In a comparative Andreev-reflection study of normal-superconductor point contacts on the c plane of ${\mathrm{UPt}}_3$, ${\mathrm{CeCu}}_2$${\mathrm{Si}}_2$, and ${\mathrm{URu}}_2$${\mathrm{Si}}_2$ crystals at temperatures down to T=30 mK and in a magnetic field up to B=10 T, differences are found in the current-voltage characteristics. The behavior of the differential resistance dV/dI(V) of ${\mathrm{UPt}}_3$ is attributed to the presence of nodes in the superconducting order parameter Δ(k^) and is compared with theoretical predictions for the symmetry of the pairing state. The data for ${\mathrm{CeCu}}_2$${\mathrm{Si}}_2$ and ${\mathrm{URu}}_2$${\mathrm{Si}}_2$ point to the absence of zeros in Δ(k^).

The short-range structure in ${\mathrm{La}}_{2\mathrm{-}\mathit{x}}$${\mathrm{Ba}}_{\mathit{x}}$${\mathrm{CuO}}_4$ is examined by obtaining the pair distribution function from neutron powder diffraction data. In contrast to the predictions of the crystal structure models, locally, the ${\mathrm{CuO}}_6$ octahedra do not change their tilt direction at the low-temperature tetragonal (LTT) to low-temperature orthorhombic (LTO) phase transition: they always tilt in the [110] (LTT) directions. The long-range structures of the high-temperature phases result from coherent superpositions of the local LTT variants. The local tilt order extends over ∼1 nm. We discuss the implications of this local structure for the properties.

We introduce a new Ising spin-glass model and use it to study the relation between quenched disorder, frustration, ground state mulitplicity, and dimension. The Hamiltonian is of Edwards-Anderson type in any finite volume but the coupling magnitudes scale nonlinearly with volume. We find a mapping between the ground state structure of this model and the global connectivity structure of invasion percolation in the same dimension. We argue that our model has a singular pair of ground states below eight dimensions and infinitely many above.

Amorphous ${\mathrm{Co}}_2$Ge was synthesized by ball milling crystalline ${\mathrm{Co}}_2$Ge, a state which cannot be obtained by traditional rapid solidification. It exhibits a single transition from the paramagnetic to the spin-glass state at 41 K (${\mathit{T}}_{\mathit{f}}$) as defined by a sharp asymmetric cusp in the lowest field ac susceptibility. In fields ≥30 Oe the cusp in both ac and dc susceptibility curves becomes a rounded maximum and ${\mathit{T}}_{\mathit{f}}$ decreases. Below ${\mathit{T}}_{\mathit{f}}$ the magnetization reveals thermal hysteresis. Using the Sherrington-Kirkpatrick theory the spin-glass order parameter is derived and a spin-glass phase was synthesized by mechanical milling. This phase can be described by mean-field theory.

We present the first experimental evidence of macroscopic one-dimensional patterns and forced wavelength selection in magnetic colloidal suspensions in an oscillating magnetic field. The resulting dramatic enhancement of the domain growth kinetics gives rise to concentration patterns composed of a main periodic structure and similar periodic substructures, which have a wave vector increasing with the excitation frequency, and decreasing with the suspension concentration.

The flow of embryonic tissues during morphogenesis has been ascribed to tissue interfacial tensions arising from cell adhesion. Testing this explanation requires the demonstration that tissue interfacial tensions are measurable physical quantities. We describe a device that continuously records all parameters necessary to determine the tensions of living tissues at the interface with the surrounding medium. We monitor the relaxation of an imposed stress in two embryonic tissues, measure their interfacial tensions, and demonstrate that these are consistent with these tissues’ mutual spreading behavior.

We demonstrate that stochastic resonance, where an increase in the noise acting on a nonlinear dynamical system increases the signal-to-noise ratio describing the response to periodic driving, can occur in quantum systems as well as classical ones. We show that quantum stochastic resonance can be observed experimentally by measuring conductance fluctuations in mesoscopic metals and describe the experimental parameters for which it occurs.

We provide a streamlined proof of Hardy’s theorem, that almost every entangled state for a pair of quantum particles admits a ‘‘proof of nonlocality’’ without inequalities. Moreover, our analysis covers a larger class of observables. Thus we also strengthen Hardy’s assertion that the argument fails for maximally entangled states, such as the singlet state. At the same time, we formulate the argument in such a manner that the relations which must be satisfied for local hidden variables are entirely deterministic, making no reference whatsoever to probability, let alone probablistic inequalities.

We present a measurement setup based on the deflection of atoms from a quantized electromagnetic field and a strategy which leads to the knowledge of the complete quantum state of this field. The same setup reveals the expectation value of the phase operator $e^{i\phi }$.

It is suggested that an axino mass in the 10 MeV region and a gravitino mass in the sub-eV region can provide an explanation for the observed power spectrum. In this case, cold axions act as cold dark matter and axino decay products (gravitinos and axions) control the commencement of the matter domination.

Two-neutrino oscillations in vacuum are studied as a possible solution of the solar neutrino problem. New constraints on the parameter ${\sin }^2$2θ, characterizing the mixing of the electron neutrino with another active or sterile neutrino, as well as on the mass-squared difference Δ${\mathit{m}}^2$ of their massive neutrino components, are derived using the latest results from the four solar neutrino experiments. Oscillations into a sterile neutrino are ruled out at 98% C.L. by the observed mean event rates even if one includes the uncertainties of the standard solar model predictions in the analysis.

We demonstrate that band-structure effects suppress bremsstrahlung of neutrino pairs by electrons in the crusts of neutron stars at temperatures of the order of 5×${10}^9$ K and below. Taking this into account, together with the fact that recent work indicates that the masses of neutron star crusts are considerably smaller than previously estimated, we find neutrino pair bremsstrahlung to be much less important for the thermal evolution of neutron stars than earlier calculations suggested.

We present a solution of the problem of a free massless scalar field on the half line interacting through a sinusoidal potential on the boundary. For a critical value of the period, this system is a conformal field theory with a nontrivial and explicitly calculable S matrix for scattering from the boundary. It describes the critical behavior of a number of condensed matter systems, including dissipative quantum mechanics and of barriers in ‘‘quantum wires.’’

Using the CLEO II detector, we have obtained evidence for a new meson decaying to ${\mathit{D}}^0$${\mathit{K}}^{+}$. Its mass is 2573.$2_{\mathrm{-}1.6}^{+1.7\mathrm{}}$±0.8±0.5 MeV/${\mathit{c}}^2$ and its width is ${16}_{\mathrm{-}4}^{+5\mathrm{}}$±3 MeV/${\mathit{c}}^2$. Although we do not establish its spin and parity, the new meson is consistent with predictions for an L=1, S=1, ${\mathit{J}}^{\mathit{P}}$=$2^{+}$ charmed strange state.

We present results of a search for the top quark decaying to a charged Higgs boson (${\mathit{H}}^{+}$) in p p¯ collisions at √s =1.8 TeV at the Fermilab Tevatron. Assuming that ${\mathit{H}}^{+}$→τ${\nu }_{\mathrm{\tau }}$ is the dominant ${\mathit{H}}^{+}$ decay mode, we exclude regions of the (${\mathit{m}}_{\mathit{H}}^{+}$,${\mathit{m}}_{\mathit{t}}$) plane for values of the branching ratio, B(${\mathit{H}}^{+}$→τ${\nu }_{\mathrm{\tau }}$)=0.5, 0.75, and 1.0. We interpret the results in terms of the parameter tan β in the two-Higgs-doublet model.

The nucleon-nucleon potential obtained from the most general effective chiral Lagrangian involving low momentum pions, nonrelativistic nucleons, and Δ isobars was considered to third order in the chiral expansion. The parameters of the potential were adjusted to reproduce the low energy nucleon-nucleon scattering phase shifts as well as the properties of the deuteron. Reasonable fits are obtained in this first application of a nucleon-nucleon potential based on chiral symemtry.

The cross section for quasielastic ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$(e,e’p) scattering has been measured at momentum transfer ${\mathit{Q}}^2$=1, 3, 5, and 6.8 (GeV/c${)}^2$. The results are consistent with scattering from a single nucleon as the dominant process. The nuclear transparency is obtained and compared with theoretical calculations that incorporate color transparency effects. No significant rise of the transparency with ${\mathit{Q}}^2$ is observed.

A new region characterized by Lévy diffusion exists in collective motion between the adiabaic and diabatic limits. Repeated chaotic scattering off of level crossings, whose repulsive or attractive nature changes dynamically, can result in localization of the collective motion for arbitrarily periods of time, and anomalous diffusion.

The ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$(e,e’x) reaction has been investigated for excitation energies between 8 and 26 MeV and momentum transfers from 0.25 to 0.66 ${\mathrm{fm}}^{\mathrm{-}1}$ at the continuous-wave electron accelerators MAMI at Mainz S-DALINAC at Darmstadt. A multipole decomposition of the cross sections reveals strongly fragmented E2 (plus E0) strength around 14 and 17 MeV in contrast to all theoretical predictions. Angular correlations of proton decay are described over the entire energy range by a continuum random-phase-approximation approach. A comparison of the branching ratios to statistical model calculations provides information on the dominant damping mechanism.

For electron impact ionization of hydrogen the S matrix is determined by calculating Feynman’s path integral semiclassically. The total ionization probability is in excellent agreement with the experiment. At a critical excess energy of 3.3 eV the differential cross section for the energy sharing between the continuum electrons undergoes a qualitative change which limits the range of the threshold behavior. The Wannier threshold law is confirmed, but only in the limt of vanishing excess energy.