Geophysical Laboratory, Carnegie Institution of Washington, Washington, DC 20015, USA.
Proc Natl Acad Sci U S A. 2013 Aug 20;110(34):13757-62. doi: 10.1073/pnas.1312256110. Epub 2013 Jul 31.
Theoretical calculations and an assessment of recent experimental results for dense solid hydrogen lead to a unique scenario for the metallization of hydrogen under pressure. The existence of layered structures based on graphene sheets gives rise to an electronic structure related to unique features found in graphene that are well studied in the carbon phase. The honeycombed layered structure for hydrogen at high density, first predicted in molecular calculations, produces a complex optical response. The metallization of hydrogen is very different from that originally proposed via a phase transition to a close-packed monoatomic structure, and different from simple metallization recently used to interpret recent experimental data. These different mechanisms for metallization have very different experimental signatures. We show that the shift of the main visible absorption edge does not constrain the point of band gap closure, in contrast with recent claims. This conclusion is confirmed by measured optical spectra, including spectra obtained to low photon energies in the infrared region for phases III and IV of hydrogen.
理论计算和对最近的实验结果的评估为高压下氢的金属化提供了一个独特的情景。基于石墨烯片的层状结构的存在导致了与在碳相中得到很好研究的石墨烯中独特特征相关的电子结构。在高密度下，首先在分子计算中预测的蜂窝状层状氢结构产生了复杂的光学响应。氢的金属化与最初通过向密堆积单原子结构的相变提出的金属化非常不同，也与最近用于解释最近的实验数据的简单金属化不同。这些不同的金属化机制具有非常不同的实验特征。我们表明，与最近的说法相反，可见光吸收边缘的移动并不限制带隙闭合的点。这一结论得到了测量的光学光谱的证实，包括对氢的相 III 和相 IV 在红外区域的低光子能量获得的光谱的证实。
