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Fluctuation magnetoconductivity in YBa/sub 2/Cu/sub 3/O/sub 7/ : Gaussian, three-dimensional XY, beyond three-dimensional XY, and lowest-Landau-level scaling

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Fluctuation magnetoconductivity in YBa/sub 2/Cu/sub 3/O/sub 7/ : Gaussian, three-dimensional XY, beyond three-dimensional XY, and lowest-Landau-level scaling

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Título Fluctuation magnetoconductivity in YBa/sub 2/Cu/sub 3/O/sub 7/ : Gaussian, three-dimensional XY, beyond three-dimensional XY, and lowest-Landau-level scaling
Autor Costa, Rosangela Menegotto
Pureur Neto, Paulo
Gusmao, Miguel Angelo Cavalheiro
Senoussi, Sadok
Behnia, K.
Abstract Systematic measurements of the in-plane fluctuation magnetoconductivity in a YBa₂Cu₃O₇ single crystal are presented. Fields between 0 and 14 T were applied either parallel or perpendicular to the Cu-O atomic planes. The data reveal the occurrence of a large Gaussian regime in the normal phase. Far above Tc , the mean-field fluctuation spectrum is effectively two dimensional. Decreasing the temperature towards Tc , a crossover to a three-dimensional (3D) Gaussian regime is seen at low applied fields. The analysis of these results allows the estimation of the coherence length perpendicular and parallel to the Cu-O planes, and reveals that superconductivity in YBa₂Cu₃O₇ is characterized by a double planar periodicity. The c lattice parameter is the relevant periodicity length of the 2D behavior, whereas the smallest distance between the double Cu-O layers plays an important role in the 3D fluctuation spectrum. In fields above 5 T applied parallel to the c axis, the fluctuation magnetoconductivity scales as predicted by the 3D lowest-Landau-level approximation of the Ginzburg-Landau theory. Very close to Tc , and for quite low values of the applied field, the results clearly show the occurrence of a genuine critical regime, where the exponent is consistent with the predictions of the full dynamic 3D XY universality class. Still closer to Tc , evidence is found for a fluctuation regime beyond 3D XY scaling. This new scaling raises the interesting possibility for the ultimate weakly first-order character of the superconducting transition in YBa₂Cu₃O₇₋₈. The whole set of data is condensed on H-T diagrams, which display the regions of stability for the observed fluctuation regimes, in fields oriented parallel or perpendicular to the Cu-O layers.
Contido em Physical review. B, Condensed matter and materials physics. Woodbury. Vol. 64, no. 22 (Dec. 2001), 214513 9p.
Assunto Compostos de bário
Compostos de ítrio
Expoentes críticos
Flutuacoes em supercondutores
Magnetoresistencia
Supercondutores de alta temperatura
Transicoes supercondutoras
Origem Estrangeiro
Tipo Artigo de periódico
URI http://hdl.handle.net/10183/103851
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