Phase separation in the non-equilibrium Verwey transition in magnetite

Abstract

We present equilibrium and out-of-equilibrium studies of the Verwey transition in magnetite. In the equilibrium optical conductivity, we find a step-like change at the phase transition for photon energies below about 2 eV. The possibility of triggering a non-equilibrium transient metallic state in insulating magnetite by photo excitation was recently demonstrated by an x-ray study. Here we report a full characterization of the optical properties in the visible frequency range across the non-equilibrium phase transition. Our analysis of the spectral features is based on a detailed description of the equilibrium properties. The out-of-equilibrium optical data bear the initial electronic response associated to localized photo-excitation, the occurrence of phase separation, and the transition to a transient metallic phase for excitation density larger than a critical value. This allows us to identify the electronic nature of the transient state, to unveil the phase transition dynamics, and to study the consequences of phase separation on the reflectivity, suggesting a spectroscopic feature that may be generally linked to out-of-equilibrium phase separation.

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• Ferromagnetic resonance in the complex permeability of an Fe${}_3$O${}_4$ nanosuspension at radio and microwave frequencies
• Laser-driven first-order spin reorientation and Verwey phase transitions in the magnetite Fe${}_3$O${}_4$ beyond the range of thermodynamic equilibrium
• Visible pump -- mid infrared pump -- broadband probe: development and characterization of a three-pulse setup for single-shot ultrafast spectroscopy at 50 kHz
• Ultrafast generation of hidden phases via energy-tuned electronic photoexcitation in magnetite
• Dual-stage structural response to quenching charge order in magnetite
• Time-resolved multimode heterodyne detection for dissecting coherent states of matter
• Simultaneous mapping of the ultrafast time and fluence dependence of the laser-induced insulator-to-metal transition in magnetite