Nondiverging vortex pinning barriers at low current densities across the putative elastic vortex-glass–vortex-liquid transition inYBa2Cu3

Abstract

A detailed analysis of the electric field-current density (EϪJ) characteristics of YBa 2 Cu 3 O 7Ϫ␦ films across the putative thermally induced elastic vortex-glass-vortex-liquid transition predicted by the E(J) curve scaling reveals that the expected increase of the collective pinning barriers with decreasing J is cut off in the low-J region, signaling a dissipation process which involves the plastic deformation of the vortex system. The temperature and magnetic field dependence of the pinning barriers at low J does not change across the scaling-predicted glass transition line. For the investigated magnetic field range ͑0.5-7 T͒, over a relatively large temperature interval, in YBa 2 Cu 3 O 7Ϫ␦ films there appears a continuous crossover in a pinned plastic vortex assembly, rather than a thermally induced elastic vortex-glass-vortex-liquid transition.

Vortex activation energy in the AC magnetic response of superconducting YBa2Cu3O7thin films with complex pinning structures

“…At long t, the averaged U * (DC) divided by T becomes of the order unity close to the IL (figure 1(b)), where one enters the thermally assisted flux flow (TAFF) regime [33], with a linear E( J) at low J, whereas the AC U * value from the main panel of figure 4 leads to a J exponent U * (AC)/T∼10.8. This suggests that the TAFF regime at long t just below the IL does not correspond with the thermally activated vortex hopping in the AC response, because the appearance of TAFF is only possible when U * /T3 [8,34], i.e., in the case of AC measurements, at significantly higher temperatures. Moreover, the logarithmic U AC (diverging at low J) would be in conflict with a TAFF regime, which, on the other hand, is entirely possible for the plastic vortex-creep (negative p) at long t (see figure 1(b)), with a finite pinning barrier in the low-J limit.…”

Plastic vortex creep and dimensional crossovers in the highly anisotropic superconductor HgBa$_2$CuO$_{4+x}$

“…They further showed that this described data collected on a YBa 2 Cu 3 O 7−x crystals, in a regime in which there was other evidence of plastic dynamics, such as a decrease in U with magnetic field (whereas an increase is predicted for elastic creep). Consequently, it has become common to identify a change from elastic to plastic creep as a sudden change in slope on a log U − log(1/J) plot, identifying the plastic flow regime as U pl ∼ (1/J) p , for p < 0, and many studies have observed a sharp change in slope with (in some cases) strikingly linear behavior on both sides of the transition [23,25,29,48,[54][55][56][57][58][59][60][61][62][63]. At high temperatures and fields H > H ep in our samples, we see that the slope of the U * versus 1/J plot shown in Fig.…”