High resolution STM/STS studies of the role of oxygen in superconductivity of Bi-2122 and optimization of T_c

Abstract

The presence of excess oxygen intercalated in Bi-O redox layers has been found to be detrimental to the Tc of the Bi-2122 phase. High resolution STM has been effectively used to locate intercalated oxygen and STS studies have revealed Bi-O layers becoming more insulating with intercalation. By suitable nitrogenation when the excess oxygen is depleted, more conducting redox layers give rise to an improved coupling between Cu-O planes of the neighbouring demi-unit cells in the c-direction, and it is this improved coupling that is responsible for enhanced Tc. In this way it has been possible to optimize Tc(R=0) for the single phase Bi-2122 cuprate at 96 K with a transition width of 3 K, which is the best value reported to date for the bulk ceramic sample of this material.