Current transfer and initial dissipation in high- superconductors

Abstract

Various aspects of the problem of current transfer in high- superconductors (HTSs) are reviewed. The spatial inhomogeneities of various types are identified as a primary cause of non-uniformity of both normal currents and supercurrents in real samples of HTSs. The role these inhomogeneities play in transport features of the samples is discussed. The case of grain boundaries in polycrystalline samples is elaborated in detail. The local structural and transport properties of isolated grain boundaries are first reviewed and then integrated into the knowledge of global (macroscopic) charge transport. The paper emphasizes the common ingredients characterizing the transport in various forms and families of HTS samples in small magnetic fields. The phenomenon of percolation is identified as the most obvious one and is shown to dominate a large number of observations covered by this report. The experimental results focused on by this report elaborate primarily the problems of critical currents, initial dissipation and current-voltage characteristics, penetration depth, resistive and metal-insulator transition, resistance noise and magneto-optical studies of current paths. Various models for current transfer (disordered bonds, brick wall and railway switch) are also reviewed and discussed.

Magneto-transport characterization of Dy123 monodomain superconductors

“…However, one can observe a change in curvature toward a linear regime when the temperature is lowered. This crossover effect shifts from 87 K down to 65 K, when magnetic field raises from 2 to 6 T. This might indicate that the initial drop in resistivity is initially due to Josephson or tunnel junctions [25]. Finally electrical resistivity vanishes at the percolation temperature shifting from 89 K at zero magnetic field down to 61 K at 6 T field.…”

Manifestation of vortex depinning transition in nonlinear current–voltage characteristics of polycrystalline superconductor Y1−xPrxBa2Cu3O7−δ

“…On the other hand, it is of great importance (from both fundamental and application points of view) to study the evolution of the different current transfer driven dissipation processes in doped superconductors [3]. Probably one of the most recognized dissipation mechanisms is the so-called Kosterlitz-Thouless (KT) topological transition.…”

Thermal Behaviour and Refrigeration of High-Temperature Superconducting Fault Current Limiters and Microlimiters

“…T cI the temperature at which dρ/dT presents its maximum, and T c0 , the minimum temperature for which ρ = 0 are indicated. In the CVC shown in figure 2, symbols represent the experimental data measured at the indicated temperatures and the solid lines the fits to the usual power law function (Prester, 1998;. In figure 3 circles correspond to the field cooling (FC) of the sample and squares to its zero field cooling (ZFC).…”

“…E − J curves measured in a piece of the superconducting elements employed in the limiter. The solid lines represent the fittings to the usual power law function (Prester, 1998). In figure 6(a) it is shown the rms values of the five voltage signals and in figure 6(b) the corresponding temperature readings.…”