A new universal behavior has been observed in the zero-bias resistance of two-dimensional superconducting films of amorphous Mo-Ge in a perpendicular magnetic field. The behavior is thermally activated, with a single field-dependent activation energy ∼$H^{\mathrm{-}2/3}$. Additionally, a continuous crossover between two different limiting behaviors is observed, with no evidence for a sharp phase transition. Although the observed universal behavior appears to depend crucially upon the existence of pinning, it is qualitatively different from conventional flux-flow or depinning phenomena.

A capacitance-spectroscopy technique based on accurate phase detection has been developed to measure the unoccupied states at silicide-silicon contacts. For Pd and Ni silicides, a dispersed group of states was found to exist in the Si band gap with its peak at a level 0.63–0.65 eV above the valence-band edge. Silicide formation alters their density and distribution to reflect the changes in the structural perfection and barrier height. Observations on the epitaxial ${\mathrm{NiSi}}_2$-Si(111) interfaces reveal that the characteristics of these states are controlled by the degree of structural perfection of the interface instead of the specific epitaxy. This seems to be the first correlation of the structural and electronic properties of a silicide-silicon interface.

We report the first detection of resonant longitudinal-field ${\mathrm{\mu }}^{+}$ spin relaxation via dynamic depolarization at a level-crossing resonance between the ${\mathrm{\mu }}^{+}$ Zeeman splitting and the induced quadrupolar coupling of the muon’s nearest-neighbor nuclei. The ${\mathrm{\mu }}^{+}$ relaxation rate as a function of external magnetic field B has a peak at the level-crossing resonance. In single-crystal Cu at 20 K with the [111] axis parallel to B the resonance occurs at a field of ${\mathrm{B}}_{\mathrm{res}=80.9\mathrm{}\pm 0.4}$ G with a full width at half maximum of 21.7±1.7 G. This approach should help clarify the controversial low-temperature motion of the ${\mathrm{\mu }}^{+}$ in Cu.

Transport, thermal, and magnetic data for the heavy electron system ${\mathrm{URu}}_2$${\mathrm{Si}}_2$ indicate that a charge- or spin-density-wave transition opens an energy gap of ∼11 meV over a portion of the Fermi surface below ${\mathrm{T}}_0$≊17.5 K and demonstrate that bulk superconductivity occurs below ${\mathrm{T}}_{\mathrm{c}}$≊1.5 K. The pressure dependences of ${\mathrm{T}}_0$ and ${\mathrm{T}}_{\mathrm{c}}$ support this interpretation. The unusually large initial slope of the upper critical magnetic field (9.2 T/K) is consistent with the high values of the electronic-specific-heat coefficient and the electrical resistivity.

We study the Aharonov-Bohm effect in single normal-metal rings and show that averaging the conductance over many energies is equivalent to ensemble averaging. Thus raising the temperature T above a crossover ${\mathrm{T}}_{\mathrm{c}}$ changes the flux periodicity of magnetoresistance oscillations from h/e to h/2e. ${\mathrm{T}}_{\mathrm{c}}$ is determined by an energy correlation range, hD/${\mathrm{L}}^2$. The persistence of the h/e oscillations to high fields is explained.

The volume magnetostriction is reported for a series of well-known intermediate-valence and heavy-fermion systems with Ce, Eu, and Yb. An expression is derived which reproduces the volume magnetostriction of all these systems quantitatively with the aid of independently measured microscopic parameters. A very large difference is found between superconducting and nonsuperconducting ${\mathrm{CeCu}}_2$${\mathrm{Si}}_2$. .AE

We have measured the self-diffusion coefficient (${\mathrm{D}}_{\mathrm{S}}$) of a dye molecule (azobenzene) in solution in porous Vycor glass by the technique of forced Rayleigh scattering. We find that the value of ${\mathrm{D}}_{\mathrm{S}}$ for motion in the pore space is about 2 orders of magnitude less than for free diffusion in bulk solution. By derivatizing the active surface sites we have separated the roles of the chemical and physical features of the pore space on diffusion. We believe this to be the first measurement of self-diffusion in solution in porous Vycor which has been proposed to have a fractal pore structure.

An anomalous variation of critical indices has recently been observed in a homologous series of micellar binary solutions. Examination of existing theories of micellar structure shows that a generalization of the Ising model is needed to describe correctly the critical behavior in micellar solutions. It implies the existence of a term that is marginal under renormalization-group transformations. Modified Migdal-Kadanoff recursion relations for this model exhibit a nonuniversal line of fixed points, in qualitative agreement with the experimental behavior.

Expressions are derived for the expected abundance of clusters and voids in a sample of randomly distributed objects.

We calculate the renormalization of charge in the Villain version of the U(1) lattice gauge theory due to monopole loops with their Biot-Savart-type long-range interactions, up to tenth order. The agreement with recent Monte Carlo data is very good except in the extreme vicinity of the critical point.

Quantum-optical considerations and the energy dependence of the inelasticity distribution predict that the relative broadening of the multiplicity distribution with increasing energy in hadron-hadron reactions must stop. Upper and lower bounds for the width of the multiplicity distribution are given. Other experimental consequences testable at presently available energies are also predicted.

Primakoff production of the $K^{0\mathrm{*}}$(896) by incident $K_L$’s was observed in the energy range 100–200 GeV. Production from Cu and Pb targets was measured simultaneously leading to a new value for the $K^{0\mathrm{*}}$(896) radiative width Γ($K^{0\mathrm{*}}$(896)→$K^0$+γ) of 116.5±9.9 keV. The result agrees with a previous determination while being considerably more precise and allows for more stringent tests of quark-model relations among the radiative widths of the low-lying vector mesons.

Leading-logarithmic radiative corrections to β decay are summed via the renormalization group and structure-dependent O(α) effects are estimated by a form-factor analysis. These refinements reduce the Kobayashi-Maskawa quark-mixing-matrix element ‖$V_{\mathrm{ud}}$‖ by 0.13% to 0.9729±0.0012. Combined with $K_{e3}$-, hyperon-, and b-decay constraints, this implies ‖$V_{\mathrm{ud}}$${\Vert }^2$+‖$V_{\mathrm{us}}$${\Vert }^2$+‖$V_{\mathrm{ub}}$‖ 2 =0.9954±0.0025. Although consistent with unitarity at the 2σ level, our result leaves open the possibility of a fourth fermion generation which at 90% confidence level may have mixing ‖$V_{\mathrm{ub}\mathcal{’}}$‖ as large as 0.088.

The spontaneous breaking of a global symmetry leads to the existence of Nambu-Goldstone bosons which, through their coupling to electrons and/or photons, can transport energy from the cores of stars and affect significantly the course of stellar evolution. We find by following in detail the evolution of stars that if the couplings to electrons and/or photons is too strong, helium never ignites—in contradiction with the observational evidence. Our limits restrict the axion mass to less than 0.01 eV, the familon breaking scale to >7×${10}^9$ Gev, and the triplet majoron vacuum expectation value to <9 keV.

We have carefully reexamined the results of the experiment of Eötvös, Pekár, and Fekete, which compared the accelerations of various materials to the Earth. We find that the Eötvös-Pekár-Fekete data are sensitive to the composition of the materials used, and that their results support the existence of an intermediate-range coupling to baryon number or hypercharge.

We fit low-energy and pp¯ collider data with a model based on a Su(2)⊗U(1)⊗U(1) electroweak group, where the additional U(1) arises from $E_6$ as required by symmetry breaking in some superstring models. We find that the extra Z must have a mass greater than 143 GeV if its decays to exotic fermions are kinematically suppressed. The production and decays of this boson are discussed.

β-decay half-lives have been measured for eight neutron-rich isotopes produced by bombardment of a ${}_{}{}^{181}{}_{}{}^{}\mathrm{Ta}$ target with an ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ beam at 30 MeV/nucleon. The previously unknown half-lives of ${}_{}{}^{14}{}_{}{}^{}\mathrm{Be}$ (4.2±0.7 ms) and ${}_{}{}^{17}{}_{}{}^{}\mathrm{C}$ (202±17 ms) have been obtained along with the half-lives of ${}_{}{}^9{}_{}{}^{}\mathrm{Li}$, ${}_{}{}^{11}{}_{}{}^{}\mathrm{Li}$, ${}_{}{}^{12}{}_{}{}^{}\mathrm{Be}$, ${}_{}{}^{14}{}_{}{}^{}\mathrm{B}$, and ${}_{}{}^{15}{}_{}{}^{}\mathrm{B}$. This experiment represents the first half-life measurements using the Michigan State reaction product mass separator.

The Mori formalism is used to study the nuclear response function at finite temperatures. This formalism rather naturally leads to an extension of the zero-temperature random-phase approximation for finite temperatures, and it provides a prescription for the calculaton of the damping widths of vibrational states at finite temperatures.

Four series of Rydberg states converging to vibrationally excited ${\mathrm{H}}_3$${\mathrm{}}^{+}$ have been excited from long-lived levels of ${\mathrm{H}}_3$ in a fast (1.5 keV) molecular beam and have been observed to autoionize to ${\mathrm{H}}_3$${\mathrm{}}^{+}$+e. A fifth Rydberg series converging to ${\mathrm{H}}_3$${\mathrm{}}^{+}$ in its ground vibrational state has been detected through field ionization. A first analysis of the ionization potentials, quantum defects, and the nature of the long-lived species of ${\mathrm{H}}_3$ is presented.

Intensity-dependent fluorescence line-shape asymmetries have been observed for two-level atoms in a standing-wave excitation field. These asymmetries are attributed to the force experienced by the induced atomic dipoles in the field gradient of the standing wave. Preliminary calculations support the experimental observations.