Superconductivity of YBa₂Cu_3-xM_xO_y (M = Co, Fe, Ni, Zn)

Abstract

The superconductivity of YBa 2 Cu 3- x M x O y , (M = Co, Fe, Ni, Zn; x = 0.1-0.4) was examined by means of ac susceptibility measurements. The results indicated that Cu in the Cu2 site (between the Y and the BaO layer) plays a more substantial role in superconductivity than that in the Cu1 site (between the BaO layers). Combining this with our earlier results for the La 1+ x Ba 2- x Cu 3 O y system, we suggest that holes doped mainly in the O 2 p orbitals of the rock-salt-type BaO layers form Cooper pairs through some medium (spin fluctuations or possibly other collective modes) excited in the Cu2 layer.