Study of superconducting fluctuations in the high-temperature superconductor YBa2Cu3O7 by magneto-transport measurements

The contributions of thermodynamic fluctuations of the superconducting order parameter to the normal-state magneto-conductivity tensor are investigated. Complementary measurements of the electrical resistivity, the Hall effect and the magnetoresistance at temperatures above Tc in thin films of the high-Tc superconductor YBa2Cu3O7 reveal the coherence lengths in the ab-plane, ζab(0) = 1.4 nm, and parallel to the c-axis, ζc(0) = 0.15 nm, respectively. The indirect (Maki-Thompson) fluctuation contribution can be detected in the excess Hall effect, but exhibits a different temperature dependence than predicted for s-wave pairing symmetry. It is smaller at higher temperatures than previously estimated from magnetoresistance measurements when the normal state magnetoresistance is correctly included. The results indicate an uncoventional pairing state in the cuprate superconductors.