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

Measurements of the temperature dependence of the electrical resistivi ty and the Hall effect in epitaxial films of YBa2Cu3O7 are reported. T he resistivity is close to linear in T and the cotangent of the Hall a ngle proportional to T2 at temperatures sufficiently above T(c). Devia tions from this behavior near T(c) are attributed to thermodynamic flu ctuations and are analyzed in terms of theories for direct (Aslamazov- Larkin) and indirect (Maki-Thompson) fluctuation contributions in a la yered superconductor. We obtain an unequivocal fit to both paraconduct ivity and excess-Hall-effect data with a consistent set of three param eters, 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 el ectron-hole asymmetry parameter beta = -0.17. We observe a sign change of the excess Hall effect close to T(c), when the Aslamazov-Larkin pr ocess becomes dominant.