Superconductivity Behavior in Epitaxial Ti N Films Points to Surface Magnetic Disorder

Thin superconducting films are important components of modern low-temperature electronics, and their performance can degrade with decreasing thickness, owing to various factors that are often difficult to disentangle. The authors analyze material properties, electron-phonon coupling, and transport in high-quality epitaxial TiN films down to 3 nm in thickness. The thinnest films show a reduction of the superconducting transition temperature by almost a factor of 3, which is associated with a minute amount of magnetic disorder. In thin films the magnetic scatterers occur predominantly on the surface, and can originate from O vacancies in a naturally oxidized surface layer.