LT-STM/STS observations on electrical field etched surfaces of YBa2Cu3O7-delta single crystal

Surface degradation of YBa2Cu3O7-delta makes it difficult to get a reliable and reproducible tunneling spectra. Therefore, most of tunneling spectra h ave shown some smeared superconducting gap structures with extremely high c onductance levels at the zero biased voltage. In this study, to investigate the stability of YB2Cu3O7-delta crystal surfa ce, and to get more reliable spectra, tunneling spectrum observations were carried out on in situ prepared crystal surface by electrical field etching technique with use of a scanning tunneling microscope. As a result, it is found that the crystal surface obtained by this treatmen t is enough stable at 4.2 K for a long time (at least For 2 h). and that th e tunneling spectra observed on the locally etched surface show a fairly re producible superconducting gap structure with a low conductance level at th e zero biased voltage. The tunneling spectra also showed asymmetrical bump structures below the Fermi level outside the gap region, as observed on Bi2 Sr2CaCu2O8+delta and YBa2Cu4O8-delta. This result shows a possibility that the asymmetric bump structure may be closely related with superconducting e lectronic states of CuO2 plane commonly to all of HTSs. (C) 2001 Elsevier S cience B.V. All rights reserved.