TEMPERATURE-DEPENDENCE OF THE MAKI-THOMPSON FLUCTUATION PROCESS IN YBA2CU3O7 PROBED BY MAGNETOTRANSPORT MEASUREMENTS

The contributions of thermodynamic fluctuations of the superconducting order parameter to the normal-state magnetoconductivity tenser are investigated. An analysis of complementary measurements of the electrical resistivity, the Hall effect and the magnetoresistance at temperatures above T-c in thin films of the high-T-c superconductor YBa2Cu3O7 provides a separation between the direct (Aslamazov-Larkin) and indirect (Maki-Thompson) fluctuation contributions. The direct contribution is not significantly affected by a possible unconventional pairing state and reveals consistent values for the coherence lengths in the ab plane, xi(ab)(0) = 1.4 nm, and parallel to the c-axis, xi(c)(0) = 0.15 nm, respectively. The excess Hall effect provides the most efficient way to detect the indirect fluctuation contribution, which is found to drop more rapidly towards higher temperatures than predicted for s wave pairing symmetry. An analysis of magnetoresistance measurements with proper correction for the magnetoresistance of the normal-state quasiparticles also indicates that the Maki-Thompson fluctuation process is smaller at higher temperatures than previously estimated.