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

Abstract

We have used x-ray diffraction, oxygen content, positron annihilation technology, and simulation methods to investigate systematically the cuprates YBa2Cu3−x(Al,Zn,Co)xO7−δ (x=0–0.5). The experimental results and simulation calculations support the existence of a cluster effect. Moreover, it is concluded that the cluster effect is an important factor in the suppression of superconductivity and that Tc does not depend directly on the valence electron density in the samples.