Spatially resolved vacuum tunneling spectroscopy on Bi₂Sr₂CaCu₂O₈ by STM at 4.8K

We report scanning tunneling spectroscopy investigations on in-situ cleaved superconducting Bi₂Sr₂CaCu₂O₈ 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 higly reproducible spectra while scanning single crystal surfaces in many different areas and taking a spectra every 5Å along lines of several hundred Ångstroms. Furthermore, we show that the spectra are independent of modifacations 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.