SPATIALLY-RESOLVED VACUUM TUNNELING SPECTROSCOPY ON BI2SR2CACU2O8 BY STM AT 4.8K

We report scanning tunneling spectroscopy investigations on in-situ cleaved superconducting Bi2SrCaCu2O8 single crystals. Although many investigators report reproducible tunneling studies on high temperature superconductors, there nevertheless remains uncertainties about the correct intrinsic shape of the tunneling spectra. We have been able to obtain highly reproducible spectra while scanning single crystal surfaces in many different areas and taking a spectra every 5 angstrom along lines of several hundred Angstroms. Furthermore, we show that the spectra are independent of modifications of the barrier obtained by changing the tip/sample distance. The experimental density of states clearly shows some filling of the gap which does not fit with a BCS-like s-wave prediction, even if some scattering in the tunneling process is accounted for.