Proximity Effect in Gold Coated $YBa_2Ca_3O_{7-\delta}$ Films Studied by Scanning Tunneling Spectroscopy

TL;DR

This study investigates how superconductivity penetrates gold layers on YBCO films, revealing that the proximity effect is mainly due to (100) facets and exhibits an s-wave symmetry with a penetration depth of about 30 nm.

Contribution

It provides detailed measurements of the proximity effect in gold-coated YBCO films, highlighting the facet dependence and s-wave symmetry of the induced order parameter.

Findings

Proximity-induced gap decreases exponentially with distance from (100) facets.

Superconductivity penetrates approximately 30 nm into the gold layer.

The interface gap is around 15 meV, aligning with previous experiments.

Abstract

Scanning tunneling spectroscopy on gold layers over-coating \textit{c}-axis $YBa_2Ca_3O_{7-\delta}$ (YBCO) films reveals proximity induced gap structures. The gap size reduced exponentially with distance from \textit{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 $\sim 30$ nm, in good agreement with estimations for the dirty limit. The extrapolated gap at the interface is $\sim 15$ meV, consistent with recent point-contact experiments. The proximity-induced order parameter appears to have predominant \textit{s}-wave symmetry.