Changes in the sign of the longitudinal magnetoresistance as a function of applied magnetic and electric fields are observed in single crystals of $p$-type Cd${\mathrm{Cr}}_2$${\mathrm{Se}}_4$. A phenomenological theory for the non-Ohmic behavior associated with spin-wave-carrier interaction is developed, and its comparison with the experimental results indicates the existence of spin-wave amplification by the drifting carriers. All the experimental results can be explained in terms of spin-wave-carrier interaction and spin-disorder scattering.

Low-field (third-derivative) electroreflectance spectra taken on fully depleted space-charge regions are shown to be linear in the modulation potential and free from experimentally induced line-shape distortions due to modulation wave-form, dc bias, or barrier-potential effects. Using a metal-semiconductor (Schottky diode) configuration, accurate threshold energies of the ${E_0}^{\prime }$ triplet of Ge are obtained. The observed spin-orbit-splitting energy of the valence band confirms that the highest transition also occurs at $\Gamma$.

A self-consistent second-order Green's-function theory of a one-dimensional Heisenberg antiferromagnet, exhibiting spin waves without long-range order, is shown to yield qualitatively different results than a hybrid version treated by Richards. Comparison with exact and computer solutions for energy shows that the self-consistent solution represents a substantial improvement in local spin behavior at low temperatures. Long-range spin behavior at low temperatures is not correctly predicted by the self-consistent theory.

The inelastic-electron-scattering form factors in ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$ for the $E0\mathrm{}$ transitions from the $0^{+}$ ground to the 6.72- ($0^{+}$ and 7.20-MeV ($0^{+}$) states are presented. The monopole matrix elements and transition charge radii are extracted from the form factors.

Proton spin-flip in ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}(p, p_1){}_{}{}^{12}{}_{}{}^{}\mathrm{C}(2^{+}, 4.44 \mathrm{MeV})$ has been measured in the region of the narrow ${\frac{3}{2}}^{-}$ resonance near 8.18 MeV proton energy. Large interference is observed between the resonant and background spin-flip. The configuration of the resonant state in terms of a proton coupled to the $2^{+}$ level of ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ was obtained from a model-independent analysis. The data are sufficient to allow a self-consistent test of the theoretical formulation.

We report the first results of a Bevatron heavy-ion experiment on the inclusive spectra of isotopically identified nuclei, $3<~Z<~7$, produced by the fragmentation of 29-GeV ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$ ions in carbon and hydrogen. The preliminary values of the partial differential cross sections at 0° give evidence that the modes of fragmentation of ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$ projectiles are independent of the target nucleus.

Time-differential attenuation coefficients of the $\gamma$-ray angular distribution of Coulomb-excited Hf nuclei recoiling into vacuum have been measured using a plunger technique. The data have been interpreted in terms of a new model which assumes a stochastic process with Gaussian probability distribution of the perturbing magnetic field strengths and arbitrary correlation times. Reasonable fits to all existing applicable measurements are obtained with a correlation time considerably larger than previously assumed.

A crossover is observed in the differential cross sections for the inelastic processes $K^{0}p\to Q^{0}p$ and ${\overline{K}}^{0}p\to {\overline{Q}}^{0}p$, from ${K_L}^{0}p$ data in the momentum range from 4 to 12 GeV/c. This phenomenon is evidence that Regge, in addition to Pomeranchukon, exchanges contribute to $Q$-meson production.

Dramatic behavior is observed in the correlation between ${\pi }^{-}\text{'}\mathrm{s}$ as a function of their rapidity separation $\Delta y$. At small $\Delta y$, the $\pi \text{'}\mathrm{s}$ are strongly positively correlated. At large $\Delta y$ the correlation length is measured to be 0.52±0.03. Particle-production and particle-particle correlations are distinguished and studied.

We have measured the linear polarization correlation of the photons emitted in an atomic cascade of calcium. It has been shown by a generalization of Bell's inequality that the existence of local hidden variables imposes restrictions on this correlation in conflict with the predictions of quantum mechanics. Our data, in agreement with quantum mechanics, violate these restrictions to high statistical accuracy, thus providing strong evidence against local hidden-variable theories.

Higher members of ${}_{}{}^1{}_{}{}^{}P$ autoionization states of He are calculated in the elastic scattering region and compared with experiments. The third resonance series was previously believed to be absent from the observed spectrum of Madden and Codling. In the present work, we find that these energy levels lie very close to some other states which were identified. By calculating the oscillator strength, we find that these "missing states" contribute significantly to the observed line intensity.

Laser-induced fluorescence line narrowing has been observed for the first time in a nonresonantly excited rare-earth system. Excitation with the 4727-Å $A^{+}$ line into the ${}_{}{}^4{}_{}{}^{}G_{\frac{11}{2}}^{}{}_{}{}^{}$ level of ${\mathrm{Nd}}^{3+}$ in glass results in narrowing of transitions from the ${}_{}{}^4{}_{}{}^{}F_{\frac{3}{2}}^{}{}_{}{}^{}$ to both the ${}_{}{}^4{}_{}{}^{}I_{\frac{9}{2}}^{}{}_{}{}^{}$ ground manifold and the ${}_{}{}^4{}_{}{}^{}I_{\frac{11}{2}}^{}{}_{}{}^{}$ excited manifold. The concentration dependence of the line narrowing provides information regarding resonant ion-ion energy transfer within the inhomogeneously broadened system.

The specific heats of ${\mathrm{He}}^3$ and ${\mathrm{He}}^4$ films adsorbed on exfoliated graphite have been measured between 0.04 and 4.2 K, for fractional monolayer coverages between 0.25 and 0.63. ${\mathrm{He}}^3$ films show anomalies around 0.1 K that are absent in the ${\mathrm{He}}^4$ results. A possible explanation is given in terms of spin ordering of the ${\mathrm{He}}^3$ atoms.

We have studied the production, destruction, and lifetimes of the ${\mathrm{He}}_2\left(a{{}_{}{}^3{}_{}{}^{}\Sigma _{\mathrm{u}}^{}{}_{}{}^{}}^{+}\right)$ and $\mathrm{He}\left(2\mathrm{}{}_{}{}^3{}_{}{}^{}S\right)$ metastable states of helium that are produced in electron-bombarded superfluid helium. The characteristic lifetime of a metastable molecule in the superfluid is shown to exceed 0.1 sec, while the lifetime of a metastable atom is only about 15 μsec. The production rates for the ${\mathrm{He}}_2\left(a{{}_{}{}^3{}_{}{}^{}\Sigma _{\mathrm{u}}^{}{}_{}{}^{}}^{+}\right)$ and $\mathrm{He}\left(2\mathrm{}{}_{}{}^3{}_{}{}^{}S\right)$ metastable states are about 500 and 450 per incident 160-keV electron, respectively.

It is proposed that a resonant mechanism should cause significant absorption of energy from intense laser pulses in plasma targets, and that the energy should be deposited in such a way as to form a very non-Maxwellian high-temperature tail on the electron velocity distribution.

We have made sound-velocity measurements in the liquid crystal $p$-methoxy-benzylidine, $p-n$-butyl-aniline. Near the nematic-isotropic phase transition we observe a dispersion in the sound velocity. Quantitative measurements are presented on the sound-velocity anisotropy in an oriented liquid crystal.

A simple theory is developed for calculating the electron-phonon coupling constant $\lambda$.

Using a polarized target of Ca${\mathrm{F}}_2$, we have measured the spin-dependent part of the scattering amplitude of slow neutrons on ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$. A value $\beta =a_{+}-a_{-}=-0.135\mathrm{}\pm 0.002$ F was found, 10 times smaller than a recent theoretical estimate. A control experiment measuring $\beta =a_{+}-a_{-}$ for the proton by Bragg scattering on a single crystal of LiH yielded the correct value within experimental error.

An axial EPR spectrum has been observed for the holes that result when Nb is substituted for Mo in Mo${\mathrm{S}}_2$. From the values of the $g$ tensor it is determined that the holes are in a $d_{z^2}$ band into which the spin-orbit interaction admixes some $d_{\mathrm{xz}}$ and $d_{\mathrm{yz}}$ orbitals. The EPR results are discussed in terms of the various energy-band structures that have been proposed for Mo${\mathrm{S}}_2$. The data are found to be consistent with the band structure suggested by Wilson and Yoffe.

Surface polaritons are optically excited in semi-infinite crystals of GaP. Infrared radiation is coupled from silicon prisms into the sample via attenuated total reflection. The results give the first experimental dispersion relation for surface polaritons.