Through magnetization and conductivity measurements, the effect of dimensionality on the superconducting fluctuations has been investigated for Tl 2 Ba 2 CaCu 2 O 8 ͑Tl-2212͒, YBa 2 Cu 3 O 7 ͑YBCO͒, and ͑Tl,Bi͒Si 2 CaCu 2 O 7 ͑Tl-1212͒. Our results show that the bilayered thallium compound ͑i.e., Tl-2212 which is the most anisotropic compound͒ is clearly two-dimensional ͑2D͒ while a 3D-2D crossover is evidenced for Tl-1212 and YBCO. This crossover occurs through an intermediate region between two asymptotic behaviors: 3D near the transition and 2D at higher temperatures.

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International audienceno abstrac

By measuring the temperature dependence of the magnetoresistivity, we have studied the activation energy U of two Tl-based superconducting oxides having different electronic anisotropies ͑Tl-2212, which is very anisotropic, close to Bi-2212, and Tl-1212, the anisotropy of which is about 10͒. The activation energies are described in terms of movements of half loops of vortices, with a lateral size of about the intervortex spacing a 0 . Taking into account the field dependence of the elastic coefficients C 44 and C 66 , this activation energy is estimated and compared to the experimental data. The precise magnetic-field dependence of the activation energy in Tl-2212 and Tl-1212 are different. This difference is taken into account in the frame of a single model considering two different regimes according to the anisotropy value.