  We investigate the effect of mass imbalance in binary Fermi mixtures loaded
in optical lattices. Using dynamical mean-field theory, we study the transition
from a fluid to a Mott insulator driven by the repulsive interactions. For
almost every value of the parameters we find that the light species with
smaller bare mass is more affected by correlations than the heavy one, so that
their effective masses become closer than their bare masses before a Mott
transition occurs. The strength of the critical repulsion decreases
monotonically as the mass imbalance grows so that the minimum is realized when
one of the species is localized. The evolution of the spectral functions
testifies that a continuous loss of coherence and a destruction of the Fermi
liquid occur as the imbalance grows. The two species display distinct
properties and experimentally-observable deviations from the behavior of a
balanced Fermi mixture.
