Mott transitions in correlated electron systems with orbital degrees of freedom

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 fillingn 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 J50 to discontinuous for any finite J. This result is confirmed using the exact-diagonalization method for M52.