Hydrogen at Ultra-High Pressure

这项个人研究者奖将支持超高压和超高温下的氢研究。早期在高压高温条件下研究氢的尝试受到氢气在压力电池材料中的扩散和样品损失或电池材料的脆化和失效的阻碍。利用脉冲激光加热可以克服这个问题，因为样品是热的，可以扩散的时间被限制在脉冲的短时间内。重点将放在沿氢熔化线及以上的研究上。据预测，氢在其熔化线上有一个峰值，而最近的实验证明，这个峰值出现在兆巴以下。熔化线的研究将扩展到更高的压力。在较低的压力下，氢从分子固体融化成分子液体。在熔点以上，随着温度的升高，氢会解离，变成具有金属导电性的单原子。当压力超过峰值时，熔化温度可能下降到零开尔文，人们可以直接观察到从分子相到原子相的熔化。预计原子金属液体将表现出双组分超导性（电子和质子）以及超流动性。金属氢由于势垒被预测为亚稳态。这两相之间的屏障可能是在低温下抑制固体分子向原子金属转变的原因。在高温下，热能可使分子相克服势垒，转变为金属氢。这项研究更广泛的影响是开发了在极端条件下研究材料的新方法，丰富了科学界。这个项目涉及各个层次的年轻研究人员——高中、本科、研究生和博士后，因为他们发展成为未来的科学家。70多年前，维格纳和亨廷顿预测，在高压下，氢将从分子固体转变为原子金属固体，后来预测氢可能是一种室温超导体（对电流没有阻力），它是亚稳态的，也就是说，当压力释放时，它将保持在金属相。由于其极端的量子性质，理论在准确预测氢的性质方面面临挑战，需要实验指导。氢气被加压到预期转变压力的10倍以上，并保持分子绝缘。最近的理论预测在熔化线上有一个峰值，随着压力的增加超过峰值，熔化温度可能下降到零开尔文。氢是一种原子金属液体，电子和质子都具有超导性。早期在极端压力-温度状态下研究氢的尝试失败了，因为氢倾向于在高温下从高压装置中扩散出来或进入组成装置的材料中。使用一种新开发的脉冲激光加热方法，氢现在可以在这种状态下进行研究。预测的熔化线峰值已经被观察到，这个研究计划将扩展研究到更高的压力，以寻找金属状态。在更广泛的层面上，为科学界开发了高压和高温/低温新技术；如果金属氢可以被制造出来，并且是亚稳态的，它将是一种高能量密度的材料，也是人类可用的最强大的火箭推进剂。各级学生和博士后研究员，下一代科学家，都参与了开发和研究。

TechnicalThis individual investigator award will support studies of hydrogen at ultra high pressures and temperatures. Earlier attempts to study hydrogen in the high-pressure high-temperature regime were thwarted by diffusion of hydrogen in the pressure cell materials and loss of sample or embrittlement and failure of cell materials. By utilizing pulsed laser heating this problem has been overcome since the time that the sample is hot and can diffuse is limited to the short time of the pulse. The emphasis will be on studies along and above the melting line of hydrogen. Hydrogen was predicted to have a peak in its melting line and this peak was recently experimentally demonstrated to occur below a megabar. The melting line studies will be extended to higher pressures. At lower pressures hydrogen melts from a molecular solid to a molecular liquid. With increasing temperature above the melting line hydrogen will dissociate and become monatomic with metallic conductivity. With increasing pressure beyond the peak the melting temperature may descend to zero Kelvin and one may observe melting directly from the molecular to the atomic phase. The atomic metallic liquid is expected to demonstrate two-component superconductivity (electrons and protons) as well as superfluidity Metallic hydrogen is predicted to be metastable due to a potential barrier. This barrier between the two phases may be responsible for inhibiting the transition from solid molecular to atomic metallic at low temperature. At high temperature thermal energy may allow the molecular phase to overcome the barrier and make the transition to metallic hydrogen. The broader impact of this research is the development of new methods to study materials under extreme conditions enriching the scientific community. This program involves young researchers at all levels-high school, undergraduate, graduate, and postdoctoral, as they develop to become the scientists of the future.Non-technicalOver 70 years ago Wigner and Huntington predicted that at high pressure hydrogen will transform from a molecular solid to an atomic metallic solid, later predicted to be a possible room temperature superconductor (no resistance to the flow of electricity) that is metastable, i.e., will remain in the metallic phase when pressure is released. Because of its extreme quantum nature, theory is challenged to make accurate predictions of hydrogen's properties and needs experimental guidance. Hydrogen has been pressurized to more than 10 times the predicted transition pressure and remains molecular insulating. Recent theory predicted a peak in the melting line and with pressure increasing beyond the peak the melting temperature could descend to zero Kelvin. Hydrogen would be an atomic metallic liquid with superconductivity of both the electrons and protons. Earlier attempts to study hydrogen in the extreme pressure-temperature regime were frustrated due to the proclivity for hydrogen to diffuse out of the high pressure apparatus or into the materials comprising the apparatus at high temperature. Using a newly developed method of pulsed laser heating, hydrogen can now be studied in this regime. The predicted peak in the melting line has been observed and this research program will extend studies to higher pressures in search of the metallic state. On a broader level, new techniques for high pressure and high-temperature/low-temperature are developed for the scientific community; if metallic hydrogen can be produced and is metastable it will be a high energy density material as well as the most powerful rocket propellant available to man. Students and postdoctoral fellows on all levels, the next generation of scientists, are involved in the developments and research.