DC features and RF losses of Nb-based superconducting thin films

Superconducting thin films of Nb, NbN, and NbZr have been realized in view of their application to superconducting accelerating cavities. The samples have been sputtered on different planar substrates, i.e., glass, sapphire, and copper. The electrical and superconducting features of the films have been measured in the temperature range of 300 K to 4.2 K and in the presence of a magnetic field of up to 5 T. The residual resistivity, critical temperatures T_c, and upper critical fields H_c2 of the films are reported. The expected RF properties are discussed. Measurements of the RF dissipation of Nb₇₅Zr₂₅ films sputtered on copper substrates have been performed in a cylindrical TE₀₁₁ cavity. For Nb₇₅ Zr₂₅ thin films, the authors have measured the superconducting energy gap and the surface resistance in a cylindrical TE₀₁₁ cavity in order to compare the experimental value to the theoretical BCS (Bardeen-Copper-Schrieffer) computation result