  Metal-insulator transitions (MIT) occurring in non-adiabatic conditions can
evolve through high-energy intermediate states that are difficult to observe
and control via static methods. By monitoring the out-of-equilibrium structural
dynamics of a magnetite (Fe3O4) crystal via ultrafast electron diffraction, we
show that MITs can evolve through different pathways by properly selecting the
electronic excitation with light. Near-infrared (800 nm) photons inducing d-d
electronic transitions is found to favor the destruction of the long-range
zigzag network of the trimerons and to generate a phase separation between
cubic-metallic and monoclinic-insulating regions. Instead, visible light (400
nm) further promotes the long-range order of the trimerons by stabilizing the
charge density wave fluctuations through the excitation of the oxygen 2p to
iron 3d charge transfer and, thus, fosters a reinforcement of the monoclinic
insulating phase. Our experiments demonstrate that tailored light pulses can
drive strongly correlated materials into different hidden phases, influencing
the lifetime and emergent properties of the intermediate states.
