Nb/Al2O3/Al/MgB2 large area thin films heterostructures: Possible observation of tunneling from both dirty and clean limit MgB2

We report the demonstration of dc and ac Josephson effects as well as conductance spectra measurements on Nb/Al2O3/Al/MgB2 thin films heterostructure. The heterostructure exhibits moderately hysteretic current-voltage characteristic with a dc Josephson current branch and regular microwave-induced Shapiro steps. Conductance spectra measurements point toward a two-gap scenario and are explained with the probable presence of tunneling both from dirty limit regions, reflecting a proximized order parameter Delta(dirty) approximate to 2 meV, and from clean limit regions, reflecting a proximized order parameter Delta(3D) approximate to 0.9 meV.