Three-photon magnetoabsorption measurements in fields up to 9 T are presented for the first time. A narrow exciton line of ${\Gamma }_5^{-}$ symmetry is resolved in CsI at 5.8076 eV. A $g$ value of 1.17 is deduced from the Zeeman splitting of this exciton. At high magnetic fields an exciton of ${\Gamma }_3^{-}$ symmetry is detected. The analysis of the field-dependent mixing of the ${\Gamma }_3^{-}$ and ${\Gamma }_5^{-}$ excitons yields a zero-field shift of the ${\Gamma }_3^{-}$ exciton to lower energies of 0.54 meV and an effective $g$ value for the admixture of 1.20.

Within the theory of weak collective pinning a random pin ensemble is completely characterized by its "strength" $W$ and "range" $r_p$. We give, for the first time, a definition of $r_p$ and calculate $W$ and $r_p$ for a very general case. For point pins we find $W\sim b$ at $b\lesssim 0.3$ ($b$ is reduced induction), and $r_p=0.195a$ ($a$ is flux-line spacing) except for $b<<1\mathrm{}$ or low temperatures where $r_p\approx \mathrm{r}\mathrm{a}\mathrm{d}\mathrm{i}\mathrm{u}\mathrm{s}\mathrm{o}\mathrm{f}\mathrm{t}\mathrm{h}\mathrm{e}\mathrm{f}\mathrm{l}\mathrm{u}\mathrm{x}-\mathrm{l}\mathrm{i}\mathrm{n}\mathrm{e}\mathrm{c}\mathrm{o}\mathrm{r}\mathrm{e}$. For extended pins $r_p=0.195a$ always holds but $W\left(b\right)\mathrm{}$ depends on the type and size of the pins.

Velocity distributions of In atoms in their ground (${}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}$) and excited (${}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{}$) states ejected from In foils by bombardment with 5-keV ${\mathrm{Ar}}^{+}$ ions are measured with a multiphoton resonance-ionization technique. We show for the first time that the ${}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{}$ level is not significantly populated during sputtering and that the only path for population of this state is via laser-induced photodissociation of ${\mathrm{In}}_2$ during the detection process. A new deexcitation model for sputtered excited neutral atoms is proposed which is based on the electronic localization of the fine-structure orbital.

We consider a system of $2^n$ orientational interacting tunneling dipoles in $n$ transverse near-neighbor-well tunneling fields ${}_{}{}^{\alpha }{}_{}{}^{}\Delta$ ($1>~\alpha >~n$). We show that the partition function for the system can be expressed as a product of $n$ Ising-model partition functions in transverse fields. The results are valid in one, two, and three dimensions as well as for random $\Delta$ s and random general interaction potentials.

Using Monte Carlo techniques, we show that vortex strings are responsible for the phase transition in the three-dimensional planar model. The phase structure for a generalized planar model with vortex suppression is determined. This latter model has the unusual feature of long-range order in a ground state with finite, disordering entropy.

We propose a new functional integral representation of the Hubbarda and Anderson models of lattice fermions. The simplest saddle-point approximation leads, at zero temperature, to the results derived from the Gutzwiller variational wave function. This approach uncovers the limitations of the Gutzwiller approximation and clarifies its connection to the "auxiliary-boson" mean-field theory of the Anderson model. This formulation leads to a novel strong-coupling mean-field theory which allows for a unified treatment of antiferromagnetism and ferromagnetism, metal-to-insulator transition, and Kondo compensation effects.

It is shown that the structural phase transformations and relative stabilities among cubic phases of $\mathrm{sp}$-bonded nonmetals can be successfully predicted within a simple, universal tight-binding model by a total-energy-minimization procedure. The model elucidates the physical mechanisms determining the chemical trends and predicts semiquantitatively the stable crystal structures, bond lengths, bulk moduli, and transition pressures of structural phase transformations. The theory explains the puzzling strong cation and weak anion dependence of the observed structural transition pressures.

A two-band model of spinless fermions in one dimension is constructed. Density-density couplings, umklapp scattering, and interband transitions are included. Renormalization-group equations are derived and discussed. In addition, it is shown that with one condition on the couplings and the velocities the model may be transformed to two uncoupled sine-Gordon Hamiltonians, which makes it possible to obtain solutions in regions where the renormalization-group equations are not valid. An important property of the model is that there can be superconductivity with repulsive interactions.

In an electric circuit made from only one metal with a thermal gradient over a point contact in the chain, thermoelectric voltages emerge as a result of the finite size of the contact. The phenomenon is described in terms of the difference in the transport properties of a point contact and the bulk, yielding the phonon drag as a major contribution to the measured thermopower at temperatures $T<\mathrm{}\frac{{\theta }_{\mathrm{D}}}{2}$.

An explicit realization of $\mathrm{U}\mathrm{}\left(n\right)\mathrm{}$ quantum holonomy is presented in the context of nonrelativistic (2 + 1)-dimensional electrodynamics and used to construct the adiabatic effective action. It is shown that the U(1) subgroup of the $\mathrm{U}\mathrm{}\left(n\right)\mathrm{}$ holonomy gives rise to an effective Chern-Simons topological mass term and its relationship with the fractional quantum Hall effect is discussed.

A simple systematic method is presented for the evaluation of the derivative expansion of the functional determinant with covariant differential operators, space-time-dependent background fields, and internal symmetry. The results are directly applicable to the one-loop perturbative effective-action expansion for bosons and fermions. Derivative expansions up to four-derivative terms for $\mathrm{Tr}\ln [-{\Pi }^2+U(X\left)\right]$ and the effective action of the $\mathrm{SO}\mathrm{}\left(N\right)\mathrm{}$ linear $\sigma$ model are calculated.

An infinite-dimensional representation of SU (2,2/1) can combine meson and baryon trajectories with daughters into an infinite supermultiplet.

It is suggested that a broad structure $X^0\mathrm{}\left(1480\right)\mathrm{}$ recently observed in the reaction $\overline{p}n\to {\pi }^{-}{X}^0\to 3{\pi }^{-}2{\pi }^{+}$ may be interpretable in terms of an unstable quasinuclear bound state of the (complex) nucleon-antinucleon ($N\overline{N}$) potential. The observed mass, production branching ratio, and preference for the $X^0\to {\rho }^0{\rho }^0$ rather than ${\pi }^{+}{\pi }^{-}$ decay mode are consistent with a quantum-number assignment $J^{\mathrm{PC}}\left(I^G\right)=2^{++}\left(0^{+}\right)$. Prospects for finding the lower-lying $0^{++}$($0^{+}$) and $1^{--}$($0^{-}$) members of the expected natural-parity quasinuclear band are discussed.

Forward-angle yields of targetlike products in reactions between a ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ beam and a ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$ target have been measured at laboratory energies between 100 and 170 MeV. The ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ and ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ yields are found to be higher than those of ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$ over the measured range of energies. This is interpreted as evidence for the equilibration of charge and mass in orbiting reactions.

The $\alpha$-particle cluster structure of ${}_{}{}^{44}{}_{}{}^{}\mathrm{Ti}$, which is of considerable interest for investigation of the persistence of $\alpha$ clustering in the region of the $\mathrm{sd}$-shell closure, is studied within the frame of a local-potential approach. It is shown that the model leads to specific predictions if continuity with existing unique $\alpha +{}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ optical potentials ïs insisted upon; in particular, the existence of an as yet experimentally unknown $\alpha$-cluster negative-parity band, starting just above the $\alpha +{}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ threshold, is strongly suggested.

We have studied the dissociation of HeH molecules produced in the charge exchange between fast He${\mathrm{H}}^{+}$ ions and Cs. The released kinetic energy is measured by detection in a delayed coincidence technique of the neutral He-H pairs formed after dissociation. First direct evidence is reported for quasibound, predissociative states of HeH with energy levels in agreement with theoretical predictions. HeH* molecules are formed with large rotational and little vibrational excitation. The decay mechanisms of the low electronic excited states of HeH are discussed.

We have observed coherent multiple-foil transition radiation in the x-ray energy region.

Three-dimensional double layers are generated in a strongly magnetized collisionless plasma column. The position and shape of the double layers are controlled by the formation of mirror configuration of magnetic field, which simulate the magnetic field structure above the Earth's auroral oval. The double layers are found to induce electrostatic oscillations with frequencies above the ion-cyclotron frequency and its harmonics, in contrast to one-dimensional double layers. The oscillations are driven by the large inhomogeneous radial electric field and propagate azimuthally with mode number $m=1,2,3,\dots$.

By use of the technique of rapidly melting moderately spin-polarized solid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$, the viscosity of transiently produced spin-polarized liquid has been investigated. Partial melting makes a 10% polarized liquid near 50 mK with a viscosity decreased by 25% from the 8-T equilibrium value. Complete melting produces a liquid near 320 mK which shows no comparable polarization effect. These observations support a class of microscopic models in which the liquid is "nearly localized."

In many physical problems where renormalization-group transformations are exact, periodic oscillating corrections to power-law behavior are usually expected. The magnetoresistance of a normal-metal self-similar network, which exhibits such behavior in the weak localization regime, is shown to provide the first experimental evidence for this phenomenon.