Photoinduced excess charge at a GaAs interface barrier relaxes nonexponentially. A fit to experiment with a statistically motivated Kohlrausch formula is possible but unjustified. Serial relaxation by hierarchies of systems with increasing spatial separation of carriers furnishes a convincing explanation and exemplifies recent theoretical proposals to describe nonexponential relaxation processes.

The incompressible states of interacting two-dimensional electrons in a high magnetic field has been studied by finite-size calculations in the spherical geometry. The excitation spectrum at $\frac{1}{3}$ Landau-level filling is described, and the Laughlin-Jastrow character of the Coulomb-interaction ground state is unambiguously confirmed. As the interaction is varied, a transition to a gapless compressible state is observed.

We have performed magnetoresistance and Hall-resistance measurements on low-carrier-concentration $n$-type samples of ${\mathrm{Hg}}_{0.76}$${\mathrm{Cd}}_{0.24}$Te at millikelvin temperatures. We observe an abrupt rise in the Hall resistance and magnetoresistance at a characteristic field $H_c$ which is a significant function of temperature and which allows us to reject magnetic freezeout or localization by disorder as possible mechanisms. We believe our data provide compelling evidence for a model where the magnetic field induces localization of the electrons into a three-dimensional Wigner lattice.

High-resolution spectroscopy of ${\pi }^{+}$ from $K^{-}$ absorption at rest has been used for the first time to identify ${\Sigma }^{-}$ hypernuclear states. The observed spectrum from a ${\left(\mathrm{CH}\right)}_n$ target has revealed a $p_{\frac{3}{2}}-p_{\frac{1}{2}}$ doublet of ${}_{{\Sigma }^{-}}{}^{12}{}_{}{}^{}\mathrm{Be}$ with narrow widths. The spin-orbit splitting of ${\Sigma }^{-}$ is deduced to be 5 MeV, 0.8 times that for nucleons.

We describe a design for producing a soft x-ray laser via $3p-3s$ transitions in Ne-like selenium (wavelength of about 200 Å). A 0.53-μ m laser, focused in a 1.2×0.02-cm spot to ∼ 5×${10}^{13}$ W/${\mathrm{cm}}^2$, heats and burns through a thin foil of Se. Besides ionizing the Se to a Ne-like state, the laser explodes the foil, creating a region of uniform electron density. This allows propagation of the x rays down the 1-cm-long gain direction without debilitating refraction. Gains of 4 to 10 ${\mathrm{cm}}^{-1\mathrm{}}$ are predicted for various transitions.

We report observations of amplified spontaneous emission at soft x-ray wavelengths. An optical laser ionized thin foils of selenium to produce a population inversion of the $2p^{5}3p$ and $2p^{5}3s$ levels of the neonlike ion. Using three time-resolved, spectroscopic measurements we demonstrated gain-length products up to 6.5 and gain coefficients of 5.5±1.0 ${\mathrm{cm}}^{-1\mathrm{}}$ for the $J=2\mathrm{} \mathrm{to} 1$ lines at 206.3 and 209.6 Å. We also observed considerable amplification for the same transitions in yttrium at 155.0 and 157.1 Å.

The roughness of the liquid-vapor interface for pure water was measured by a technique of x-ray reflectivity. With synchrotron radiation ($\lambda \sim 1.5$ ÅA), the angular dependence of the x-ray reflectivity was measured from grazing incidence (∼0.0021 rad), where the reflectivity was greater than 0.96, to an incident angle of ∼0.05 rad, where the reflectivity was ∼7×${10}^{-8\mathrm{}}$. A fit to the data by a theory with only one adjustable parameter obtains 3.2 ÅA for the root-mean-square roughness of the water surface.

We demonstrate that the equations of hydrodynamics for a simple compressible fluid, including nonlinearities and thermal fluctuations, display a transition, at sufficiently high densities and low temperatures, to a glass. The theory leads to predictions for the behavior of viscosities, sound speeds, and correlation functions near the transition.

The application of near-edge, surface, extended x-ray absorption fine structure to the study of a clean surface is reported. Direct evidence is found for surface recrystallization of ion-damaged (amorphized) Si, whereas no such evidence is seen for evaporated (amorphous) Si. The procedures described here are applicable to almost all clean or adsorbate-covered surfaces.

Rigorous expressions are derived for the line shape for an isolated vibrational mode of an atom or molecule adsorbed on a metallic surface in the presence of electron-hole damping. It is shown that this mechanism necessarily produces an asymmetric line shape with long tails. The experimental presence or absence of such a line shape should therefore play an important role in establishing whether or not electron-hole-pair production is an effective energy-transfer mechanism near metallic surfaces.

The magnetic susceptibility of ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ adsorbed on sintered silver powder has been measured in the temperature range from 0.8 mK to about 10 mK with a SQUID magnetometer for eight different film thicknesses between monolayer and 15 layers. The measured susceptibility of films less than about 5 layers thick obeys the Curie law with the Curie constants given by the free localized model. In films more than 5 layers thick, the measured susceptibility is described by the Curie-Weiss behavior with a Curie-Weiss temperature of about 0.4 mK.

Ion shadowing and blocking measurements show that the solid-liquid transition at the (110) surface of lead starts at approximately 40 K below the bulk melting point of lead $T_m$. The thickness of the liquid surface film increases dramatically as the temperature approaches $T_m$.

A class of amide-I (C=O stretch) related excitations and their contribution to the spectral function for infrared absorption is determined by use of the Davydov Hamiltonian. The treatment is a fully quantum, finite-temperature one. A consistent picture and a quantitative fit to the absorption data for crystalline acetanilide confirms that the model adequately explains the anomalous behavior cited by Careri et al. The localized excitation responsible for this behavior is the vibronic analog of the small Holstein polaron. The possible extension to other modes and biological relevance is examined.

From measurements of the dispersion of the lowest two conduction bands in silicon by $k$-resolved inverse photoemission the energies of the $L_1^c$ and $L_3^c$ critical points were determined as 2.40±0.15 and 4.15±0.10 eV relative to the valence-band edge, respectively. A comparison with energies derived from photoemission and optical data reveals a large excitonic lowering of the $E_1$ transition by 0.5±0.2 eV. The lowest unoccupied surface state on the Si(111) 2×1 surface at $\overline{\Gamma }$ is identified at 1.2±0.1 eV.

Hopping of photoexcited carriers directly between localized, band-tail states gives rise to a new regime of energy relaxation which is manifested at low temperatures: For times shorter than a characteristic "segregation time," carriers hop directly to lower-energy states; at longer times, thermal excitation—resulting in multiple trapping—is more important. Even in the multiple-trapping regime, however, the current is carried at a transport energy within the band tail. We present a simple description which includes both of these processes in a single, self-consistent model, and estimate the segregation time.

Evidence is presented for mean free path (mfp) and spin-orbit effects contributing to the spinglass transition temperature, $T_g$, from a study of the addition of nonmagnetic impurities to spinglasses. We find a finite $T_g$ even in the limit of zero mfp and dilute moment concentration. We suggest that there must be an interaction between moments which is long ranged and yet mfp independent. For multiple-moment systems $T_g$ can be qualitatively understood, but an appropriate theoretical description is lacking.

The thermal critical properties of random-field systems in the observable, linear, local-response regime are considered. A consistent nonperturbative approach yields an effective reduced dimension $\overline{d}=\frac{[d+\frac{1}{\nu \left(\overline{d}\right)}]}{2}$ for the thermal exponents if $\alpha \left(\overline{d}\right)<~0$. The consequences for Ising systems are particularly reliable at the upper and lower critical dimensions ($d_{\mathrm{u}.\mathrm{c}.\mathrm{d}.\mathrm{}}=6\mathrm{}$ and $d_{\mathrm{l}.\mathrm{c}.\mathrm{d}.\mathrm{}}=2\mathrm{}$, respectively) as well as at $d=3\mathrm{}$ where $\alpha =0\mathrm{}$ (logarithmic divergence). The results are in agreement with measurements on random antiferromagnets of the specific heat (by linear birefringence) and the correlation length (by neutron scattering).

We present a Monte Carlo calculation of the quark-liberating phase transition in lattice quantum chromodynamics. The transition temperature as a function of the lattice coupling $g$ does not scale according to the perturbative beta function for $\frac{6}{g^2}<6.1\mathrm{}$. We use finite-size scaling in analyzing the properties of the lattice system near the transition point.

We describe a rigorous argument establishing infrared asymptotic freedom and other related properties (e.g., scaling with logarithmic corrections) of the weakly coupled massless lattice ${\phi }^4$ model in four Euclidean dimensions. Our method combines the block-spin renormalization-group analysis with the technique of convergent high-temperature expansions. It should also extend to the ultraviolet asymptotically free models such as the negative-coupling continuum ${\phi }_4^4$ theory.

Direct photon production in hadronic events from $e^{+}{e}^{-}$ annihilation has been studied at $\sqrt{s}=29\mathrm{}$ GeV with use of the MAC detector at the PEP storage ring. A charge asymmetry $A=(-12.3\mathrm{}\pm 3.5)\%$ is observed in the final-state jets. The cross section and the charge asymmetry are in good agreement with the predictions of the fractionally charged quark-parton model. Both the charge asymmetry and total yield have been used to determine values of quark charges. Limits have been established for anomalous sources of direct photons.