Two-band Eliashberg equations and the experimental Tc of the diboride Mg1-xAlxB2

The variation of the superconducting critical temperature T, as a function of x in the diboride Mg1-xAlxB2 has been studied in the framework of the two-bands Eliashberg theory and traditional phonon coupling mechanism. We have solved the two-bands Eliashberg equations using first-principle calculations or simple assumptions for the variation of the relevant physical quantities. We have found that the experimental T-c curve can be explained only if the Coulomb pseudopotential changes with x by tuning the Fermi level toward the sigma band edge. In polycrystal samples the x dependence of the sigma and pi-band gap has been found and is in agreement with experiments. (C) 2004 Elsevier B.V. All rights reserved.