We report anomalies in the temperature- and pressure-dependent electrical resistivity of Ce${\mathrm{Pd}}_3$ and its alloys that occur on a temperature scale ≈ 40 K, which correlates with the scale for the neutron-scattering from-factor ($5d$ susceptibility) anomaly. We outline an argument that the reported effects demonstrate the existence of an energy scale $T_{\mathrm{coh}}$ [related to the single-ion spinfluctuation scale $T_{\mathrm{sf}}$ by a factor $\frac{1}{\mathrm{}(2J+1)\mathrm{}}$] over which coherence develops among spin fluctuations on different sites.

We report here an entirely new phenomenon, namely magnetic-field-induced superconductivity in Ce${\mathrm{Pb}}_3$, a system which at zero field is a heavy-fermion antiferromagnet. This phenomenon is novel in several respects. It is the first reported heavy-fermion magnetic-field-induced superconductor. It is also the first reported magnetic-field-induced superconductor that is also an antiferromagnet. Moreover, it has the simplest crystal structure, ${\mathrm{Cu}}_3$Au, of any known heavy-fermion or magnetic-field-induced superconductor.

The low-temperature diffusion length of photogenerated electron-hole pairs in hydrogenated amorphous germanium and silicon has been determined from measurements of photoluminescence spectra and quantum efficiency in multilayer structures, as a function of the sublayer thicknesses. When the sublayer thickness is small compared with this diffusion length, the photoluminescence in amorphous germanium is enhanced by more than 2 orders of magnitude.

It is shown that the Migdal approximate-renormalization recursion formulas always bring the initial state into the high-temperature region for the U(1)-invariant models at the critical dimensions. This means that the Migdal recursion formulas fail to exhibit the Kosterlitz-Thouless transitions. This is also the case for the recursion formulas of Kadanoff type. The method developed here is extended to non-Abelian systems by some additional tricks.

The frequency of a nuclear spin-flip ($\left|\Delta m_I\right|=1\mathrm{}$) transition in ${}_{}{}^9{}_{}{}^{}\mathrm{Be}_{}^{+}{}_{}{}^{}$ has been compared to the frequency of a hydrogen maser transition ($\left|\Delta F\right|=1\mathrm{}$, $\Delta m_F=0\mathrm{}$) to see if the relative frequencies depend on the orientation of the ${}_{}{}^9{}_{}{}^{}\mathrm{Be}_{}^{+}{}_{}{}^{}$ ions in space. The present null result represents a decrease in the limits set by Hughes and Drever on a spatial anisotropy by a factor of about 300.

We use a scaling analysis to estimate critical exponents for the electrical conductivity, elastic constants, and fluid permeability near the percolation threshold of a class of disordered continuum systems (Swiss-cheese models), where the transport medium is the space between randomly placed spherical holes. We find that the exponents are significantly larger than their counterparts in the standard discrete-lattice percolation networks, except for the case of electrical conductivity in two dimensions, where they are equal.

We show that states of systems which, in a very general sense, are approximately localized at time $t=0\mathrm{}$ in a finite region, with exponentially bounded tails outside, violate Einstein causality at later times. Implications are discussed.

We report the results of a Fermilab Tevatron experiment using a ${\Sigma }^{-}$ beam with a measured polarization of 0.22 ± 0.04. We find the electron asymmetry in ${\Sigma }^{-}$ beta decay to be ${\alpha }_e=-0.53\mathrm{}\pm 0.14$ on the basis of a sample of 25 000 events, in agreement with the Cabibbo model and in contradiction with previous experiments. The corresponding value for the ratio of axial-vector to vector form factors is $\frac{g_1}{f_1}=-0.29\mathrm{}\pm 0.07$.

A Monte Carlo calculation is performed for a theory of SU(5) gauge fields interacting with adjoint scalar matter fields. The tree-level scalar potential is chosen to break SU(5) to SU(3) ⊗ SU(2) ⊗ U(1), but it is found that radiative corrections due to the gauge bosons give rise to the possibility of breaking to a metastable (perhaps even stable) SU(4) ⊗ U(1) phase for certain ranges of the bare scalar mass. The transitions between the various phases of the theory are found to be first order. The implications of these results for continuum physics are as yet unclear.

We formulate the renormalization-group-improved theory for an $m_r\ne 0$ (massive) QCD Lagrangian. The Green's functions are parametrized in terms of two renormalization-group-invariant quantities, $M_0$ and ${\Lambda }_c$. The theory exhibits usual analyticity structure for every $M_0>{\Lambda }_c{e}^{\frac{1}{6}}$. In the limit $M_0={\Lambda }_c{e}^{\frac{1}{6}}$, $m_r$ becomes zero. The theory exhibits bifurcation in this limit, and chiral symmetry remains broken. $〈\overline{\psi }\psi 〉$ is calculated in this limit.

The vorton method, developed earlier by one of us, is applied to the problem of the mutual penetration of two and four vorton rings. (A vorton is a vortex singularity.) Abrupt jumps of vorticity as well as major changes in the energy spectrum are observed in the process of destruction of vorton rings and in the instability of a system of vortons near collapse.

A velocity analyzer with high angular resolution ($\frac{d\Omega }{4\pi }={10}^{-4\mathrm{}}$) has been used to measure the electron distribution function $f(v, \theta , \phi )$ in a neutral sheet of a large laboratory plasma. Contours of $f\left(\mathrm{v}\right)=\mathrm{const}$ form surfaces in velocity space. As $f\left(\mathrm{v}\right)$ decreases, anisotropic tails form detached surfaces which send filaments out toward the main body. The highly anisotropic structures occur at the Doppler-shifted phase velocity of observed whistler-wave turbulence. Instability analysis of $f\left(\mathrm{v}\right)$ is consistent with the observed whistler- and Langmuir-wave turbulence.

We present observations on two-level-system tunneling of dislocation kinks as well as direct evidence of the suppression of the tunneling due to dissipation, obtained by turning on and off a damping mechanism. The results are based on measurements of sound velocity in the superconducting and normal states of aluminum, in the presence of a bias stress used to generate the two-level system.

We report electron-microscopy and high-resolution x-ray-scattering measurements of rapidly quenched ${\mathrm{Al}}_6$Mn. The electron-diffraction pattern shows icosahedral symmetry. Peaks in the x-ray-diffraction pattern can be indexed to a mixture of fcc Al and a phase whose reciprocal lattice is described by a sum of icosahedral vectors. The half-width of the sharpest x-ray peak is 0.01 ${\mathrm{\AA }}^{-1\mathrm{}}$. A comparison is made with current theories of quasicrystalline order.

It is shown experimentally that the photocurrent of silicon avalanche photodiodes exhibits frequency-dependent noise. The measured photocurrent noise-power spectral density presents a broad peak in the low-frequency portion of the spectrum. The origin of the peak is attributed to a correlation existing in the process of photomultiplication of carriers in the high-field region of the photodiode.

The three-dimensional random-field Ising model is studied by Monte Carlo simulations on $L\times L\times L$ lattices with $L<~64$. Our results are completely consistent with there being a ferromagnetically ordered state at low temperatures. For $T\to T_c^{+}$, the susceptibility and correlation length have effective exponents similar to the pure two-dimensional Ising model. However, for the random-field values studied, the transition is actually first order, driven by large fluctuations in the disconnected correlation functions. We suggest that the transition is first order, even for arbitrarily small values of the random field.

The low-temperature scanning tunneling microscope is used in a new spectroscopic mode to obtain real-space images of the superconducting character of a ${\mathrm{Nb}}_3$Sn surface. These images show strong spatial variations, with reproducible transitions between fully normal and fully superconducting behavior on length scales as small as 13 nm. Images taken above and below the critical temperature confirm that the observed effects are due to superconductive tunneling. Additional confirmation comes from a successful fit of the current-voltage characteristics to a simple tunneling model.

A random-phase-approximation theory is given for the electronic collective modes of a film containing $N$ equally spaced layers of two-dimensional electron gas. Raman line shapes are predicted. The Giuliani-Quinn surface-plasmon intensity is enhanced in transmission geometry.

We report the observation of two-dimensional electron systems and enhanced mobilities in Si/${\mathrm{Si}}_{0.5}$${\mathrm{Ge}}_{0.5}$ strained-layer multilayer structures. The built-in strain is measured by phonon Raman spectroscopy. The mobility enhancement depends strongly on the position of the doped region within the layers. The experimental results can be explained in a consistent way when carrier confinement in the Si layer is assumed. The importance of the built-in strain in lowering the conduction band in Si is emphasized.

A uniaxially anisotropic $p$-wave interaction is shown to lead to either a polar or an axial state. We calculate the anisotropy of $H_{c2\mathrm{}}\mathrm{}\left(T\right)\mathrm{}$ with the assumption that $E_{\mathrm{F}}\gg k_{\mathrm{B}}{T}_c$. Weak-interaction anisotropy leads to a kink in $H_{c2,\perp }\mathrm{}\left(T\right)\mathrm{}$. Otherwise, our results are qualitatively similar to those for an anisotropic $s$-wave material. Our results indicate that the anisotropy of the $H_{c2\mathrm{}}\mathrm{}\left(T\right)\mathrm{}$ data obtained for U${\mathrm{Pt}}_3$ cannot be explained as intrinsic for a $p$-wave superconductor unless $E_{\mathrm{F}}\cong k_{\mathrm{B}}{T}_c$.