dipolar forces alone can create an orientationally ordered liquid state. It is also the first time that the existence of a ferroelectric nematic phase has been established for a model fluid.

We have measured a large specific heat of polycrystalline ${\mathrm{C}}_{60}$ from T=1.4 to 20 K. The data were adequately fitted by a model containing Debye terms, Einstein oscillators, and a linear contribution. An analysis incorporating both vibrational and strongly coupled rotational degrees of freedom expected for the simple-cubic structure at low temperatures is proposed. We also discuss a possible interpretation based on a fairly narrow feature in the excitation spectrum. The large linear term may be a consequence of disorder resulting in a distribution of two-level tunneling centers.

We report the first measurement of the thermal conductivity of single crystal ${\mathrm{C}}_{60}$. We observe that orientational disorder significantly reduces the thermal conductivity, evidenced by a large jump in the thermal conductivity at the 260 K orientational-order transition. The temperature and time dependences of the thermal conductivity below 260 K are shown to be described by a phenomenological model that involves thermally activated jumping motion between two nearly degenerate orientations, separated by an energy barrier of ∼260 meV.

The superfluid response to a perturbation of wave number k is calculated using a vortex-ring theory of the ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ λ transition. Rings of diameter greater than ${\mathit{k}}^{\mathrm{-}1}$ cannot follow the perturbation, and this leads to a finite-size broadening of the superfluid density near ${\mathit{T}}_{\lambda }$. The vortex theory provides a new perspective on the Feynman-Onsager proposal that rotons are vortex rings of the smallest size.

Bak, Tang, and Wiesenfeld introduced a sandpile model to study the so-called self-organized critical phenomena [P. Bak, C. Tang, and K. Wiesenfeld, Phys. Rev. A 38, 364 (1988)]. There were several proposals to connect this discrete cellular automaton model with diffusion processes. We show how one may interpret the dynamics of this model as a discretized version of an anomalous diffusion equation, and we study the time evolution of the model off criticality.

Lateral segregation occurring at advancing steps is identified as the origin of a new long-range-ordered phase in ${\mathrm{Si}}_{\mathit{x}}$${\mathrm{Ge}}_{1\mathrm{-}\mathit{x}}$ alloys, which has been imaged directly. The segregation occurs at monolayer-height type-${\mathit{S}}_{\mathit{B}}$ steps under island growth conditions and is strongly dependent on growth kinetics.