Phase separation in the non-equilibrium Verwey transition in magnetite

TL;DR

This study investigates the non-equilibrium phase transition in magnetite, revealing transient metallic states and phase separation dynamics through optical spectroscopy, advancing understanding of ultrafast electronic phase changes.

Contribution

It provides a comprehensive characterization of the optical properties during the non-equilibrium Verwey transition, linking phase separation to transient metallic states.

Findings

Identification of a transient metallic phase post photo-excitation

Observation of phase separation influencing optical reflectivity

Spectroscopic features associated with out-of-equilibrium phase separation

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.