Three-dimensional and two-dimensional high field vortex fluctuations in deoxygenated YBa2Cu3O7-x depending on the vicinity of Tc(H)

• Published in: Physica. C, Superconductivity Superconductivity, 2006-09, Vol.443 (1-2), p.1-4
• Main Authors: SALEM-SUGUI, S, DA SILVA, E. Z, ALVARENGA, A. D
• Format: Article
• Language: English
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Exact sciences and technology; Physics; Properties of type I and type II superconductors; Superconductivity; Vortex lattices ,flux pinning, flux creep
• ISSN: 0921-4534; 1873-2143
• DOI: 10.1016/j.physc.2006.04.087

We analyzed reversible magnetization data, M versus T curves, of three single crystals of YBa2Cu3O7-x (Y123), with superconducting transition temperatures Tc=62.5 (x=0.35), 52 (x=0.5), and 41K (x=0.6). M versus T curves of each sample exhibited a field independent crossing point, M(T*), occurring close to the superconductor critical temperature. These crossing points were shown to be due to fluctuations of vortices. Besides the reversible data of each sample were shown to obey a two-dimensional diamagnetic lowest-Landau-level (LLL) fluctuation theory, it is shown here that the data, within a temperature region where the crossing points occur for two samples (62.5K and 52K), are also explained by a three-dimensional version of this fluctuation theory. Since the crossing points for these two samples occur close to Tc, these are interpreted as been due to three-dimensional vortex fluctuations instead two-dimensional ones. An expression for the field independent magnetization, M(T*), which is expected to occur at the crossing point of the various M versus T curves, is obtained for the case of three-dimensional vortex fluctuations, and compared to the experimental values of M(T*). This comparison produced consistent values for the coherence length along the c-axis of the samples with Tc=62.5 and 52K, solving an inconsistent result previously published, when experimental values of M(T*) were compared with an expression obtained from two-dimensional vortex-fluctuations. The results of the present work show that, despite the fact that two-dimensional LLL fluctuations scaling is obeyed in a much wider temperature range for two studied samples (Tc=52 (x=0.5), and 62.5K (x=0.35)) when compared to the 3D-LLL scaling form, these systems behave as three-dimensional for temperatures close to Tc(H).