EVIDENCE OF THE DIRECT ROLE OF DOPANT OXYGEN IN HIGH-TEMPERATURE SUPERCONDUCTIVITY

The critical compositions u(c) of Cu-site Ni and Zn necessary to destr oy superconductivity in Nd2-zCezCuO4 La2-betaSrbetaCuO4, Bi2Sr2CaCu2O8 , Bi1.8Pb0.2Sr2Ca2Cu3O10, YBa2Cu3O7 and YBa2Cu4O8 scale approximately exponentially with the distance of the impurity sites from the dopant oxygen in the charge-reservoir regions of the crystals. This indicates that the superconducting condensates are primarily in the charge rese rvoirs, where they are directly controlled by dopant oxygen-not in the cuprate planes where they would be remotely controlled, as is assumed by all cuprate-plane theories. The critical temperatures also show a trend with the same distance, suggesting that the transition temperatu re may be increased by fabricating superconductors whose charge reserv oirs lie farther from the cuprate planes.