Max Planck Institute for Chemistry, Biogeochemistry Department, PO Box 3060, 55020 Mainz, Germany.
Nat Mater. 2011 Nov 13;10(12):927-31. doi: 10.1038/nmat3175.
Molecular hydrogen is expected to exhibit metallic properties under megabar pressures. This metal is predicted to be superconducting with a very high critical temperature, T(c), of 200-400 K, and it may acquire a new quantum state as a metallic superfluid and a superconducting superfluid. It may potentially be recovered metastably at ambient pressures. However, experiments carried out at low temperatures, T<100 K, showed that at record pressures of 300 GPa, hydrogen remains in the molecular insulating state. Here we report on the transformation of normal molecular hydrogen at room temperature (295 K) to a conductive and metallic state. At 200 GPa the Raman frequency of the molecular vibron strongly decreased and the spectral width increased, evidencing a strong interaction between molecules. Deuterium behaved similarly. Above 220 GPa, hydrogen became opaque and electrically conductive. At 260-270 GPa, hydrogen transformed into a metal as the conductance of hydrogen sharply increased and changed little on further pressurizing up to 300 GPa or cooling to at least 30 K; and the sample reflected light well. The metallic phase transformed back at 295 K into molecular hydrogen at 200 GPa. This significant hysteresis indicates that the transformation of molecular hydrogen into a metal is accompanied by a first-order structural transition presumably into a monatomic liquid state. Our findings open an avenue for detailed and comprehensive studies of metallic hydrogen.
在兆巴压力下，氢气有望呈现金属特性。这种金属预计具有非常高的超导临界温度 T(c)，在 200-400 K 之间，并且可能会获得一种新的量子态，即金属超流和超导超流。它可能会在环境压力下以亚稳状态恢复。然而，在 100 K 以下的低温实验表明，在创纪录的 300 GPa 压力下，氢气仍处于分子绝缘状态。在这里，我们报告了室温（295 K）下正常氢气向导电和金属态的转变。在 200 GPa 时，分子振子的拉曼频率大幅下降，谱宽增加，表明分子之间存在强烈相互作用。氘的行为类似。在 220 GPa 以上，氢气变得不透明且具有导电性。在 260-270 GPa 时，氢气转变为金属，因为氢气的电导率急剧增加，在进一步加压至 300 GPa 或冷却至至少 30 K 时变化不大；并且样品很好地反射光。在 200 GPa 下，金属相在 295 K 下又变回了分子氢气。这种显著的滞后表明，氢气向金属的转变伴随着可能进入单原子液态的一级结构转变。我们的发现为深入全面研究金属氢开辟了道路。
