Determine the microscopic origin and structure of the low-gap regions

Determine the microscopic origin, spatial distribution, and volume fraction of the low-gap regions in compressively stressed sputtered niobium films, including the extent to which their superconducting gap is modified by proximitization effects.

Background

The microwave measurements are consistent with a dominant bcc-niobium phase accompanied by a secondary low-gap component whose effective microwave contribution increases with compressive stress. Candidate explanations include an inhomogeneous-gap landscape, an additional crystalline phase such as omega-niobium, or a proximity-induced gap in otherwise normal omega-niobium regions.

The available microwave and X-ray diffraction data do not uniquely resolve the microscopic identity, spatial arrangement, or volume fraction of the low-gap component. Resolving these alternatives requires additional structural characterization and improved measurements of the relevant phases and interfaces.