Diamagnetic fluctuations in YBa2Cu3O7−x and Bi2Sr2CaCu2O8+x: Possible observationof phase correlations persisting above Tc

• Autor(a) principal: Salem-Sugui Júnior, Said
• Data de Publicação: 2009
• Outros Autores: Mosqueira, J., Alvarenga, Ana Paula Dornelles de
• Tipo de documento: Artigo
• Idioma: eng
• Título da fonte: Repositório Institucional do INMETRO
• Texto Completo: http://hdl.handle.net/10926/1435

We report on isofield curves of −M vs T, where M is the reversible magnetization, of YBa2Cu3O6.95, YBa2Cu3O6.65, and Bi2Sr2CaCu2O8+x with the magnetic field, H, applied parallel to the c axis of the samples and also parallel to the ab planes for YBaCuO . For temperatures close to the critical temperature, Tc, the quantity −M is proportional to the order parameter amplitude . Curves of −M vs T allowed to study the asymptotic behavior of the form Ta−T m of near Tc, as a function of field. Results for the studied samples produced values of Ta H lying above Tc, suggesting that the magnetic field gradually allows to probe a region of temperatures where phase correlations persist above Tc. The study performed here in YBaCuO samples allowed to study how phase correlations evolve with doping in the pseudogap region of YBaCuO. −M vs T curves for all samples show a rather large amplitude fluctuation with no phase correlation extending well above Ta H which is interpreted in terms of a Gaussian Ginzburg-Landau approach with a total-energy cutoff in the fluctuation spectrum. Resulting values for the exponent m found for all samples, 0.5 m 0.7, are interpreted as due to phase fluctuations of the d-wave pairing symmetry of the order parameter in the ab planes.