Low-temperature resistivity of single crystals YBa₂Cu₃O₆₊ₓ in the normal state

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A scan of the superconductor -- nonsuperconductor transformation in single crystals YBa₂Cu₃O₆₊ₓ (x about 0.37) was done in two alternative ways, namely, by applying the magnetic field and by reducing the hole concentration through the oxygen rearrangement. The in-plane normal-state resistivity ρab obtained in both cases was quite similar; its temperature dependence can be fitted by logarithmic law in the temperature range of almost two decades. However, a different representation of the σab=1/ρab by a power law typical for a 3D-material near a metal -- insulator transition is also plausible. The vertical conductivity σc=1/ρc followed the power law and neither σc(T), nor ρc(T) could be fitted by log(T). It follows from the ρc measurements that the transformation at T=0 is split into two transitions: superconductor -- normal-metal and normal-metal -- insulator. In our samples, they are distanced in the oxygen content by Δx≈0.025.