Scanning tunneling microscopy and spectroscopy in lanthanide substituted Bi2Sr2CuOy

We have performed scanning tunneling microscopy and spectroscopy experiments on Bi2Sr1.57La0.43CuOy and Bi2Sr1.52Nd0.48CuOy. The atomic images showing the incommensurate modulated structure and the tunneling spectra have been successfully obtained at 4.2 K. The observed superconducting gap values in both samples have evolved spatially on the length scale of about 20 nm. This length scale is much longer than that reported in Bi2Sr2CaCu2Oy. The distribution of the gap value seems to originate from the inhomogeneous distribution of the lanthanide ions.