Table of contents

The nonlinear dynamical behaviour of a Josephson tunnel junction shunted by a large inductivity is investigated experimentally. The system exhibits spontaneous oscillations in the voltage signal when biased with a constant current. We observe mode-locking and quasi-periodicity if an a.c.-current is added to the bias. Return maps are constructed from the measured time signal, showing that the dynamical behaviour can be described in terms of a 1D circle map. Numerical calculations reproduce and extend the experimental results.

We suggest that the concept of self-organized criticality (SOC) is relevant for understanding the processes underlying earthquakes. Earthquakes are an important part of the relaxation mechanism of the crust which is submitted to inhomogeneous increasing stresses accumulating at continental-plate borders. The SOC concept then implies that earthquakes in turn organize the crust both at the spatial and temporal levels. This idea allows to rationalize observations on occurrences and magnitudes of earthquakes. Variants of SOC as well as a novel type of dynamics based on "waiting times" are discussed within a mean-field-like approach which shows the existence of 1/f noise in the time gap between large earthquakes. The corresponding long-time correlations have important implications for the statistical long-time forecasting of earthquakes.

We report anomalous diffusion by a flexible self-avoiding polymer moving through a random anisotropic medium in Monte Carlo simulations. The chain moves among randomly placed, infinitely long parallel hard rods with anomalous centre-of-mass diffusion R²(t) ∼ t^0.68±0.06 N^−0.9±0.2 perpendicular to the rods over three decades of time. At the termination time τ ∼ N^3.2±0.7, there is a crossover from anomalous to ordinary diffusion R²(t) ∼ tN^−2.0±0.2. The configurational relaxation time of the polymer scales according to τ_p ∼ N^3.0±0.3. The results are discussed with respect to various possible effects due to entanglements, entropic traps and the disorder of the medium.

It is pointed out that the topological Ward identity of the three-dimensional topologically massive non-Abelian gauge theory receives contribution from the Chern-Simons term only. The kinetic term, i.e. the curvature squared term does not contribute at zero momentum. The physical implication of this observation is discussed.

The time-dependent electric-energy density surrounding a two-level atom fixed at r = 0 is studied, the atom being taken in its ground state at t = 0 and the field having initially only one photon in a delocalized mode. The atom-field coupling includes both rotating and counterrotating terms. The energy density in the rotating wave approximation is shown to behave noncausally, while in the presence of the complete coupling it is shown to be affected only within a sphere of radius r = ct centred on the atom. It is concluded that the counterrotating terms in the atom-field coupling are essential in order to ensure causality and cannot be neglected in any accurate treatment of photon absorption. Some consequences of this conclusion on the operation of photodetectors in one-photon absorption are discussed.

The interaction of deuterium gas with titanium has produced a flow of neutrons in two experiments reported here. This seems to show that it is not necessary to use electrolysis in order to obtain a low-temperature fusion reaction between deuterium nuclei. The experiment confirms also that nonequilibrium conditions are necessary in order to produce such a phenomenon.

Hydrogenlike and heliumlike xenon ions have been produced at GANIL. All Lyman and Balmer lines of both ions have been observed, for the first time. The energies of these lines, belonging to the heaviest ions ever studied, have been compared with detailed multi-configurational Dirac-Fock calculations.

Circular two-electron atoms, i.e. Rydberg atoms where the angular momentum of one of the valence electrons is maximum, have been prepared in barium (n = 21) by using the adiabatic crossed-field method already tested in alkali atoms. This simple and versatile method proves to be very efficient for heavy atoms with large quantum defects. Circular alkaline-earth atoms represent a decisive step for the preparation of doubly-excited Rydberg states with long autoionization lifetimes.

A front which connects a stable and an unstable state and propagates into the unstable one selects a distinct, unique propagation velocity. If the instability of the unstable state is oscillatory with a nonvanishing group velocity, then it is found that the velocity of the propagating front is modified by this group velocity. The predictions made are compared with explicit time-dependent numerical simulations of front propagation in magnetic fluids in the Taylor-Couette system (which serves as a prototype example for front propagation) and excellent quantitative agreement is found.

We discuss theoretically the possibility of a spontaneous nematic splay phase for polar nematogens. This novel liquid crystal phase is similar to the cholesteric phase for chiral nematogens (spontaneous twist), since it is spatially inhomogeneous and breaks translational symmetry, and to the cholesteric blue phases, since it contains defects. In contrast to analogous defect structures in nonpolar nematic liquid crystals, which are enforced by special boundary conditions only, the splay phase is the thermodynamically stable ground state for some temperature interval.

We have prepared glass spherical particles, with one hemisphere hydrophilic, and the other one hydrophobic. These objects, named "Janus beads", may be considered as amphiphilic solids. We have studied the properties of such beads at oil/water interfaces and point out that they do behave differently from ordinary solid particles. These observations are interpreted semi-quantitatively and open up the way to further prospects and applications.

Anisotropic structures in the inelastic scattering cross-section of x-rays from single crystal Li and of fast electrons from single crystal Na are found to arise from zone boundary collective states (ZBCS), whose properties depend crucially on the symmetry and on the strength of the crystal potential. These ZBCSs are important in discussing various many-body effects. For Na the ⟨110⟩-ZBCS is consistent with a NFE band structure. This contrasts with the reduced bandwidth observed in photoemission and believed to be caused by many-body effects beyond the RPA. In Li a ⟨200⟩-ZBCS falls into a (q, ω) regime beyond the plasmon where structures have been associated with short-range correlations.

Finite source-drain voltage V causes smearing of quantum steps in the I(d) function of microconstraint (d is the diameter of a constraint, I the current through it). The number of steps is restricted by the value ñ = 2E_F/eV, where E_F is the Fermi energy of the 2D electron gas. In the differential conductance G = ∂I/∂V additional steps occur, their width is proportional to V and their heights are multiples of half-integer quanta e²/2πℏ. As a by-product we derive the d(V_G) function (V_G is the gate voltage) that could be compared with the experimental data on G(V_G).

Low-temperature electrochemical measurements were carried out on interfaces between different polycrystalline high-T_c superconductors (YBa₂Cu₃O_7-δ with 0 ⩽ δ ⩽ 0.5, YBa₂Cu_3(1-x)Zn_3xO_7-δ with 0 ⩽ x ⩽ 0.06, Tl₂Ba₂CaCu₂O₈, Tl₂Ba₂Ca₂Cu₃O₁₀) and Ag β''-alumina as a solid electrolyte. By using a special transient routine, cell currents were measured vs. time at a constant potential. From the d.c. limits of the transients, a significant increase of the current is observed around T_c which cannot be explained by a specific property of the solid electrolyte. This effect must be correlated to Cooper pairs changing the electrochemical double-layer structure and possibly penetrating the energy barrier at the interface HTSC/solid electrolyte. The results are interpreted as an enhancement of the electrode kinetics or a proximity effect.

A model for thermal fluctuations of the Abrikosov flux lattice is considered which describes the continuous phase transition from the flux lattice to the Meissner phase. We calculate the density of flux lines, the characteristic decay length of the longitudinal density correlations and the characteristic oscillations of the transversal density correlations near the phase transition point.

We have performed torque measurements on Tb-Fe amorphous alloys. At low temperatures we find torque curves which are nearly reversible and which can be accounted for by a uniaxial anisotropy. The anisotropy axis is movable and so the anisotropy is a memory effect similar to that found in Cu-Mn alloys. The macroscopic anisotropy is uniaxial in nature for rotation about a single axis as expected since the microscopic anisotropy is uniaxial. For rotation about more than one axis our results are consistent with a triad anisotropy.

Nitrogen-14 NQR experimental data previously obtained in molecular polycrystalline pyrrole are reanalysed in terms of an incommensurate structure.

The scattering properties of gelatin containing W/O microemulsions near the sol-gel transition are discussed. The fractal dimension of the aggregates and network is found to be 1.65 ± 0.05 for length scales larger than the radius of gyration of the gelatin containing aqueous microemulsion droplets (nanogels, R_g ≃ 30 nm from light scattering). At smaller length scales (SAX-scattering) the interface of the droplets appears relatively rough with a surface fractal dimension D_s ≃ 3.0. The results agree with the concept of a network being built up by polymers cross-linking the nanogels.