Substrate induced proximity effect in superconducting niobium nanofilms

TL;DR

This study investigates how substrate-induced interfacial layers influence the superconducting properties of niobium nanofilms, revealing a strong proximity effect that alters critical temperature based on film thickness and substrate type.

Contribution

It demonstrates the role of interfacial oxide layers in inducing proximity effects in Nb nanofilms, highlighting substrate-dependent variations in superconducting behavior.

Findings

Interfacial oxide layers cause a strong proximity effect in Nb films.

Critical temperature depends on film thickness and substrate type.

Proximity effects modify superconducting properties, especially on SiO₂ substrates.

Abstract

Structural and superconducting properties of high quality Niobium nanofilms with different thicknesses are investigated on silicon oxide and sapphire substrates. The role played by the different substrates and the superconducting properties of the Nb films are discussed based on the defectivity of the films and on the presence of an interfacial oxide layer between the Nb film and the substrate. The X-ray absorption spectroscopy is employed to uncover the structure of the interfacial layer. We show that this interfacial layer leads to a strong proximity effect, specially in films deposited on a SiO$_2$ substrate, altering the superconducting properties of the Nb films. Our results establish that the critical temperature is determined by an interplay between quantum-size effects, due to the reduction of the Nb film thicknesses, and proximity effects.