CROSSOVER BETWEEN ASLAMAZOV-LARKIN AND SHORT-WAVELENGTH FLUCTUATION REGIMES IN HIGH-TEMPERATURE-SUPERCONDUCTOR CONDUCTIVITY EXPERIMENTS

We present paraconductivity measurements in three different high-tempe rature superconductors: a melt-textured YBa2CU3O7 sample, a Bi2Sr2CaCU 2O8 epitaxial thick film, and a highly textured Bi2Sr2Ca2Cu3O10 tape. The crossovers between different temperature regimes in excess conduct ivity have been analyzed. The Lawrence-Doniach (LD) crossover, which s eparates the two-dimensional and three-dimensional regimes, shifts fro m lower to higher temperatures as the compound anisotropy decreases. O nce the LD crossover is overcome, the fluctuation conductivity of the three compounds shows the same universal behavior: for epsilon = lnT/T -c > 0.23 all the curves bend down according to the 1/epsilon(3) law. This asymptotic behavior was theoretically predicted previously for th e high-temperature region where the short-wavelength fluctuations beco me important.