This Letter reports the first observation of spin-split Landau levels in graphite. These are observed in both natural single crystals and in pyrolytic samples. Experimental splittings are compared with the theory of McClure and Yafet. Discrepancy between theory and experiment is partially accounted for by large shifts in the Fermi energy with field.

A pronounced decrease in the TO Raman scattering efficiencies of CdS has been observed as the incident photon energy approaches the direct-energy gap. Previous resonant Raman measurements have shown only monotonically increasing efficiencies. A decrease of the $F_{2g}$ mode in Si has also been observed as the resonance with the indirect-energy gap is approached. The observed decreases in CdS and Si can both be accounted for by extending Loudon's theory to include a destructive interference between the resonant and nonresonant contributions to the Raman scattering amplitudes.

The theories of $A^N{B}^{8-N}$ semiconductors and salts due to Phillips and Van Vechten and to Wemple and DiDomenico are compared and their similarities discussed. The dispersion energy is found to be proportional to ionicity. A simple operational definition of ionicity, based on experimentally determined moments of ${\epsilon }_2\left(\mathcal{E}\right)$, is proposed. This definition can potentially be extended to provide a useful scaling parameter for other classes of materials such as metals and intermetallic compounds.

A direct observation of ferroelectric domains in x-irradiated K${\mathrm{H}}_2$As${\mathrm{O}}_4$ and K${\mathrm{D}}_2$As${\mathrm{O}}_4$ using electron paramagnetic resonance (EPR), and in the case of K${\mathrm{H}}_2$As${\mathrm{O}}_4$ also using electron-nuclear double-resonance (ENDOR), is reported. The nature of the observed domain splittings and consequently the effects of an externally applied electric field on the EPR and ENDOR spectra are explained. Moreover, the higher resolution possible with the ENDOR technique, has, for the first time, made it possible to use protons as microscopic probes and to identify in general lines from individual domains in all directions.

A sum rule is discussed for the isoscalar part of form factors describing monopole excitations of nuclear levels by inelastic electron scattering. A model is subsequently introduced for the form factor of the first excited state in ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ which compares reasonably well with recent experimental data.

The (${}_{}{}^3{}_{}{}^{}\mathrm{He},t$) reaction on ${}_{}{}^{64,66}{}_{}{}^{}\mathrm{Zn}$ and ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$ to the $0^{+}$ analog and antianalog states has been studied at 35 MeV. The angular distributions for the $T_{<}{0}^{+}$ states show an $L=1\mathrm{}$ shape, implying a need for modifications in the conventional description of (${}_{}{}^3{}_{}{}^{}\mathrm{He},t$) reactions.

The expansion of the solar wind is likely to cause low-energy cosmic-ray particles to lose a significant fraction of their energy in the interplanetary medium. It is shown that because of this effect, most of the protons observed below ∼100 MeV and alpha particles below ∼60 MeV/nucleon originate at higher energies, making it impossible to sample directly the interstellar spectra at these energies.

We have measured the asymmetry of the cross section for $\gamma p\to {\pi }^{+}n$ from a polarized target at 5 and 16 GeV. The range of four-momentum transfer was $0.02<~-t<~1.0$ Ge${\mathrm{V}}^2$. The ${\pi }^{+}$ mesons were produced in a polarized butanol target and detected with the Stanford Linear Accelerator Center $20-\frac{\mathrm{GeV}}{c}$ spectrometer. A sizable asymmetry was found at both 5 and 16 GeV, a typical value being -0.6 near $-t=0.3\mathrm{}$ Ge${\mathrm{V}}^2$. A small amount of data on the asymmetry of other photoproduction processes was also obtained.

Two new sharp absorption systems have been observed in the excited-state electronic spectrum of ruby. Both systems originate from the lowest spin doublet state of chromium ion ${}_{}{}^2{}_{}{}^{}E$ and are found at 15 006 and 27 465 ${\mathrm{cm}}^{-1\mathrm{}}$ above the originating level. Both of the sharp systems are completely polarized perpendicular to the principal optic axis.

Results of computer simulations of electrostatic "anomalous resistivity" are reported. One- and two-dimensional plasma simulations were performed in which an external (nonself-consistent) spatially constant electric field was imposed to drive a current in the plasma. In these calculations the electron distribution is subject to collective runaway with beaming and thermal energy increasing about equally.

We have obtained a thermodynamic state of thin helium films which permits precision measurements of their properties. Third-sound resonances indicate a cutoff for the propagation of third sound in these films. This cutoff is accompanied by an exponential rise in the dc thermal resistance of the helium film which indicates the formation of high-energy excitations of 0.08 eV. The dissipation at resonance is consistent with Bergman's theory for hydrodynamic dissipation of third sound.

From measurements of the velocity of second sound and the osmotic pressure the inertial mass of ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ in superfluid ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ has been obtained as a function of temperature and concentration. The results indicate that (i) the ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ quasiparticle spectrum is not quite parabolic and (ii) part of the quasiparticle effective interaction is velocity dependent or "non-local" and resembles the interaction of spheres moving through a nonviscous classical fluid.

An exact theory of plasma filaments observed in coaxial accelerators is derived from a steady-state ($\frac{\partial }{\partial t}=0\mathrm{}$) description of the three-dimensional flow of deuterium plasma. Ionization and recombination reactions are considered. Magnetic structure of the filaments (bundles of helical field lines), density distributions, and flow field fit the experimental evidence.

Measurement of the tilt angle of the smectic $C$ phase of terephthal-bis-($4-n-\mathrm{b}\mathrm{u}\mathrm{t}\mathrm{y}\mathrm{l}\mathrm{a}\mathrm{n}\mathrm{i}\mathrm{l}\mathrm{i}\mathrm{n}\mathrm{e}$) has been made using conoscopic observation and circularly polarized light. The new phenomenon of a smectic $C$ phase with a temperature-dependent tilt angle is reported. Terephthal-bis-($4-n-\mathrm{b}\mathrm{u}\mathrm{t}\mathrm{y}\mathrm{l}\mathrm{a}\mathrm{n}\mathrm{a}\mathrm{l}\mathrm{i}\mathrm{n}\mathrm{e}$) has nematic, smectic $A$, smectic $C$, and smectic $B$ liquid-crystalline phases. The tilt angle of smectic $C$ changes from 0° at the smectic-$A-\mathrm{s}\mathrm{m}\mathrm{e}\mathrm{c}\mathrm{t}\mathrm{i}\mathrm{c}-C$ transition to approximately 26° at the $\mathrm{s}\mathrm{m}\mathrm{e}\mathrm{c}\mathrm{t}\mathrm{i}\mathrm{c}-C-\mathrm{s}\mathrm{m}\mathrm{e}\mathrm{c}\mathrm{t}\mathrm{i}\mathrm{c}-B$ transition temperature.

The low-temperature behavior of all the quantum cluster integrals $b_l$ is calculated by using a perturbation scheme in which a hyperspherical representation for the many-body problem is used. Definitions of the usual equations for the $T$, $R$, and $S$ scattering matrices as well as the many-body eigenphase shift are given. The technique for calculating the energy eigenvalues is outlined and a relationship between the level shift and the eigenphase shift is given. It is found that for an everywhere-finite short-ranged potential without bound states, $b_l$ behaves as a polynomial in $\lambda =\frac{h}{{\left(2\mathrm{}\pi mkT\right)}^{\frac{1}{2}}}$ in the low-temperature limit.

Experimental three-axis spectrometer data of critical neutron-scattering data from Fe are reanalyzed and compared with the recent theoretical prediction by Résibois and Piette. The reason why the spin-diffusion parameter did not obey the prediction of dynamical scaling theory is indicated. Double-axis spectrometer data have previously been interpreted in terms of a non-Lorentzian susceptibility $\chi \mathrm{}\left(q\right)\mathrm{}$. It is shown that with proper corrections for the inelasticity of the scattering the data are consistent with a Lorentzian form of $\chi \mathrm{}\left(q\right)\mathrm{}$.

EPR spectra of $\mathrm{F}\mathrm{e}-V_{\mathrm{O}}$ pairs were used to study how the order parameter of SrTi${\mathrm{O}}_3$ varies with uniaxial stress applied to a (111) face. A second-order cubic-trigonal phase boundary appears above the stress-free transition temperature $T_a$. A first-order tetra-gonal-trigonal phase boundary is found below $T_a$. An independently determined Landau potential describes the results.

A stable dc supercurrent with an extended negative-resistance region has been observed in the $I-V$ characteristics of very small Josephson tunnel junctions. This supercurrent and its response to external noise are in accord with recent theoretical predictions of Ivanchenko and Zil'berman.

Superconductivity has been observed in the hydrides and deuterides of thorium with H-or D-to-metal atom ratios of 3.6 to 3.65. Transition temperatures fall in the range from 8.05 to 8.35 K. These materials are apparently type-II superconductors with $H_{c2\mathrm{}}$ of the order of 25-30 kG at 1.1 K. There is no evidence for an isotope effect within the limits of experimental uncertainty.

An excess tunneling current due to order-parameter fluctuations has been found in tin—tin oxide—lead junctions just above the transition temperature of tin. Details of the variation of the excess current with voltage, magnetic field, and temperature are in agreement with a calculation by Scalapino in which the excess-current voltage characteristic is a direct measure of the frequency— and wave-number—dependent pair susceptibility characteristic of the superconducting transition. Estimates of the pair relaxation frequency in tin based on the data are 50% greater than theoretical predictions.