We report a de Haas-van Alphen (dHvA) study of the electronic structure of Al
doped crystals of MgB2​. We have measured crystals with ∼7.5% Al which
have a Tc​ of 33.6 K, (∼14% lower than pure MgB2​). dHvA frequencies
for the σ 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 σ orbit is
lighter than the pure case indicating a reduction in electron-phonon coupling
constant λ. These observations are compared with band structure
calculations, and found to be in excellent agreement.Comment: 4 pages with figure