Finite-Size Effects and Dynamical Scaling in Two-Dimensional Josephson Junction Arrays

In recent years many groups have used Fisher, Fisher, and Huse (FFH) dynamical scaling to investigate and demonstrate details of the superconducting phase transition. Some attention has been focused on two dimensions where the phase transition is of the Kosterlitz-Thouless-Berezinskii (KTB) type. Pierson et al. used FFH dynamical scaling almost exclusively to suggest that the dynamics of the two-dimensional superconducting phase transition may be other than KTB-like. In this work we investigate the ability of scaling behavior by itself to yield useful information on the nature of the transition. We simulate current-voltage (IV) curves for two-dimensional Josephson junction arrays with and without finite-size-induced resistive tails. We find that, for the finite-size effect data, the values of the scaling parameters, specifically the transition temperature and the dynamical scaling exponent z, depend critically on the magnitude of the contribution that the resistive tails make to the IV curves. In effect, the values of the scaling parameters depend on the noise floor of the measuring system.Comment: 24 pages, 8 figures; submitted to Physical Review

Second-peak effect in a superconducting Tl, Bi -1212 single crystal by ac susceptibility : evidence for vortex plastic behavior

A second peak effect is observed for a ~Tl, Bi!-1212 single crystal using ac susceptibility measurements. The analysis of the frequency dependence of the second peak position shows that plasticity governs the vortex dynamics on both sides of the second peak line. This suggests that no particular change in the vortex dynamics occurs by crossing this line. We propose that this second peak effect is due to the temperature activated form of the characteristic relaxation times and to the fact that the characteristic activation energy Uc and the critical current density Jc have inverse variations with the magnetic field B ~when one increases with B the other decreases!. We also propose that the time dependence of the second peak field position should indicate the vortex dynamics behavior: an increasing second peak field position with time is a fingerprint of elastic behavior while a decreasing second peak field position with time is a fingerprint of plastic behavior. The latter case agrees well with our experimental result

Absence of dynamical crossover in the vortex creep near by the second peak effect in superconducting Hg-1201 single crystals

PACS. 74.60.Ge Flux pinning and creep, and flux-line lattice dynamics - 74.72.Gr Hg-based cuprates,

Study of vibratory behavior of interconnected porous PZT by impulse method

Performances in ultrasonic active transducers of interconnected porous lead zirconate titanate (PZT) piezoelectric disks with a porosity ranging from 30 to 70%, and polarized along their axial axis, are investigated. The characterization method used is based on the measurement of the voltage, which appears between the two faces of the piezoelectric element when it is excited by a current impulse. The device used, allows the acquisition of axial and radial vibrations of the transducer, and from these data, electromechanical and acoustic parameters are deduced. One observes that interconnected porosity causes the disappearance of the radial vibrations, and for large porosities the disk vibrates exclusively according to the axial mode. kt is increased, the acoustic impedance is reduced, and the axial propagation velocity reaches ∼2500 m s−1 for 30% of porosity. These results show that interconnected porous PZT are suitable for making ultrasonic active transducer, such as biomedical imaging device

Study of vortex motion in a sintered high Tc superconductor by a vibrating reed technique

Using a vibrating reed technique in a subresonant excitation mode, dissipation mechanisms have been studied in sintered YBa2Cu307-, superconductors with different grain sizes. Experimental results are interpreted within the critical state model. Results deduced from vibrating reed technique are compared with ac susceptibility measurements. It is shown that both techniques give consistent result

Study of Vortex Motion in a Sintered High Tc Superconductor by a Vibrating Reed Technique

Using a vibrating reed technique in a subresonant excitation mode, dissipation mechanisms have been studied in sintered YBa2Cu3O7-x superconductors with different grain sizes. Experimental results are interpreted within the critical state model. Results deduced from vibrating reed technique are compared with ac susceptibility measurements. It is shown that both techniques give consistent results

Vortex Dynamics Studied Over a Wide Range of Time Scale in Bi-2212 Crystals

Three experimental methods are used to study the dissipation in Bi-2212 single crystals (direct measurements of the electrical resistivity, AC susceptibility and DC magnetic relaxation measurements). This allows the resistivity to be registered over 14 orders of magnitude. There is no gap in this wide range of measurements and some overlapping of the ranges obtained by different methods have been obtained. A crossover in the dissipation has been evidenced by this technique due to the extended range of measurement. In the $H$-$T$ phase diagram, this crossover line does not correspond to the irreversibility line and separates a phase at low temperatures in which the relaxation is slow from a phase at high temperatures in which the relaxation is fast. This transition is limited at high fields by a critical point and at low fields by the so called “fish-tail"

Vortex Dynamics Studied Over a Wide Range of Time Scale in Bi-2212 Crystals

Three experimental methods are used to study the dissipation in Bi-2212 single crystals (direct measurements of the electrical resistivity, AC susceptibility and DC magnetic relaxation measurements). This allows the resistivity to be registered over 14 orders of magnitude. There is no gap in this wide range of measurements and some overlapping of the ranges obtained by different methods have been obtained. A crossover in the dissipation has been evidenced by this technique due to the extended range of measurement. In the $H$-$T$ phase diagram, this crossover line does not correspond to the irreversibility line and separates a phase at low temperatures in which the relaxation is slow from a phase at high temperatures in which the relaxation is fast. This transition is limited at high fields by a critical point and at low fields by the so called “fish-tail"