We present the first experimental evidence of tunneling and transport of electrons from quantum states in a GaAs/GaAlAs superlattice or a quantum well to a GaAs surface activated to negative electron affinity. The photocurrent versus light excitation energy shows definite structures which appear exactly at the calculated energies of the allowed optical transitions between the quantized levels of the valence and conduction bands. The 300- and 30-K results for the superlattice are successfully compared to luminescence experiments, and could lead to the production of highly polarized electron beams.

When 500-keV electron irradiation was used to induce defects in polycrystalline copper films maintained at 90 K, the spectral density of the $\frac{1}{f}$ noise voltage across the films increased by as much as 1 order of magnitude, while the resistivity increased by at most 10%. When the films were annealed at progressively higher temperatures, both the $\frac{1}{f}$ noise and the resistivity were reduced; however, at lower annealing temperatures, the fractional reduction in the added noise was substantially more than that in the added resistivity.

The coherent voltage oscillations (narrow-band noise), induced by sliding charge-density waves, were investigated in Nb${\mathrm{Se}}_3$ at $T=45\mathrm{}$ K. By applying nonperturbing potential sensors on the surface of the sample we show that a significant portion of the narrow-band noise is generated in the bulk. We found evidences for domain structure in the velocity-velocity correlation function of the sliding charge-density waves. We attempt to resolve the contradiction with previous experimental studies.

By digital simulations and experiment, we study a Josephson system in a highly nonlinear regime. High experimental noise values appear to correspond in simulations to intrinsic chaotic motion in some regions and to noise-induced hopping between periodic solutions in others. Focusing on the latter, we find correlation between high noise sensitivity and the fractal dimension of the boundary between the basins of the periodic attractors. We show that if enough noise is present to push the orbits into the basin boundary, behavior similar to intrinsic chaos results.

The plasma frequencies of Cd, In, and Sn are determined from a calculation of the long-wavelength, frequency-dependent dielectric function. The mutual interaction between core- and valence-electron charge fluctuations is included within the random-phase approximation. Core polarization is shown to be an important effect and its inclusion leads to values of the plasma frequency in excellent agreement with experiment.

A thresholdlike behavior of the far-infrared photoconductivity due to cyclotron resonance and a drastic deviation of the cyclotron-resonance line shape from a Lorentzian has been observed in $n$-GaAs at low temperatures by applying a high-power cw far-infrared laser. Both effects may consistently be explained in terms of generation-recombination-induced nonequilibrium phase transitions showing that, besides impact ionization of impurities, cyclotron resonance can critically control the conductivity of the semiconductors.

An energy level of $E_v+0.38\mathrm{}$ eV related to the 0 to + charge transition of substitutional manganese in silicon has been determined with a combination of deep-level-transient spectroscopy and ESR measurements. There is no evidence for ordinary amphoteric or negative-$U$ behavior in the lower half of the band gap. This is the first identified energy level of a $3d$ substitutional impurity in silicon.

The temperature dependence of kinetic processes involving activation over a potential barrier is studied in the temperature range where quantum effects are important. Deviations form the Arrhenius law are determined and a simple formula for the dominant quantum corrections is obtained. The dissipative coupling to the environment is explicitly taken into account and the role of long-time memory is emphasized.

We report the observation of an order-disorder transition in the semiconductor strained-superlattice system GeSi/Si, which doubles the lattice periodicity in a $〈111〉$ direction. This phenomenon may be representative of a class of order-disorder transitions in strained-semiconductor systems, even when the lattice mismatch is small.

We study an extension of Lévy flight to include self-repulsion in the path of the walk. We call the extension node-avoiding Lévy flight and we show its equivalence to the $n\to 0$ limit of a statistical mechanical model for a magnetic system with long-range interactions between the spins. By use of this equivalence we are able to make a detailed comparison between the results of the $\epsilon$ expansion for the magnetic model, a Monte Carlo simulation of the Lévy flight model, and the results of a Flory-type argument. This is the first comparison of the $\epsilon$ expansion for $\epsilon \ll 1$ with a numerical simulation for any model. Some speculations are made on applications of the model of node-avoiding Lévy flight.

The asymptotic expansions derived for high-frequency scattering by cylinders and spheres are reexamined in detail. It is found that earlier results require small but significant corrections. The accuracy of the new analytical results is confirmed by comparison with numerical evaluations.

Permanent quark confinement is established for four-dimensional hierarchical lattice gauge theories in which the Migdal-Kadanoff approximate renormalization recursion formulas hold exactly. This holds for gauge groups $G=\mathrm{SU}\mathrm{}\left(N\right)\mathrm{}$ as well as $G=\mathrm{U}\mathrm{}\left(N\right)\mathrm{}$.

The ${\rho }^0$-meson spin alignment is studied in $\overline{p}p$ interactions at 22.4 and 12 GeV/c and in the reaction $\overline{p}p\to 2{\pi }^{+}+2\mathrm{}{\pi }^{-}+\mathrm{neutrals}$ at 5.7 GeV/c. An essential ${\rho }^0$-meson spin alignment is observed. The values of the ${\rho }_{00}^T$ element of the ${\rho }^0$-meson spin-density matrix in the transversity frame are 0.56 ± 0.07, 0.53 ± 0.05, and 0.54 ± 0.04 for the above-mentioned interactions, respectively. An increase of ${\rho }_{00}^T$ with ${\rho }^0$ transverse momentum is obtained.

We have measured the ratio $\frac{\Gamma (K_L\to {\pi }^{+}{\pi }^{-})}{\Gamma (K_L\to \pi l\nu )}$ to be (3.13 ± 0.14) × ${10}^{-3\mathrm{}}$ For $K_L$ with a mean laboratory momentum of 65 GeV/c. This value corresponds to the $\mathrm{CP}$-nonconservation parameter $\left|{\eta }_{+-}\right|=(2.28\mathrm{}\pm 0.06)\times {10}^{-3\mathrm{}}$, and is consistent with the world average $\left|{\eta }_{+-}\right|=(2.274\mathrm{}\pm 0.022)\times {10}^{-3\mathrm{}}$ which is derived from measurements with $K_L$ laboratory momenta less than 10 GeV/c. In this experiment we find no evidence for an energy dependence of $\left|{\eta }_{+-}\right|$.

We report new and precise measurements of the decay branching fractions of the $\tau$ lepton to one and three charged particles. The data, corresponding to an integrated luminosity of 176 ${\mathrm{pb}}^{-1\mathrm{}}$, were collected by the high resolution spectrometer HRS at the $e^{+}{e}^{-}$ storage ring PEP at SLAC operated at $\sqrt{s}=29\mathrm{}$ GeV. The fractions of $\tau$ decays into one and three charged particles are 0.869±0.002±0.003 and 0.130±0.002±0.003, respectively.

An experimental determination of the neutral-current structure functions of the nucleon is obtained by measuring the ratio of the neutral-current $x$ distribution to the charged-current $x$ distribution. The analysis is based on deep-inelastic neutrino-nucleon scattering data gathered in a massive fine-grained neutrino detector exposed to a narrow-band neutrino beam at Fermilab.

Differential-cross-section and vector-analyzing-power angular distributions of the reaction ${}_{}{}^{48}{}_{}{}^{}\mathrm{Ca}(d_{\mathrm{pol}}, \alpha ){}_{}{}^{46}{}_{}{}^{}\mathrm{K}$ at $E_d=79.4\mathrm{}$ MeV unambiguously reveal $J^{\pi }=7^{+}$ transitions to states at 4.54 and 5.95 MeV in ${}_{}{}^{46}{}_{}{}^{}\mathrm{K}$, the latter of which is quite strong. Such transitions result from the pickup of a stretched ${\left(1\mathrm{}{f}_{\frac{7}{2}}\right)}_{J=7,T=0\mathrm{}}^2$ configuration proton-neutron pair. A comparison of strength to the $7^{+}$ transition in ${}_{}{}^{50}{}_{}{}^{}\mathrm{Ti}(d, \alpha ){}_{}{}^{48}{}_{}{}^{}\mathrm{Sc}$ (1.10 MeV) implies a relatively large $1f_{\frac{7}{2}}$ proton occupation number of 0.65 ± 0.20 for the ${}_{}{}^{48}{}_{}{}^{}\mathrm{Ca}$ ground state.

Barriers to the mass-asymmetric fission of ${}_{}{}^{111}{}_{}{}^{}\mathrm{In}$ are calculated in the liquid-drop and in the Yukawa-plus-exponential finite-range models. The calculated barrier heights are compared to those previously inferred from fission excitation functions for $3<~Z<~11$. The liquid-drop-model barriers are about 12 MeV too high, while the finite-range model gives barriers an average of 1.6 MeV too high. This type of experimental data should make possible a more precise determination of the surface-energy and surface-asymmetry coefficients in semiempirical nuclear mass formulas.

A quantum-mechanical model for the emission of fast nucleons in low-energy nucleus collisions is presented. The role of a classical emission function is shown to be played by the time derivative of an impact-parameter-integrated, time-dependent, distorted-wave Wigner function. Correlations between the emitted particles are shown to be caused by the Pauli principle, by the impact-parameter dependence of the emission process, and by two-body collisions including the final-state interactions, as well as those due to the size of the emitting source.

The correlation between the spin orientations of the two ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$($2^{+}$) nuclei in mutual inelastic ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ + ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ scattering has been deduced from the directional correlations of the particle-coincident $\gamma$ rays measured with a crystal-ball detector. Resonances in the cross section are found to be nearly uniquely associated with the mutually aligned component. The strong resonance structure as well as the characteristic behavior of the angular distributions of this reaction component are suggestive of the formation of a rotating dinuclear complex in the sticking configuration.