Three-dimensionalXYscaling of the resistivity ofYBa2Cu3O7−δsingle crystals

The electrical resistivity of a single-crystal sample of ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ has been measured. The results are consistent with the existence of a critical regime governed by three-dimensional XY critical exponents. Evidence is also found for the divergence of the conductivity along a line ${\mathit{H}}_{\mathit{g}}$(T)∝(1-T/${\mathit{T}}_{\mathit{c}}$ ${)}^{2\nu }$, the vortex glass transition line. The vortex glass exponents characteristic of this line are ${\mathit{z}}_{\mathit{g}}$(${\nu }_{\mathit{g}}$-1)≊5±1. The results are not consistent with the lowest Landau-level scaling.