STM IMAGES AND STS OF BI2SR2CACU2O8+DELTA

Clear atomic images of Bi2Sr2CaCu2O8+delta cleaved surfaces were observed al 4.2 K and 300 K by using scanning tunneling microscopy (STM). The atomic image taken under bias voltages much lower than the semiconducting gap of the Bi-O plane is of a square-lattice, which seems to be of the Cu-O plane. A modulation structure along the b-axis is seen as the change in brightness with the period of similar to 5 atomic intervals. The tunneling spectrum at 4.2 K is almost the same in both relatively bright and dark regions of the modulation structure, and in qualitative agreement with that of a gapless superconductor.