The temperature dependence of the upper critical fields, HC2(T) of the 2-gap superconductors Mg1-xAlxB2 (x = 0, 0.1, 0.2 or 0.3) was obtained by resistivity measurements. The HC2(T) values were analyzed, within the dirty-limit 2-gap model, using the calculated electron–phonon coupling constants and Coulomb pseudopotentials. As the Al contents increased, both TC and HC2(0) decreased, which was the direct manifestation of the increasing number of electrons. At the same time, the 3-dimensional π bands became much dirtier when Al was doped. In contrast, the intraband scattering of the 2-dimensional σ bands was relatively unaffected by the Al doping. These behaviors could be understood when the characters of both bands were considered. In all the samples investigated, the σ bands were dirtier than the π-bands.

The Upper Critical Field and Two-Gap Nature in Mg1-xAlxB2. M.S.Park, H.J.Kim, B.Kang, S.I.Lee: Superconductor Science and Technology, 2005, 18, 183-6