Growth and Characterization of Thin-film A15 Nb-Al Intermetallics for Superconducting Quantum Electronics: Part 2

A15s are a family of superconducting compounds with critical temperatures and magnetic fields higher than their comprising elements. Though extensively studied in the latter half of the twentieth century, key characteristics of the superconducting state in these compounds are largely missing from the literature. In this work, we synthesize thin films of Nb₃Al in the A15 structure and extensively characterize their electrical properties at DC and microwave frequencies. For a range of samples with T_c’s between 14 and 16 K, we measured the temperature dependence of critical magnetic fields corresponding to zero-temperature critical fields greater than 20 T and estimated coherence lengths on the order of 5 nm. Additionally, we present the first measurements of loss tangent and kinetic inductance performed on microwave resonators fabricated on A15 Nb₃Al films.