An evaluation of A15 Nb3Al superconducting thin films for application in quantum circuits

Abstract

A15 superconductors are distinguished by their high critical temperatures, magnetic fields, and current-carrying capabilities. Among them, Nb$_3$Al is of particular interest for superconducting quantum circuits as a means to extend device operating temperatures, provided that its electrodynamic properties are well understood. Here, we report on the synthesis of Nb$_3$Al thin films by magnetron co-sputtering followed by rapid thermal processing, yielding superconducting transition temperatures above 16~K. Microwire devices patterned from these films exhibit a coherence length of $3.2\,\mathrm{nm}$ and superfluid densities as low as $1.1\times 10^{26}\,\mathrm{m}^{-3}$, suggesting that Nb$_3$Al may enable high kinetic inductance in thinner films. Coplanar waveguide resonators fabricated on Nb$_3$Al demonstrate single-photon internal quality factors up to $2.26\times 10^{5}$. These results establish Nb$_3$Al as a promising material platform for the development of superconducting quantum circuits operating at elevated temperatures, contingent on appropriate control of interfacial chemistry and surface morphology.