Paraconductivity and excess Hall effect in epitaxial ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$ films induced by superconducting fluctuations

Measurements of the temperature dependence of the electrical resistivity and the Hall effect in epitaxial films of ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_7$ are reported. The resistivity is close to linear in T and the cotangent of the Hall angle proportional to ${\mathit{T}}^2$ at temperatures sufficiently above ${\mathit{T}}_{\mathit{c}}$. Deviations from this behavior near ${\mathit{T}}_{\mathit{c}}$ 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 ${\xi }_{\mathit{c}}$(0)=1.5 Å, the phase-relaxation time ${\mathrm{\tau }}_{\mathrm{\phi }}$=8.6×${10}^{\mathrm{-}14}$ s at 100 K, and the electron-hole asymmetry parameter β=-0.17. We observe a sign change of the excess Hall effect close to ${\mathit{T}}_{\mathit{c}}$, when the Aslamazov-Larkin process becomes dominant.