Magnetoresistance measurements on polycrystalline ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$

The magnetoresistance of a polycrystalline sample of ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ has been measured by an ordinary resistive method at temperatures from about 1 to 15 K above ${\mathit{T}}_{\mathit{c}}$ and in magnetic fields up to 12 T. From our experimental results and the theory of Hikami and Larkin, we obtain values of the coherence lengths ${\xi }_{\mathit{a}\mathit{b}}$=15.6 Å and ${\xi }_{\mathit{c}}$=3.6 Å and of the phase-breaking time ${\mathrm{\tau }}_{\mathrm{\phi }}$=1.8×${10}^{\mathrm{-}13}$ s.