A large number of experimental facts and theoretical arguments favoured a 2-gap model for superconductivity in MgB2. However, this model predicted strong suppression of the critical temperature by interband impurity scattering and, presumably, a strong correlation between the critical temperature and the residual resistivity. No such correlation was observed. It was argued that this fact could be understood if the band disparity of the electronic structure was taken into account, not only in the superconducting state, but also in normal transport.

Superconductivity in MgB2 - Clean or Dirty? I.I.Mazin, O.K.Andersen, O.Jepsen, O.V.Dolgov, J.Kortus, A.A.Golubov, A.B.Kuzmenko, D.Van Der Marel: Physical Review Letters, 2002, 89[10], 107002 (3pp)