Nanoscale modulation of local barrier height on Bi-based cuprate superconductors observed by scanning tunneling microscopy/spectroscopy

The atomically resolved local barrier height (LBH) of a Bi2Sr2CaCu2O8+delta (Bi2212) superconducting single crystal is investigated by using scanning tunneling microscopy/ spectroscopy (STM/STS). The LBH distribution is found to be strongly related with the well-known supermodulation structure of the Bi2212 surface with a period of similar to 2.7 nm. In particular, the magnitude of the LBH is anticorrelated to the Bi-Bi atomic distance that is affected by supermodulation. A comparison with simultaneously obtained conductance spectra shows that there is a small correlation between the spatial modulation of the gap amplitude (A) and the LBH, this indicates that the measured A is slightly affected by the topmost BiO surface, but dominantly reflects information on the inner CuO2 layer, which is responsible for the superconductivity.