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.