The difference in ‘‘spin up’’ and ‘‘spin down’’ angular intensities of photoelectrons emitted from inner core levels of atoms in a magnetic crystal gives a spin hologram. The reconstructed holographic image peaks at the positions of neighboring magnetic atoms with peaks proportional to the component of their spins in the direction that the detected electrons are spin analyzed. Measuring the spin difference in three orthogonal directions determines a vector hologram which gives an image of the atomic spin vectors.

Tunneling microscopy and spectroscopy, in conjunction with tight-binding molecular dynamics, provide compelling evidence that the ‘‘missing As’’ defect on GaAs(110) is indeed an As vacancy. Neighboring Ga atoms relax upward by about 0.7 Å, but do not rebond. The defect is positively charged and most likely in a +2 state. Both the relaxation and the preponderance of As vacancies on p-GaAs are explained by the energetics of the defect levels. The essential features of the observations can be understood from qualitative arguments based on hybrid orbitals.

The dependence of the structural relaxation around phosphorous vacancies in InP(110) and GaP(110) surfaces on their charge state was investigated by scanning tunneling microscopy. Two charge transition levels were localized within the band gap. The symmetry of the vacancies is lowered with an increasing number of electrons bonded in the electronic defect states. The vacancies on InP(110) and GaP(110) surfaces have essentially the same structure.

Fluorescence spectra of ${\mathrm{C}}_{60}$ in n-hexane at room temperature, obtained under excitation at 514.5 and 337.1 nm, are presented. The spectra were measured with subnanosecond laser excitation in a 5-ns gate synchronous with the excitation. The emission, in the range 1.5 to 2.2 eV for excitation at 514.5 nm (2.41 eV), is characterized by a narrow peak at 2.05 eV (i.e., 606 nm, 7.2 nm FWHM) which is predominant in the spectrum, while many resolved vibronic structures emerge, down to energies as low as 0.4 eV, in the spectrum obtained with excitation at 337.1 nm (3.68 eV).

We calculate the structural and electronic properties of the ${\mathrm{Na}}_6$${\mathrm{C}}_{60}$ fulleride using the Car-Parrinello method as well as standard local density approximation band structure calculations. In contrast to previous claims we find that metal clusters do not form but, like the potassium and rubidium fullerides, sodium intercalation gives rise to a conventional ionic compound. Unlike the case of heavier alkali fullerides, a characteristic new kind of low-lying electron state appears that is not the ${\mathrm{C}}_{60}$ state. Effects of temperature on the electronic nature of the compound are discussed as well as consequences of these findings for higher fullerides.

A series of atomistic calculations is performed in order to establish criteria for dislocation emission from cracks in a model hexagonal lattice. We find that except for special orientations, additional tensile broken-bond effects must be added to existing theories based on shear effects, in order to correctly estimate the critical stress intensity ${\mathit{K}}_{\mathit{e}}$ required for dislocation emission. From this, a new ductility criterion for materials is proposed which does not depend on the intrinsic surface energy, but contains only the unstable stacking fault parameter.

A well-defined spectrum component characterized by a large nuclear quadrupole interaction is observed in the Mössbauer spectra of Te-doped ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As under conditions where the presence of DX centers is confirmed by electrical techniques. Upon illumination after cooling in the dark this component transforms partly into an unsplit Mössbauer line, reflecting photoionization of the DX center into a substitutional shallow donor. The lifetime of the photoionized centers is determined from the time evolution of the Mössbauer spectra. The hyperfine interaction parameters derived from the Mössbauer spectra are consistent with large lattice relaxation and a pure p-electron imbalance at the DX center.

Measurements have been made of the Larmor frequency of the normal ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ Fermi liquid with resolution better than 1/${10}^7$. The Larmor frequency was observed to increase on increasing temperature from the superfluid transition to above 40 mK in a constant 0.12 T external magnetic field. The shift has a temperature dependence that is negative and approximately proportional to the inverse temperature. The magnitude is of order 1/${10}^6$ and depends on pressure in the investigated range 0.3 to 21.7 bars decreasing substantially at the highest pressures.

High-resolution nuclear magnetic resonance measurements of bulk superfluid ${}_{}{}^3{}_{}{}^{}\mathit{B}$ have been performed at temperatures above 0.5 mK and at pressures from 0.3 to 21.7 bars. We have found that the resonance frequency is shifted from the Larmor frequency of the normal fluid. According to the theory of Greaves the shift at the superfluid transition determines a specific combination, ${\mathrm{\beta }}_{345}$, of the 5 fourth-order coefficients of the order parameter invariants used in the Ginzburg-Landau description of superfluid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$. We found that ${\mathrm{\beta }}_{345}$ approaches the weak coupling limit at low pressure, and decreases at higher pressures qualitatively consistent with the theory of Sauls and Serene but in disagreement with the results of Tang et al.

Nuclear adiabatic demagnetization has been done for both hcp and bcc solid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ with exchange interactions of the order of 10 μK. Observed isochoric pressure increase during the demagnetization for the bcc sample at a molar volume of 19.99 ${\mathrm{cm}}^3$/mol showed clear magnetic transitions at the upper and the lower critical fields as is known for lower density solids. On the other hand, no pressure increase was observed for the hcp sample at 19.07 ${\mathrm{cm}}^3$/mol down to a zero magnetic field. These observations give strong evidence that the ground state in hcp ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ is ferromagnetic.

We have studied melting-freezing waves on helium-4 crystal surfaces which are tilted by a small angle φ with respect to the c facets. We present the first experimental evidence that a crossover exists from stepped to rough behavior as a function of angle. We demonstrate this by the independent measurement of the two components ${\gamma }_{\mathrm{\parallel }}$ and ${\gamma }_{\mathrm{\perp }}$ of the surface stiffness. In the stepped regime, below the crossover angle ${\mathrm{\phi }}_{\mathit{c}}$≊3°, we also measured both elastic and entropic contributions to the step interactions.

We show that, contrary to previous modeling and experiments, threading dislocation annihilation plays the dominant role in obtaining low threading dislocation densities during low temperature growth of compositionally graded SiGe layers. This is demonstrated by measuring the number of dislocations nucleated, which together with the density of threading dislocations, provides a direct measure of the number of annihilation events. Thread annihilation happens on a much larger scale than expected because the dislocation reproduction mechanism results in the ‘‘self-alignment’’ of the sources, leading to an (almost) perfect network of zigzagging dislocations.

We repeat the numerical experiments for diffusion limited aggregation (DLA) and show that there is a potentially infinite set of conserved quantities for the long time asymptotics. We connect these observations with the exact integrability of the continuum limit of the DLA (quasistatic Stefan problem). The conserved quantities of the Stefan problem (harmonic moments) when discretized are our conserved quantities. These numerical experiments show that the exact integrability of the Stefan problem may be continued beyond the formation of cusps in the moving boundary.

Scattering by a single impurity introduced in a strongly correlated electronic system is studied by exact diagonalization of small clusters. It is shown that an inert site which is spinless and unable to accommodate holes can give rise to strong resonant scattering. A calculation of the local density of states reveals that, for increasing antiferromagnetic exchange coupling, d,- s,- and p-wave symmetry bound states in which a mobile hole is trapped by the impurity potential induced by a local distortion of the antiferromagnetic background successively pull out from the continuum.

We demonstrate the level statistics in the vicinity of the Anderson transition in d>2 dimensions to be universal and drastically different from both Wigner-Dyson in the metallic regime and Poisson in the insulator regime. The variance of the number of levels N in a given energy interval with 〈N〉≫1 is proved to behave as 〈N${\mathrm{〉}}^{\gamma }$ where γ=1-(νd${)}^{\mathrm{-}1}$ and ν is the correlation length exponent. The inequality γ<1, shown to be required by an exact sum rule, results from nontrivial cancellations (due to the causality and scaling requirements) in calculating the two-level correlation function.

The Kondo effect in a repulsively interacting electron system (Tomonaga-Luttinger liquid) is studied. By using the poor man’s scaling method it is shown that the Kondo coupling in this model flows to the strong-coupling regime not only for the antiferromagnetic but also for the ferromagnetic case. The ground state is governed by stable strong-coupling fixed points where the impurity spin is completely screened; the fixed-point Hamiltonian consists of two semi-infinite Tomonaga-Luttinger liquids and a spin singlet. Specific heat, susceptibility, and conductance are calculated for low temperatures.

We describe periodic, one dimensional Schrödinger operators, with the property that the widths of the forbidden gaps increase at large energies and the gap to band ratio is not small. Such systems can be realized by periodic arrays of geometric scatterers, e.g., a necklace of rings. Small, multichannel scatterers lead (for low energies) to the same band spectrum as that of a periodic array of (singular) point interactions known as δ’. We consider the Wannier-Stark ladder of δ’ and show that the corresponding Schrödinger operator has no absolutely continuous spectrum.

A system of electrons in a half-filled Landau level is investigated in spherical geometry. For systems of size from N=1 to 14 electrons with flux ${\mathit{N}}_{\mathrm{\phi }}$=2(N-1) the angular momentum of the ground state is as predicted by Hund’s second rule for composite fermions of one electron and two vortices at zero magnetic field. Low lying excitations also fit this interpretation and trial wave functions give excellent overlaps. The two-particle correlation function shows a significant correlation hole at short distances and suggests an asymptotically oscillating form at long distances, as in a Fermi liquid.

We have operated a five-junction electron pump with an error for transferring electrons of approximately 0.5 part per ${10}^6$. The error predicted from existing theory is several orders of magnitude smaller, thus implying that our present understanding of the Coulomb blockade is incomplete. We conjecture that the errors arise from photon-assisted tunneling, where the photon energy is supplied by noise from the environment.

We consider the one-dimensional Hubbard model at half filling. We show that both excitation spectrum and S matrix are determined by the SO(4) symmetry of the model. The complete set of excitations is given by the scattering states of four elementary excitations, which form the fundamental representation of SU(2)×SU(2). We evaluate the exact S matrix, which satisfies the Yang-Baxter relation. The results for the repulsive and attractive Hubbard model are related by an interchange of spin and charge degrees of freedom.