The concept of mean-field rigidity percolation at average coordination number 〈r〉=2.4 in covalently bonded inorganic glasses is shown to be relevant to the liquid-state behavior of glass-forming chalcogenide systems. In particular it correlates with remarkable variations in ‘‘fragility’’ and excess heat capacity which we observe in the model ternary system Ge-As-Se. Except near ${\mathrm{As}}_2$${\mathrm{Se}}_3$, ${\mathit{T}}_{\mathit{g}}$ itself depends only on 〈r〉 anywhere in the system up to 〈r〉=2.5. These findings provide an important link between key structural concepts of glass science, the relaxation phenomena, and the thermodynamic problem embodied in the Kauzmann paradox.

I map evaporation onto thermodynamic phase diagram. I demonstrate that when temperature increases, the evaporation rate may decrease, have a maximum and minimum, and change almost discontinuously. Some of these features are in agreement with recent data on the escape of two-dimensional electrons from a bulk helium surface; the others call for new specific experiments.

Neutron inelastic scattering combined with neutron-polarization analysis has been used to observe new, nonlinear excitations in the planar antiferromagnet (${\mathrm{CD}}_3$${)}_4$ ${\mathrm{NMnCl}}_3$ (TMMC) at low temperatures and in the presence of a large, transverse magnetic field. The new excitations result from a field-induced nonlinear coupling of in-plane and out-of-plane magnons.

We have measured the field and temperature dependences of the logarithmic flux-creep relaxation in an oriented-grain sample of YBaCuO in the critical state. The data indicate that the effective activation energy ${\mathit{U}}_0$ increases continuously with increasing T between 6 and 30 K, and that ${\mathit{U}}_0$(T) tends to increase rather than decrease with increasing applied field. These results are compared to predictions of the thermally activated flux-creep model.

The current-voltage characteristics of submicron normal-metal tunnel junctions at millikelvin temperatures are observed to exhibit a sharp Coulomb blockade with high-resistance thin-film leads, but to be heavily smeared for low-resistance leads. As the temperature is lowered, the zero-bias differential resistance tends asymptotically to a limit that is greater for junctions with high-resistance leads. Both observations are explained in terms of a model in which quantum fluctuations in the external circuit enhance the low-temperature tunneling rate. The predictions are in reasonable agreement with the data.

We have measured the specific heat, C, of single-crystal ${\mathrm{UPt}}_3$ in the superconducting regime as a function of temperature, T, and magnetic field, H, parallel to the c axis. We find that C(T) at fixed H<${\mathit{H}}_{\mathit{c}2}$ shows no evidence for different superconducting states. In contrast, our field-sweep data, C(H) at fixed T, have sharp changes in slope at H≊${\mathit{H}}_{\mathit{c}2}$/2. The phase diagram deduced from these features agrees with neutron-scattering and torsional-oscillator results on the same samples. These thermodynamic measurements as a function of magnetic field constrain theories of exotic superconductivity in ${\mathrm{UPt}}_3$.

High-resolution torque-magnetometry data have been obtained on an untwinned single crystal of ${\mathrm{Y}}_1{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-\delta }$ in the temperature range $63<T<\mathrm{}88\mathrm{}$ K ($T_c=90.5\mathrm{}$ K). At $T=80\mathrm{}$ K and above, the data are fitted extremely well with the accepted three-dimensional phenomenological theory, but below this temperature an anomalous torque develops when the magnetic field lies close to the Cu-O planes. The qualitative and quantitative features of our results provide strong evidence that breakdown of the three-dimensional description below 80 K is associated with a crossover to two-dimensional superconducting behavior.

We report on a systematic experimental investigation of the dielectric, mechanic, and piezoelectric properties of piezoelectric porous ceramics as a function of void fraction in a large porosity range. Our results are compatible with the predictions of a scaling theory developed recently for these systems. Our measurements provide the first experimental test of the critical properties of piezoelectric ceramics in the percolation regime.

We study the classical dynamics of a ballistic charged particle in a two-dimensional (2D) periodic potential and an applied magnetic field. We find chaotic behavor, in particular in the form of normal diffusion and anomalous diffusion associated with 1/f noise. The mechanisms for the onset of 1D diffusion and 2D diffusion are explained in terms of homoclinic intersections and Kolmogorov-Arnol’d-Moser theory. The model may be used as a classical approximation for ballistic-electron dynamics in lateral superlattices on semiconductor heterojunctions.

Low-frequency ac currents have been observed to induce a dc voltage ${\mathit{V}}_{\mathrm{dc}}$ across macroscopic percolating films of lead and aluminum in the vicinity of their superconducting transition. This conversion is observed down to a frequency of 10 Hz, which rules out an inverse-Josephson-effect interpretation. ${\mathit{V}}_{\mathrm{dc}}$ shows sharp oscillations as a function of a magnetic field. This pattern dependence on the angle between the sample and the applied field identifies these oscillations as an Aharonov-Bohm effect.

The Schottky barrier of Pb grown epitaxially on n-type Si(111) has been studied. Two structures can be formed, which differ only in the arrangement of the first layer of Pb and Si atoms at the interface. One, a Si(111)(7×7)-Pb structure, has a Schottky-barrier height of 0.70 eV. The other, a Si(111)(√3 × √3 )R30°-Pb structure, has a barrier height of 0.93 eV. These results emphasize the importance of the local electronic structure for Schottky-barrier formation at ordered interfaces.

The temperature dependence between 10 and 300 K of the positron lifetime was measured in the high-temperature superconductors ${\mathrm{YBA}}_2$(${\mathrm{Cu}}_{1\mathrm{-}\mathit{x}}$${\mathit{M}}_{\mathit{x}}$${)}_3$${\mathrm{O}}_{6+\mathrm{\delta }}$, where M=Zn and Ga with x=0.0 to 0.07 and δ>0.8. In the undoped and Ga-doped samples, the positron lifetime in the Bloch state, ${\mathrm{\tau }}_{\mathit{b}}$, was observed to decrease below ${\mathit{T}}_{\mathit{c}}$. In the Zn-doped samples, a dramatic x-dependent temperature variation of ${\mathrm{\tau }}_{\mathit{b}}$ was observed: from a decrease of ${\mathit{T}}_{\mathit{b}}$ below ${\mathit{T}}_{\mathit{c}}$ for x=0.01 to an increase of ${\mathrm{\tau }}_{\mathit{b}}$ for x>0.02. These new experimental results are interpreted in terms of a change in the local charge density of high-${\mathit{T}}_{\mathit{c}}$ oxides associated with the superconducting transition.

We compute the ground-state spin-spin correlation function for the one-dimensional antiferromagnetic Heisenberg model of spin 1/2, 1, and 3/2. The spin-1 chain has a disordered ground state with a correlation length of 6.2 lattice spacings whereas the spin-1/2 and the spin-3/2 chains both have (ln(r)${)}^{\mathrm{\sigma }}$/r decaying correlation functions. The logarithmic corrections are different for the spin-1/2 and the spin-3/2 chains. Finite-size scaling is used to analyze the data for chains of up to 128 spins.

Theoretical and experimental results for the charge state and energy loss of low-energy He scattered off a Ni(110) surface are compared. A first-principles theory is used to analyze both the charge state and the energy loss. Charge-exchange processes are of primordial importance to explain the energy-loss spectra. Energy straggling plays an important role in the system under study.

Anomalies in vibrational spectra measured by neutron and Raman scattering and spatial inhomogeneities in ${}_{}{}^{18}{}_{}{}^{}\mathrm{-}_{}^{16}{}_{}{}^{}$O exchange lead to a two-region micromorphological model of YBCO. This model explains why among ‘‘single-phase’’ high-temperature superconductors only YBCO exhibits a nearly zero isotope effect. This small isotope effect has been used as the justification for many exotic nonphonon models of high-temperature superconductivity, but the present discussion shows that such models are unnecessary.

In two space dimensions we generalize the boson-vortex duality picture for spinless particles to boson-vortex-Skyrmion duality for spin-1/2 particles. The spin-singlet fractional quantum Hall effect and spin-singlet anyon superconductivity can be understood as the condensation of vortices and Skyrmions into various fractional quantum Hall states.

Tracing the neutron spin on its passage through a magnetic field which rotates at various frequencies it was possible to observe geometrically induced phase shifts of a quantum-mechanical state even for incomplete revolutions of this field. The experiments show that we can extract such purely geometric effects also from nonadiabatic evolutions.

The results of a test of the gravitational redshift effect at Saturn are reported. Measurements of the redshift were obtained with the Voyager 1 spacecraft during its encounter with Saturn in 1980. Because the spacecraft was equipped with an ultrastable crystal oscillator (USO), it is possible to test the redshift effect at an interesting level of accuracy. Assuming that radiation in the Saturn magnetosphere has had a negligible effect on the USO, we verify the prediction of general relativity to an accuracy of one percent. This limit could be of interest for constraining possible alternative theories of gravity.

Models of unitary matrices are solved exactly in a double scaling limit, using orthogonal polynomials on a circle. Exact differential equations are found for the scaling functions of these models. For the simplest model (k=1), the Painlevé II equation with constant 0 is obtained. There are possible nonperturbative phase transitions in these models. The scaling function is of the form ${\mathit{N}}^{\mathrm{-}1/(2\mathit{k}+1)}$×f(${\mathit{N}}^{2\mathit{k}/(2\mathrm{}\mathit{k}+1)}$(${\lambda }_{\mathit{x}}$-λ)) for the kth multicritical point. The specific heat is ${\mathit{f}}^2$, and is therefore manifestly positive. Equations are given for k=2 and 3, with a discussion of asymptotic behavior.

A measurement of the reaction ${\nu }_{\mathit{e}}$+${\mathit{e}}^{\mathrm{-}}$→${\nu }_{\mathit{e}}$+${\mathit{e}}^{\mathrm{-}}$ was performed using a beam-stop source of ${\nu }_{\mathit{e}}$. Based upon 234±35 events, we obtain a cross section of σ(${\nu }_{\mathit{e}}$e)=[9.9±1.5(stat)±1.0(syst)]×${10}^{\mathrm{-}42}$ ${\mathrm{cm}}^2$ ×[${\mathit{E}}_{\nu }$ (GeV)]. This reaction is mediated by the exchange of W and Z bosons and is thus sensitive to the interference between them. This interference is measured to be -1.07±0.17(stat)±0.11(syst), consistent with the destructive interference (-1.08) predicted by the standard model.