Vortex creep crossover in YBCO/PrBCO superlattices during standard magnetization relaxation measurements

Abstract

We investigated the relaxation of the irreversible magnetization in a series of 200 nm thick YBa 2 Cu 3 O 7 /PrBa 2 Cu 3 O 7 [(YBCO) n /(PrBCO) m ] superlattices, where the thickness m of the nonsuperconducting PrBCO layer (measured in unit cells) was kept to m = 4 (sufficient to decouple the superconducting YBCO layers), whereas the thickness n of the YBCO layer was varied between 2 and 20 unit cells. The analysis of standard zero-field-cooling dc magnetization relaxation data obtained in the low temperature T region with the applied magnetic field H oriented along the c axis reveals the occurrence of a crossover elastic (collective) vortex creep at low T -plastic vortex creep at high T , generated by the T dependent macroscopic currents induced in the sample during measurements. For thin superlattices (n < 20) the creep crossover temperature T cr ∝ n, and T cr decreases linearly with increasing ln(H ) for a fixed n. This crossover represents an alternative to the elastic vortex glass behavior reported for superlattices, as well as to 'quantum vortex creep' at unexpectedly high T inferred for thin films. We also discuss the absence of an increase of the magnetically determined critical current density with decreasing YBCO thickness in our superlattices, which apparently contradicts the collective pinning theories.

Pinning properties of FeSeTe thin film through multifrequency measurements of the surface impedance

“…Hence, this fact reinforces the above scenario of small ξ 3 size of the jumping portion of the vortices ‡. It would be interesting ‡ Another common interpretation [69,70] of the maximum in U (T ) is a crossover from low-T elastic to determine if in samples with extended defects (as those obtained with ion irradiation [77]), a creep connected to extended pins would appear (n < 3) or if also in that pinning landscape microwaves would sense only jumping volumes ∝ ξ 3 . As a last observation, U decreases with lowering T faster than the theoretical predictions, but consistently with other results reported in literature [68].…”

“…As for k p , the temperature trend is model-independent, so that the same considerations hold, while the absolute values differ for roughly a scale factor of 2, which is intimately linked to the different assumptions of the models [32] (creep above sinusoidal pinning potential in the CC mode, thermal relaxation of the pinning constant in the Brandt model). Differently from χ, U exhibits a non-monotonous T evolution, with a hump around 12 K. This feature has been observed in several experiments of magnetic relaxation [68,69], also in other materials [70], and of magnetoresistivity [68,71].…”

Influence of Field Decrements on the Relaxation Behavior of Thin High- $T_{c}$ Superconductors Measured Using a Levitation Balance

“…3) Due to the much higher anisotropy, the vortices in Bi-2223 are of the pancake type; thus, a much faster relaxation is observed. With regard to the collective pinning theory [2], [44], in ZFC experiments (as done here), there is a crossover from collective creep (at low T ) to plastic creep at high T . This defines a crossover temperature T cr .…”

AC magnetic response of superconducting YBa2Cu3O7/PrBa2Cu3O7 superlattices

“…3, main panel) exhibit a strong downward curvature, as a signature of plastic (dislocated mediated) flux creep. 19 More importantly, the Arrhenius plot at long t constructed with the (T,t) pairs for |m| = 2×10 plot from the upper inset of Fig. 1, while t 0 is in the range of a macroscopic time scale for creep (orders of magnitude higher than the microscopic attempt time 1/ f 0 ).…”