Vortex motion in YBa2Cu3O7−δ twinned single crystals and epitaxial films

Abstract

The transport properties of superconductive YBa2Cu3O7−δ (YBCO) twinned single crystals and epitaxial thin films are similar in the flux creep regime. In particular, the activation energy of the individual vortices is proportionnal to the temperature in the low temperature range. As a matter of fact, data from the literature show that this energy takes the form Ea=4πνkBT, where ν is an integer. To investigate this behavior, the current–voltage characteristics of epitaxial YBCO thin film microbridges were measured. The activation energy of these samples has proved to take the form given above. This common behavior of single crystals and thin films is interpreted in the framework of a critical state model according to which the vortices move along the sample twin boundaries that behave as arrays of weak links.

Dynamics of vortex matter in YBCO sub-micron bridges

“…The parameter I 0 allows us to get the main hopping distance d which is of the order of a few nanometers, in agreement with previous results [45,46]. I-V curves reveal the various transport regimes, and this can be qualitatively mapped on the 'phase diagram' reported in Fig.…”

“…5 the activation energies of the two samples are reported. The maximum of E a is about 10 times smaller than what found in wider samples [45,49] as direct consequence of the lower energies of pinning profiles. Furthermore the trend of E a change signs at about T 0 % T C =2 % 40 K (see Fig.…”

“…For J > J C the pinned vortices experience a vortex creep velocity, which is not monotonous in temperature in analogy to what has been found in wider samples [45,49]. In Fig.…”

“…(For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.) lines ''in motion'' and retrieves information on the thermal dependence of creep velocity which varies in temperature as exp ÀE a ðTÞ=k B T f g [45]. In Fig.…”

“…The approach used in Refs. [45,46] to take into account vortex motion in micrometer wide YBCO bridges in the Kim-Anderson model [47] allows to derive information on the activation energy for flux motion E a . The expression used to fit I-V characteristics is…”