Research to Produce Pressures of 600 GPa or Higher on Hydrogen and to Produce Metallic Hydrogen

这个凝聚态物理项目研究的是处于超高压下的分子氢。氢是最简单的元素或材料之一，其物理性质仍未被理解为压力的函数。一个基本的问题是，它是保持其绝缘状态，还是经历到其他状态的相变，可能是导电或金属状态。一种理论预测在450 Gpa附近会发生金属相变。另一种理论认为，在400 Gpa附近转变为接近零的带隙半导体，然后在600 Gpa附近转变为立方金属。在之前的工作中，首席研究员曾在其他材料中达到560 Gpa的压力，但在氢气中被限制在342 Gpa，因为氢与达到超高压所需的钻石顶盒发生反应。一种新的氢扩散屏障已经被开发出来，它应该可以减少或消除这个问题。其他技术进步，包括砧尖直径的减小，表明最大可达到的压力可能会增加1.4倍。光学反射率测量可以用来检测到半导体或金属状态的任何转变。此外，迈斯纳效应的测量将在压力下进行，以检测超导状态。这项研究涉及对博士后助理进行独特和尖端研究技术的培训，这些技术将为在学术界、行业和政府的职业生涯做准备。常压下的氢以分子气体的形式存在，分子是由两个氢原子通过典型的化学键结合在一起形成的。然而，这个简单的系统包含了许多物理知识，仍然没有完全被理解。报道援引著名物理学家维克托·韦斯科夫的话说：“除非我们了解了固态氢，否则我们不会了解固态物理学。”氢可以冷却和压缩，首先形成液体，然后形成固体。正是这些阶段，特别是固相，对理解理论和实验都提出了相当大的挑战。这项研究的目标是使用最新的钻石顶锤技术来实现超高压，将最初绝缘的固态氢转化为金属导电状态，甚至可能转化为超导状态。这将需要达到闻所未闻的600 Gpa的静态压力，这远远高于地球中心的压力。已经计算出，金属氢将是一种超导体，具有很高的T_c，可能是室温的。最近低原子序数材料MgB_2在常压下的高T_c和高原子序数材料Li在高压下的高T_c的研究结果增加了这一计算的可信度。氢在室温附近超导电性的发现将极大地刺激人们在其他低Z材料中寻找超导电性。这项研究涉及对博士后助理进行独特和尖端研究技术的培训，这将为他们在学术界、行业和政府的职业生涯做好准备。

This condensed matter physics project deals with molecular hydrogen subjected to ultrahigh pressures. The physical properties of hydrogen, one of the simplest elements or materials, are still not understood as a function of pressure. One fundamental question is whether it retains its insulating state or undergoes phase transitions to other, perhaps conducting or metallic states. One theory predicts a metallic transition near 450 GPa. Another theory suggests a transition to a near zero band gap semiconductor, near 400 GPa, subsequently converting to a cubic metal near 600 GPa. In previous work, the principal investigator has reached pressures of 560 GPa in other materials, but has been limited to 342 GPa in hydrogen, because hydrogen reacts with the diamond anvil cells required to reach ultrahigh pressures. A new hydrogen diffusion barrier has been developed that should reduce or eliminate this problem. Other technical advances, including reduction in the anvil tip diameter, suggest that the maximum attainable pressures may be increased by a factor of 1.4. Optical reflectivity measurements can be used to detect any transition to a semiconducting or metallic state. In addition, Meissner effect measurements will be made at pressure to detect a superconducting state. The research involves the training of post-doctoral associates in unique and cutting edge research techniques that will prepare the for careers in academe, industry and government. Hydrogen at ordinary pressures exists as a molecular gas, the molecule being formed by two hydrogen atoms held together by the prototypical chemical bond. However, this simple system contains much physics and is still not completely understood. One famous physicist, Victor Weiskopf, was quoted as saying, "we will not understand solid state physics until we understand solid hydrogen". Hydrogen can be cooled and compressed, first forming a liquid, and then a solid. It is these phases, particularly the solid phase that present considerable challenges to both theory and experiment to understand. The goal of this research is to use the latest diamond anvil techniques to achieve ultrahigh pressures to convert initially insulating solid hydrogen to a metallic, conducting state, and possibly even to a superconducting state. This will require reaching the unheard of static pressure of 600 GPa, which is far above the pressure at the center of the earth. It has been calculated that metallic hydrogen will be a superconductor with a very high Tc, possibly room temperature. This calculation has been given added credence by the recent findings of high Tc's in the low atomic number materials MgB2 at ambient pressure, and Li at high pressure. A discovery of superconductivity near room temperature in hydrogen would be a great stimulus to search for superconductivity in other low-Z materials. The research involves the training of post-doctoral associates in unique and cutting edge research techniques that will prepare them for careers in academe, industry and government.