Finite-element simulation of the liquid-liquid transition to metallic hydrogen
Finite-element simulation of the liquid-liquid transition to metallic hydrogen
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DOI：
10.1103/physrevb.100.134106
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发表时间：
2019-02
影响因子：
3.7
通讯作者：
Matthew Houtput;J. Tempere;I. Silvera
中科院分区：
文献类型：
--
作者：
Matthew Houtput;J. Tempere;I. Silvera
高温高压下的氢经历了从液态分子相到导电原子态或液态金属氢的相变，有时被称为等离子体相变(PPT)。PPT相线是在最近的一次实验中观察到的，该实验研究了激光脉冲加热的金刚石压腔中的氢，压力范围为$\sim 100-170\Text{Gpa}$，温度高达$\sim 2000\Text{K}$。转变的实验特征是(I)负的压力-温度斜率，(Ii)加热曲线上的平台，假定与相变的潜热有关，和(Iii)样品反射率的突然增加。我们提出了一种有限元模拟，它准确地考虑了激光脉冲所沉积的热的位置和时间相关性。计算了样品的加热曲线以及样品的反射率和透射率。这一模拟证实了观测到的平台与相变有关，但我们发现需要较大的潜热，这可能表明相变时的动力学比目前模型中所考虑的要复杂得多。最后，提出了可以区分由于过渡到金属状态或由于分子氢的带隙关闭而引起的光学性质变化的实验。
Hydrogen at high temperature and pressure undergoes a phase transition from a liquid molecular phase to a conductive atomic state, or liquid metallic hydrogen, sometimes referred to as the plasma phase transition (PPT). The PPT phase line was observed in a recent experiment studying laser-pulse heated hydrogen in a diamond anvil cell in the pressure range $\sim 100 - 170 \text{GPa}$ for temperatures up to $\sim 2000 \text{K}$. The experimental signatures of the transition are (i) a negative pressure-temperature slope, (ii) a plateau in the heating curve, assumed to be related to the latent heat of transformation, and (iii) an abrupt increase in the reflectance of the sample. We present a finite element simulation that accurately takes into account the position and time dependence of the heat deposited by the laser pulse. We calculate the heating curves and the sample reflectance and transmittance. This simulation confirms that the observed plateaus are related to the phase transition, however we find that large values of latent heat are needed and may indicate that dynamics at the transition are more complex than considered in current models. Finally, experiments are proposed that can distinguish between a change in optical properties due to a transition to a metallic state or due to closure of the bandgap in molecular hydrogen.