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High-Resolution STM/STS Studies of Doping Effects on Bi-O Layers in Bi-2122 High-Tc Cuprate

Effects arising from the presence of excess oxygen in the Bi-O layer of Bi-2122 compound have been studied with the STM/STS technique which has been effectively used for obtaining atomically resolved images. The excess oxygen is incorporated by substituting Dy3+ at the Ca2+-site as well as by oxygenating the pure sample. It has been possible to detect and directly observe the excess oxygen atoms in the Bi-O layer which is in accord with the information inferred from neutron diffraction and HRTEM studies of other workers. The controversial issue of whether the Bi-O layer is conducting or insulating has been discussed in the light of the SIS findings on doped samples. The results show that there is a gradual increase in its room temperature gap and a decrease in the LDOS, indicating the Bi-O layer to become insulating with incorporation of excess oxygen.