It was argued, on the basis of band structure calculations and the Eliashberg theory, that the observed decrease of TC of Al- and C-doped MgB2 samples could be understood mainly in terms of a band-filling effect due to electron doping by Al and C. A simple scaling of the electron-phonon coupling constant lambda by the variation of the density of states as a function of electron doping was sufficient to capture the experimentally observed behavior. The long-standing open question, of the experimental observation of a nearly constant π gap as a function of doping, was also explained by compensation of the effect of band filling and interband scattering. Both effects together generated a nearly constant π gap and shift the merging point of both gaps to higher doping concentrations, resolving the discrepancy between experiment and theoretical predictions based on interband scattering only.

Band Filling and Interband Scattering Effects in MgB2 - Carbon Versus Aluminum Doping. J.Kortus, O.V.Dolgov, R.K.Kremer, A.A.Golubov: Physical Review Letters, 2005, 94[2], 027002 (3pp)