Superconducting fluctuations in Tl-based single crystals: Evidence of universal features and derivation of basic parameters

The critical fluctuations of the magnetization near the Hc2(T) line have been studied in four different single crystals of Tl-based compounds (Tl0.5{Pb}0.5Sr₂{CaCu}₂O₇, Tl₂{Ba}₂Ca₂{Cu}₃O₁₀, Tl₂{Ba}₂CaCu₂{O}₈$, and ${TlBa}₂Ca₂{Cu}₃O₉) with the magnetic field applied along the c axis. It is shown that the magnetization can be scaled in reduced units according to the two-dimensional scaling developed by Ullah-Dorsey and Tesanovic et al., exhibiting the universality of the fluctuations. From this analysis, we deduce the values of the Ginzburg parameter (Gᵢ), the coherence length [ξab(0)], and the penetration depth [λab(0)] of each phase. The values of the Ginzburg fluctuation parameter in the different compounds are put in relation with the relative location of their irreversibility lines.