We introduce a renormalization scheme of novel type that allows us to characterize the critical state and the scale invariant dynamics in sandpile models. The attractive fixed point clarifies the nature of self-organization in these systems. Universality classes can be identified and the critical exponents can be computed analytically. We obtain τ=1.253 for the avalanche exponent and z=1.234 for the dynamical exponent. These results are in good agreement with computer simulations. The method can be naturally extended to other problems with nonequilibrium stationary states.

An experimental study of the acoustic emission generated during a martensitic transformation is presented. A statistical analysis of the amplitude and lifetime of a large number of signals has revealed power-law behavior for both magnitudes. The exponents of these distributions have been evaluated and, through independent measurements of the statistical lifetime to amplitude dependence, we have checked the scaling relation between the exponents. Our results are discussed in terms of current ideas on avalanche dynamics.

We compare a new theory of nucleated wetting with experimental data for the critical liquid mixture hexadecane+acetone. Good agreement is obtained for t≥8×${10}^{\mathrm{-}5}$. We determine that the droplet line tension scrL=${\mathit{scrL}}_0$${\mathit{t}}^{\mathit{x}}$ where ${\mathit{scrL}}_0$∼1×${10}^{\mathrm{-}7}$ erg/cm and x=0.76±0.02 while the spreading pressure S≊${\mathit{S}}_0$${\mathit{t}}_1^{\mathrm{\beta }}$ where ${\mathit{S}}_0$∼0.007 erg/${\mathrm{cm}}^2$. Theory and experiment exhibit a minimum in the nucleation data at a reduced temperature of ${\mathit{t}}_{\mathit{m}}$ (≊0.000 22 for an upper hexadecane-rich bulk phase of height L=0.56 cm); theory predicts that ${\mathit{t}}_{\mathit{m}}$ scales as ∼${\mathit{L}}_1^{2/3(\mathrm{\beta }}$-β).

The elementary process of droplet coarsening has been studied for phase-separating binary liquid mixtures. For a slightly asymmetric quench, we have found two new types of coarsening behavior: (i) a multiple collision caused by the coupling effect between the shape relaxation after binary collision and the geometrical configuration of neighboring droplets and (ii) a collision-induced collision likely caused by collision-diffusion coupling. For a nearly symmetric mixture the droplet density is so high that we probably need to consider new mechanisms of droplet coarsening unique to fluid systems, which originate from the coupling between concentration and velocity fields.

We calculate the overlap between two many-body wave functions for a superfluid film containing a vortex at shifted positions. Comparing the results to phenomenological theories, which treat vortices as point particles, we find that the results are consistent if the point-particle vortices are considered as under the action of the Magnus force and in weak interaction with sound waves of the superfluid. We are then able to resolve the disagreement concerning the effective mass of vortices, showing it is finite.

We explain the anomalous temperature dependence of spin diffusion in liquid ${}_{}{}^3{}_{}{}^{}\mathrm{\uparrow }$ and ${}_{}{}^3{}_{}{}^{}\mathrm{-}_{}^4{}_{}{}^{}$He mixtures. The anomaly is an experimental manifestation of a unique zero-temperature attenuation in the Fermi liquid theory. We extended our microscopic theory of spin dynamics in spin-polarized Fermi liquids to finite temperatures. The zero-temperature attenuation changes the behavior of the spectrum near the singular point. The data indicate that the superfluid transition temperature for ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ in ${}_{}{}^3{}_{}{}^{}\mathrm{-}_{}^4{}_{}{}^{}$He mixtures is much lower than the current estimates.

Recent experiments show that low temperature diffusion on semiconductor surfaces such as Ge(111) can be many orders of magnitude slower than expected. We present a model which provides a detailed explanation for the observed rate of diffusion on this surface. The effect is shown to be the result of complicated motions that allow surface adatoms to exchange places by hopping in an orchestrated manner between low-energy positions.

Using scanning tunneling microscopy, the epitaxial growth of a monolayer of CaF on the Si(111)-7×7) surface has been studied. We observe how the Si atoms of the 7×7 structure rearrange into a bulklike structure and find that four excess Si atoms per 7×7 unit cell are produced in the transition to the bulklike structure. These excess Si atoms seem to remain in the epitaxial CaF layer, creating defects.

We report the vapor phase growth of partially filled graphitic fibers, 20-30 nm in diameter and up to a micron in length, during a manganese catalyzed carbon electric arc discharge. The fiber morphology resembles that of catalytic chemical vapor deposited carbon filaments but the inside hollow contains intermittent precipitates and continuous filling of Mn that at times occupy >50% of fiber lengths. Transmission electron microscopy and electron energy loss line spectra show that the fillings form as solid cores and may correspond to pure metal.

Self-consistent determination of electron escape rate and barrier traversal time under the influence of the electromagnetic environment reveals that the escape rate increases monotonically with increasing ratio of the elementary charging energy to the barrier height but that the traversal time peaks at one certain ratio. As the freuqency of the electromagnetic mode increases, an effective potential for a tunneling electron changes from linear to parabolic, dominated, respectively, by the zero-point fluctuations of the charge on the junction and its static polarization. Possible experimental situations for observing these predictions are discussed.

We show how the addition of a phonon field to the Hubbard model deforms the superconducting su(2) part of the global symmetry Lie algebra su(2)⊗su(2)/${\mathit{openZ}}_2$, holding at half filling for the customary model, into a quantum [su(2)${]}_{\mathit{q}}$ symmetry, holding for a filling which depends on the electron-phonon interaction strength. Such symmetry originates in the feature that in the presence of phonons the hopping amplitude turns out to depend on the coupling strength. The states generated by resorting to this q symmetry exhibit both off-diagonal long-range order and pairing.

We discuss the Hall effect and resistivity above ${\mathit{T}}_{\mathit{c}}$, using a variant of the bipolaron theory which takes into account Anderson localization of the bosons by disorder. The model supposes that ${\mathit{R}}_{\mathit{H}}$=1/2${\mathit{en}}_{\mathit{b}}$c, where ${\mathit{n}}_{\mathit{b}}$ is the number of delocalized carriers. Temperature and doping dependences of ρ, ${\mathit{R}}_{\mathit{H}}$, cot${\mathrm{\theta }}_{\mathit{H}}$, and the ‘‘spin’’ gap in ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ are explained.

We describe measurements on high-current-density Nb-${\mathrm{AlO}}_{\mathit{x}}$-Nb tunnel junctions and demonstrate that the development of excess subgap current with increasing barrier transparency is the result of multiple Andreev reflections. We present a model for the barrier consistent with measured junction resistance, the high transparency required for multiple traversals, and the observed single-particle and Josephson characteristics. We argue that excess subgap current and subharmonic gap structure in superconducting tunnel junctions are generally likely to be due to pinhole defects in the barriers.

We present extensive experimental data on charge transport by Andreev reflection through a mesoscopic superconducting island coupled to two normal metal leads through small tunnel junctions and to a capacitive gate. The data show the systematic dependence on the gate-induced charge ${\mathit{Q}}_0$ of both the Coulomb blockade of Andreev reflection and of striking voltage thresholds that correspond to specific tunneling processes. The magnitude of this Andreev current and its dependence on ${\mathit{Q}}_0$ are in excellent agreement with recent theory, provided that interference between the two tunneling electrons is taken into account.

Magnetization with applied field parallel to the ab plane has been measured in single crystals of ${\mathrm{Nd}}_{1.85}$${\mathrm{Ce}}_{0.15}$${\mathrm{Cu}}_2$${\mathrm{O}}_{4\mathrm{-}\mathit{y}}$. The data present the first direct measurement of Josephson decoupling between ${\mathrm{CuO}}_2$ planes at a critical field ${\mathit{H}}_{\mathit{J}}$. For field below ${\mathit{H}}_{\mathit{J}}$, the Meissner effect is observed; at the critical field ${\mathit{H}}_{\mathit{J}}$, magnetization abruptly changes to zero, an indication of a magnetic transparent state. The results are discussed in terms of a recent theoretical model for extremely anisotropic layered superconductors.

Vortex pinning by columnar defects in a ${\mathrm{NbSe}}_2$ crystal irradiated with 2.2 GeV ${\mathrm{Au}}^{+24\mathrm{}}$ ions is studied by scanning tunneling microscopy (STM) at 3 K. The vortex arrangement is clearly resolved in magnetic fields up to 500 mT and compared to the defect locations, also extracted from STM data. At vortex densities much larger than the defect density, the triangular vortex lattice is perturbed close to the defects. At vortex densities comparable or smaller, only some defects trap a vortex and the whole vortex arrangement is disordered, although less random than the defect distribution.

Elastic constant and thermal expansion data for a high quality single crystal of ${\mathrm{CeCu}}_2$${\mathrm{Si}}_2$ are presented. The data yield a detailed B-T phase diagram exhibiting a previously unknown high-field phase. From the unusual behavior of the elastic constants and the thermal expansion on entering the superconducting phase we deduce that, in contrast to other heavy-fermion superconductors, the superconducting phase of ${\mathrm{CeCu}}_2$${\mathrm{Si}}_2$ does not coexist with the surrounding phase.

The dynamic spin correlation function near the commensurate point Q=(π,π) in the superconducting state is calculated within mean field theory. We take the generalized t-J model as used by Tanamoto et al. For d-wave superconductor at T=0 K, we find that there will be no energy gap at incommensurate point, while the energy gap ${\mathit{E}}_{\mathit{g}}$=2μ develops at commensurate point in the particle-hole channel. On the other hand for s-wave superconductor a large energy gap develops irrespective of the nature of antiferromagnetic fluctuations. Therefore the d-wave model describes the neutron scattering data from both ${\mathrm{La}}_{1.86}$${\mathrm{Sr}}_{0.14}$${\mathrm{CuO}}_4$ by Mason et al. and ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{6+\mathit{x}}$ by Rossat-Mignod et al. quite well, while the s-wave model is incompatible with these experimental results.

Neutron scattering measurements characterizing the polarization, energy, and temperature dependence of the magnetic excitations of the longitudinally polarized spin density wave phase of chromium are presented. Careful consideration of spectrometer resolution effects has resulted in the first quantitative expressions for the cross sections associated with the longitudinally and transversely polarized excitations. These results, together with a simple parametrization of the dynamic susceptibility, χ’’(ω)∝A(ω)/ω, reveal a simple dependence of these excitations on energy at all temperatures below the spin-flip transition.

The motion of a heavily damped Brownian particle in a periodic potential subject to a dichotomously fluctuating perturbation is considered. We show that even if the net force is always zero, flow is induced by a fluctuation of the energy barrier, but only at flipping times roughly in between the adiabatic adjustment times on the left and right of the barrier. Predictions of our model are consistent with recent experimental data obtained by Svoboda et al. [Nature (London) 365, 721–727 (1993)] for a single kinesin molecule moving along a biopolymer.