Ultrafast generation of hidden phases via energy-tuned electronic photoexcitation in magnetite

Abstract: 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.