Quantum tunneling of the apex oxygen atoms in YBa2Cu3O7− δ superconductors: Anharmonic effects on the out of plane electrical resistivity

Abstract

We evaluate the effects of the anharmonic vibrations of the apex oxygen atom on the out of plane electrical resistivity ϱ c in YBa 2 Cu 3 O 7− δ . 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; (b) in a weak coupling regime, ϱ c ∼ T 0.4 at temperatures higher than 2 T c and the absolute values are below the Mott-Ioffe-Regel limit in YBa 2 Cu 3 O 7 in agreement with the experiments. dϱ c / dT is slightly negative in the region of critical fluctuations. Therefore the O(4) atom should be weakly coupled to the electrons. At higher oxygen depletions, the tunneling is slowed down and the charge transfer along the c-axis is reduced: ϱ c increases and a non metallic behaviour is obtained.