Structural and electronic properties of 3D metals up to Warm Dense Matter conditions

This seminar presents the results of my PhD thesis investigating iron (Fe) and copper (Cu) under extreme pressure and temperature. Conducted in collaboration with First Light Fusion (FLF), the study aims to constrain the Equations of State (EOS) for the metallic components used in their nuclear fusion technology. Beyond fusion, these results are critical for geophysics to model planetary interiors.

Using the High-Power Laser Facility at the ESRF, we subjected these metals to laser-driven shock waves, reaching the Warm Dense Matter (WDM) regime with conditions up to 300 GPa and 7000 K. The microscopic structural and electronic changes were probed with ultra-fast (100 ps) X-ray Absorption Spectroscopy. A significant part of this work focused on overcoming the difficulty of measuring temperature under shock. We used a promising method by extracting temperatures directly from EXAFS oscillations, supported by DFT-MD simulations and FEFF modelling to identify crystalline phases.

The results provide new constraints on the melting curves of both metals, as well as on the structural phase of iron in the vicinity of its melting curve at pressures relevant for the Earth’s core and the fcc-to-bcc phase transition in copper at multi-megabar pressures. Finally, we observed a contrasting evolution in the electronic structure of these two metals- a redshift in the absorption edge for iron and a blueshift for copper. While current theories predict these trends, they consistently overestimate the effect, highlighting the need for further study of 3d transition metals under dynamic compression.