We present paraconductivity (AL) measurements in three different high
temperature superconductors: a melt textured YBa2Cu3O7 sample, a
Bi2Sr2CaCu2O8 epitaxial thin film and a highly textured
Bi2Sr2Ca2Cu3O10 tape. The crossovers between different temperature
regimes in excess conductivity have been analysed. The Lawrence-Doniach (LD)
crossover, which separates the 2D and 3D regimes, shifts from lower to higher
temperatures as the compound anisotropy decreases. Once the LD crossover is
overcome, the fluctuation conductivity of the three compounds shows the same
universal behaviour: for ϵ=lnT/Tc>0.23 all the curves bend down
according to the 1/ϵ3 law. This asymptotic behaviour was
theoretically predicted previously for the high temperature region where the
short wavelength fluctuations (SWF) become important.Comment: 4 pages, Revtex, 1 PostScript figure available upon request
([email protected]); submitted to Physical Review B rapid communication