The universal scaling function of the fine-size contribution to the free energy of O(N) symmetric systems confined between two parallel plates at distance L is calculatd by field-theoretical methods close to ${\mathit{T}}_{\mathit{c},\mathrm{b}\mathrm{u}\mathrm{l}\mathrm{k}}$ and for five different boundary conditions. The asymptotic behavior for large L of the specific heat at ${\mathit{T}}_{\mathit{c},}$b is computed explicitly, thus allowing quantitative experimental tests. We discuss the implications of our results for surface forces and wetting films. Universal amplitudes for the surface free energy are also presented.

A new method is developed for obtaining thermodynamic information over a wide range in parameter space from a series expansion involving the first few cumulants of a distribution function which is generated at one point in parameter space. The method is employed to obtain the temperature dependence of the Gibbs free energy, the enthalpy, and the lattice parameter of a Lennard-Jones crystal from Monte Carlo simulations. Good agreement with independent calculations is found over a temperature range of approximately 75% of the melting temperature.

Preliminary results on the atomic decoration of a random-cluster model for icosahedral-phase alloys are presented. The calculated neutron and x-ray intensities compare quite favorably with experimental intensity data on i-AlMnSi. The origin of the peak at Q=1.62 A${\mathrm{̊}}^{\mathrm{-}1}$, associated with the prepeak found in ‘‘amorphous’’ AlMnSi, as well as the ubiquitous ‘‘diffuse’’ scattering, seen experimentally under the groups of strong peaks in all icosahedral-phase alloys, are revealed selectively in the calculated partial intensities for Al-Al, Al-Mn, and Mn-Mn correlations.

We consider a system of interacting particles, diffusing under the influence of both thermal noise and a random, external electric field which acts in a subspace of m dimensions. In the nonequilibrium steady state, the net current is zero. When the interparticle interaction is short ranged and attractive, a second-order phase transition is expected. Analyzing this system in field-theoretic terms, we find the upper critical dimension to be 4-m and its behavior to fall outside the universality classes of the equilibrium Ising model and the usual driven diffusive system. A new fixed point and critical exponents are computed.

The chemical lithiation of 2H-${\mathrm{TaS}}_2$ was investigated by Monte Carlo simulations on a 10×64×64 lattice. A phenomenological model applicable to layered transition-metal dichalcogenides is presented which yields reaction fronts, coexistence of several density domains, and superlattice ordering in excellent agreement with observations. Particle transport along domain boundary channels controls the reaction.

Different direct perturbation theories show that the Peierls substitution leads to quantitative and qualitative errors in calculations of the energy difference with and without magnetic field for both nearly free and tight-binding two-dimensional electrons. The sources of these errors are clarified. The lowering of the electron kinetic energy in a magnetic field is shown to be in general an artifact of the Peierls substitution. Spontaneous orbital ferromagnetism is shown to be impossible. Credibility of the usual theory of Landau diamagnetism for two dimensions is reestablished.

Monte Carlo simulations of the magnetic structure factor of the two-dimensional Hubbard model are in qualitative agreement with the slave-boson approach and, in the low-temperature intermediate-coupling limit, they are in even better quantitative agreement with the random-phase approximation, as long as a renormalized repulsion U is used. This renormalization comes from maximally crossed diagrams, which account for two-body short-range correlations. One of the consequences is that Stoner ferromagnetism is not a generic property of the two-dimensional one-band Hubbard model.

The analytical expression for the ambipolar in-plane diffusion constant of excess carriers in n-i-p-i doping superlattices is derived. Shockley-Haynes–type experiments quantitatively confirm the predicted huge enhancement of the diffusion constant (in the tested case by factors of about 300) and the long diffusion lengths.

A new method, combining mean-field and Monte Carlo approaches, is applied to frustrated Ising systems in d=2 and 3, in zero and nonzero uniform fields. The method brings to mean-field theory the hard-spin condition and uses much less sampling then the Monte Carlo simulation. The phase diagram of the d=2 triangular antiferromagnet is easily obtained with remarkable global quantitative accuracy. The phase diagram of the d=3 stacked triangular antiferromgnet shows three ordered phases, in a new multicritical topology of lines of XY, Ising, and three-state Potts transitions, accessible to experiments with layered magnets.

The indirect nuclear spin-spin coupling between Cu nuclei in the ${\mathrm{CuO}}_2$ planes of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$, deduced from ${}_{}{}^{63}{}_{}{}^{}\mathrm{Cu}$ transverse relaxation, is shown to yield information about the wave-vector dependence of the real part of the planar Cu static electron-spin susceptibility. The coupling is evaluated with no adjustable parameters using the antiferromagnetic Fermi-liquid theory of Millis, Monien, and Pines, providing a new test of that model. At 100 K, the theoretical relaxation time is 190±75 μsec versus the experimental 130±10 μsec.

Granular systems built from well-defined Bi clusters with rhombohedral bulk structure show, in contrast to bulk Bi, the occurrence of superconductivity. The experimental facts of a strong size dependence of ${\mathit{T}}_{\mathit{c}}$ and an influence of the surrounding matrix or adsorbed gas on normal-state resistivity ρ(0) and ${\mathit{T}}_{\mathit{c}}$ can be satisfactorily explained by assuming the occurrence of surface superconductivity due to a strongly increased density of states N(${\mathrm{\epsilon }}_{\mathit{F}}$) at the cluster surface.

A new nonsingular mapping between bosons and fermions is introduced in connection with the fractional quantum Hall effect. The mapping connects a fermion system of filling ${\nu }_{\mathit{f}}$ to a boson system of filling ${\nu }_{\mathit{b}}$ through the relation ${\nu }_{\mathit{f}}^{\mathrm{-}1}$=${\nu }_{\mathit{b}}^{\mathrm{-}1}$+1. The ground state of the boson system is shown to map accurately to that of the fermion system if and only if they are both incompressible quantum Hall states. The accuracy of the mapping is shown to be related to the validity of the mean-field theory. The relevance of this mapping to off-diagonal long-range order is discussed by numerically studying the binding of wave-function zeros to particle positions.

The separation distance between droplets of quark-gluon plasma (QGP) in the early Universe and in relativistic heavy-ion collisions is calculated in isothermal fluctuation theory. It is found that experimental information on the size of the QGP from relativistic heavy-ion collisions has the potential possibility of constraining the degrees of the inhomogeneous baryon-number density distribution and the formation of strange-quark matter at the epoch of the cosmic phase transition in quantum chromodynamics.

We derive the Wess-Zumino term for the chiral-boson model formulated by Sonnenschein using an iterative process, previously introduced by the author in the context of the chiral Schwinger model, that transforms the second-class chiral constraints into first-class ones. Because of the peculiar features of this model the Wess-Zumino term found is made of an infinite number of terms, using an infinite number of auxiliary fields.

The yield of J/ψ and ψ’ vector-meson states has been measured for 800-GeV protons incident on deuterium, carbon, calcium, iron, and tungsten targets. A depletion of the yield per nucleon from heavy nuclei is observed for both J/ψ and ψ’ production. This depletion exhibits a strong dependence on ${\mathit{x}}_{\mathit{F}}$ and ${\mathit{p}}_{\mathit{t}}$. Within experimental errors the depletion is the same for the J/ψ and the ψ’.

In molecular collisionand reaction dynamics the precision of data obtainable from an experiment is determined by the extent the vectors of linear and angular momentum are specified. The highest degree of specification comes from four-vector correlation, two before and two after the collision. Here we introduce the new technique of two-color sub-Doppler circular dichroism and demonstrate the first four-vector correlation molecular-dynamics experiment. Results are given for elastic and inelastic collisional processes between ${\mathrm{Li}}_2$ and the rare gases Ar and Xe.

The positive-energy spectrum of the hydrogen atom in a magnetic field is deduced by making use of the complex-rotation method combined with Sturmian-type expansions. This yields the energies and widths of the resonances especially for fields of atomic interest. Accidental destructive interference generates ultranarrow resonances above the ionization threshold as experimentally observed.

We present a detailed comparison of the observed and computed negative- and positive-energy spectrum of a Rydberg atom in a strong magnetic field. The study extends from -30 to +30 ${\mathrm{cm}}^{\mathrm{-}1}$ at a field of 6 T. The experimental resolution is sufficiently high to provide well-resolved spectra over the entire range. The spectrum calculated for hydrogen is in remarkable agreement with the spectrum observed in lithium.

It is suggested that there exists a novel ‘‘molecular’’ state of binding of antiprotons to atoms in which an excited highly polarized electron is located between the nucleus and the antiproton. The lifetime of this state is expected to be decided by the radiative lifetime of the excited electronic state.

We have experimentally demonstrated the squeezing of optical solitons, resulting in a detected photocurrent noise power (32±3)% (1.7 dB) below the shot-noise limit over a broadband of frequencies. The squeezing is accomplished using the Kerr nonlinearity of a polarization-preserving single-mode optical fiber at liquid-nitrogen temperature. Squeezed solitons, 1.1 dB below the shot-noise limit, were observed at room temperature.