Extreme High-Energy-Density Matter Probed by High-Precision X-ray Spectroscopy*

Extreme high-energy-density (HED) conditions of matter, often encountered in astrophysical objects like stars and inertial confinement fusion targets, can now be created by powerful lasers in laboratories. Accurate knowledge of extreme HED matter is essential for better understanding planetary science, astrophysics, and reliably designing fusion energy targets. Over the past decade, research has revealed that traditional plasma-physics models often fail to describe the physics of matter under extreme HED conditions since strong coupling and electron degeneracy play a crucial role in such quantum many-body systems. Probing extreme HED matters in experiments mostly relies on measuring x-ray induced fluorescence and/or absorption to infer what happens inside extreme HED matter. On the theoretical/computational side, ab initio methods such as density functional theory (DFT) can provide a self-consistent picture to understand the underline physics. Combining both high-precision x-ray spectroscopy experiments and ab initio calculations, we have revealed some new HED physics phenomena over the past few years, which include the Fermi-surface rising in warm dense matter [1], interspecies radiative transition in super-dense matter [2], and a better understanding of implosion x-ray spectroscopy through DFT-based kinetic modeling [3]. This talk will cover what we have learned so far and what we are still struggling in exploring extreme HED matter.



[1] S. X. Hu, Phys. Rev. Lett. 119, 065001 (2017).

[2] S. X. Hu et al., Nat. Commun. 11, 1989 (2020).

[3] S. X. Hu et al., Nat. Commun. 13, 6780 (2022).

*In collaboration with P. M. Nilson, D. T. Bishel, D. A. Chin, V. V. Karasiev, S. B. Hansen, I. E. Golovkin, M.-F. Gu, V. Recoules, N. Brouwer, M. Torrent, D. I. Mihaylov, N. R. Shaffer, S. Zhang, T. Walton