Persistence of superconductivity in niobium ultrathin films grown on R-Plane Sapphire

TL;DR

This study investigates the structural and electronic properties of ultrathin niobium films on R-plane sapphire, revealing the persistence of superconductivity down to 3 nm thickness and potential for quantum device applications.

Contribution

It demonstrates that niobium films as thin as 3 nm can remain superconducting and are compatible with nanofabrication, highlighting their suitability for quantum technologies.

Findings

Superconductivity persists in niobium films down to 3 nm thickness.

Superconducting critical temperature rises sharply within a monolayer range.

Films can be processed into stable nanostructures for quantum devices.

Abstract

We report on a combined structural and electronic analysis of niobium ultrathin films (from 2 to 10 nm) deposited in ultra-high vacuum on atomically flat R-plane sapphire wafers. A textured polycrystalline morphology is observed for the thinnest films showing that hetero-epitaxy is not achieved under a thickness of 3.3nm, which almost coincides with the first measurement of a superconducting state. The superconducting critical temperature rise takes place on a very narrow thickness range, of the order of a single monolayer (ML). The thinnest superconducting sample (3 nm/9ML) has an offset critical temperature above 4.2K and can be processed by standard nanofabrication techniques to generate air- and time-stable superconducting nanostructures, useful for quantum devices.