The hot-electron energy loss rate (ELR) is studied by using the nonequilibrium Green’s function approach. The effect due to the anharmonic interaction is considered. As a result, hot electrons lose their energy primarily by creating pairs of acoustic phonons via LO phonons. When acoustic phonons are kept at the lattice temperature, the nonequilibrium distribution for LO phonons is derived by imposing the steady state condition. We show that our result is able to account for the dramatic enhancement of the hot-electron ELR observed in GaAs/GaAlAs semiconductors at low temperatures.

Local surface photovoltage (SPV) measurements were used to measure how the electric field of a scanning tunneling microscope tip perturbs the electronic band structure at Si(001), Si(111)-(7×7), and H-terminated Si(111) surfaces. The results demonstrate that tip-induced band bending is important under typical STM conditions even on surfaces whose surface Fermi levels are nominally ‘‘pinned.’’ Spatially resolved measurements of band bending as a function of sample bias show that atomic-scale contrast in SPV images can result from local variations in the ability of the surface states under the tip to screen external electric fields.

We report the first observation of sharp and spatially localized maxima in the density of a two-dimensional electron gas (2DEG) created by impinging the alpha particles. The 5 MeV alpha particles were each found to generate a positive charge in the ${\mathit{n}}^{+}$ doped AlGaAs, which in turn created the potential notch for the 2DEG at the GaAs/AlGaAs interface. This notch was found to decay logarithmically over a time scale of several seconds. The expected profile of the potential minima was roughly determined by the influence the potential had on the conductance of the nearby quantum point contact. Alpha particles hitting within about 5 μm from the point contact could be detected.

We consider the neutron scattering in the magnetic phases with zero average sublattice magnetization (double- or triple-spin correlator as an order parameter). External magnetic field induces different magnetizations on the different sublattices in such a system. As a result, the new purely magnetic Bragg peaks for the elastic neutron scattering appear. We present the estimates of intensities in the Bragg peaks and their angular dependence on the external magnetic field. This could serve as a test whether the nontrivial magnetic order exists in some heavy fermion compounds, like ${\mathrm{URu}}_2$${\mathrm{Si}}_2$ or ${\mathrm{UPt}}_3$ and possibly in the high-${\mathit{T}}_{\mathit{c}}$ oxides.

We show that the spontaneous symmetry breaking mechanism in quantum antiferromagnets is due to the collapse, in the thermodynamical limit, of an infinite set of excited states onto the ground state. We characterize both the nature and the scaling of the relevant tower of states for the quantum antiferromagnet on the triangular lattice. Comparison with recent numerical results for the S=1/2 case gives strong support for the existence of long range order in this system.

We report an induced spin polarization in epitaxially grown bcc-textured Ru adlayers on Fe(100) as well as in the Ru spacer layer in exchange-coupled Fe/Ru/Fe trilayers. The measured spin polarization has a maximum value of ${\mathit{P}}_{\mathrm{Auger}}$=(10±2)% at the Fe interface which, in a crude approximation, corresponds to 0.7${\mathrm{\mu }}_{\mathit{B}}$ per atom. The polarization profile in Ru away from the interface is either a steep decrease or a strongly damped rapid oscillation.

Third-order spin-orbit contributions to two-photon absorption rates were introduced by Judd and Pooler when the second-order theory was found to be inadequate to explain the experimental data for ${\mathrm{Gd}}^{3+}$ ions in ${\mathrm{LaF}}_3$. However, only one of the two perturbation terms that arise in thrid order was considered. When the omitted term is added, ‘‘unlinked’’ parts are canceled and the good agreement with experiment is lost. Inclusion of previously overlooked scalar two-electron contributions can restore the agreement between theory and experiment.

Excitation spectra and optical anisotropy for laser-induced ${\mathrm{Ga}}^0$ emission initiated by defects on GaAs(110) surfaces have been measured. It is found that the ${\mathrm{Ga}}^0$ emission yield is enhanced sharply when the photon energy increases across both 1.87 and 2.55 eV and that the enhancement is much larger for photons polarized parallel to the [11¯0] direction than for those polarized perpendicular. The result indicates that electron-hole pairs on the surface are particularly effective in the defect-initiated emission of ${\mathrm{Ga}}^0$.

We present new sum rules for magnetic dichroism in spin polarized photoemission from partly filled shells which give the expectation values of the orbital and spin magnetic moments and their correlations in the ground state. We apply this to the 4f photoemission of rare earths, where the polarization effects are 2 orders of magnitude larger than in 3d transition metals. The very strong dichroism in the 4f electron yield opens new perspectives for the characterization of magnetic rare earth surfaces and thin films.

The probabilistic element of quantum theory can be combined with the unitary time evolution of Schrödinger’s equation in a natural and consistent way using the idea of a quantum trajectory, the quantum analog of the trajectory traced out in phase space as a function of time by a point representing the state of a closed classical system. A family of quantum trajectories can be defined using bases for the quantum Hilbert space at different times chosen so that an appropriate noninterference condition, related to the Gell-Mann and Hartle notion of medium decoherence, is satisfied. The result is a generalization of the consistent histories approach to quantum mechanics.

We consider a model of a D-dimensional tethered manifold interacting by excluded volume in ${\mathit{openR}}^{\mathit{d}}$ with a single point. By use of intrinsic distance geometry, we first provide a rigorous definition of the analytic continuation of its perturbative expansion for arbitrary D, 0<D<2. We then construct explicitly a renormalization operation ssR, ensuring renormalizability to all orders. This is the first example of mathematical construction and renormalization for an interacting extended object with continuous internal dimension, encompassing field theory.

We study the Lorentz gas in small external electric and magnetic fields, with the particle kinetic energy held fixed by a Gaussian ‘‘thermostat.’’ Starting from any smooth initial density, a unique stationary, ergodic measure is approached for times t→∞. The steady-state electric current J(B,E) is given by a Kawasaki formula and the entropy production J⋅E/T, with T the ‘‘temperature,’’ is equal to both the asymptotic decay rate of the Gibbs entropy and minus the sum of the Lyapunov exponents. The Einstein and Kubo formulas hold, i.e., J(B,E)=σ(B)⋅E + higher order terms, with the diffusion matrix D(B) at E=0 given by ${\mathit{k}}_{\mathit{B}}$T times the symmetric part σ̃(B) of the conductivity matrix.

From the October 1989 launch to the first December 1990 Earth gravity assist, we regularly obtained frequency measurements of the spacecraft clock—an ultrastable crystal oscillator (USO) supplied by Frequency Electronics Inc. The solar gravitational redshift in frequency was readily detectable, and because of the unique variations in heliocentric distance, we could separate the general relativistic effects from the USO’s intrinsic frequency variations. We have verified the total frequency shift predicted by general relativity to 0.5% accuracy, and the solar gravitational redshift to 1% accuracy. This is the first test of the solar redshift with an interplanetary spacecraft.

Tensor-scalar theories of gravity are shown to generically contain an attractor mechanism toward general relativity, with the redshift at the beginning of the matter-dominated era providing the measure for the present level of deviation from general relativity. Quantitative estimates for the post-Newtonian parameters γ-1, β-1, and Ġ/G are given, which give greater significance to future improvements of solar-system gravitational tests.

It is shown that a wide class of tensor-scalar theories can pass the present weak-field gravitational tests and exhibit nonperturbative strong-field deviations away from general relativity in systems involving neutron stars. This is achieved without requiring either large dimensionless parameters, fine tuning, or the presence of negative-energy modes. This gives greater significance to tests of the strong gravitational field regime, notably binary pulsar experiments.

The recent measurement of anisotropies in the cosmic microwave background by the Cosmic Background Explorer (COBE) satellite and the recent South Pole experiment offer an excellent opportunity to probe cosmological theories. We test a class of theories in which the Universe today is flat and matter dominated, and primordial perturbations are adiabatic parametrized by an idex n. In this class of theories the predicted signal in the South Pole experiment depends on n, the Hubble constant, and the baryon density. For n=1 a large region of this parameter space is ruled out, but there is still a window open which satisfies constraints from COBE, measurements of the age of the Universe, the South Pole experiment, and big bang nucleosynthesis. We also explore the effect of varying n.

A construction of ${\mathit{W}}_3$ algebra for the SU(3) parafermion model is proposed, in which a Z algebra technique is used instead of the popular free-field realization. The central charge of the underlying algebra is different from known W algebras.

We present measurements from events with two isolated prompt photons in p¯p collisions at √s =1.8 TeV. The differential cross section, measured as a function of transverse momentum (${\mathit{P}}_{\mathit{T}}$) of each photon, is about 3 times what next-to-leading-order QCD calculations predict. The cross section for photons with ${\mathit{P}}_{\mathit{T}}$ in the range 10–19 GeV is 86±27(stat${)}_{\mathrm{-}23}^{+32\mathrm{}}$(syst) pb. We also study the correlation between the two photons in both azimuthal angle and ${\mathit{P}}_{\mathit{T}}$. The magnitude of the vector sum of the transverse momenta of both photons, ${\mathit{K}}_{\mathit{T}}$=‖${\mathbf{P}}_{\mathit{T}1}$+${\mathbf{P}}_{\mathit{T}2}$‖, has a mean value of 〈${\mathit{K}}_{\mathit{T}}$〉=5.1±1.1 GeV.

The nuclear S-wave pion production is described by the axial charge density operator of the two-nucleon systen. It is shown that the short range axial exchange charge operator implied by the nucleon-nucleon interaction enhances the predicted cross section for the reaction pp→pp${\mathrm{\pi }}^0$ near threshold by factors 3–5. This suffices to explain most of the underprediction obtained with the single-nucleon and S-wave pion rescattering operator. The result implies that the cross section for pp→pp${\mathrm{\pi }}^0$ can provide direct information on the short range components of the nucleon-nucleon interaction.

Perturbative analysis of parton kinetics for high energy nuclear collisions shows that thermal equilibration of gluons happens very fast, while quark production is much slower. A simple ‘‘minimal model’’ is proposed which includes only incoming quarks and antiquarks. We have found that a smaller quark number is more than compensated by the fact, that they are imbedded into the hotter glue. Predicted yield of dileptons and photons in the interesting kinematic region are larger than considered before, and are quite observable at the BNL Relativistic Heavy Ion Collider and the CERN Large Hadron Collider.