Simple Molecular Systems at Ultrahigh Pressures

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Nontechnical Abstract: The millions of atmospheres of pressure that can now be produced in the laboratory can impart profound effects on atoms and molecules, molding matter to make new materials with unprecedented properties. Conventional understanding fails to predict such effects, beginning with hydrogen, the first element in the Periodic Table, and extending to other "simple" elements. This project explores this new world of materials when compressed up to five million atmospheres (5 megabars or 500 gigapascals). A key property to be explored is superconductivity - the ability of a material to conduct electricity without resistance - at very high temperatures, including possibly room temperature and above. Advanced experimental techniques to study materials to very high pressures while at variable temperatures are employed to synthesize and characterize these materials, and theoretical and computational methods are used to interpret the results as well as to predict new materials and their properties to guide syntheses. The results have implications for fields beyond condensed-matter physics, including chemistry, advanced technology, planetary science, and astrophysics. An important goal is education and training of graduate students and undergraduates in the field. There is also a component that impacts locally STEM education and the public understanding of science.Technical Abstract: Pressure is not a simple thermodynamic parameter but an effective tool for the creation of exotic materials and phenomena not accessible at ambient conditions. Materials subjected to pressures up to several hundred gigapascals exhibit unexpected properties, including very high-temperature superconductivity, counterintuitive bonding patterns and electronic topological states, entirely new crystal structures, and potentially new physics. Investigations of materials at these conditions thus test both the limits of experimental techniques as well as fundamental theory. Addressing these questions in "simple" elemental and molecular systems at ultrahigh pressures, the project is divided into the following tasks: 1. Very High Tc Superconductivity; 2. Metallization and Novel Transitions in Dense Hydrogen; 3. High-Pressure Electrides; 4. Novel Interfacial Phenomena at Megabar Pressures; 5. Unconventional and Exotic Compounds; and 6. Methods and Technique Development. Each of the tasks involve tightly integrated experiment and computational theory. In particular, the experimental effort takes advantage of new developments in diamond-anvil techniques and capabilities at advanced radiation facilities to explore the nature of these materials in extreme conditions.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.