A new lattice model of polymer crystallization is described. Results of numerical solutions of rate equations for crystallization of a two-dimensional "crystal" are presented. It is shown that the crystal thickness varies inversely with supercooling and that kinetics similar to secondary nucleation occurs. This is true even though the growth face is intrinsically rough and hence there cannot be any nucleation. The presence of a low-entropy saddle point during growth is explained, and its influence on the crystal thickness and lamellar morphology is discussed.

We report measurements of the melting velocity of amorphous Si relative to that of (100) crystalline Si. These measurements permit the first severe experimental test of theories describing highly nonequilibrium freezing and melting. The results indicate that freezing in Si is inherently slower than melting; this asymmetry can be interpreted in terms of an entropy-related reduction in the freezing rate.

We show that the cooperative-ring-exchange phenomenon and the consequent fractional quantization as suggested by Kivelson et al. can persist in a quantum fluid which is incompressible, like the Laughlin state. Simple arguments are given to suggest that the very existenct of the cooperative ring exchange may imply a melting instability of the triangular Wigner solid towards an incompressible fluid.

A new technique developed to study the spin dynamics of a static positive muon interacting with neighboring nuclear spins is reported. The method is based on the Trotter formula and leads to exact results even when the dimensionality of the composite spin system is very large. First results are presented for the case of muons localized at the interstitial octahedral site in copper in an arbitrary magnetic field.

We have measured the effective mass of electrons tunneling through thin barriers in (Al, Ga) As/GaAs superlattices by performing cyclotron-resonance experiments with the magnetic field oriented perpendicular to the growth direction. The effective mass is shown to increase with the barrier height at a rate that is in rough agreement with a model that includes the change in band mass in the barrier.

We calculate the spin anisotropy of ferromagnetic monolayers of Fe, Ni, and V. We find that the easy direction of magnetization is perpendicular to the plane of the monolayer for Fe and V, but in the plane for Ni. The result for Fe explains why spin splitting but no spin polarization is observed in recent photoemission experiments on Fe overlayers.

We show that the tendency for superconductivity of a weakly coupled 2D electron system can be significantly enhanced if the Fermi energy is close to a logarithmic Van Hove singularity in the density of states. Using results from perturbation theory, supported by quantum Monte Carlo simulations, we calculate $T_c$ and explore the effects of the quasiparticle lifetime and higher-order interactions on this enhancement. This mechanism suggests possible new directions in the search for 2D excitonic superconductivity.

We report the observation of negative absolute mobility of electrons (i.e., a drift toward the negative electrode) in $p$-modulation-doped GaAs quantum wells. This unusual effect results from "carrier drag" on the electrons by the high-mobility hole plasma via electron-hole scattering.

We define a hopping Hamiltonian for independent electrons on a two-dimensional quasiperiodic Penrose lattice. This problem is then investigated numerically, up to systems of 3126 sites, and for various boundary conditions. We find the following results for the density of states: (1) There is a central peak of zero width at zero energy, consisting of about 10% of the total number of states. (2) These states are strictly localized; we calculate the wave functions explicitly. (3) The remainder of the states lie in two bands, symmetric about zero energy, separated from the localized states by a finite gap $E_0$.

A method is presented for computing the mixing parameters in the Anderson model for heavyrare-earth compounds, based on a linear combination of atomic orbitals fit to a self-consistent band-structure calculation. An appropriate average of these parameters is used in a many-body calculation of the valence-band x-ray-photoemission and inverse-photoemission spectra of YbP, with the Coulomb integral $U$ as the only adjustable quantity. The calculated inverse-photoemission spectrum agrees qualitatively with room-temperature low-resolution data by Baer et al.

A very large high-energy shift of exciton resonances in GaAs multiple-quantum-well structures is observed during irradiation of the sample with femtosecond nonresonant radiation. This effect is discussed in terms of excitons "dressed" by photons.

Microwave reflectivity measurements in Voigt geometry were performed on a polished surface of Mn${\mathrm{F}}_2$. We observed nonreciprocal behavior in the reflectivity with respect to the magnetic field reversal. The nonreciprocal behavior of the antiferromagnet's reflectivity gives clear evidence for the existence of nonreciprocal dipolar antiferromagnetic surface spin-wave excitations. The results are quantitatively explained. They give very accurate values for antiferromagnetic resonance and spin-wave damping.

Band-edge discontinuities are calculated for tellurium-based II-VI heterojunctions. Contrary to the widely accepted common-anion rule, large valence-band discontinuities are found in most cases, including HgTe-CdTe. The common-anion rule is examined and predicted to fail, not only here, but for all lattice-matched II-VI and III-V heterojunctions. An experiment is proposed to test these predictions.

The film linearized-augmented-plane-wave method with a refined set of basis functions in the jellium-vacuum region is used to calculate the electronic structure of a model system simulating a W(100) surface covered by a Cs overlayer from zero to monolayer coverage. The work function decreases rapidly with coverage at the initial stage of adsorption, reaches a minimum at $\theta =0.22\mathrm{}$, and rises again at higher coverage, in good agreement with experiment. The changes of the electron distribution and potential reveal that the initial decrease of the work function is caused by electron transfer from the Cs to the W surface.

The exact $T=0\mathrm{}$ susceptibility times spin-wave velocity of an isotropic spin-$s$ antiferromagnetic chain is calculated by use of the Wess-Zumino-Witten $\sigma$ model, with Kac-Moody central charge $k=2s$, as the critical theory. The result, ${\chi \upsilon }_s=\frac{k}{2\pi }$, agrees exactly with Bethe-Ansatz results for integrable models and well with numerical results ($s=\frac{1}{2}$), Fisher's classical limit, and experiments on Cu${\mathrm{Cl}}_2$ · 2N${\mathrm{C}}_5$${\mathrm{H}}_5$ ($s=\frac{1}{2}$) and ${\left(\mathrm{C}{\mathrm{H}}_3\right)}_4$NMn${\mathrm{Cl}}_3$ ($s=\frac{5}{2}$). (${\chi }_{\parallel }$ is also calculated exactly for $s=\frac{1}{2}$ and arbitrary planar anisotropy.) This suggests that ${\left(\mathrm{C}{\mathrm{H}}_3\right)}_4$NMn${\mathrm{Cl}}_3$ is an experimental realization of this new universality class.

An irreversible kinetic surface-reaction model, based upon the reaction of carbon monoxide and oxygen on a catalyst surface, is presented. It is found by computer simulation that the adsorbed molecules on the surface undergo both first- and second-order kinetic phase transitions. These transitions correspond to the "poisoning" phenomenon seen on catalysts. Interesting transient and periodic behavior is also seen.

Simulations of Su(3) lattice gauge theory with four species of light quarks show a large peak in the bulk specific heat near $\beta =\frac{6}{g^2}\approx 5.10$ separating strong and weak coupling. $〈\overline{\psi }\psi 〉$ satisfies asymptotic-freedom scaling for $\beta =\frac{6}{g^2}\gtrsim 5.10$ and $\frac{{〈\overline{\psi }\psi 〉}^{\frac{1}{3}}}{{\Lambda }_{\overline{\mathrm{MS}}}}=(2.6\mathrm{}\pm 0.1){\left(\frac{{4\pi }^2\beta }{25}\right)}^{\frac{4}{25}}$ ($\overline{\mathrm{MS}}$ denotes the modified minimal-subtraction scheme). Finite-temperature simulations on a 6 × ${10}^3$ tice show a smooth but rapid crossover at $\frac{T}{{\Lambda }_{\overline{\mathrm{MS}}}}=2.14\mathrm{}\pm 0.10$. We find no evidence for metastable states.

A multiply discriminating, three-loop superconducting monopole detector was operated for 1 yr. During this period 8523 h of data were accumulated. The sensing area averaged over solid angle for trajectories passing through a loop was 178 ${\mathrm{cm}}^2$. With inclusion of double-coincidence events from trajectories passing through the shield but not through a loop, the total sensing area averaged over solid angle was 1195 ${\mathrm{cm}}^2$. No candidate monopole events were observed; this leads to an upper limit on the flux of cosmic-ray magnetic monopoles of 5.0 × ${10}^{-12\mathrm{}}$ ${\mathrm{cm}}^{-2\mathrm{}}$ ${\mathrm{sr}}^{-1\mathrm{}}$ ${\mathrm{s}}^{-1\mathrm{}}$ with a 90% confidence level.

It is shown that a non-Abelian gauge theory with Higgs fields and the addition of a Chern-Simons term in 2 + 1 space-time dimensions exhibits finite-energy electrically charged vortex solutions. A novel feature of the vortices is that their electric charge $Q$ is quantized in units of the fundamental charge $e$, $\frac{Q}{e}=\frac{n}{2}$ with $n$ an integer, and their angular momentum is $J=\frac{Q}{2e}=\frac{n}{4}$.

The effects of spin-dependent charge-symmetry-breaking forces can be measured in elastic $n-p$ scattering. We find that a term in the one-pion exchange potential arising from the neutron-proton mass difference is dominant. This, together with single-photon exchange, gives a result in agreement with a recent precise measurement made at TRIUMF. Other shorter-ranged effects associated with rho exchange, meson mixing, two-pion exchanges, and quark interactions give smaller contributions.