In-plane paraconductivity in a single crystal of superconducting ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{x}}$

Resistivity measurements have been made in the a-b plane on a single-crystal sample of superconducting ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{x}}$. The resistivity versus temperature curve shows a highly linear region between 150 and 240 K, with an upward deviation from linearity at 240 K. With decreasing temperature below 150 K, the resistivity curve also deviates from linearity; this deviation has been analyzed in terms of the Aslamazov-Larkin, Lawrence-Doniach, and Maki-Thompson paraconductivity theories. All three theories can be fit to the data, but the Lawrence-Doniach model gives the best fit to the data, with physically reasonable parameters. We find that the Ginzburg-Landau coherence length in the c direction, extrapolated to low temperature with the theoretical temperature dependence, is approximately 0.44 Å.