Anharmonic vibrations of apex oxygen atom in YBa 2Cu 3O 7− δ and doping effects on the out-of-plane electrical resistivity

Abstract

The effects of the quantum tunneling of the apex oxygen atom O(4) on the electrical resistivity ϱ c in YBa 2Cu 3O 7− δ have been investigated at different oxygen depletions. Path techniques have been applied to derive the temperature-dependent coupling constants between the double-well potential (DWP) provided by the O(4) atom and the normal electrons. It is found that: (a) in a strong-coupling regime, the scattering mechanism gives rise to ϱ c ∼ T α with 1.5<α<2; (2) in a weak-coupling regime, ϱ c ∼ T 0.4 at temperatures higher than 2 T c whereas dϱ c dT is slightly negative in the region of critical fluctuations. ϱ c is below the Mott-Ioffe-Regel limit in YBa 2Cu 3O 7 in agreement withthe experiments. Therefore the O(4) atom should be weakly coupled to the electrons and the tunneling energy between the minima of the DWP is ∼ 10 meV at T=100 K, consistent with the estimation given in Ref. [8]. By reducing the oxygen content, the tunneling is slowed down and the charge transfer along the c-axis is smaller; then, the ϱ c values increase and a non-metallic temperature dependence is obtained.