Evidence for two-band superconductivity from break-junction tunneling on MgB2 -: art. no. 127002

Superconductor-insulator-superconductor tunnel junctions have been fabricated on MgB2 that display Josephson and quasiparticle currents. These junctions exhibit a gap magnitude, Delta similar to 2.5 meV, that is considerably smaller than the BCS value, but which clearly and reproducibly closes near the bulk T-c. In conjunction with fits of the conductance spectra, these results are interpreted as direct evidence of two-band superconductivity.