Multiphoton ionization spectroscopy has yielded the first evidence for triplet absorption bands in ${\mathrm{Li}}_2$ in the spectral region from 6215 to 5875 Å. This spectrum is the first of a new class of spectra resulting from a two-photon transition from a bound (${{}_{}{}^3{}_{}{}^{}\Sigma _{\mathrm{u}}^{}{}_{}{}^{}}^{+}$) van der Waals state to a previously unknown bound ${}_{}{}^3{}_{}{}^{}\Lambda _{\mathrm{u}}^{}{}_{}{}^{}$ state (where $\Lambda =0, 1, or 2$) through an intermediate free state (${}_{}{}^3{}_{}{}^{}\Pi _{\mathrm{g}}^{}{}_{}{}^{}$). The final state either autoionizes or collisionally forms the ${{}_{}{}^2{}_{}{}^{}\Sigma _{\mathrm{g}}^{}{}_{}{}^{}}^{+}$ ground state of ${\mathrm{Li}}^{2+}$.

In a very large laboratory plasma the process of magnetic-field-line reconnection has been diagnosed carefully. The temporal evolution of a narrow ($\sim \frac{3c}{{\omega }_{\mathrm{pe}}}$) neutral layer with Petschek slow shocks is observed. Electrostatic fields are found to be as important as induced electric fields.

Processes involving magnetic-field reconnection in collisionless plasmas and relying on the effects of electron Landau resonance for their excitation are found to require the consideration of the self-consistent electric potentials and the systematic analysis of four consecutive asymptotic regions. The new effects found are relevant to both laboratory and space plasmas.

The motion of ions along vortex lines in the presence of a transverse radio-frequency electric field has been investigated. An anomaly in the velocity-versus-electric-field relation, associated with the "resonant" generation of vortex waves, is observed. These measurements constitute the first observation of vortex waves at frequencies larger than a few hertz.

The Christoffel elastic equations are solved for long-wavelength elastic waves of arbitrary direction in cubic crystals, and exact explicit closed expressions are obtained for the phase and group velocities and displacement amplitudes. The velocity expressions that hold in the special directions are shown to follow from the general result. The problem of determining the elastic constants from the phase velocities in a general crystallographic direction is discussed with particular reference to Brillouin scattering.

We study the magnetic polarization induced around vacancies in two-dimensional quantum crystals of fermions. A vacancy creates a ferromagnetic spin polaron in an alternate lattice, but does not in a triangular (nonalternate) lattice. The situation of ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ in confined geometries is discussed, in particular with respect to the observed tendency to ferromagnetism.

$T_1$ and $T_2$ data at 5.5 K measured at 33 MHz are reported for solid matrices of normal hydrogen in argon with hydrogen mole fraction $0.004<x<\mathrm{}0.33\mathrm{}$. The results are interpreted in terms of a theory developed by Ebner and Myles in their study of solid ortho-para hydrogen mixtures. The crystal field consistent with the data is estimated to be 0.2 K. The $T_2$'s, taken from the far-infrared detectors, are smaller than those predicted.

The highly structured profile of the ${\Gamma }_1$ biexciton level of CuCl is studied experimentally by resonant coherent nonlinear scattering. A theoretical model is presented which accurately describes the ${\Gamma }_1$ biexciton line shape in terms of a Fano interference, evidencing the autoionizing character of biexcitons.

Electromagnetic effects are shown to govern the transition from superconductivity to ferromagnetism. A first-order transition to uniform ferromagnetism is predicted generally, but preceded by magnetic critical scattering which peaks at a finite wave vector.

Energy distributions of electrons ejected from clean and CO-covered Pd(111) surfaces by impact with metastable He* $2{}_{}{}^1{}_{}{}^{}S$ (excitation energy $E^{*}=20.6\mathrm{}$ eV) and $2{}_{}{}^3{}_{}{}^{}S$ ($E^{*}=19.8\mathrm{}$ eV) atoms were measured. The operation of the Penning mechanism, viz., ${\mathrm{He}}^{*}+A\to \mathrm{He}+A^{+}+e^{-}$, is demonstrated for adsorbed CO whose valence orbitals could be identified. Thereby a new surface spectroscopic technique with extreme sensitivity to the outmost atomic layer is established.

The effect of tunnel currents in superconducting junctions on the energy gap is calculated. For certain parameters, two different gaps can exist. The stability of these solutions is investigated and at a certain voltage a "first-order transition" is found. This result explains the experimentally observed inhomogeneous state in superconducting tunnel junctions.

The time dependence of the optical absorption and the gain of a hot electron-hole plasma in GaAs is measured by means of tunable picosecond light pulses. The electrons and holes (∼${10}^{17}$ ${\mathrm{cm}}^{-3\mathrm{}}$) are photoexcited via two-photon absorption. Our measurements provide a detailed picture of the temperature evolution, showing that in 250 ps the plasma cools from over 100 K down to ∼ 40 K and does not reach the lattice temperature. The energy relaxation process is shown to be polar LO-phonon emission of hot electrons and holes.

Using a localized orbital theory, we have studied the electronic and electrical properties of A1 chemisorbed on GaAs(110). We find that both the microscopic data and the macroscopic induced barrier are fully explained by the electronic structure of a new Al-As-Ga complex on the surface. This complex results from an exchange reaction in which Al replaces the surface Ga and an unexpected structural relaxation induced by the chemisorption of the metal.

Measurements of the temperature and frequency dependence of the proton and deuteron spin-lattice relaxation time $T_1$ show the presence of a dynamic central peak in paraelectric K${\mathrm{H}}_2$P${\mathrm{O}}_4$ which exhibits a dramatic narrowing on deuteration. The observed centralpeak narrowing on deuteration qualitatively agrees with a continued-fraction calculation demonstrating that small dynamic intrinsic clusters may occur in K${\mathrm{H}}_2$P${\mathrm{O}}_4$-type crystals above $T_c$ in addition to large static defect-induced clusters observed in light-scattering experiments.

Microscopic calculations of the phase diagrams of a two-component degenerate Coulomb Fermi liquid—the electron-hole liquid in $〈111〉$-stressed Ge—have been made for various values of stress. The coexistence curves for three-phase equilibrium which summarize the most interesting features of these phase diagrams are reported. A particularly striking case which occurs at lower stress is one in which the two liquid phases coexist in two separate temperature ranges.

We report on the first successful double-scattering low-energy electron diffraction experiment, which clearly reveals spin-polarization effects. Polarization and intensity of the specular beam from W(001) have been measured as functions of the azimuthal angle of incidence ("rotation diagrams"). The agreement of the data with their theoretical counterparts is quite satisfactory. High polarization sensitivity and detector efficiency in the present experiment demonstrate the feasibility of a new type of spin-polarization detector.

Self-consistent pseudopotential and tight-binding techniques are used to study glassy Se. Both onefold and threefold corrdinated defects give rise to nondegenerate, nonhydrogenic gap states. The former state arises from an interaction, unique to the chalcogenides, between a dangling bond and a neighboring lone pair. The latter state is surprisingly delocalized, involving interactions between many orbitals. It is shown that defect electronic configurations, and repulsive interatomic terms, are crucial to the calculation of total energies.

We present here a new mean-field theory of ferromagnetic superconductors in an external magnetic field. Simple models for the pure superconductor and the pure ferromagnet are chosen and the theory is considered in more detail. Phenomena predicted include both the destruction of superconductivity by the ferromagnetic order and the coexistence of ferromagnetism and superconductivity, as well as the magnetic field dependence of zero-temperature magnetization. Results obtained are in qualitative agreement with the experiments.

We construct the manifold of zero-energy eigenstates for a nonrelativistic spin-½ particle moving in a plane in an external magnetic field $B\left(\overrightarrow{\mathrm{x}}\right)=\Sigma {n=0\mathrm{}}^N{\lambda }_n(\overrightarrow{\mathrm{x}}-{\overrightarrow{\mathrm{c}}}_n)$, with $\left\{{\lambda }_n\right\}$ and $\left\{{\overrightarrow{\mathrm{c}}}_n\right\}$ arbitrary reals and $\left\{k_n\right\}$ positive integers. For a given $B$ the ground state is infinitely degenerate and the manifold of eigenfunctions is parametrized by a point in $R^{2(2k_{max}+1)}$. For such $B$'s we prove paramagnetism with arbitrary external potential $V\left(\overrightarrow{\mathrm{x}}\right)$.

General covariance and maxium four-dimensional Yang-Mills gauge symmetry lead to these results: (1) Gravity is characterized by a dimensionless constant $F\sim {10}^{-19\mathrm{}}$; (2) the Newtonian force is always attractive; (3) space-time has a torsion; (4) gravitational spin-force between two protons is about ${10}^{19}$ times stronger than the corresponding Newtonian force. A possible experimental test is discussed.