Low-leakage thin-film superconductor-insulator-normal metal tunnel junctions on co-evaporated Ba1−xRbxBiO3 and rf-sputtered Ba1−xKxBiO3

Abstract
The oxide superconductors Ba1−xKxBiO3 and Ba1−xRbxBiO3 exhibit ideal BCS‐like characteristics with Tc∼30 K. We report the deposition of thin films with zero‐resistance temperatures up to 25 K and transition widths less than 1 K by thermal co‐evaporation and rf sputtering. Thin‐film S‐I‐N tunnel junctions fabricated by evaporating Ag or Au onto a native barrier exhibit low leakage over 1 mm2 junctions and near‐ideal BCS‐like behavior with a value of 2Δ(0)/kBTco=3.5±0.2.