We study entangled charged polymers in an electric field with a new biased-reptation model. Two microscopic time scales are relevant: the usual tube disengagement time $T_D$, and a new chain stretching time constant ${\tau }_{\mathrm{str}}$. When ${\tau }_{\mathrm{str}}<T_D$, i.e., for long chains and/or high electric fields, the chains are stretched in the field direction. As an example, we discuss DNA gel electrophoresis in terms of these results. Experimental and theoretical investigations are suggested.

The dissociation of ${\mathrm{H}}_2$ at metal surfaces is discussed with particular reference to the role of $d$ electrons. It is shown that the $d$ holes of a transition metal serve initially as sinks for $s$ electrons. This reduces the Pauli repulsion and so the entrance-channel activation barrier. $s-d$ transfer continues into the chemisorption region and allows the formation of metal-H bonds with only a moderate weakening of the metal-metal bonds.

${\mathrm{Al}}_{84}$${\mathrm{Mn}}_{16}$ multilayer films have been amorphized by room-temperature ion-beam irradiation. The amorphous phase was transformed into the quasicrystalline state through two routes: thermal and ion-beam-assisted thermal. The intensity of the quasicrystalline electron diffraction increases continuously with annealing between 270 and 350 °C. Ion irradiation of the amorphous phase produces a more complete set of icosahedral diffraction lines than thermal annealing.

Surface layers of icosahedral ${\mathrm{Al}}_{84}$${\mathrm{Mn}}_{16}$ have been formed for the first time by ion-beam mixing of deposited Al/Mn layers on Al substrates at ∼80°C and by either of two rapid electron-beam heat treatments of such layers. The well-defined temperature histories allow us to place limits on the melting point ($660°\mathrm{C}<T_m<930\mathrm{}°\mathrm{C}$) and the time needed for nucleation of the icosahedral phase from the melt at 660°C (${\tau }_n<900\mathrm{}$ ns). The microstructures observed place restrictions on a proposed microtwinning structural model.

The formation of a heavy-electron state in a magnetically ordered material is established by measurements of the low-temperature specific heat of U${\mathrm{Cu}}_5$ and UAg${\mathrm{Cu}}_4$. In U${\mathrm{Cu}}_5$ this state undergoes a continuous but hysteretic phase transition which removes parts of the Fermi surface with a high density of electronic states and leads to a resistivity increase of almost an order of magnitude.

High-resolution transmission-electron-microscopic lattice images of 10-nm-thick cross sections of ${10}^3$-nm $a$-Si films deposited at room temperature on clean Si wafers reveal 3-nm clusters, which are orientationally ordered within 80 nm of the substrate-film interface. All previous studies were done in plan view, on films not deposited on clean crystalline substrates, and so did not observe this new effect. Independent evidence suggests that deposition on a clean crystalline substrate generates superior submicrocrystalline morphological order throughout the entire ${10}^3$-nm film.

${}_{}{}^3{}_{}{}^{}\mathrm{He}$ film flow has been observed. The maximum flow rate, at 0.7 mK, over a rim 0.9 mm above the ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ level, was 1.2 ${\mathrm{mm}}^3$/h corresponding to an approximate flow velocity of 0.2 mm/sec. A flow rate of 0.2 ${\mathrm{mm}}^3$/h (∼0.1 mm/sec) was measured with the rim 14 mm above the level. The transition to superflow occurred at 3.5 ± 0.5 mK for the 0.9-mm film and 2.0 ± 0.5 mK for the 14-mm film. This flow is in a regime where the film thickness is less than or comparable to the bulk superfluid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ coherence length (∼ 1000 Å at 0.8 mK) and the temperature is higher than the bulk ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ superfluid transition temperature (1.08 mK) and corresponds, we believe, to a two-dimensional superfluid phase of ${}_{}{}^3{}_{}{}^{}\mathrm{He}$.

We have studied the temperature dependence of the fractional quantum Hall effect at Landaulevel filling factors $\nu =\frac{1}{3}, \frac{2}{3}, \frac{4}{3}, \frac{5}{3}, \frac{2}{5}, \mathrm{and} \frac{3}{5}$ in magnetic fields up to 28 T to determine the magnitude of the associated energy gaps. The data suggest a single activation energy for $\nu =\frac{1}{3}, \frac{2}{3}, \frac{4}{3}, \mathrm{and} \frac{3}{5}$. Its magnitude, much smaller than predicted by current theories, vanishes for $B\lesssim 6$ T and saturates at $B\gtrsim 18$ T. The data also suggest a single activation energy for $\nu =\frac{2}{5} \mathrm{and} \frac{3}{5}$ which is smaller than predicted.

We report resistance oscillations as a function of magnetic field for individual aluminum and silver thin-film rings, 1-2 μm in diameter, between 1.2 and 10 K. This is the first observation in single rings of oscillations with a flux period of $\frac{h}{2e}$ predicted by Al'tshuler et al. Oscillations periodic in $\frac{h}{e}$ are also seen in the 1-μm Ag rings at higher fields. These electron interference effects in metal rings are the solid-state analog of the Aharonov-Bohm effect for electrons in vacuum.

We find the tunneling decay rate $D$ of the zero-voltage states of a Josephson junction driven by a small ac current $I_{1}cos\left(\Omega t\right)$, when the dc current is close to the critical one. In the high-frequency limit $\Omega \gg {\omega }_p$ (${\omega }_p$ is the plasma frequency) for a high-$Q$ junction, the amplitude $I_1$ enters into the tunneling exponent with a large exponential factor and $\ln D\propto I_1\exp \left(\frac{1.77\Omega }{{\omega }_p}\right)$.

In addition to Anderson's mechanism for a "negative effective $U$" induced in localized systems by lattice distortions, we propose an independent microscopic mechanism—stabilization of electron-rich configurations through exchange interactions. This is illustrated for an unrelaxed interstitial Cr impurity in Si through a self-consistent local-spin-density Green's-function calculation.

The conductance of any metallic sample is predicted to fluctuate as a function of chemical potential or magnetic field by an amount of order $\frac{e^2}{h}(\simeq 4\times {10}^{-5\mathrm{}}{\Omega }^{-1\mathrm{}})$ independent of sample size and degree of disorder as long as the temperature is low enough so that $\mathrm{kT}$ and the inelastic-scattering rate are less than the inverse time to diffuse across the sample. The theory is shown to be in excellent agreement with numerical simulations and explains many features of experiments on small wires and rings.

The far-infrared absorption of oxide-coated small Ag particles in a Teflon insulating host has been measured. Excellent agreement between the experimental absorption and the Maxwell-Garnett theory is obtained when the particle size distribution and oxide coating are taken into account. We show for the first time experimental evidence that a highly absorbing oxide coating will enhance the electric-dipole absorption. Moreover, we explicitly show that the anomalous absorption of oxide-coated Ag particles is mainly due to clustering.

The thermodynamic properties of a soliton-bearing system without translation invariance—the dilute $S=\frac{1}{2}$ anisotropic $\mathrm{XY}$ chain—are calculated. At low temperatures the dominant contribution comes from a low-energy complex mode, which assumes zero energy when translational symmetry is restored in the pure system. The density of states of the complex modes is found to exhibit a scaling property with a fractional spectral dimensionality $\tilde{d}=\frac{2\ln c}{\ln \lambda }$, with $c$ the concentration of magnetic sites and $\lambda$ related to the anisotropy. Consequently, the specific heat shows the anomalous behavior $C\left(T\right)\mathrm{}\propto T^{\tilde{d}}$.

We present an exact solution to the problem of a random walk on an ultrametric space with arbitrary transition probabilities. The solution provides a description of fluctuation dynamics of systems with many degenerate states separated by a hierarchy of energy barriers. Dynamical behavior is found to depend on the scaling of barriers with ultrametric distance. We find a range of interesting behavior, from temperature-dependent power-law decay to the Kohlrausch law.

The dispersion of Xe-$5p$ valence-band states is studied layerwise for multilayers of Xe physisorbed on Al(111) by means of the layer-dependent shifts of photoelectron energies due to screening of the photohole. While the bilayer band structure is essentially the sum of two singlelayer band dispersions, Xe bulk bands begin to form with the third layer. Nondispersive peaks are also observed in the photoemission spectra, and are assigned to indirect transitions from critical points in the Xe surface Brillouin zone.

In a crystal of fluorene ${\mathrm{C}}_{13}$${\mathrm{H}}_{10}$ doped with phenanthrene ${\mathrm{C}}_{14}$${\mathrm{D}}_{10}$ a proton spin polarization of 42% has been obtained by means of microwave-induced optical nuclear polarization involving the photoexcited triplet state of the guest. This result makes the system a promising candidate for frozen targets and for the study of magnetic ordering of nuclear spins, where the paramagnetic centers used in conventional dynamic nuclear polarization cause great complications.

Stimulated by ESR measurements in Sm${\mathrm{B}}_6$:${\mathrm{Er}}^{3+}$ we have ascribed the unusual $g$-factor behavior of the ${\mathrm{Er}}^{3+}$ ground state, which is extraordinarily isotropic, to a new kind of Jahn-Teller-type phenomenon. The $4f-5d$ hybridization deformations of the Sm neighborhood adopt the role which in conventional Jahn-Teller systems is played by nuclear distortions. Arguments for this proposition and numerical results are given.

A system of $N$ identical point vortices on a plane, e.g., a superfluid-${}_{}{}^4{}_{}{}^{}\mathrm{He}$ thin film, is studied with use of elementary quantum mechanics. We find the surprising result that the system obeys fractional or $\theta$ statistics which depends on $N$, where $\theta \mathrm{}\left(N\right)=\frac{\pi }{N}$ or $\frac{\pi }{N}+\pi$. This result arises from the angular momentum contained in the zero-point motion of the vortices.

We show that several schemes for compactification of the extra dimensions in Kaluza-Klein theories are unstable to a quantum gravitational process of barrier penetration: The Universe can tunnel from a state with static extra dimensions to a de Sitter expansion of all dimensions. We estimate the tunneling rate and find that the present state of the Universe is probably long-lived (in good agreement with observation).