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 t he as-cleaved surfaces showed significant scattering, ranging from sem iconducting 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 th at during the tip scanning the background conductance suddenly changed from a flat shape to a V shape accompanied with discontinuity in an S TM image, suggesting that the V-shaped tunneling conductance reflects the electronic nature of the tip apex. (C) 1998 Elsevier Science B.V.