Gaussian, three-dimensional-XY,and lowest-Landau-level scalings in the low-field fluctuation magnetoconductivity ofBi2Sr2CaCu2O8

Abstract

Systematic measurements of low-field fluctuation magnetoconductivity in a single crystal of ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{8}$ 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 ${T}_{c},$ 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 ${T}_{c}$ a crossover occurs to a narrow three-dimensional (3D) mean-field regime. Still closer to ${T}_{c},$ a scaling consistent with the predictions of the full dynamic 3D-$\mathrm{XY}$ 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.