The role of band matching in the proximity effect between a superconductor and a normal metal

TL;DR

This study combines experimental and theoretical methods to investigate how different atomic stackings of a Co overlayer on Ru(0001) influence the proximity effect and superconductivity, revealing the importance of interface transparency.

Contribution

It demonstrates how stacking variations affect proximity effects and superconductivity, highlighting the role of interface transparency and local electronic states.

Findings

Weak proximity effect with magnetic hcp stacking due to low interface transparency.

Strong proximity effect with extepsilon-like stacking due to lifted momentum conservation.

Identification of an edge state caused by a local hcp rim around the extepsilon core.

Abstract

We combine density functional theory and scanning tunneling microscopy to study the proximity effects between a bulk Ru(0001) superconductor and an atomically thin overlayer of Co. We have identified that the Co monolayer can grow in two different stackings: the hcp and a reconstructed \textepsilon-like stacking. We analyze their electronic structure from both experiments and density functional theory. While the magnetic hcp stacking shows a weak proximity effect in combination with Shiba states and with almost no suppression of superconductivity of the substrate, the more complex \textepsilon-like stacking becomes almost fully superconducting and displays an edge state at the island rim. We identify this edge state as a trivial state caused by a local hcp rim around the \textepsilon-core. We explain the weak proximity effect between Ru and the magnetic hcp islands by a low transparency of the interface, while the large chemical unit cell of the non-magnetic \textepsilon-like stacking lifts the momentum conservation at the interface making it transparent and causing a clear proximity effect.