JETP Letters -- June 10, 1997 -- Volume 65, Issue 11 pp. 870-876

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

V. F. Gantmakher, D. A. Pushin, D. V. Shovkun, and G. E. Tsydynzhapov
Institute of Solid State Physics, Russian Academy of Sciences, 142432 Chernogolovka, Moscow Region, Russia
L. P. Kozeeva and A. N. Lavrov
Institute of Inorganic Chemistry, Siberian Branch of the Russian Academy of Sciences, 630090 Novosibirsk, Russia

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

PACS: 72.15.Rn, 61.50.Ah, 74.62.Bf, 71.30.+h