Homogeneity investigations of superconducting transition of Nb3Ge films

Superconducting transition curves of Nb3Ge films prepared by cosputtering or by chemical vapor deposition on sapphire substrates were determined using voltage probes on the sample of variable distance between the contacts. Noticeable reduction of transition width ΔT with decreasing voltage probe separation is found, ΔT-values determined from the slope at the midpoint of transition of the order of 0.2 K resulting for contact separations below 1 mm, with transition temperatures Tc(midpoint) up to 22.3 K. No dependence between Tcand ΔT was observed, however there exists a noticeable correlation between Tc-values of adjacent sample regions. A very similar spatial correlation is found for the residual resistivity ratio RRR. Locally determined RRR- and Tc-values exhibit for a given specimen qualitively a similar correlation as reported by Testardi et al.