The proximity effect and critical field behavior of Re/Al bilayers

Abstract We report the perpendicular critical field H _c2 properties of disordered Re-Al bilayers via magneto-transport measurements. The bilayers consisted of a {d}_Re=3 nm bottom layer of Re and an upper Al layer with thickness varying between d _Al = 0 − 3 nm. We find that in this range of Al thicknesses, the bilayer transition temperature T _c increases with increasing Al thickness, although their monolayer counterparts have {T}_c^Re>{T}_c^Al. Furthermore, H _c2 of the bilayers has a local maximum at an Al coverage of 1.5 nm with a critical field that is 50% larger than that of the standalone 3 nm Re film. At higher Al thicknesses H _c2 drops rapidly but remains more than an order of magnitude greater that that of comparable thickness standalone Al film. Our data show that a thin, disordered Re under-layer can dramatically increase the magnetic field tolerance of the Al over-layer. This would allow one to retain the desirable chemical and metallurgical properties of Al without sacrificing high field compatibility in quantum circuits, such as topological qubit devices and superinductor circuits.