Disorder and the upper critical field of Nb3Ge

The upper critical field, Hc2, as determined from experimental values of Tcand (dHc2/dT)Tc, has been investigated in Nb3Ge superconducting thin films with different degree of structural disorder. An increase of Hc2(O) up to 36.9 T was found for samples with resistivities ranging from 40 μΩcm to 60μΩcm and a decrease of Hc2(O) to 5.7 T for ρ=150 μΩcm. Based on the Ginsburg-Landau solution for Hc2(O) and the change of the coherence length with the electron mean free path a model is presented which describes the change of Hc2(O) with resistivity, qualitatively.