The discovery of a charge-density wave (CDW) in $\alpha$-U at ∼43 K is reported. The mode corresponds to the condensation of a longitudinal-optic phonon near $\overrightarrow{\mathrm{q}}=[\frac{1}{2}, 0, 0]$ in which the atoms are displaced by ∼0.006 ÅA from their special positions. Large precursor effects are seen in the phonon spectra. The wave vector of the CDW is related to that of the fundamental lattice in a rather complex way, which is discussed in terms of discommensurations between the CDW (${\alpha }^{\prime }$ phase) and the primary $\alpha$ phase.

With use of diamond-anvil x-ray techniques a reversible, first-order phase transition has been observed from Stage-2 K${\mathrm{C}}_{24}$, in both single-crystal and highly oriented pyrolytic graphite forms, to a Stage-3 structure of K${\mathrm{C}}_{24}$ at ∼2 kbar and 300 K. Coexistence of Stage-2 and -3 sequences is observed over the pressure range 2-12 kbar. The transition is accompanied by a 2×2 superlattice ordering of the potassium layers. The results are in qualitative agreement with a recent theory in which staging is driven by long-range elastic interactions.

A highly precise method for locating the valence-band edge in x-ray photoemission spectra is reported. The application to measuring semiconductor interface potentials is discussed. X-ray photoemission-spectroscopy experiments on Ge and GaAs(110) crystals have given Ge $3d$, Ga $3d$, and As $3d$ core level to valence-band edge binding-energy differences of 29.55, 18.81, and 40.73 eV to a precision of ±0.02 eV. For illustration, the valence-band discontinuity at an abrupt Ge/GaAs(110) heterojunction is determined to be 0.53±0.03 eV.

Existing data at high pressures of Berman, Binzarov, and Kurkin show that the various metallic forms of Te have considerable variation of their superconduction temperatures, $T_c$, depending upon the phase and the pressure; the observed $T_c\text{'}\mathrm{s}$ ranged from 2.5 to 4.3°K over the pressure span of 40 to 150 kbar. The present experiments, with use of a diamond-tipped apparatus with a cryogenic arrangement, have extended the pressure range to over 300 kbar. The results indicate that a new metallic phase develops in the 150-180-kbar region, which has a higher $T_c$ of about 6.5°K.

Substitutional nitrogen donors in single-crystal silicon have been produced by pulsed ruby-laser annealing of amorphous silicon created by 4×${10}^{15}$ 160-keV (0.995 ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}_{}^{+}{}_{}{}^{}$ + 0.005 ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}_2^{+}{}_{}{}^{}$)/${\mathrm{cm}}^2$. EPR measurements indicate that these isolated N donors are trigonally distorted as a result of Jahn-Teller effects and give rise to deep donor levels with an ionization energy of ≈ 0.58 eV. They are similar in electronic structure to N donors in diamond and appear to undergo structural modification for $T\gtrsim 430°$C.

For neutron-irradiated Mo containing voids, a temperature dependence of the positron trapping intensity is observed between 9 and 400 K. Shallow traps are responsible and have an activation energy of 0.1±0.05 eV. Deep microstructural traps are identified as small loops and dislocation tangles are presumed to be the shallow traps. Evidence of positronium formation in the voids at high temperature is presented.

Antiferromagnetic ordering in insulating transition-metal compounds is explored in the magnetic transition state scheme proposed by Slater. A model is developed in the framework of a spin-polarized, one-electron, self-consistent, molecular-cluster theory. Using a discrete variational method with the necessary constraints on molecular-orbital occupation numbers and the potential field, we determine the spin-flip energy and hence the Néel temperature $T_{\mathrm{N}}$ for NiO which is in excellent agreement with experiment.

It is shown that the beta decay of quarks in degenerate quark matter is kinematically allowed. The resulting neutrino emissivity is dramatically larger than that of neutron matter and comparable to that of matter with pion condensate. Thus a star with a quark-matter core would cool at a rate comparable to that for a star with a pion-condensed core, and much faster than an ordinary neutron star.

It is shown that the energy flux, ${\dot{E}}_T$, from quark matter in "quark stars" due to the simple URCA process is roughly comparable to that from pion condensates even when quark-quark interaction (QQI) effects are ignored. The form of ${\dot{E}}_T$ is then independent of the ambiguous electron density and the effective gluon coupling in the "quark star" and accounts for the neutrino in momentum conservation. It is concluded that one need not invoke QQI to explain the recent null x-ray detection of "neutron"-star surface temperatures by the presence of a quark core.

It is pointed out that for very massive particles in our universe there exist stringent bounds on their possible properties. New experiments which will search primarily for proton decay can usefully extend the domain of these bounds.

The muonic isomer shifts of three transitions between levels of ${}_{}{}^{207}{}_{}{}^{}\mathrm{Pb}$ have been measured. Evidence is found for an interaction between the anomalous magnetic moment of the neutron hole and the electric field of the $1s$ muon. The agreement obtained between predicted and measured values removes the necessity to postulate a more serious reaction in the proton core to changes in the state of the valence neutron than predicted by the weak coupling model.

A technique is presented which can be used to compute the complex poles of the resolvent (defined as resonances) directly by use of a square-integrable basis without a coordinate rotation and without explicitly imposing a boundary condition such as a Siegert resonant boundary condition. Such a technique is directly applicab$\stackrel{\mathrm{`}}{\mathrm{l}}$e to all phenomena which can be put in the form of a resonance such as photoionization, field ionization, and electron resonances in atoms and molecules.

By use of neutron correlation spectroscopy a soft mode has been found for the Rayleigh-Bénard instability with frequency $\omega \sim {(\frac{R}{R_c}-1)}^{0.5}$, $R$ denoting the Rayleigh number. The power spectrum shows periodic states split into a narrow band, and some low, perhaps solitary, states. Guided by the autocorrelation function the main features are modeled by phase modulation of the soft mode by the slower modes. A connection is made to the central-mode problem in structural phase transitions.

The previous theoretically predicted diverging confinement time of a high-$\beta$ linear sharp plasma column as $\beta \to 1$ is removed by including the magnetic tension effect near the column throats. This result explains our own simulation as well as those of Brackbill, Menzel, and Barnes, and is in good agreement with experimental values. The confinement time $\tau$ of a plasma with thickness $a$ and length $L$ at $\beta =1\mathrm{}$ is found to be $\tau =\frac{3}{4}{\left(\frac{3}{2\pi }\right)}^{\frac{1}{2}}\left(\frac{L}{2c_S}\right){\left(\frac{L}{a}\right)}^{\frac{1}{2}}$.

Measurements are reported of short-pulse (100 psec), 1.06-μm laser backscatter from a high-pressure nitrogen gas target. Spectral measurements clearly show the expected Brillouin red shift. The backscatter fraction saturated at ∼40% at 2×${10}^{15}$ W/${\mathrm{cm}}^2$ and what appears to be multiple Brillouin scattering in a long-gradient-length plasma is observed.

On the basis of systematic low-temperature expansions "to all orders", it is shown that an infinite sequence of spatially modulated commensurate phases, with wave vectors $\frac{\pi j}{\mathrm{}(2j+1)a}$ ($j=0, 1, 2, \dots$), occurs in simple, anisotropic Ising models with nn couplings $J_0$, $J_1>0\mathrm{}$, in between spin-½ layers, and competing nnn interlayer couplings $J_2=-k{J}_1$ along one axis. The free energies, interfacial tensions, and phase boundaries are found for low $T$ in $d>\mathrm{}2\mathrm{}$ dimensions.

A novel technique is described for time-resolved Raman scattering for studying the dynamics of nonequilibrium excitations on a picosecond time scale. The generation and the decay of nonthermal LO phonons in GaAs is measured, and ${\tau }^{\prime }=7\mathrm{}\pm 1$ ps is obtained for the relaxation time of the phonon population at 77 K.

Higher-order diffraction from the smectic-$A$ liquid-crystalline phase of cyanooctylbiphenyl (COB) has been measured. The dominant short-range disorder, described by the relative intensities, is in agreement with our estimate of the smectic order parameter based on McMillan's mean-field theory.

A population analysis of the one-electron eigenfunctions of random-network models of amorphous silicon shows fluctuations of the net atomic charge of about 0.2 electron units rms. The majority of the charge is calculable from a linear function of the deviations of first-neighbor distance and of the interbond angle from their values in the crystal.

The magnitude, anisotropy, and temperature dependence of the $H_{c2\mathrm{}}$ for Nb are calculated from the underlying electronic structure. Excellent agreement between theory and experiment results if experimental Fermi velocities are used and if Fermi-velocity-anisotropy, strong-coupling, and impurity effects are included.