SPATIALLY CONTINUOUS ZERO-BIAS CONDUCTANCE PEAK ON (110)YBA2CU3O7-DELTA SURFACES

We report the observation of a pronounced high zero-bias conductance p eak (ZBCP) in the conductance spectra of (110)-oriented YBa2CU3O7-delt a epitaxial thin-film surfaces by low-temperature scanning tunneling m icroscopy/spectroscopy at 4.2 K. On firms with very low surface roughn ess, both the superconducting gap structure and the ZBCP could be clea rly observed in the spectra and neither depended on the measurement po sition or on the distance between the tunneling tip and the sample sur face. This result is in agreement with the recent theoretical predicti on of the formation of bound states on surfaces of d-wave superconduct ors that lead to a ZBCP with a maximum for (110)-oriented surfaces.