Losses in superconducting Niobium Films caused by Interface Tunnel   Exchange
  Identifying the loss mechanisms of niobium film cavities enables an accurate determination of applications for future accelerator projects and points to research topics required to mitigate their limitations. Measurements on samples show that the electric field is a dominant loss mechanism for niobium films, acting through interface tunneling between localized states in surface oxides and delocalized states in the superconducting niobium. 
Tobias Junginger, Wolfgang Weingarten, Carsten Welsch
physics.acc-ph cond-mat.supr-con