Metallization of hydrogen as a key problem in modern physics is the pressure-induced evolution of the hydrogen electronic band from a wide-gap insulator to a closed gap metal. However, due to its remarkably high energy, the electronic band gap of insulating hydrogen has never before been directly observed under pressure. Using high-brilliance, high-energy synchrotron radiation, we developed an inelastic x-ray probe to yield the hydrogen electronic band information in situ under high pressures in a diamond-anvil cell. The dynamic structure factor of hydrogen was measured over a large energy range of 45 eV. The electronic band gap was found to decrease linearly from 10.9 to 6.57 eV, with an 8.6 times densification ($\rho /{\rho }_0\sim 8.6$) from zero pressure up to 90 GPa.

中文翻译：

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通过高达90 GPa的非弹性X射线散射探测固体氢的电子带隙

氢金属化是现代物理学中的一个关键问题，是氢电子带从宽间隙绝缘体到密闭间隙金属的压力诱导演化。但是，由于其能量极高，因此从未在压力下直接观察到绝缘氢的电子带隙。使用高亮度，高能量的同步加速器辐射，我们开发了一种无弹性的X射线探头，可在高压下在金刚石砧座中原位产生氢电子能带信息。在45 eV的大能量范围内测量了氢的动态结构因子。发现电子带隙从10.9 eV线性下降至6.57 eV，致密化为8.6倍（$\rho /{\rho }_0〜8.6$）从零压力到90 GPa。