Superconducting properties of MgB 2 thin films prepared by sequential deposition of boron and magnesium

Abstract

The structural and superconducting properties of MgB 2 thin films, deposited on sapphire or silicon substrates by sequential deposition of boron and magnesium thin films, using electron beam evaporation, have been studied. Post deposition in situ annealing at 650°C results in smooth thin films with onset critical temperature T con ≅ 36 K and zero-resistance superconductivity below 29 K. A sensitive measurement of temperature dependence of microwave losses in 10 GHz frequency band confirms a presence of a weak link medium in the films with intergranular weak links appearing just below the zero-resistance critical temperature T c0 ≅29 K . The effort to prepare MgB 2/Al 2O 3/Nb junctions of sandwich or edge-type showed considerable problems of clean interface realisation. Although the junctions quality was relatively low, the non-zero critical current and visible Shapiro steps in the junction current–voltage characteristics confirmed the interaction of Josephson radiation with external microwave radiation.