Critical and gaussian conductivity fluctuations in yba2cu3o7-delta

• Autor(a) principal: Pureur Neto, Paulo
• Data de Publicação: 1993
• Outros Autores: Costa, Rosangela Menegotto, Rodrigues Junior, Pedro, Schaf, Jacob, Kunzler, Julio Vitor
• Tipo de documento: Artigo
• Idioma: eng
• Título da fonte: Repositório Institucional da UFRGS
• Texto Completo: http://hdl.handle.net/10183/104229
• topic: Física da matéria condensada; Propriedades eletrônicas; Flutuacoes em supercondutores

We report on systematic conductivity fluctuation measurements on three different samp1es of YBa2Cu30 7 - δ • We show, using the temperature derivative of the resistivity and the logarithmic derivative ofthe conductivity with respect to temperature, that the transition is a two-step process. In the normal phase, contributions from Gaussian and criticai ftuctuations are c1early evidenced. Far from Tc the Gaussian exponents indicate that a fractal topology might be adequate to describe the space dimensionality of the ftuctuation spectrum. Closer to Te we observe a crossover to a three-dimensional (3D) homogeneous Gaussian regime. Still closer to Tc we unambiguously identify the exponent λcr~O. 33, predicted by the simplest full dynamic scaling theory of criticai superconducting fluctuations. The obtained exponent is consistent with a 3D, two-component, order parameter. Near the zero-resistance state, the temperature dependence of our data is rather consistent with power-law behavior, suggesting the occurrence of a phase-transition phenomenon related to the percolation granular network.