A measurement of a permanent electric dipole moment on xenon atoms has yielded the null result $d\left({}_{}{}^{129}{}_{}{}^{}\mathrm{Xe}\right)=(-0.3\mathrm{}\pm 1.1)\times {10}^{-26\mathrm{}} e·$ cm, achieved by use of spin exchange with optically pumped rubidium atoms to determine the precession frequency of the xenon nuclear spins as a function of applied electric field. This measurement improves the limit on an atomic dipole moment by over four orders of magnitude. It is sensitive to time-reversal-asymmetric forces within the atom, setting a new upper limit of ${10}^{-6\mathrm{}}{G}_{\mathrm{F}}$ on a short-range tensor-pseudotensor electron-nucleon coupling.

Orthopositronium annihilation rates have been measured as a function of density near the vapor-liquid critical point of ethane. An unexpected and sharp enhancement in the annihilation rates is observed at a density of about 115 amagats at 305.45 K. These results are interpreted in terms of density fluctuations in the fluid.

Na atoms in a buffer gas are compressed to a steep front by a laser beam tuned into the red Doppler wing of the Na $D$ transition. The Na densities on either side of the front differ by a factor of 500. The front formation is due to a laser-induced drift which is a consequence of the state dependence of the diffusion cross sections involved. The Na drift velocity is deduced to be ∼ 4 m/s.

In our experiments on a loop of fluid heated with a constant flux on the bottom half and cooled at a constant temperature on the top half, we have observed three chaotic flow regimes: a globally chaotic regime whose essential features can be described by a one-dimensional cusp-shaped map, a subcritical regime in which the flow can be either chaotic or steady, and a transient regime in which the flow remains chaotic for a time and then decays into a steady flow.

Results from the first radial measurements of the $n=2\mathrm{}$ to $n=1\mathrm{}$ x-ray transitions of high-$Z$ elements in deuterium tokamak plasmas are presented. The observed line intensity ratios cannot be explained by electron-impact excitation and dielectronic recombination processes. Radiative and charge-transfer recombination are proposed as additional population mechanisms. The emission lines emitted in the cascade following capture constitute a unique diagnostic probe of the neutral component of plasmas.

The solidification of ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ in Vycor glass and in sintered Ag powder has been studied between 0.8 and 2.5 K. At 0.8 K, elevation of the melting pressure by 12 bars is seen in Vycor and by 0.3 bar in the Ag sinter. In each material a range of melting pressures, corresponding to different pore sizes, is observed. The location of the $\lambda$ transition in the liquid in Vycor is determined up to solidification pressure.

Accurate measurements of the interfacial tension between solid and superfluid ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ show for the first time that it decreases between 1.2 and 1.76 K. The magnitude of this effect is compared with various recent theoretical predictions. A significant contribution is found to come from the entropy of Rayleigh waves. We also discuss the effect of the progressive disappearance of the condensate along the melting curve, near the $\lambda$ transition.

The self-energy of a particle has a nearly singular behavior at a free surface of a Fermi liquid, as a result of the coupling to surface excitations. The imaginary part has a linear dependence on energy near the Fermi energy, whereas the effective mass shows a logarithmic divergence. The self-energy is calculated in semi-infinite nuclear matter with use of interactions constrained by self-consistency; the predictions are in qualitative agreement with experiment and more elaborate calculations for finite nuclei.

We report the first observation of a cholesteric phase which appears as an island surrounded by smectic-$A$ phases in a temperature-concentration phase diagram. The island of cholesteric form results from large fluctuations of two, collinear, incommensurate density waves whose coexistence violates smectic-$A$ ordering. It provides novel evidence that smectic-$A$ fluidity cannot support two incommensurate lengths.

Using polarization-dependent angle-resolved photoemission we show that two dominating structures in the photoemission spectra are due to direct transitions from the uppermost two valence bands in silicon. The final-state band for these transitions at photon energies 10.2-21.2 eV is found to have free-electron-like dispersion. Our results imply that that threefold-symmetry emission often assigned to back-bond surface states on Si(111)2×1 is really due to bulk photoemission.

By means of Penning-ionization electron spectroscopy the outermost surface layer of a pentacene film on a graphite substrate (cleavage plane) was selectively observed. Ultraviolet photoelectron spectroscopy was also applied to observe several layers from the surface. From the analyses of the two types of spectra the subtle changes in the electronic state and the molecular orientation of the outermost layer and also those of inner layers were probed separately during the layer-by-layer epitaxial growth of the film.

The coverage dependence of Raman scattering from CN on Ag island films is found to be highly nonlinear. It can be explained by a classical calculation of microscopic local fields taking into account the electronic polarizabilities of nearby adsorbates and the two-photon nature of spontaneous Raman scattering.

Subharmonic steps in the dc $I-V$ characteristics are reported in the model compound Nb${\mathrm{Se}}_3$, when subjected to combined dc and ac drives. The steps occur at currents which correspond to frequencies ${\omega }_{\mathrm{int}}=\left(\frac{p}{q}\right){\omega }_{\mathrm{ext}}$, with $p$ and $q$ integers. These steps cannot be explained in terms of the familiar classical equation of motion in a single degree of freedom, because the inertial term is too small. The observed behavior is compared with the devil's staircase, and a fractal dimension of 0.91 ± 0.03 is extracted.

A theoretical description of the temperature-dependent dephasing rate of rare-earth ions in glass is given for temperatures $T<\mathrm{}1\mathrm{}$ K. The model invokes elastic dipole-dipole interactions between the rare-earth ions and atomic tunneling systems. The calculation explains features of a recent photon-echo experiment on Si${\mathrm{O}}_2$:${\mathrm{Nd}}^{3+}$, namely, the magnitude and $T^{1.3}$ dependence of the dephasing rate.

Temperature-induced changes in the electronic structure of Fe(100) have been investigated by spin- and angle-resolved photoemission for temperatures between room temperature and the Curie temperature $T_{\mathrm{C}}$. States nearly stationary in energy (${\Gamma }_{25}^{\prime \uparrow }$, ${\Gamma }_{12}^{\uparrow }$) have been observed for photon energy $h\nu =60\mathrm{}$ eV. However, from a strong increase in minority-spin intensity for $h\nu =31\mathrm{} \mathrm{and} 21$ eV, a downwards shift of the ${\Delta }_5^{\downarrow }$ band is inferred to occur upon heating towards $T_{\mathrm{C}}$ for large $k$ vectors.

A series of twenty homogeneous ${\mathrm{Sr}}_{1-x}{\mathrm{Ca}}_x\mathrm{Ti}{\mathrm{O}}_3$ mixed crystals has been measured dielectrically between 4.2 and 300 K. In the tetragonal phase, the dielectric constant perpendicular to the $c$ axis becomes peaked above $x_c=0.0018\mathrm{}$, the quantum mechanical onset for displacive ferroelectricity. The polarization $\perp c$ can be switched between the two equivalent $a$ axes, i.e., the system is an $\mathrm{XY}$, $n=2\mathrm{}$, quantum ferroelectric. Above $x_r=0.016\mathrm{}\pm 0.002$, the $\epsilon \mathrm{}\left(T\right)\mathrm{}$ peaks round in a distinct manner which we attribute to the onset of a random-field-induced domain state.

We report the observation of negative differential resistance and dynamic instability in the sliding charge-density-wave state of Nb${\mathrm{Se}}_3$. The instabilities are characterized by an unusually large $\frac{1}{f}$ noise and intermittent chaoticlike response. We interpret our results in terms of domain coupling in the charge-density-wave condensate, resulting in hopping between distinct current-carrying states.

A precession of the conduction-electron spin polarization $\overrightarrow{\mathrm{P}}$ away from the initial direction defined by the direction of the circularly polarized pumping light beam is found in photoemission experiments from GaAs(110)/(Cs,O). This precession occurs in the band-bending region about specific crystallographic directions and arises from the spin-orbit-induced spin splitting of the conduction band. These findings open new possibilities for the investigation of the electronic properties of this important interface region.

Because of complicated topology of the configuration space for indistinguishable particles in two dimensions, Feynman's path-integral formulation allows exotic statistics. All possible quantum statistics in two-space are characterized by an angle parameter $\theta$ which interpolates between bosons and fermions. The current formalisms in terms of topological action of multivalued wave functions can be derived in a model-independent way.

A notion of length for quantum mechanical trajectories is introduced within the realm of stochastic mechanics. Using a stochastic calculus of variation, one shows that the geodesic dynamics is not the free one, but the quantum evolution in the time-dependent quadratic potential associated with the Wiener process in stochastic mechanics. The length for the free evolution is also examined.