Three-dimensional XY critical fluctuations of the dc electrical conductivity in Bi2Sr2CaCu2O8+delta single crystals

• A method is presented to analyze the dc critical fluctuation conductivity Delta sigma of Bi2Sr2CaCu2O8+delta single crystals in zero magnetic field. Two crossovers are obtained upon approaching T-c; first the Ginzburg crossover from the mean-held region to the initial critical regime, where the critical exponent a of Delta sigma changes from -1/2 to -2/3, and then, closer to T-c, a crossover of alpha form -2/3 to 1/3 in the critical region. Good agreement is found with the expectations from the three-dimensional XY model.

Nyckelord

high-tc superconductors

ii superconductors

phase-transitions

magnetic-field

yba2cu3o7-delta

magnetoconductivity

paraconductivity

diamagnetism

growth

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