Gaussian, three-dimensional-xy, and lowest-landau-level scalings in the low-field fluctuation magnetoconductivity of bi/sub 2/ sr/sub 2/ cacu/sub 2/ o/sub 8/

Abstract

Systematic measurements of low-field fluctuation magnetoconductivity in a single crystal of Bi2Sr2CaCu2O8 are reported. Gaussian, critical, and lowest-Landau-level scalings are observed. In the Gaussian regimes, large intervals corresponding to low-dimensional fluctuations are evidenced. Far above Tc , effects of disorder produces a fluctuation spectrum characterized by a fractal topology. Decreasing the temperature, at first a homogeneous two-dimensional behavior is observed. Then, near Tc a crossover occurs to a narrow threedimensional (3D) mean-field regime. Still closer to Tc , a scaling consistent with the predictions of the full dynamic 3D-XY universality class is clearly evidenced. This genuine critical regime is destroyed upon the application of magnetic fields above a few mT. For fields above a certain limit and in large temperature intervals, fluctuation magnetoconductivity scales as predicted by the lowest-Landau-level approximation of the Ginzburg-Landau theory.