de Haas-van Alphen effect investigation of the electronic structure of Al-substituted MgB2 -: art. no. 060507

We report a de Haas-van Alphen (dHvA) study of the electronic structure of Al-doped crystals of MgB2. We have measured crystals with similar to 7.5% Al, which have a T-c of 33.6 K (similar to 14% lower than pure MgB2). dHvA frequencies for the sigma-tube orbits in the doped samples are lower than in pure MgB2, implying a 16 +/- 2 % reduction in the number of holes in this sheet of Fermi surface. The mass of the quasiparticles on the larger sigma orbit is lighter than the pure case indicating a reduction in electron-phonon coupling constant lambda. These observations are compared with band-structure calculations, and found to be in excellent agreement.