Superconductor-insulator-superconductor tunnel junctions were fabricated, on MgB2, that exhibited Josephson and quasiparticle currents. These junctions had a gap of about 2.5meV, that was considerably smaller than the BCS value, but which clearly and reproducibly closed near to the bulk TC. In conjunction with fits of the conductance spectra, these results were interpreted as direct evidence of 2-band superconductivity.

Evidence for Two-Band Superconductivity from Break-Junction Tunneling on MgB2. H.Schmidt, J.F.Zasadzinski, K.E.Gray, D.G.Hinks: Physical Review Letters, 2002, 88[12], 127002 (3pp)