飞秒X射线衍射揭示金刚石向暖态致密物质的多步跃迁
Multistep transition of diamond to warm dense matter state revealed by femtosecond X-ray diffraction
摘要：
本文从理论上研究了自由电子激光脉冲能量为6100 eV，脉宽为5 fs，辐照剂量为$\sim 19-25$ eV/原子吸收剂量的金刚石块体到致密态的升温过程。我们的混合代码XTANT的模拟显示在100 fs以下的时间尺度上的无序，衍射峰（220）比峰（111）消失得更快。热致密物质的形成是金刚石的非热损伤，带隙坍塌引发原子无序。在（220）峰消失和（111）峰消失之间的几飞秒内，发现了短寿命类石墨态。得到的结果进行了比较，从最近的实验在SACLA的数据，显示定性协议。仍然存在的挑战，为准确建模的固体温暖的致密物质状态的过渡和补充测量的建议进行了详细讨论。
英文摘要：
Diamond bulk irradiated with a free-electron laser pulse of 6100 eV photon energy, 5 fs duration, at the $\sim 19-25$ 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.
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