Proximity Effect in Gold-Coated YBa_2Cu_3O_(7-δ) Films Studied by Scanning Tunneling Spectroscopy

摘要

Scanning tunneling spectroscopy on gold layers overcoating c-axis YBa_2Cu_3O_(7-δ) (YBCO) films reveals proximity-induced gap structures. The gap size reduces exponentially with the distance from a-axis facets, indicating that the proximity effect is primarily due to the (100) YBCO facets. The penetration depth of superconductivity into the gold is ～30 nm, in good agreement with estimations for the dirty limit The extrapolated gap at the interface is ～15 meV, similar to the value of an s-wave component of the order parameter measured at the YBCO surface in recent point-contact experiments.