Magneto-optic Kerr-effect measurements (bulk sensitive) and spin-polarized low-energy electron diffraction (surface sensitive) reveal that the surface and the bulk Curie temperatures of epitaxial EuS(111) on Si(111) are identical to within ±0.04 K. In the critical region of the bulk, the surface magnetization $m_1$ of this model substance for an isotropic Heisenberg ferromagnet decreases as $m_1\sim {(1-\frac{T}{T_C})}^{{\beta }_1}$, with ${\beta }_1=0.72\mathrm{}\pm 0.03$. This differs significantly from current theoretical estimates of ${\beta }_1$, possibly pointing to a very strong surface anisotropy.

A midgap absorption band is observed in the quasi one-dimensional semiconductor [Pt${\mathrm{}\left(\mathrm{en}\right)\mathrm{}}_2$]-[Pt${\mathrm{}\left(\mathrm{en}\right)\mathrm{}}_2$${\mathrm{Cl}}_2$]${\left(\mathrm{C}\mathrm{l}{\mathrm{O}}_4\right)}_4$ under hydrostatic pressures at room temperature, where en is ethylenediamine. The transition is allowed only for the polarization parallel to the -Cl-${\mathrm{Pt}}^{\mathrm{II}}$-Cl-${\mathrm{Pt}}^{\mathrm{IV}}$- chain. The peak position remains near the middle of the Peierls gap at any pressure up to 2.2 GPa. The intensity increases exponentially with the peak shift. The gap states responsible for this band are attributed to soliton excitations corresponding to kinks of the charge-density wave.

One-, three-, and five-monolayer (ML) films of fcc iron grown epitaxially on Cu(001) are found to be ferromagnetic by spin-polarized photoelectron emission measurements of the magnetization as function of perpendicularly applied field and temperature. The hysteresis loop of the 5-ML film at 30 K is quadrangular, and shows a remanence magnetization directed along the surface normal and a coercive field of 650 Oe. The extrapolated temperature dependence of the saturation magnetization leads to a Curie temperature of 230 K for the 1-ML film and 390 K for the 3- and 5-ML films.

The observation of a many-body, Fermi-energy edge singularity in the low-temperature photoluminescence spectra of InGaAs-InP quantum wells is reported. Strong enhancement of the photoluminescence intensity towards the electron Fermi energy ($E_{\mathrm{F}}^e$) is observed, due to multiple electron-hole scattering processes to states above $E_{\mathrm{F}}^e$. Recombination of electrons in states up to $E_{\mathrm{F}}^e$ is allowed by hole localization. The many-body processes are analogous to the core-hole phenomena in the soft-x-ray emission spectra of metals.

We investigate the soliton excitations in the quarter-filled Hubbard-Peierls model in both the large-and small-$U$ limits. For a strictly one-dimensional system at zero temperature, we find that the solitons in both limits are in one-to-one correspondence. In the presence of weak three-dimensional coupling, the large-$U$ system differs qualitatively from the small-$U$ system in that the spin associated with the solitons ceases to be a sharp quantum observable. We suggest a natural explanation of both the magnetic and the dielectric response measured in ${\left(\mathrm{NPM}\right)}_x{\left(\mathrm{Phen}\right)}_{1-x}\mathrm{TCNQ}$ [${(N-\mathrm{methylphenazinium})}_x{\left(\mathrm{phenazine}\right)}_{1-x}\left(\mathrm{tetracyanoquinodimethanide}\right)$] and Qn${\mathrm{}\left(\mathrm{TCNQ}\right)\mathrm{}}_2$ (quinolinium ditetracyanoquinodimethanide).

Ab initio calculations on a ${\mathrm{Pt}}_{10}$-K-${\mathrm{H}}_2$O cluster show that the ${\mathrm{H}}_2$O molecule coadsorbed with K is tilted 160° relative to the surface normal, with the hydrogen atoms pointing towards the surface. This unusual bonding geometry is supported experimentally by studies of ${\mathrm{H}}_2$O-K coadsorption on Pt(111). For K coverages ${\theta }_{\mathrm{K}}<0.10\mathrm{}$ the adsorption of ${\mathrm{H}}_2$O is fully reversible and characterized by a large work-function increase. The ${\mathrm{H}}_2$O-K interaction is short ranged and increases the ${\mathrm{H}}_2$O adsorption energy. The calculation suggests that the orientational change of the molecule is driven by the electrostatic interaction with the K ion.

We report the results of an experiment designed to study the role of thermal processes in pulsed-laser-induced ablation of polymers. Using nonabsorbing polymer films on absorbing substrates and time-resolved reflectivity measurements, we show that laser-induced nanosecond heat pulses can cause rapid decomposition of polymers. This process exhibits all properties of so-called "ablative photodecomposition," namely high spatial resolution, nanosecond rates, and the presence of a threshold in laser energy density.

Neutron stars formed in supernovae are very intense sources of neutrinos of all species and masses ≤ 100 MeV. If such neutrinos decayed via ${\nu }_H\to {\nu }_e+e^{-}+e^{-}$ inside the Galaxy, annihilation of the trapped positrons would yield a 511-keV line exceeding the experimental bounds by many orders of magnitude. This allows us to exclude decay lifetimes in the range ${10}^4$-${10}^{15}$ sec for neutrinos of mass 1-100 MeV. Our result corroborates and extends earlier astrophysical bounds.

The quark potential of a string with extrinsic curvature is calculated in the limit $d\to \infty$, via a saddlepoint approximation. The saddle point has an anisotropic gap matrix ${\lambda }^{\mathrm{ij}}$ ($\ne \lambda g^{\mathrm{ij}}$ in contrast to an unjustified assumption in all previous discussions). The anisotropy enters the nonleading $-\frac{\mathrm{}(d-2\mathrm{})\mathrm{}\pi c}{24R}$ part of the potential. $c$ is calculated, the entire potential is plotted, and simple analytic expressions are found which approximate all quantities involved very closely.

We present bounds from the one-loop renormalization-group equations on Higgs-boson masses in a two-doublet extension of the standard model and the Gelmini-Roncadelli model. We show how these bounds vary as functions of the momentum scale $\Lambda$ where new physics is assumed to intervene. In particular, the bounds are less stringent than those previously derived from an ultraviolet-fixed-point approach.

For the charge-symmetry-breaking reaction $d+d\to {}_{}{}^4{}_{}{}^{}\mathrm{He}+{\pi }^0$ at $T_d=0.8\mathrm{}$ GeV around 100° c.m., an upper limit on the production cross section of ≈0.8 pb/sr is obtained. This represents about a factor of 20 improvement on previous measurements, but is still a factor of 5 above expected violations.

We demonstrate that momentum-dependent nuclear interactions (MDI) have a large effect on the dynamics and on the observables of high-energy heavy-ion collisions: A soft potential with MDI suppresses pion and kaon yields much more strongly than a local hard potential and results in transverse momenta intermediate between soft and hard local potentials. The collective-flow angles and the deuteron-to-proton ratios are rather insensitive to the MDI. Only simultaneous measurements of these observables can give clues on the nuclear equation of state at densities of interest for supernova collapse and neutron-star stability.

The ground state and several excited states of ${}_{}{}^9{}_{}{}^{}\mathrm{He}$, the most neutron-rich nucleus to date, have been identified by means of the reaction ${}_{}{}^9{}_{}{}^{}\mathrm{Be}({\pi }^{-}, {\pi }^{+}){}_{}{}^9{}_{}{}^{}\mathrm{He}$. The mass excess of the ground state has been measured and it is found that the nucleus is unbound against single-neutron decay by 1.13±0.10 MeV only. It is found that the excited-state spectrum of this nucleus, which is very far from the valley of stability, is in good agreement with the predictions of "no-core" shell-model calculations whose parameters were optimized for the stable nuclei in the valley.

The transition probability $P$ in the optical adiabatic rapid passage is calculated for a two-level model with dephasing. In the limit $\frac{T_2}{{\tau }_p}\to 0$, where $T_2$ is the dephasing time and ${\tau }_p$ is the time scale of passage through the resonance region, $P$ is given by $P=\frac{[1-\exp (-\frac{\pi {\chi }^2}{\left|\dot{\omega }\right|}\left)\right]}{2}$ in which $\chi$ is the Rabi flopping frequency at resonance and $\dot{\omega }$ is the time derivative of the offset angular frequency. Generally, $P$ takes its maximum value at an intermediate $\dot{\omega }$ for fixed $\chi$ and is bounded by the above formula and by $P=1-\exp (-\frac{\pi {\chi }^2}{2\left|\dot{\omega }\right|})$, which gives the asymptotic value in the limit $\frac{T_2}{{\tau }_p}\to \infty$.

The effective viscosity of ${}_{}{}^3{}_{}{}^{}\mathrm{He}$-$B$ has been measured by means of a torsional pendulum with a characteristic dimension of 135 μm. A comparison between the experimental results and theory—including the effects of (normal) fluid slip, Knudsen flow, and Andreev scattering of quasiparticles from spatial variations of the order parameter—reveals that while the experimental results at high pressure are bounded by the theoretical extremes considered, the low-pressure data are not; in fact, the disparity is seen to increase at lower pressures and lower temperatures.

He-atom-beam scattering has been used to investigate the reconstruction of the W(001) surface. At low surface temperatures $T_s$ a sharp $(\sqrt{2}\times \sqrt{2})R45\mathrm{}°$ diffraction pattern is observed. When $T_s$ is raised, the fractional-order beams broaden and shift towards the specular. At $T_s\approx 450$ K the time-of-flight spectra reveal two different surface phonons along the $〈110〉$ direction, a normal Rayleigh mode and a strongly anomalous mode with a maximum at a wave vector $Q$ at one-half of the zone boundary $Q_{\mathrm{BZ}}$ and an energy approaching zero at $Q\sim 0.8Q_{\mathrm{BZ}}$. This mode softens with decreasing temperature, identifying the structural transformation as a continuous displacive transition.

Specific-heat measurements are reported for cubic ($c$), icosahedral ($i$), and amorphous ($a$) phases of ${\mathrm{Mg}}_3$${\mathrm{Zn}}_3$${\mathrm{Al}}_2$ in the temperature range 0.04-5 K. All three phases are superconducting, with $T_c=0.32, 0.41, \mathrm{and} 0.75$ K, respectively. The electronic density of states $N\left(0\right)\mathrm{}$ is comparable to that expected in the free-electron model for all three phases. Compared to the $c$ phase, significant lattice softening is observed in the $i$ phase and, especially, in the $a$ phase, indicating an increase in the electron-phonon coupling parameter $\lambda$ with decreasing order.

Using fourth-sound techniques, we have measured the depression of the superfluid fraction of ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ confined in small pores of packed powder over wide temperature ($0.2<\mathrm{}\frac{T}{T_c}<1\mathrm{}$) and pressure ($0.5<p<\mathrm{}20\mathrm{}$ bars) ranges. From the analysis of the data we determine the magnitude and the pressure dependence of the healing length. The healing length decreases from 520 Å at 0.5 bar to 200 Å at 20 bars. The values are in fair agreement with those expected from the BCS expression.

It is shown that the measurement of the dielectric constant within the commensurate phase as a function of the bias electric field makes possible a direct observation of the interaction potential between discommensurations. In ${\mathrm{Rb}}_2$Zn${\mathrm{Cl}}_4$ our results indicate that the exponential interaction changes to an oscillatoric one at $T\sim 150$ K.

It is found by x-ray-absorption fine-structure measurements that the Cu sites in the stable icosahedral phase ($T2\mathrm{}$ phase) and the $R$ phase of Al-Cu-Li alloys are nearly identical. We infer that the structural unit in the $T2\mathrm{}$ phase is a truncated icosahedron composed of 105 atoms. We speculate that the $T2\mathrm{}$ phase and icosahedral Al-Mn-Si have the same structure except for a different structural unit. This is supported by recent x-ray diffraction measurements of both diffraction-peak positions and widths of the $T2\mathrm{}$ phase.