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

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****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.