Mott transitions in correlated electron systems with orbital degrees of freedom

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Mott metal-insulator transitions in an M-fold orbitally degenerate Hubbard model are studied by means of a generalization of the linearized dynamical mean-field theory. The method allows for an efficient and reliable determination of the critical interaction Uc for any integer filling n and different M at zero temperature. For half-filling a linear dependence of Uc on M is found. Inclusion of the (full) Hund's rule exchange J results in a strong reduction of Uc. The transition turns out to change qualitatively from continuous for J=0 to discontinuous for any finite J.