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

Low-temperature resistivity of YBa₂Cu₃O_{6 + 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 YBa₂Cu₃O_{6 + x} (x0.37) 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 _ab 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 _ab = 1/_ab by a power law, typical for a 3D material near a metal-insulator transition, is also plausible. The vertical conductivity _c = 1/_c followed a power law, and neither _c(T), nor _c(T) could be fitted by log T. It follows from the _c 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 x0.025.

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