  Tailoring transport properties of strongly correlated electron systems in a
controlled fashion counts among the dreams of materials scientists. In copper
oxides, varying the carrier concentration is a tool to obtain high-temperature
superconducting phases. In manganites, doping results in exotic physics such as
insulator-metal transitions (IMT), colossal magnetoresistance (CMR), orbital-
or charge-ordered (CO) or charge-disproportionate (CD) states. In most oxides,
antiferromagnetic order and charge-disproportionation are asssociated with
insulating behavior. Here we report the realization of a unique physical state
that can be induced by Mo doping in LaFeO$_3$: the resulting metallic state is
a site-selective Mott insulator where itinerant electrons evolving in
low-energy Mo states coexist with localized carriers on the Fe sites. In
addition, a local breathing-type lattice distortion induces charge
disproportionation on the latter, without destroying the antiferromagnetic
order. A state, combining antiferromangetism, metallicity and CD phenomena is
rather rare in oxides and may be of utmost significance for future
antiferromagnetic memory devices.
