Andreev reflections on Y1-xCaxBa2Cu3O7-delta evidence for an unusual proximity effect

TL;DR

This study investigates Andreev reflections in Y_{1-x}Ca_{x}Ba_{2}Cu_{3}O_{7- ext{delta}} thin films, revealing an unconventional proximity effect that alters the superconductor's pair potential near the surface.

Contribution

It provides experimental evidence for an unusual proximity effect influencing the pair potential symmetry in high-temperature superconductors.

Findings

The conductance spectra fit a mixed d_{x^{2}-y^{2}}+is pair potential symmetry.

The 'is' component amplitude increases with contact transparency.

An unusual proximity effect modifies the surface pair potential in the superconductor.

Abstract

We have measured Andreev reflections between an Au tip and Y_{1-x}Ca_{x}Ba_{2}Cu_{3}O_{7 - \delta} thin films in the in-plane orientation. The conductance spectra are best fitted with a pair potential having the "d_{x^{2}-y^{2}+is" symmetry. We find that the amplitude of the "is" component is enhanced as the contact transparency is increased. This is an indication for an unusual proximity effect that modifies the pair potential in the superconductor near the surface with the normal metal.