Metallic Properties of the Isotopes of Hydrogen

【非技术内容】氢原子是由一个质子和一个电子结合而成的。氘原子核由一个质子和一个中子组成，所以质量是氢的两倍。本研究的目的是研究氢同位素的性质：氢、氘和金属相的氘化氢（氚省略，因为它是放射性的），统称为氢。一般来说，元素的同位素效应很小，只有百分之一或两个数量级。在氢中，D2与H2的质量比为200%，对行为的影响非常大。例如，氢的一个重要的量子方面是凝聚态相的零点能量或运动。结果是，在零温度极限下，原子或分子不在晶格位置的固定位置上，而是在这些位置周围运动。这类材料的凝固温度非常低（氢分子约14k，氘约18k）。氦比氢分子的量子性更强，而且不是固态，在T= 0K时仍为液态。原子氢本身被预测为液体基态。研究小组计划研究高压对氢的影响。该团队已经通过实验证明，氘化氢是一种稳定的分子，在~ 200gpa的压力下变得不稳定，它会解离并重新结合，形成HD、D2和H2的稳定混合物。因此，在这项研究中，同位素在超高压和低温下的性质将被研究。技术摘要：研究项目是研究氢在压力下的金属性质。在研究计划中，已经证明氢在~500 GPa时变成金属。预计氘的压力会更高，因为分子氘的质量较大，其零点能较小，结合能较大。HD应该有很多惊喜，在~ 200gpa以上，它变成了0.5 HD和0.25 （H2+D2）的混合物。它可能需要500gpa的压力才能解离H2分子，但HD在更低的压力下可能变得不稳定。这项研究有望带来惊喜。一旦同位素被金属化，基态将被x射线分析研究。对氢的一个有趣的预测是，它可能是一种室温超导体，这将被研究。它也被预测为亚稳态，即当压力解除时，它可能保持在金属状态。研究同位素亚稳性的方法是先在低温下减压，然后再升高温度，直到样品转化回分子相。可能氢不是亚稳态的，但氘是亚稳态的，因为它的零点能量较小。最后，提出了一种超高压的压力标度。500+GPa没有好的刻度。研究氮空位纳米金刚石中荧光谱线的位移，可以得到一种新的压力刻度。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Non-technical AbstractThe hydrogen atom is composed of a single proton and a single electron bonded together. The deuterium nucleus is composed of a proton and neutron, so twice the mass of hydrogen. The objective of this research is to study the properties of the hydrogen isotopes: hydrogen, deuterium, and hydrogen deuteride in the metallic phases (tritium is omitted as it is radioactive), collectively referred to as the hydrogens. In general isotopic effects of elements are small, of order a percent or two. In the hydrogens, the mass ratio of D2 to H2 is 200% and the impact on the behavior can be very large. For example, one of the important quantum aspects of hydrogen is the zero-point energy or motion in the condensed matter phase. The consequence is that in the zero temperature limit, the atoms or moleules are not in fixed positions in lattice sites, but have motion around these sites. Such materials have very low temperatures of solidification (molecular hydrogen, about 14 K; deuterium about 18 K). Helium is even more quantum than the molecular hydrogens and does not have a solid state, remaining liquid to T= 0K. Atomic hydrogen itself is predicted to have a liquid ground state. The research team plans to study the effects of high pressure on the hydrogens. The team has already shown experimentally that hydrogen deuteride, which is a stable molecule, becomes unstable at a pressure of ~200 GPa, dissociating and recombining to form a stable mixture of HD, D2 an H2. Thus, in this research the properties of the isotopes at ultra high pressures and low temperatures shall be studied.Technical AbstractThe program of research is to study the properties of the hydrogens at pressure where they are metallic. In the research program it has already been shown that hydrogen becomes a metal at ~500 GPa. It is expected that the pressure will be higher for deuterium as, due to its larger mass, molecular deuterium will have smaller zero-point energy and a larger binding energy. HD should have many surprises as above ~200 GPa it becomes a mixture of 0.5 HD and 0.25 (H2+D2). It may require a pressure of 500 GPa to dissociate the H2 molecules, but the HD may become unstable at still a lower pressure. Surprises are expected in this study. Once the isotopes are metallized, the ground state will be studied by xray analysis. One of the intriguing predictions for hydrogen is that it may be a room temperature superconductor, which will be studied. It has also been predicted to be metastable, i.e. it may remain in the metallic state when the pressure is relieved. The metastability of the isotopes shall be studied by reducing the pressure at low temperature, then raising the temperature until the sample converts back to the molecular phase. It may be that hydrogen is not metastable, but deuterium is, due to its smaller zero point energy. Finally, a pressure scale for ultrahigh pressures will be developed. There is no good scale at 500+GPa. A study of the shift of the fluorescence line in nitrogen vacancy nano-diamond can lead to a new pressure calibration scale.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.