PARACONDUCTIVITY AND EXCESS HALL-EFFECT IN EPITAXIAL YBA2CU3O7 FILMS INDUCED BY SUPERCONDUCTING FLUCTUATIONS

Measurements of the temperature dependence of the electrical resistivity and the Hall effect in epitaxial films of YBa2Cu3O7 are reported. The resistivity is close to linear in T and the cotangent of the Hall angle proportional to T2 at temperatures sufficiently above T(c). Deviations from this behavior near T(c) are attributed to thermodynamic fluctuations and are analyzed in terms of theories for direct (Aslamazov-Larkin) and indirect (Maki-Thompson) fluctuation contributions in a layered superconductor. We obtain an unequivocal fit to both paraconductivity and excess-Hall-effect data with a consistent set of three parameters, i.e., the c-axis coherence length xi(c) (0) = 1.5 angstrom, the phase-relaxation time tau(phi) = 8.6 X 10(-14) s at 100 K, and the electron-hole asymmetry parameter beta = -0.17. We observe a sign change of the excess Hall effect close to T(c), when the Aslamazov-Larkin process becomes dominant.