Low-energy excitations between charge-density-wave metastable states are revealed in low-temperature specific-heat measurements in quasi-one-dimensional materials as an excess contribution (to the lattice one) following a ${\mathrm{C}}_{\mathrm{p}}$=${\mathrm{T}}^{\nu }$ law with ν<1. In the same temperature range the energy relaxation is not exponential but follows a stretched exponential variation. Aging effects are also demonstrated. Analogies and differences with other glassy materials are briefly discussed.

A new reconstruction structure, having a √3×√3)R30° unit cell, is reported for the Si(111) surface. Analysis of low-energy electron-diffraction intensity spectra by multiple-scattering theory revealed a vacancy model. The bonds between the first- and second-layer atoms are of the ${\mathrm{sp}}^2$ type, resulting in a highly compressed surface bilayer. Measured intensity spectra of the clean and Ag-deposited (√3×√2)R30° surfaces are very similar. This leads us to conclude that the Ag-Si interface is not sharp and that the Ag atoms do not form a lattice structure that has long-range ordering.

This article describes a novel mechanism believed to be responsible for the incommensurate-incommensurate phase transition in ${\mathrm{NbTe}}_4$.

High-resolution, small-angle, synchrotron x-ray-scattering techniques were used to determine the phase diagram, structure factor, and pair distribution function for a charged colloidal suspension from 6% to 30% volume fraction. The expected correlated liquid and fcc and bcc solid phases were observed along with a glass phase at high concentration with structure similar to metallic glasses. At high volume fractions the finite core size leads to substantial deviation from predictions resulting from a screened Coulomb interaction.

The proton nuclear transverse relaxation $T_2$ of HD impurities and ortho-${\mathrm{H}}_2$ impurities in solid parahydrogen is observed to be essentially temperature independent below 8 K, passes through a minimum near 9.2 K on warming, and then increases exponentially on approaching the melting point. The low-temperature values of $T_2$ are pressure dependent and a factor of 5.4 larger than the rigid lattice values. This ‘‘line narrowing’’ is attributed to quantum tunneling of the HD impurities at low temperatures. The minimum in $T_2$ is attributed to the breakup of coherent tunneling due to scattering by phonons and vacancies.

A scaling relation between nuclear relaxation $T_1^{\mathrm{-}1}$ and magnetic susceptibility ${\chi }_s$ is established for (TMTSF${)}_2$${\mathrm{PF}}_6$ and (TMTSF${)}_2$${\mathrm{ClO}}_4$ organic conductors over a wide domain of temperature at ambient pressure. The analysis in terms of quantum scaling demonstrates the important role played by 1D paramagnon magnetic excitations in the Bechgaard salts. Similar observations made on (TMTTF${)}_2$${\mathrm{PF}}_6$ clarify the nature and the dimensionality of correlations of the nonordered phases in both (TMTSF${)}_2$X and (TMTTF${)}_2$X series compounds.

Spin configurations of fractions z<ν<2 are examined by angular and n-dependent activation studies. Energy gaps Δ(θ) and intercepts ${\sigma }_{\mathrm{xx}}^c$(θ) that probe the quasiparticle charge $e^{\mathrm{*}}$ quantify a dramatic difference between (4/3 and (5/3 states consistent with assignments (4/3↑↓, and (5/3↑↑ (↑↓,↑↑=zero, maximum polarization). A field-induced phase transition ${}_3{}^4{}_{}{}^{}\to _3^4{}_{}{}^{}$ (partial polarization) in which $e^{\mathrm{*}}$ changes from e/3 to e/5 is mapped out. The (7/5 state formed from e/3 quasiparticles is destroyed at the (4/3 transition. High-order assignments ${}_5{}^7{}_{}{}^{}$(↑↑ or ↓), ${}_5{}^8{}_{}{}^{}$ ↑↓, ${}_7{}^{10}{}_{}{}^{}$ ↑↓, and ${}_7{}^{11}{}_{}{}^{}\mathrm{\uparrow }$ are consistent with experiment.

We observe a novel transition between distinct fractional quantum Hall states sharing the same filling fraction ν=(8/5. The transition is driven by tilting the two-dimensional electron-gas sample relative to the external magnetic field and is manifested by a sharp change in the dependence of the measured activation energy on tilt angle. After an initial decline, the activation energy abruptly begins to increase as the tilt angle exceeds about 30°. A plausible model for these results implies a transition from a spin-unpolarized quantum fluid at small angles to a polarized one at higher angles.

Although small (spatially compact) bipolarons readily localize, large bipolarons (like large polarons) can be mobile. As such, large bipolarons are a suitable basis for bipolaronic superconductivity. However, large bipolarons can only form in multidimensional ionic solids if the static dielectric constant greatly exceeds twice the optical dielectric constant. The formation as well as normal-state and superconducting properties of large bipolarons appear consistent with observations of the high-temperature superconductors.

We have used a mechanical oscillator to study energy dissipation due to flux-line dynamics in ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{x}}$ thin films oriented in a parallel magnetic field. The dissipation is finite at low temperatures and diverges strongly at the superconducting transition. We argue that this behavior is a consequence of the existence of a pinned vortex glass in which flux-line motion between pinning sites occurs by configurational tunneling at low temperature and thermal activation near the transition temperature.

The elastic moduli of the two-dimensional flux-line lattice in a uniaxial superconductor are evaluated for an arbitrary orientation of vortices (i.e., of the magnetic induction) within the crystal in intermediate fields. For the flux lines in the basal a-b plane the ratio of the simple shear moduli, corresponding to displacements normal and parallel to the basal plane, is shown to equal (${\mathrm{m}}_3$/${\mathrm{m}}_1$${)}^2$ where ${\mathrm{m}}_3$ and ${\mathrm{m}}_1$ are the masses along the c axis and the basal plane, respectively. For ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$ this amounts to a factor exceeding 600. The uniaxial crystal symmetry defines a preferred orientation to the flux lattice and doubles the number of independent elastic constants.

We have measured ultrasonic velocity changes with temperature (T≤1 K) to study two-level-tunneling systems (TLS) interactions with electrons and with phonons in the high-${\mathrm{T}}_{\mathrm{c}}$ superconductor ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ and in a niobium compact. In ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$, at T≪${\mathrm{T}}_{\mathrm{c}}$, TLS relaxation is dominated by conduction electrons, as in normal metallic glasses. In niobium, at T≪${\mathrm{T}}_{\mathrm{c}}$, this relaxation is dominated by phonons, as in other disordered, conventional superconductors. We also review recent specific-heat measurements in light of these results.

Point-contact spectroscopy is used for the first time to measure directly the Zeeman splitting of the crystal-field levels (CEF) in an intermetallic rare-earth compound. The anisotropic magnetic-field dependence of the CEF levels has been observed in a ${\mathrm{PrNi}}_5$ single crystal together with the onset of new transitions which are forbidden in zero magnetic field. The analysis of the spectra yields a set of CEF parameters which also account for the previously observed physical properties.

A low density of vacancies in a 2D, spin-(1/2, Heisenberg antiferromagnet leads (for a range of effective couplings) to a metallic phase with incommensurate antiferromagnetic order, i.e., with the staggered magnetization rotating in a plane with the wave number proportional to the density. This structure originates from the polarization of the antiferromagnetic dipole moments of the vacancies. The excitation spectrum of this spiral state includes an interesting low-lying mode. Implications for neutron scattering and normal-state resistivity are discussed.

Abrupt interfaces without substrate disruption are formed when metallic Co clusters are brought into contact with clean GaAs(110). Unique Fermi-level pinning positions 0.32 and 0.96 eV below the conduction band are nearly independent of surface coverage and appear to be related to states of the unrelaxed surface. No evidence is found for metal-induced midgap states or conventional defects. Co atom deposition induces substrate disruption at 60 and 300 K, with As surface segregation inhibited at 60 K. The temperature-dependent Schottky-barrier evolution for n-GaAs shows that pinning is not controlled simply by levels related to surface disruption.

The behavior of interacting fluid membranes is simulated using a vectorized Monte Carlo code. The Monte Carlo data give clear evidence for the existence of continuous unbinding transitions from a bound to an unbound state of the membranes. The location of the phase boundary and, thus, the macroscopic membrane state is found to be strongly affected by shape fluctuations on microscopic length scales. The observed critical behavior confirms theoretical predictions even though the accessible critical region is severely restricted by the rapid growth of relaxation times.

The direct determination of the f(α) singularity spectrum from experimental data is a difficult problem. This Letter introduces a simple method for computing f(α) based on the theorems of Shannon, Eggelston, and Billingsley which is markedly superior to other recently proposed methods, especially when dealing with experimental data from low-dimensional chaotic systems where the underlying dynamics are unknown.

We present a generalization of Hamilton’s geometric theory of turns, originally invented for SU(2), to the noncompact group Sp(2,R) relevant in a variety of physical applications.

We describe a novel feature of certain arrays of N-coupled nonlinear oscillators. Specifically, the number of stable limit cycles scales as (N-1)! To accomodate this huge multiplicity of attractors, the basins of attraction crowd ever more tightly in phase space with increasing N. Our simulations show that for large enough N, even minute levels of noise cause the system to hop freely among the many coexisting stable attractors.

By exploiting some recent results in global Riemannian geometry we construct families of probability measures on the path space associated with the set of n-dimensional (n≥3) Riemannian geometries. As an example of such construction we characterize a Gaussian stochastic process which yields a natural notion of Brownian motion on the set of Riemannian manifolds. An ultraviolet cutoff L parametrizes this class of measures. The limit L→0, as well as the probability of finding a random geometry in a given state, is discussed.