Customary optical reconstruction, until now a time-consuming process, can be replaced with digital computations to dynamically and quantitatively observe microscopic magnetic fields. Electron holograms of time-varying fields are first recorded on videotape. Next, each hologram is reconstructed and phase amplified by computation. Interference micrographs are then reedited on the videotape and are finally displayed dynamically. Using this method, the movement of magnetic fluxons trapped in a thin superconductive film of lead are observed for the first time near the critical temperature. (The fluxon diameters on the surface look thicker when the sample temperature is raised from 9 K. Fluxons then begin to move near 7 K and finally disappear at the critical temperature 7.2 K.)

Frustration in a surface structure has been observed in real space and time using the scanning tunneling microscope. The frustration is revealed as an instability of an inherent feature in the Si(111) ‘‘pseudo 5×5’’ Cu structure. A possible origin of the frustration is proposed.

Comptuer simulation on a two-dimensional anisotropic lattice-gas model of oxygen ordering in high-${\mathit{T}}_{\mathit{c}}$ supeconductors of the ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ -type shows that the ordering dynamics obey algebraic growth laws which are different in the ortho-I and ortho-II phases. It is possible to relate this dynamical scaling behavior to a similar scaling in the experimentally observed temporal variation of the superconductivity transition temperature, hence suggesting a specific coupling between the coherence of oxygen order in the basal Cu-O planes and the superconducting state.

Singular phenomena in highly strained ${\mathrm{In}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As are used to test current theories of dislocation dynamics in thin films. Strong support is found for a temperature-dependent frictional force which has an activation energy of magnitude of the Peierls energy. With this force, an abrupt temperature-dependent transition in the critical thickness of pseudomorphic growth is explained for the first time; the island-to-layer growth-mode transition which occurs at this temperature is shown to be equivalent to a similar x-dependent transition, and island growth is attributed to nucleation by misfit dislocations.

The multilayer growth of ${\mathrm{N}}_2$ on graphite has been studied by ellipsometry and stray-light measurements. Above the α-β transition temperature of bulk ${\mathrm{N}}_2$, there is incomplete wetting with a sequence of layering transitions which could be followed from the fifth to the tenth layer. At lower temperatures, the adsorption isotherms show only two stable monolayer steps; however, optically smooth layers of α solid can be grown on top of the double layer.

We report the first observation of isotope shifts in optical spectra of an impurity in a solid associated with isotopes in the impurity surrounding. Static and dynamic couplings of impurity electronic states with the crystal lattice are discussed as a possible cause of the observed isotope structure in optical spectra of ${\mathrm{LiYF}}_4$:Ho

It is shown that, at low temperatures, the absolute thermal fluctuations of the spin-stiffness constant in the classical Heisenberg model are independent of the scale L for d<4, if L is larger than the lattice spacing but smaller than the correlation length, while the relative fluctuation is proportional to ${\mathit{L}}^{4\mathrm{-}2\mathit{d}}$, where d is the dimensionality, and is thus scale independent in d=2 (with logarithmic corrections). The phenomenon is strikingly similar to the universal conductance fluctuations known for the problem of an electron in a random potential.

We present a theoretical explanation of the unusual temperature-dependent anisotropy of ${\mathit{H}}_{\mathit{c}2}$ reported by Shivaram et al. for single crystals of ${\mathrm{UPt}}_3$, which we argue provides strong support for unconventional odd-parity pairing. We show that the observed low-temperature crossover in the anisotropy ratio, ${\mathit{H}}_{\mathit{c}2}^{\mathrm{\perp }}$/${\mathit{H}}_{\mathit{c}2}^{\mathrm{?}}$, can be explained by paramagnetic limiting for H parallel to the sixfold axis within BCS pairing theory if the order parameter has odd parity and there is strong spin-orbit coupling of the pair spin to the crystal axes.

We suggest that Hartree-Fock theory is a good starting point for the solution of ab initio-derived extended Hubbard Hamiltonians for magnetic insulators like ${\mathrm{La}}_2$Cu${\mathrm{O}}_4$, as indicated by surprisingly accurate results for the superexchange frequencies and insulating gaps for this material and isostructural ${\mathrm{La}}_2$Ni${\mathrm{O}}_4$, ${\mathrm{K}}_2$Cu${\mathrm{F}}_4$, and ${\mathrm{K}}_2$Ni${\mathrm{F}}_4$. Limited configuration interaction beyond Hartree-Fock theory is then used to demonstrate that admixtures of $a_1 \left(d_{3z^2-r^2}\right)$ symmetry states at energies somewhat away from the gap edge are essential to the dispersion of the first quasiparticle branch in ${\mathrm{La}}_2$Cu${\mathrm{O}}_4$ for doped-in holes.

High-resolution electron-energy-loss spectroscopy of the surface of graphite reveals a discrete loss feature attributed to the excitation of a π-band plasmon polarized with E∥c. The frequency of the plasmon is found to be strongly temperature dependent. This arises from the contribution of thermally generated carriers to the plasma frequency, as confirmed by explicit calculations using the graphite band structure. From the observed temperature dependence of the plasmon width, we also obtain quantitative details of the plasmon decay channel, which is found to be dominated by the low-frequency electron-hole pair excitations characteristic of a semimetal. Similar effects are expected in other semimetals.

Measurements of discrete resistance fluctuations in novel metal-insulator-metal-insulator-metal tunnel junctions show the presence of single ionic defects that can be moved reversibly between adjacent lattice sites in the insulating barrier. By analyzing the change in switching lifetimes and junction conductance resulting from these displacements, it is concluded that electron tunneling is the dominant trapping mechanism, rather than metastable transitions of the defect state.

The surface-state excitation energies for the Si(111)2×1 surface have been calculated in the GW approximation. The energy position and the dispersion of the occupied and empty surface states are in excellent agreement with photoemission and inverse-photoemission experiments. The calculated quasiparticle surface-state band gap, 0.62 eV, is 0.15 eV larger than the measured onset energy for electron-hole pair excitations. The possibility that excitonic effects are responsible for this difference is examined.

Spin-polarized photoemission spectra at low photon energies from ferromagnetic ultrathin Fe layers on Cu(100) show a substantial polarization of the Cu 3d peaks. This is attributed to spin-dependent attenuation in the Fe overlayer. Values of the spin-dependent mean free path at low electron energies are obtained.

The energy of a metallic crystal is expressed as a sum of volume, surface, and curvature terms. The fully self-consistent solution of a simplified problem shows that, in the absence of shell-structure effects, this expression can be accurate even for atomic-scale properties. Thus the liquid-drop model, originally developed for finite systems (nuclei), may actually be more appropriate for infinite ones (metals). First applications are made to the face dependence of the surface energy and to monovacancy-formation and cohesive energies. Predictions of the model may be tested by experiment or by fully self-consistent Kohn-Sham calculations.

We present an exact solution of the problem of the upper critical field of an ${\mathit{E}}_1$ or ${\mathit{E}}_2$ superconductor. This resolves a long-standing difficulty in the theory of these materials, since only variational methods have been available up to this time. The solution is valid for all directions of the external field relative to the crystal axes. This makes the anisotropy of the upper critical field into an unambiguous test of unconventional superconductivity. Good agreement with experimental measurements on ${\mathrm{UPt}}_3$ is found.

We have examined the zero-bias conductance peak that is often found in high-temperature-superconductor tunnel-junction spectra. We have also measured the Bi-Sr-Ca-Cu-O thin-film energy gap. The zero-bias conductance peak can be explained in terms of quasiparticle tunneling, phase diffusion, and a supercurrent. The implications of this model are discussed.

We explore possible distinctions between multifractal scaling phenomena and Lagrangian field theories (FT’s) describing standard critical phenomena, via the operator-product expansion. While the scaling dimensions ${\mathit{x}}_{\mathit{n}}$ of multifractal moments must be convex functions of the order n, analogous FT exponents of powers of the field are concave, by stability and correlation inequalities, and cannot describe multifractal scaling. However, powers of gradients of the field may lead to a novel and unexpected multifractal convexity in a FT, such as, e.g., the nonlinear σ model.

We propose an experiment which demonstrates the nonlocal properties of a singe-photon field via phase-sensitive measurements. This is the first proposal which demonstrates nonlocality and a violation of Bell’s inequality with a single photon rather than a correlated photon pair.

We discuss the possibility that different realms of physics are described by distinct quantization constants. From the consistency of existing data, we infer limits on the differences between hypothetically distinct quantization constants for different elementary particles. Since the existence of multiple Planck constants implies violations of space-time symmetries, these limits may be viewed as precise tests of fundamental conservation laws, including the conservation of linear momentum and energy.

The usual picture of spacetime consists of a continuous manifold, together with a metric of Lorentzian signature which imposes a causal structure. We consider a model in which spacetime consists of a discrete set of points taken at random from a manifold, with only the causal structure remaining. Using only this structure, we show how to construct a metric, how to define the effective dimension, and how such quantities may depend on the scale of measurement. We discuss possible desirable features of the model.