Multistep transition of diamond to warm dense matter state revealed by femtosecond X-ray diffraction

Nikita Medvedev,Beata Ziaja

doi:10.1038/s41598-018-23632-8

Abstract

Diamond bulk irradiated with a free-electron laser pulse of 6100 eV photon energy, 5 fs duration, at the ~19–25 eV/atom absorbed doses, is studied theoretically on its way to warm dense matter state. Simulations with our hybrid code XTANT show disordering on sub-100 fs timescale, with the diffraction peak (220) vanishing faster than the peak (111). The warm dense matter formation proceeds as a nonthermal damage of diamond with the band gap collapse triggering atomic disordering. Short-living graphite-like state is identified during a few femtoseconds between the disappearance of (220) peak and the disappearance of (111) peak. The results obtained are compared with the data from the recent experiment at SACLA, showing qualitative agreement. Challenges remaining for the accurate modeling of the transition of solids to warm dense matter state and proposals for supplementary measurements are discussed in detail.

Highlights

Over the years, extensive theoretical studies of many-body systems lead to a development of two complementary approaches towards their description: (i) In case when the average kinetic energy of constituent particles is much larger than the average potential energy between them and than the Fermi energy of the system, the system is in the classical, ideal plasma state[1]
Neither of the above mentioned approaches can be rigorously applied in this specific regime, as the potential energy of interaction among the particles is of the same order as their kinetic energies
The warm dense matter (WDM) state is common in the Universe: it exists in the inner core of large planets, in white dwarf stars, and, supposedly, on the surface of neutron stars[6,7]

Summary

Introduction

Extensive theoretical studies of many-body systems lead to a development of two complementary approaches towards their description: (i) In case when the average kinetic energy of constituent particles is much larger than the average potential energy between them and than the Fermi energy of the system, the system is in the classical, ideal plasma state[1]. The modern free-electron lasers provide femtosecond intense pulses of X-ray photons, sufficiently bright to create a WDM state in a single shot[10,11,12] These new experimental opportunities create a strong demand for a theoretical support and numerical modeling to describe experimental results, to suggest and guide new experiments, and to understand the fundamental physics of the warm dense matter. Both pulse durations were 5 fs[19]

Methods

Results

Conclusion