Reproducible superconducting gap on clean surfaces of BiSrCaCuO prepared by etching with a scanning tunneling microscope tip

Tunneling properties on the basal plane of a high-T-c superconductor, Bi2Sr2CaCu2Oy, have been investigated by cryogenic scanning tunneling microscopy/spectroscopy (STM/STS). The tunneling spectra obtained on the as-cleaved surfaces showed significant scattering, ranging from semiconducting to superconducting behavior, depending on the measurement position. On fresh surfaces prepared by tip apex etching procedure at 4.2 K, a clear superconducting gap structure was reproducibly observed with a flat background conductance curve. We have also experienced that during the tip scanning the background conductance suddenly changed from a flat shape to a V shape accompanied with discontinuity in an STM image, suggesting that the V-shaped tunneling conductance reflects the electronic nature of the tip apex. (C) 1998 Elsevier Science B.V.