Excess current in contacts based on magnesium diboride

The excess current I _exc in In/MgB₂ and Pb/MgB₂ contacts was investigated as a function of the energy gaps Δ_σ and Δ_π in magnesium diboride MgB₂. It was shown that, even in the “dirty” limit, electrons from the σ and π bands do not undergo mixing; i.e., they remain confined to their bands over a long period of time. On this basis, the measurements of the excess current I _exc for contacts prepared in different crystallographic directions of the MgB₂ crystals made it possible to determine the energy gaps Δ_π ≈ 3.0 meV and Δ_σ = 7.5 meV.