In the presence of an ac sound field, we have found stable states of zero flow between two baths of liquid helium connected by a small orifice which we believe are the same as those which had been previously identified as the ac Josephson effect. We show that these states are not Josephson states.

The avalanche growth rate of C${\mathrm{O}}_2$-laser—induced gas breakdown in a magnetic field has been studied by measuring the time elapsed between the initiation of the laser pulse and the onset of observable breakdown effects such as a sharp decrease of laser transmission through the gas. The main features of the observed magnetic field dependence of this time difference can be explained in terms of the inhibition of electron diffusion from the laser focal region.

The dynamic critical behavior of a continuum analog of the kinetic Ising model is studied using a generalization of Wilson's expansion methods. Results are found which disagree with the mode-mode coupling approach and the conventional (Van Hove) theory.

Quantitative estimates are made of the maximum value of the superconductive transition temperature $T_c$ attainable through combining electron-exciton interactions with electron-phonon interactions in metal-semiconductor sandwiches. Because of covalent instabilities, it is argued that no enhancement of $T_c$ can be expected if the initial value of $T_c$ in the pure metal was greater than 5°K.

The temperature dependence of the dc conductivity and the room-temperature optical absorption were measured for a series of vacuum-evaporated amorphous Si films. Both properties were strongly dependent on annealing up to about 400°C, but insensitive from 400 to 600°C. We find a $\ln \left(\sigma \sqrt{T}\right)\propto T^{\frac{-1\mathrm{}}{4}}$ behavior which gives reasonable parameters for Mott's localized-state model for conductivity by hopping only for films that have been annealed at least to 400°C.

Luminescence spectra of ${\mathrm{Cu}}_2$O excited at various temperatures by a tunable dye laser showed no evidence of the existence of excitonic molecules (or biexcitons) as suggested recently by Gross and Kreingol'd. A pair of previously unreported peaks with an exceptionally strong temperature dependence has been observed below 3°K.

Evidence is presented from neutron diffraction measurements for the existence of an amorphous spin-polarization distribution in a sputtered rare-earth-iron alloy of composition 33 at.% Tb, 67 at.% Fe.

Measurements of the spin polarization of photoelectrons from (100) surfaces of "pure" and doped EuO monocrystals reveal a paramagnetic surface sheet existing at temperatures far below the Curie temperature of the bulk. The extra electrons that are introduced on doping produce an increase of the molecular field in the surface. ${\mathrm{Eu}}_{1-x}{\mathrm{La}}_x\mathrm{O}$ crystals exhibit the highest degree of spin polarization (∼ 80%) observed in a photoemission experiment so far.

The multiple-reaction correction of Halpern, Drake, et al. to neutron radiative cross-section measurements is shown to be important also below 14 MeV, with the consequence that previously measured uncorrected (or unrestricted to first-chance capture only) ($n,\gamma$) cross sections above the first level are in error, being from about 1% to a factor of more than 10 too high.

We have analyzed the region of $K^{*}\mathrm{}\left(890\right)\mathrm{}$ in terms of $s$ and $p$ waves, using a formula for the mass-dependent angular distributions and imposing the positivity conditions on the full density matrix which includes the $s-p$ interference effect. From this analysis we show that, independent of the production dynamics, the experimental data can accommodate little, if any, narrow-width $s$-wave state in the $K^{*}\mathrm{}\left(890\right)\mathrm{}$ region.

A quark-model state ${}_{}{}^1{}_{}{}^{}F_3^{}{}_{}{}^{}$ is assigned in the presumably $Q$-like $K\pi \pi$ peak around 2.16 GeV. The resulting Regge trajectory in linear and exchange degenerate and has an anomalous slope, ${\alpha }^{\prime }\simeq 0.67$ Ge${\mathrm{V}}^{-2\mathrm{}}$. The fundamental significance of this nonparallelism is pointed out, and measurements are proposed to confirm the assignment.

We report measurements of the nuclear magnetic susceptibility of absorbed ${\mathrm{He}}^3$ at temperatures down to 50 mK using pulsed nuclear resonance. In broad agreement with previous measurements at higher temperatures, it exhibits smaller antiferromagnetic deviations from Curie's law than bulk liquid. The deviations are too large to be explained by a statistical layer model which is adequate at higher temperatures, indicating that the adsorbate, or part of it, is more nearly ferromagnetic than the model predicts.

The drift-wave instability due to an electron temperature gradient opposite to the density gradient is analyzed as a possible explanation for the observed anomalous skin effect in tokamaks.

We present a theoretical study of formation and destruction of magnetic surfaces in toroidal systems. As applied to levitrons the theory agrees with the numerical results.

A tokamak discharge of $T_e$ ∼ 1 keV is produced in the absence of conducting-wall magnetohydrodynamic stabilization, and then compressed in major radius by a factor of 2.3 in a static toroidal field. Measurements are reported on the resultant rise of density, temperature, and plasma current.

The time dependence of current and temperature in a spatially uniform plasma, and the nature of the ion heat sink as a function of density and ion temperature, have a profound effect on the stability of ion-acoustic waves with wavelengths much longer than the electron mean free path.

Ultraviolet photoemission measurements have been used to determine the electronic structure of two of the layered transition-metal dichalcogenides, Nb${\mathrm{Se}}_2$ and Mo${\mathrm{S}}_2$, which show trigonal prismatic coordination. Although the electronic structures of the two materials have rather different character, the results are consistent with a loose interpretation of a rigid-band model. The observed energy of the Fermi level above the valence-band maximum in Mo${\mathrm{S}}_2$ indicates that the splitting between the nonbonding $d$ bands is in excess of 1 eV, a value considerably larger than some previous suggestions.

A theorem is presented which establishes an isomorphism between the eigenvalues of Keating's model Hamiltonian for the vibrations of tetrahedrally bonded solids, in the limit in which bond-bending forces are zero, and those of a simple "one-band" Hamiltonian which has been found useful in understanding features of the electronic density of states of amorphous semiconductors. We explain the similarity of the phonon spectra of amorphous and crystalline group-IV semiconductors, demonstrated in various recent experiments.

We present experimental valence-band optical densities of states for Si, Ge, and GaAs obtained from ultraviolet photoemission energy distribution curves obtained at about 25 eV of photon energy. The width of the upper two valence bands of Si and the positions of several energy-band minima for the second and third valence bands of Ge and GaAs have been accurately determined. Comparing the above-mentioned band edges with theoretical calculations based on optical data, we find good agreement for Si and observe significant differences for Ge and GaAs.

The frequency- and temperature-dependent surface impedance of a Kondo system Cu:Fe has been measured in the far infrared using sensitive transmission-line techniques. Good agreement is found with our numerical calculation of the surface impedance from the Nagaoka equations provided that coherent potential scattering effects are included.