The insulator-to-metal transition in dense fluid hydrogen is an essential phenomenon in the study of gas giant planetary interiors and the physical and chemical behavior of highly compressed condensed matter. Using direct fast laser spectroscopy techniques to probe hydrogen and deuterium precompressed in a diamond anvil cell and laser heated on microsecond timescales, an onset of metal-like reflectance is observed in the visible spectral range at P >150 GPa and T ≥ 3000 K. The reflectance increases rapidly with decreasing photon energy indicating free-electron metallic behavior with a plasma edge in the visible spectral range at high temperatures. The reflectance spectra also suggest much longer electronic collision time (≥1 fs) than previously inferred, implying that metallic hydrogen at the conditions studied is not in the regime of saturated conductivity (Mott-Ioffe-Regel limit). The results confirm the existence of a semiconducting intermediate fluid hydrogen state en route to metallization.

中文翻译：

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液态氢和氘中绝缘子-金属跃迁的光谱研究。

在气体巨行星内部以及高压缩冷凝物的物理和化学行为的研究中，高密度流体氢中的绝缘体到金属的过渡是必不可少的现象。使用直接快速激光光谱技术探测金刚石砧座中预压缩的氢和氘，并在微秒级的时间内加热激光，在可见光范围P> 150 GPa和T≥3000 K处观察到类似金属的反射现象。随着光子能量的减少，反射率迅速增加，这表明在高温下等离子边缘处于可见光谱范围内的自由电子金属行为。反射光谱还表明，电子碰撞时间（≥1fs）比以前推断的要长得多，暗示在研究条件下的金属氢不在饱和电导率范围内（Mott-Ioffe-Regel极限）。该结果证实了在进行金属化的过程中存在半导体中间流体氢态。