ATOMIC-PLANE-SELECTIVE STM IMAGING AND STS ON THE BI2SR2CACU2O8+DELTACLEAVED SURFACE

In STM experiments on Bi2Sr2 CaCu2 O-8+delta, atomic images of the Bi- O and Cu-O planes have been observed by using different bias voltages larger and smaller than, the Bi-O plane semiconducting gap, respective ly. Tunneling spectra have also been measured while observing the Cu-O plane images for three heights (h(1) > h(2) > h(3)) of the tip at 6 K . The spectra for h(3), where the tip seems to be extremely close to t he specimen. surface, show that, in comparison with those for hz and h g, the superconducting gap is reduced by similar to 30% and the spectr al weights at low voltages are enhanced with a small peak at around V = 0. These behaviors are very similar to expectations for the pair-bre aking due to non-magnetic impurities in a d-wave superconductor