STRUCTURAL AND ELECTRONIC ROLE OF LEAD IN (PBBI)2SR2CACU2O8 SUPERCONDUCTORS BY STM

The structural and electronic effects of lead substitution in the high-temperature superconducting materials PbxBi2-xSr 2CaCu2O8 have been characterized by scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). Large-area STM images of the Bi(Pb)-O layers show that lead substitution distorts and disorders the one-dimensional superlattice found in these materials. Atomic-resolution images indicate that extra oxygen atoms are present in the Bi(Pb)-O layers. STS data show that the electronic structure of the Bi(Pb)-O layers is insensitive to lead substitution within ±0.5 electron volt of the Fermi level; however, a systematic decrease in the density of states is observed at ≈1 electron volt above the Fermi level. Because the superconducting transition temperatures are independent of x(Pb) (x ≤ 0.7), these microscopic STM and STS data suggest that the lead-induced electronic and structural changes in the Bi(Pb)-O layer do not perturb the electronic states critical to forming the superconducting state in this system.