Hydrogen at Ultra-High Pressure

* 技术摘要 * 凝聚态物理学的一个突出问题和挑战是在超高压下在金属相中产生氢。 金属氢（MH）被预测为室温超导体，并且可能是亚稳态的，也就是说，当压力释放时，它仍然是金属。 如果亚稳态MH将是已知的最强大的火箭推进剂。MH有两种途径：在高压下，氢可以被加热到熔点线以上，成为新的相，即等离子体相变或PPT，在液相中，它分解成为原子金属液体。第二种途径是沿着准等温线加压，直到它离解并变成原子金属。超高压是在金刚石压砧单元中产生的，并且必须扩展到约5兆巴的压力以产生预测的相。已经开发了用于加工金刚石的技术，以增加其与氢样品的压力和温度的有用范围。使用脉冲激光器，兆巴压力范围内的氢样品被加热到几千开尔文的温度，并观察到相变。将进行测量以表明该相是金属相或PPT。最近的准等温实验揭示了一个新的相以上~2兆巴，但不是金属。研究氢到更高压力的实验，超出了新阶段的实验，将由博士后研究员，研究生和本科生在他们的教育发展中进行。非技术摘要 * 宇宙中最普遍的元素是氢;地球上发现的纯氢以双原子分子的形式结合在一起，在非常低的温度下作为透明的分子绝缘体膨胀和固化。75年来，人们一直推测，当加压时，分子会解离形成具有壮观特性的金属原子固体或液体。这些包括室温超导性，在绝对零度和数百万个大气压下存在的液体，超流性。此外，金属氢预计是亚稳态的，也就是说，当压力释放时，它将保持在金属相中，就像在高压下由碳制成的金刚石在压力释放时不会恢复为石墨一样。如果是亚稳态的，金属氢将是已知的最强大的火箭燃料，并将彻底改变火箭技术。使用金刚石砧座产生高压和光学技术研究的压力范围将扩大，旨在实现高达400万至500万个大气压的压力，并用激光将样品加热到数千度。 在这个程序中，由博士后研究员，研究生和本科生，并在可能的高中学生进行的成功，将扩展我们的知识和理解这个最简单的，但最复杂的原子在元素周期表。

****Technical Abstract****One of the outstanding problems and challenges to condensed matter physics is to produce hydrogen in the metallic phase at ultra high pressures. Metallic hydrogen (MH) has been predicted to be a room temperature superconductor, and may be metastable, that is, it remains metallic when the pressure is released. If metastable MH would be the most powerful rocket propellant known. There are two pathways to MH: at high pressure hydrogen can be heated above the melting line to a new phase, the plasma phase transition, or PPT, where in the liquid phase it dissociates to become an atomic metallic liquid. The second pathway is to pressurize along a quasi-isotherm until it dissociates and becomes atomic metallic. Ultrahigh pressures are produced in diamond anvil cells and must be extended to pressures ~5 megabar to produce the predicted phases. Techniques have been developed for processing diamonds to increase their useful range of pressure and temperature with hydrogen samples. Using pulsed lasers, samples of hydrogen in the megabar pressure range have been heated to temperatures of a few thousand Kelvin and a phase transition has been observed. Measurements will be made to show that this phase is metallic or the PPT. Recent quasi-isothermal experiments have revealed a new phase above ~2 megabar, but not metallic. Experiments to study hydrogen to much higher pressures, beyond those of the new phase will be carried out by postdoctoral fellows, graduate, and undergraduate students in their educational development.****Non-Technical Abstract****The most prevalent element in the universe is hydrogen; pure hydrogen is found on earth bound together as diatomic molecules, that liquefy and solidify at very low temperatures as a transparent molecular insulator. For over 75 years it has been speculated that when pressurized, the molecules would dissociate to form an atomic solid or liquid that is metallic, with spectacular properties. These include room temperature superconductivity, existence of a liquid at absolute zero of temperature and millions of atmospheres pressure, superfluidity. Moreover metallic hydrogen is predicted to be metastable, that is, it would remain in the metallic phase when pressure is released, just as diamond made from carbon at high pressure does not revert to graphite when pressure is released. If metastable, metallic hydrogen would be the most powerful rocket fuel known and would revolutionize rocketry. Using diamond anvil cells to generate high pressures and optical techniques of study the pressure range will be extended, aiming to achieve pressures up to 4 to 5 million atmospheres and heating samples with lasers to thousands of degrees. Success in this program, carried out by postdoctoral fellows, graduate, and undergraduate students, and where possible high school students, will extend our knowledge and understanding of this simplest, but most complex atom in the periodic table of the elements.