We present an exact calculation of the persistent current in interacting disordered 1D rings. This system exhibits a variety of interesting behaviors depending on the disorder and the strength of electron-electron interactions. We find that even for the disordered case the current at high values of interactions is strongly suppressed due to the Mott-Hubbard metal-insulator transition. We observe that no dramatic increase of the averaged current or its rms value as a result of interactions is possible for these systems.

Narrow channels containing a one-dimensional electron gas of finite length exhibit periodic conductance oscillations. We propose a microscopic theory of this phenomenon based on an exactly solvable, interacting-electron model. In contrast to previous models, the present theory is applicable irrespective of the relative magnitude of the electron-electron interaction energy and the single-particle energy-level spacing.

We have measured tunneling rates for the escape of electrons from the surface of liquid helium. They agree with calculated results using a 1D image potential previously determined by spectroscopy and a static, single-particle potential term incorporating the dynamics of the 2D electron gas.

By relying on a recent theory of transport in the mixed state and a related model of pinning in soft materials, the instantaneous critical current is introduced as a well-defined part ${\mathit{I}}_1$ of the total constant current. This nondissipative and time-dependent ${\mathit{I}}_1$ is assumed to be randomly distributed near the sample surface, and is described as a 2D turbulent homogeneous flow. Auto- and cross-correlation functions of both voltage and magnetic field noises are predicted and are in full agreement with experiments.

Microbridges with dimensions smaller than the London penetration depth λ have been prepared in epitaxial ${\mathrm{YBaCu}}_2$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ thin films by means of electron beam lithography. Typical peaks and kinks are observed in their differential resistance versus current characteristics which can be attributed to coherent flux motion. A vortex activation energy proportional to the inverse current 1/I is obtained. Both the current and the temperature dependence of the activation energy are consistent with the collective flux creep model if the dimensionality of the elastic vortex lattice equals 2.

Recent tunneling and photoemission data on the cuprate oxide superconductors may provide important information in choosing between proposed models for the superconducting order parameter in these materials. We show that corrections to the weak coupling mean-field approximation for a superconductor lead to different frequency thresholds for the spontaneous decay of the Bogoliubov quasiparticles for different order parameter symmetries and that these effects may be seen in the superconductor-insulator-superconductor tunneling conductance. Comparison with the recent data indicates that a ${\mathit{d}}_{\mathit{x}}^2$-${\mathit{y}}^2$, rather than an s-wave, order parameter is a likely candidate for describing the cuprates.

We present optical reflectivity and Raman scattering studies of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{6+\mathit{x}}$ as a function of doping using c-axis polarized light. The c-axis optical response of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$ is characterized by a Drude-like conductivity and an electronic Raman continuum, indicating a weak coupling between adjacent ${\mathrm{CuO}}_2$ bilayers which is mediated by the CuO chains. With reduced doping, the c-axis Drude and continuum responses rapidly decrease, revealing a strong sensitivity of the interbilayer coupling strength to the removal of oxygen from the chain sites. We suggest that interbilayer charge transport in ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{6+\mathit{x}}$ may be governed by carrier scattering from in-plane fluctuations.

Experimental and theoretical three-dimensional momentum densities of magnetic electrons in ferromagnetic iron are reported for the first time and are found to be in good qualitative agreement. The experimental momentum density is reconstructed from fourteen one-dimensional magnetic Compton profiles, and the theoretical one is calculated by the full-potential linearized augmented-plane-wave method. The experimental indicates that the theory slightly underestimates the negative spin polarization of the s,p-like electrons in the first Brillouin zone and slightly overestimates umklapp processes.

Magnetic systems are currently considered attractive candidates in which to look for quantum phenomena such as the tunneling of the total magnetization of a small (∼100 Å diameter) particle out of a metastable easy direction or between degenerate easy directions. The effect of nuclear spins as a dissipative environment for such a particle is considered and shown to be significant. Two dimensionless parameters characterize the dissipation: a coupling strength varying as the number of nuclear spins, and the ratio of the nuclear and electronic Larmor frequencies.

We develop a theory of photoluminescence from the magnetically induced two-dimensional Wigner crystal. It is found that the photoluminescence spectrum is a weighted measure of the single particle density of states of the electron system, which for an undisturbed electron lattice has the intricate structure of the Hofstadter butterfly. It is shown that the interaction of a localized hole with the electron lattice wipes out this structure, but that an itinerant hole can, in principle, detect it. Experimental implications are discussed.

We report strong magnetic linear dichroism at the Fe ${\mathit{L}}_{2,3}$ edge of the antiferromagnet ${\mathrm{Fe}}_2$${\mathrm{O}}_3$ (hematite). The relative difference in absorption for light polarized parallel and perpendicular to the magnetic moment is as high as 40% at the Fe ${\mathit{L}}_2$ edge. The spectra are in excellent agreement with calculations of magnetic dichroism for ${\mathrm{Fe}}^{3+}$ (3${\mathit{d}}^5$). The magnetic origin of this dichroism is demonstrated by the Morin transition at ≊-10 °C, where the moments in ${\mathrm{Fe}}_2$${\mathrm{O}}_3$ rotate by 90°. Magnetic linear dichroism may be applied to measure the spin orientation in thin films and multilayers, and to image magnetic domains.

Superconducting gap anisotropy at least an order of magnitude larger than that of the conventional superconductors has been observed in the a-b plane of ${\mathrm{Bi}}_2$${\mathrm{Sr}}_2$${\mathrm{CaCu}}_2$${\mathrm{O}}_{8+\mathrm{\delta }}$ in angle-resolved photoemission spectroscopy. For samples with ${\mathit{T}}_{\mathit{c}}$ of 88 K, the gap size reaches a maximum of approximately 20 meV along the Cu-O bond direction, and a minimum of much smaller or vanishing magnitude 45° away. The experimental data are discussed within the context of various theoretical models. In particular, a detailed comparison with what is expected from a superconductor with a ${\mathit{d}}_{\mathit{x}}^2$-${\mathit{y}}^2$ order parameter is carried out, yielding a consistent picture.

A simple dynamical criterion for crystallization of a colloidal fluid which undergoes Brownian motion is proposed, similar in spirit to the classic Lindemann melting rule. It states that the ratio of the long-time and short-time self-diffusion coefficients is a universal number very close to 0.1 along the freezing line. This phenomenological crystallization rule is confirmed both by Brownian dynamics simulations of a Yukawa liquid and by forced Rayleigh scattering experiments on charge-stabilized colloidal suspensions.

The rate at which pure initial states deteriorate into mixtures is computed for a harmonic oscillator interacting with an environment in thermal equilibrium. The decoherence process resulting from this interaction selects a set of states characterized by maximal stability (or minimal loss of predictive power) which can be quantified by the rate of increase in either linear or statistical entropy. In the weak coupling limit, coherent states are shown to produce the least entropy, thus becoming the natural counterparts of classical points in phase space.

We study geodesically complete, singularity free space-times induced by planar domain walls interpolating between supersymmetric Minkowski (${\mathrm{M}}_4$) and anti-de Sitter (Ad${\mathrm{S}}_4$) space-times. A geodesically complete space-time with [without] closed timelike curves includes a finite [infinite] number of semi-infinite ${\mathrm{M}}_4$ regions, separated by a region of Ad${\mathrm{S}}_4$. The space-times are nonsingular and exhibit Cauchy horizons with zero Hawking temperature and vanishing entropy.

A null test of the gravitational inverse-square law can be performed by testing Gauss’s law for the field. We have constructed a three-axis superconducting gravity gradiometer and carried out such a test. A lead pendulum weighing 1500 kg was used to produce a time-varying field. This experiment places a new (2σ) limit of α=(0.9±4.6)×${10}^{\mathrm{-}4}$ at λ=1.5 m, where α and λ are parameters of the generalized potential φ=-(GM/r)(1+α${\mathit{e}}^{\mathrm{-}\mathit{r}/\lambda }$).

The full E731 data set is used to provide precise determinations of several parameters of the neutral kaon. We find the ${\mathit{K}}_{\mathit{S}}$ lifetime ${\mathrm{\tau }}_{\mathit{S}}$=(0.8929±0.0016)×${10}^{\mathrm{-}10}$ s, the ${\mathit{K}}_{\mathit{L}\mathrm{-}}$${\mathit{K}}_{\mathit{S}}$ mass difference Δm=(0.5286±0.0028)×${10}^{10}$ħ ${\mathrm{s}}^{\mathrm{-}1}$ the phase of ${\mathrm{\eta }}_{+\mathrm{-}}$, ${\mathrm{\Phi }}_{+\mathrm{-}}$=42.4°±1.4°, and the phase difference between ${\mathrm{\Phi }}_{00}$ and ${\mathrm{\Phi }}_{+\mathrm{-}}$, ΔΦ=-1.6°±1.2°. Comparisons with previous experiments and with CPT symmetry are given.

A measurement of the CP-violation parameter Re(ɛ’/ɛ) has been made using the full E731 data set. We find Re(ɛ’/ɛ)=(7.4±5.2±2.9)×${10}^{\mathrm{-}4}$ where the first error is statistical and the second systematic.

With the CLEO-II detector at the Cornell Electron Storage Ring, we have measured branching fractions for tau lepton decay into one-prong final states with multiple ${\mathrm{\pi }}^0$’s ${\mathit{B}}_{\mathit{h}\mathit{n}\mathrm{\pi }}^0$, normalized to the branching fraction for tau decay into one charged particle and a single ${\mathrm{\pi }}^0$. We find ${\mathit{B}}_{\mathit{h}2\mathrm{\pi }}^0$/${\mathit{B}}_{\mathit{h}\mathrm{\pi }}^0$=0.345±0.006±0.016, ${\mathit{B}}_{\mathit{h}3\mathrm{\pi }}^0$/${\mathit{B}}_{\mathit{h}\mathrm{\pi }}^0$=0.041 ±0.003±0.005, and ${\mathit{B}}_{\mathit{h}4\mathrm{\pi }}^0$/${\mathit{B}}_{\mathit{h}\mathrm{\pi }}^0$=0.006±0.002±0.002.

Cross sections for the reaction pp¯→${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$ have been measured at s=8.9,12.4, and 13.0 ${\mathrm{GeV}}^2$. The cross sections have been analyzed to obtain the proton electromagnetic form factors in the timelike region. We find that ${\mathit{G}}_{\mathit{M}}$(${\mathit{q}}^2$)∝${\mathit{q}}^{\mathrm{-}4}$${\mathrm{\alpha }}_{\mathit{s}}^2$(${\mathit{q}}^2$) for ${\mathit{q}}^2$≥5 (GeV/c${)}^2$.