Josephson effect and tunneling spectroscopy in Nb/Al2O3/Al/MgB2 thin films junctions

摘要

We report the demonstration of dc and ac Josephson effects as well astunneling spectroscopy measurements on Nb/Al2O3/Al/MgB2 thin filmsheterostructures. Data on dc Josephson effect suggest the presence of twocharacteristic critical currents possibly accounted for the presence of twogaps in the MgB2 film. Tunneling spectroscopy measurements confirm this two-gapscenario and are explained with the presence of tunneling from both dirty limitand clean limit regions, reflecting two different order parameter amplitudes.The behavior of these two gaps is found in good agreement with the predictionsof a recently proposed multigap theory.