Studies of Alkali Metal, Noble Metal and Hydrogen-Rich Superconductors under Extreme Pressure

*技术摘要*这个单一研究人员奖的主要研究重点是在极端压缩下将典型的简单自由电子金属(如碱金属)转变为具有高度反常电子性质的材料。这些性质包括在相对较高温度下的超导电性，金属-半导体或金属-绝缘体的转变，甚至泡利顺磁到巡回铁磁的转变。本项目将深入研究部分碱金属及其合金和化合物在超高压下的超导相图和临界磁场行为。从这项研究中得到的系统学将阐明氢在压力下的性质，它已被预测在多毫巴压力下成为一种金属，并可能在室温附近具有超导电性。更令人感兴趣的现象是在高度极化的绝缘体中可能发生的绝缘体-金属转变和超导电性，如固体氙气和氢化铍BeH2，以及我们之前对最佳掺杂的Hg-1201铜酸盐所做的流体静压和单轴压力工作扩展到不足掺杂和过度掺杂两种状态。拟议的实验为本科生和研究生提供了一个学习和开发重要实验室技术的绝佳机会，并与美国和国外的团队合作。*非技术摘要*简单材料更容易理解，但复杂材料更有趣，更有可能导致创新应用。在这个单一的研究人员奖中，极高的压力高达200-300万个大气压，应用于非常柔软和简单的材料，如碱金属。这种极端的压缩能够不断地将这些金属转化为令人惊讶的复杂材料，这些材料可能是超导的、铁磁的，甚至是绝缘的。单个样本可以通过极端压缩来表现出这种异常行为，这一事实使人们能够对涉及的潜在过程有更深的理解。另一方面，这种加深的理解有助于设计在常压下具有有趣特性的材料。这样的研究提供了对数百万大气压下金属氢在室温附近可能的超导状态的洞察。拟议的实验为本科生和研究生提供了学习和开发大量基本实验技术的机会；这些学生还将受益于与美国和国外的研究小组的科学合作。

****Technical Abstract****The primary focus of the research in this single investigator award is the transformation under extreme compression of canonical simple free-electron metals, such as the alkali metals, into materials with highly anomalous electronic properties. These properties include superconductivity at relatively high temperatures, metal-semiconductor or metal-insulator transitions or even Pauli paramagnetic to itinerant ferromagnetic transitions. This project will study in depth to ultrahigh pressures the superconducting phase diagram and critical magnetic field behavior of selected alkali metals as well as their alloys and compounds. The systematics derived from this study will shed light on the properties of hydrogen under pressure which has been predicted to become a metal at multi-Mbar pressures with possible superconductivity near room temperature. Further phenomena of interest are possible insulator-metal transitions and superconductivity in highly polarizable insulators such as solid xenon and beryllium hydride BeH2, as well as the extension of our previous hydrostatic and uniaxial pressure work on the optimally doped Hg-1201 cuprate into both the underdoped and overdoped regimes. The proposed experiments give undergraduate and graduate students an excellent opportunity to learn and develop important laboratory techniques and collaborate with groups both in the US and abroad.****Non-Technical Abstract****Simple materials are easier to understand but complex materials are more interesting and more likely to lead to innovative applications. In this single investigator award extremely high pressures, as high as 2-3 million atmospheres, are applied to very soft and simple materials, like the alkali metals. Such extreme compression is able to continuously transform these metals into surprisingly complex materials which may be superconducting, ferromagnetic or even insulating. The fact that a single sample can be brought through extreme compression to exhibit such anomalous behavior allows one to gain a deeper understanding of the underlying processes involved. This enhanced understanding, on the other hand, facilitates the design of materials with interesting properties at ambient pressure. Such studies provide insight into a possible superconducting state near room temperature in metallic hydrogen under millions of atmospheres of pressure. The proposed experiments give undergraduate and graduate students the opportunity to learn and develop a multitude of essential experimental techniques; these students will also benefit from scientific collaborations with groups both in the US and abroad.