Study of the Josephson Current of ${\rm MgB}_{2}/{\rm Insula\tor/Pb}$ Tunnel Junctions

We have fabricated MgB₂/Insulator/Pb Josephson tunnel junctions on MgB₂ films deposited by hybrid physical-chemical vapor deposition using native oxide as the tunnel barrier. For the critical current of the junction on MgB₂ (0001) film, its temperature dependence follows the Ambegaokar-Baratoff relation and its magnetic field dependence exhibits a Fraunhofer pattern. From analysing the magnetic field dependence of the critical current of the junction on c-axis tilted MgB₂ film, we find small contribution of the Josephson current from the ab-plane tunneling, which may suggest a pi phase difference between the order parameters of MgB₂pi and sigma bands.