Tunneling spectroscopy of Nb/Al bilayers for superconducting computing

Niobium and aluminum, and the compounds made from them, are important materials in the superconducting computing community. However, much remains to be explored to understand the interaction of states between Nb based superconductors and Al, and how these properties can be used to improve tunnel junctions and cavities. Tunneling spectra of normal metal (N)/insulator (I)/superconducting bilayer (S) tunnel junctions are found to vary significantly as a function of the thickness of the bilayer elements. We present N/I/S tunnel junctions fabricated with various Al thicknesses in the superconducting bilayer electrode. Tunneling spectra are measured at 4 K and fit using Maki analysis to extract orbital depairing and spin-orbit parameters.