Gaussian and Three-Dimensional-XY Scalings and Effects of Disorder in the Fluctuation Magnetoconductivity of Polycrystalline DyBa2Cu3O7

Abstract

Systematic measurements of the fluctuation magnetoconductivity in granular DyBa 2 Cu 3 O 7±d in magnetic fields up to 50 kOe are reported. Gaussian and critical scalings are observed in the normal state. In the Gaussian regimes, large intervals corresponding to low-dimensional fluctuations are evidenced. Below T c , in the regime describing the approach to the zero-resistivity state, the fluctuation conductivity diverges as expected in the coherence transition of mesoscopic granular superconductors in low magnetic fields.

Phenomenology and Sign Change of the Hall Resistivity near the Superconducting Transition of Polycrystalline DyBa2Cu3O7

“…3. It is clear from these results that the sign change of the Hall effect occurs in the region of the minimum in c À1 s , which corresponds to the temperature regime where thermal fluctuations dominate the magnetotransport phenomenology of granular high-T c superconductors [13]. We are thus led to suggest that this feature in the Hall resistivity in our sample is the consequence of a fluctuation contribution having sign opposite to that of the normal effect.…”

“…A comparison between the Hall resistivity and the fluctuation contribution to the diagonal 510 J. Roa-Rojas et al magnetoconductivity, which is represented in terms of the c À1 s quantity (see the accompanying paper, Ref. [13]) is shown in Fig. 3.…”

“…3. Phenomenological comparison of the fluctuation magnetoconductivity, represented in terms of c À1 s (see [13]), and the Hall resistivity in the mixed state of polycrystalline DyBa 2 Cu 3 O 7±d…”