The dephasing time of coherently prepared ${\mathrm{Pr}}^{3+}$ impurity ions in a La ${\mathrm{F}}_3$ crystal is measured by optical free-induction decay. Above 4°K, phonon processes severely shorten the decay time. Below 4°K, we observe a temperature-independent decay time of 0.38 μsec. This is surprisingly short considering that there are no contributions from first-order hyperfine, phonon, or ${\mathrm{Pr}}^{3+}$-${\mathrm{Pr}}^{3+}$ interactions.

Angle-resolved photoemission, using polarized synchrotron radiation, from the system Ni(001) +CO shows two chemisorption peaks which exhibit strong variations in amplitude depending on polar angle of emission and optical polarization. The behavior is in agreement with a recent calculation of angular photoemission from oriented CO molecules, supporting the model of undissociated, "end-on" bonding with the molecular axis perpendicular to the surface, and thus demonstrates that angle-resolved photoemission may give adsorbate goemetries.

We have observed resonant exciton contributions to the nonlinear optical susceptibilities of CdS when the fundamental frequency was tuned through exciton resonances. We show that our data are in good agreement with quantum-mechanical calculations while the anharmonic oscillator model gives incorrect resonance denominators. We also show that selection rules for exciton contributions are different depending on whether the fundamental frequency or generated second-harmonic frequency is in resonance with exciton states.

We report spectral line-shape measurements of a singular dynamic central peak associated with a structural phase transition. The quasieleasic light scattering spectra obtained in ferroelectric lead germanate exhibit clear departures from mean-field theory.

The Mahan, Nozières, De Dominicis theory of x-ray thresholds is extended to include exchange effects which are found to reduce threshold exponents and increase the orthogonality index. For the lithium $K$ edge this represents an important previously neglected feature. Results of detailed numerical calculations of threshold exponents for Li are presented which differ considerably from previous values and which are in better agreement with edge data.

Analysis of newly detected luminescence lines in germanium indicates that two-phonon recombination processes in indirect-gap semiconductors are insensitive to selection-rule constraints, although such restrictions generally play a crucial role in the optical properties of semiconductors. The two-phonon replicas of electron-hole recombination lines are found to be constituted from well-defined groups of phonons whose momenta differ from points of high symmetry in the Brillouin zone.

A theory of correlation between the elastic and magnetic properties of transition-metal based ferromagnetic glassy alloys is developed. The specific Young's modulus, $\frac{E}{\rho }$, is shown to be related to the thermal average of the effective spin, $〈S〉$, as $\frac{E}{\rho }=V_E^{}{}_{}{}^{02}+K{〈S〉}^2$, where $E$ and $\rho$ are Young's modulus and the density, respectively, and $V_E^{}{}_{}{}^{02}$ and $K$ are constants related to the properties of the materials. The change of $\frac{E}{\rho }$ with composition in ${\left({\mathrm{Fe}}_{1-x}{M}_x\right)}_{80}{B}_{20}$ glasses ($M$ representing Co or Ni) agrees well with the present model.

Here the results are reported of a neutron-diffraction study of the critical behavior of $M$ and $M_{\mathrm{s}\mathrm{t}}$ along the line of critical points in the magnetic phase diagram of the metamagnet ${\mathrm{CsCoCl}}_3$ · 2${\mathrm{D}}_2$O. It is shown that the critical behavior of $M$ and $M_{\mathrm{s}\mathrm{t}}$ can each be represented by a single critical exponent up to the multicritical point, where a breakdown of smoothness and crossover is observed.

An energy-focused time-of-flight atom probe has been used in a search for highly charged ions of field-evaporating $5d$ transition metals. Maximum abundances of mostly new ion species were 1×${10}^{-5\mathrm{}}$ for ${\mathrm{W}}^{6+}$, 2.3×${10}^{-4\mathrm{}}$ for ${\mathrm{W}}^{5+}$, 2×${10}^{-4\mathrm{}}$ for ${\mathrm{Ta}}^{5+}$, 6.7×${10}^{-3\mathrm{}}$ for ${\mathrm{Hf}}^{4+}$, 2×${10}^{-2\mathrm{}}$ for ${\mathrm{Re}}^{4+}$, 5×${10}^{-5\mathrm{}}$ for ${\mathrm{Ir}}^{4+}$, 5×${10}^{-2\mathrm{}}$ for ${\mathrm{Pt}}^{3+}$, and 6×${10}^2$ for ${\mathrm{Au}}^{3+}$. Thus for the group Hf, Ta, and W, all $6s$ and $5d$ electrons may be coming off, while for Re to Au, at most only the $6s$ electron(s) and one pair of $5d$ electrons are removed.

The organic charge-transfer salt N-methyl-phenazinium tetracyanoquinodimethanide is described in terms of a one-dimensional disordered Hubbard model. For low temperatures and small transfer integrals this model reduces to a disordered Heisenberg anti-ferromagnet. The magnetic susceptibility of the latter can be described adequately by the disordered classical Heisenberg model. Fitting of susceptibility data by the one-dimensional classical Heisenberg model provides us with values of $t=0.055\mathrm{}$ eV, $U_{\mathrm{eff}}=0.130\mathrm{}$ eV, and $\sigma =0.136\mathrm{}$ eV for the parameters of the original Hubbard Hamiltonian.

We have measured the isomagnetic temperature dependence of the anomalous Hall effect that arises from the asymmetric scattering of the conduction electrons by the localized moments in two alloys of Au containing ∼8.1 at.% Fe or Mn. The experiment is evidently a sensitive way to detect the magnetic rearrangement in a spin-glass. It shows clearly the spin-glass transition and features that are tentatively ascribed to the presence of magnetic clusters and "loose spins."

We outline a new theory of the electronic structure of inversion layers in many-valley semiconductors which includes broken-symmetry many-body effects. This theory describes charge-density waves which account for the experimentally observed (i) degeneracy and (ii) occupancy of the electron levels, and (iii) the high cyclotron mass in the (111) surface $n$-type inversion layers of silicon. It reduces to earlier theories at the Si (100) surface, where theory and experiment are in good agreement.

Recently I argued that Yang's pure-space equations must be supplemented by restrictions on the class of allowable space-times. I now consider time-dependent solutions of the pure-space equations and prove the violation of Birkhoff's theorem. Time-dependent spherically symmetric solutions are displayed, as well as solutions representing plane gravitational waves. The suggestion is made that pure spaces are unphysical and Yang's theory requires the explicit presence of a source in vacuum, in contrast to general relativity.

We report measurements of changes in the dielectric constant $\epsilon$ of ${\mathrm{SF}}_6$ along a near critical isochore. We find an anomalous increase in $\epsilon$. The amplitude of the anomaly is about 10 times larger than the one predicted by current theories, which assume a constant polarizability.

We have measured the inclusive cross section for the reactions $p+n\to p+X$ and ${\pi }^{+}+n\to p+X$ at 100 GeV/c in the kinematic region $\mathrm{}\left|t\right|<1.0\mathrm{}$ ${\mathrm{GeV}}^2$. The data were obtained from an exposure of the Fermilab 30-in. deuterium-filled bubble chamber to a tagged positively charged beam. The differential cross sections for these reactions are observed to scale in the ratio of the $\mathrm{pn}$ and ${\pi }^{+}n$ total cross sections and to be consistent with the predictions of a Reggeized one-pion-exchange model.

The Argonne effective mass spectrometer has been used for a high-statistics study of ${\pi }^{-}+p\to K^{-}+K^{+}+n \left(110000\mathrm{} \mathrm{events}\right)$ and ${\pi }^{+}+n\to K^{-}+K^{+}+p \left(50000\mathrm{} \mathrm{events}\right)$ at 6 GeV/c. Comparison of the two reactions allows isolation of the interference between $K^{-}{K}^{+}$ states of differing isospin. We observe $f-A_2^{}{}_{}{}^0$, $f^{\prime }-A_2^{}{}_{}{}^0$, and $f-f^{\prime }$ interferences in the $Y_4^{}{}_{}{}^0$ moment and find $f^{\prime }$ production to have a substantial contribution from some mechanism besides pion exchange. New values for the $f^{\prime }$ mass, width, and branching ratio into $\pi \pi$ are presented.

We report measurements of the inclusive electroproduction reaction $e+p\to e+p+X$ for protons produced between 100° and 150° in the virtual-photon-target-proton center-of-mass system. Data were taken at the ($W,Q^2$) points (2.2 GeV, 1.2 ${\mathrm{GeV}}^2$), (2.2, 3.6), (2.65, 1.2), (2.65, 2.0), (2.65, 2.8), (2.65, 3.6), (3.1, 1.2), and (3.1, 2.0). The invariant structure function is studied as a function of $W$, $Q^2$, $x_T$, $p_T^{}{}_{}{}^2$, and $M_X^{}{}_{}{}^2$.

We construct a unitary Deck model with coupled $K^{*}\pi$ and $K\rho$ channels, including only one resonance in the $Q$ region. Adjusting the resonance parameters, we achieve a satisfactory description of the experimental phase variations and the structure in the mass spectra. The resonance is determined to belong to the $J^{\mathrm{PC}}=1^{+-}$ SU(3) octet, and is thus the $Q_B$. The relative coupling strength $\frac{K^{*}\pi }{K\rho }$ is $\sim \frac{2}{3}$.

The quantities $A_y$ and $P^y$ were remeasured for $E_p<4\mathrm{}$ MeV in the reaction ${}_{}{}^3{}_{}{}^{}H{(p,n)}^3\mathrm{He}$. Although our $A_y$ data confirm previous data, our $P^y$ values are appreciably larger than earlier results and in fact agree well with those for $A_y$. Elimination of the previously reported $A_y-P^y$ difference has important consequences. Charge-symmetry-breaking effects must be small or nonexistent in this reaction; and the previously required $f$-wave admixture to the lowest $J^{\pi }=2^{-}$ state of ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ is no longer necessary.

Large isotope effects in the $K$ x-ray yields from collisions of ${}_{}{}^A{}_{}{}^{}\mathrm{Ne}_{}^{+}{}_{}{}^{}$ - ${}_{}{}^B{}_{}{}^{}\mathrm{Ne}$ ($(A,B=20,22)$) have been observed. For slow collisions (relative velocities $\sim \frac{1}{3}$ a.u.) the $K$ x-ray yields do not scale well with either relative velocity or center-of-mass energy, whereas at higher collision velocities, the yields appear to scale well with relative velocity.