Superconducting Properties of Annealed Nb–Al–Ge Thin Films

Abstract
Annealed bulk Nb–Al–Ge possesses the highest superconducting transition temperature presently known (Tc∼20 K). In this paper we report on Tc and on other superconducting properties of annealed Nb–Al–Ge thin films which were prepared by sputtering from a 3Nb⋅0.8Al⋅0.2Ge cathode. Annealing was performed in a high vacuum environment maintained at 10−9Torr or less, for times and temperatures near the optimum conditions for bulk Nb–Al–Ge. Films with Tc's from 12 to 16 K were annealed and in all cases a rise in Tc was observed, with the maximum value obtained thus far being 17.5 K. The current carrying capacity (Jc) values, already substantially higher for unannealed thin films than for the bulk, were raised even further in the annealed samples, indicating that annealing has no detrimental effects on the flux pinning in these films.