  We analyze the nature of Mott metal-insulator transition in multiorbital
systems using dynamical mean-field theory (DMFT). The auxiliary multiorbital
quantum impurity problem is solved using continuous time quantum Monte Carlo
(CTQMC) and the rotationally invariant slave-boson (RISB) mean field
approximation. We focus our analysis on the Kanamori Hamiltonian and find that
there are two markedly different regimes determined by the nature of the lowest
energy excitations of the atomic Hamiltonian. The RISB results at $T\to0$
suggest the following rule of thumb for the order of the transition at zero
temperature: a second order transition is to be expected if the lowest lying
excitations of the atomic Hamiltonian are charge excitations, while the
transition tends to be first order if the lowest lying excitations are in the
same charge sector as the atomic ground state. At finite temperatures the
transition is first order and its strength, as measured e.g. by the jump in the
quasiparticle weight at the transition, is stronger in the parameter regime
where the RISB method predicts a first order transition at zero temperature.
Interestingly, these results seem to apply to a wide variety of models and
parameter regimes.
