Superconductivity without dependence on valence electron density in (Al, Zn, Co) doped YBCO systems

Abstract

We adopted the x-ray diffraction, oxygen contents, positron annihilation technology and simulation methods to investigate systematically YBa 2 Cu 3-x (Al, Zn, Co) x O 7-δ (x = 0-0.5) cuprates. The experimental results and simulated calculations support the existence of cluster effect. Moreover, it is concluded that the cluster effect is an important factor on suppression of the superconductivity and the T c does not depend directly on the density of valence electron in the samples.