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We have investigated the vortex state in a superconducting dice network using the Bitter decoration technique at several magnetic frustrations f=1/2 and 1/3. In contrast to other regular network geometries where the existence of a commensurate state was previouly demonstrated, no ordered state was observed in the dice network at f=1/2 and the observed vortex-vortex correlation length is close to one lattice cell., Comment: 7 pages, 6 figures, submitted to Europhysics Letter

We study the effect of disorder and interactions on a recently proposed magnetic field induced localization mechanism. We show that both partially destroy the extreme confinement of the excitations occuring in the pure case and give rise to unusual behavior. We also point out the role of the edge states that allows for a propagation of the electrons in these systems., Comment: 22 pages, 20 EPS figures

The superconducting properties of a two-dimensional superconducting wire network with a new geometry have been measured as a function of the external magnetic field. The extreme localization effect recently predicted for this periodic lattice is revealed as a suppression of the critical current when the applied magnetic field corresponds to half a flux quantum per unit cell. For this particular magnetic field, the observed vortex state configuration is highly disordered., Comment: 6 pages, 2 eps figures, submitted to Physica C. Title changed

We consider two interacting particles evolving in a one-dimensional periodic structure embedded in a magnetic field. We show that the strong localization induced by the magnetic field for particular values of the flux per unit cell is destroyed as soon as the particles interact. We study the spectral and the dynamical aspects of this transition., Comment: 4 pages, 5 EPS figures, minor misprints corrected

We report transport measurements on superconducting wire networks which provide the first experimental evidence of a new localization phenomenon induced by magnetic field on a 2D periodic structure. In the case of a superconducting wave function this phenomenon manifests itself as a depression of the network critical current and of the superconducting transition temperature at a half magnetic flux quantum per tile. In addition, the strong broadening of the resistive transition observed at this field is consistent with enhanced phase fluctuations due to this localization mechanism., Comment: 4 pages, 3 eps figures, final version with minor changes

We analyze the violations of linear fluctuation-dissipation theorem (FDT) in the coarsening dynamics of the antiferromagnetic Ising model on percolation clusters in two dimensions. The equilibrium magnetic response is shown to be non linear for magnetic fields of the order of the inverse square root of the number of sites. Two extreme regimes can be identified in the thermoremanent magnetization: (i) linear response and out-of-equilibrium relaxation for small waiting times (ii) non linear response and equilibrium relaxation for large waiting times. The function $X(C)$ characterizing the deviations from linear FDT cross-overs from unity at short times to a finite positive value for longer times, with the same qualitative behavior whatever the waiting time. We show that the coarsening dynamics on percolation clusters exhibits stronger long-term memory than usual euclidian coarsening., Comment: 17 pages, 10 figures

The Glauber dynamics of various models (REM-like trap models, Brownian motion, BM model, Ising chain and SK model) is analyzed in relation with the existence of ageing. From a finite size Glauber matrix, we calculate a time $\tau_w(N)$ after which the system has relaxed to the equilibrium state. The case of metastability is also discussed. If the only non zero overlaps between pure states are only self-overlaps (REM-like trap models, BM model), the existence or absence of ageing depends only on the behavior of the density of eigenvalues for small eigenvalues. We have carried out a detailed numerical and analytical analysis of the density of eigenvalues of the REM-like trap models. In this case, we show that the behavior of the density of eigenvalues for typical trap realizations is related to the spectral dimension of the equivalent random walk model., Comment: 22 pages, 6 figures, accepted in Jour. Phys I (France)

Using the adiabatic switching of interactions, we establish a condition for the existence of electronic quasiparticles in a Luttinger liquid. It involves a characteristic interaction strength proportional to the inverse square root of the system length. An investigation of the exact energy level separation probability distribution shows that this interaction scale also corresponds to a cross-over from the non interacting behaviour to a rather typical case for integrable systems, namely an exponential distribution. The level spacing statistics of a spin $1/2$, one branch Luttinger model are also analyzed, as well as the level statistics of a two coupled chain model., Comment: 22 pages, Latex