EPFL, Lausanne, Switzerland
30.09.2021. u 11:00h
Room ``Mladen Paić", 3rd wing, and Zoom
The complex interplay between crystal structure, charge, and orbital orders leads magnetite to undergo atypical metal-insulator transition in the neighborhood of 125 K known by Verwey Transition (VT). Despite the numerous approaches that have been adopted in the last 80 years, the leading mechanism of VT in magnetite still remains ambiguous. Here we use ultrafast electron diffraction (UED) to trace the structural changes of magnetite across the VT in the thermodynamic equilibrium and the ultrafast dynamics response of the structure under femtosecond pulsed excitations. Specifically, we study the strain evolution in magnetite following two major steps. First, in the thermodynamic equilibrium, we used symmetry arguments to determine the symmetry of the order parameter responsible for strain changes across VT. Second, out-of-equilibrium evolution: we investigated strain behavior under femtosecond pulsed light excitations. We used two excitations, 800 nm and 400nm (1.6 and 3.09 eV, respectively). These investigations are carried out in two phases, above and below VT termed as High Temperature (HT) and Low Temperature (LT) phases. In the LT phase, we distinguish two different time evolution of the strain depending on the excitation’s energy. This difference is absent in the HT phase. We presume this difference is intimately linked to the mechanism of VT. In this presentation, I will discuss the possible scenarios responsible for such differences in the dynamic responses.