Scaling behavior of conductivity and magnetization in high-temperature superconductors

Through magnetization and conductivity measurements, the effect of dimensionality on the superconducting fluctuations has been investigated for ${\mathrm{Tl}}_2$ ${\mathrm{Ba}}_2$ ${\mathrm{CaCu}}_2$ ${\mathrm{O}}_8$ (Tl-2212), ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_7$ (YBCO), and (Tl,Bi)${\mathrm{Si}}_2$ ${\mathrm{CaCu}}_2$ ${\mathrm{O}}_7$ (Tl-1212). Our results show that the bilayered thallium compound (i.e., Tl-2212 which is the most anisotropic compound) is clearly two-dimensional (2D) 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.