Renewal: Simple Molecular Systems at Ultrahigh Pressures

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Non-technical Description: Pressure is not only simple parameter familiar in many aspects of everyday life, but it is also an effective tool that can be used to create exotic materials not accessible under ordinary conditions. In many cases, altogether new materials can be synthesized when everyday substance are subjected to extreme pressures in the laboratory, for example at the kinds of pressure found in the core of Earth, or 2 million times atmospheric pressure. An example is superconductivity – the ability to conduct electricity without resistance – in newly discovered materials that contain a great deal of hydrogen. Indeed, these materials have been shown to superconduct at, and possibly above, room temperature. This project investigates these and related materials, both fundamentally and with the goal of making room-temperature superconductors that could be used in modern technology. More broadly, this study of these and related materials at high pressure is expected to inform a broad range of scientific fields, from chemistry and physics, to materials science and engineering, to planetary science and astrophysics. The findings could also lead to improved mechanisms of hydrogen storage and separation that could impact future energy needs. The techniques developed at national user facilities are made available to the scientific community. An important component of the proposed project is the education and training of the next generation of researchers, particularly those from many groups that are underrepresented in scientific and technical disciplines, for example at the University of Illinois Chicago, which is a Minority-Serving Institution. Technical Description:This project supports the study of fundamental interactions in simple elemental and molecular systems to pressures above 300 GPa (3 Mbar). A full range of state-of-the-art experimental and theoretical techniques are used to investigate the structural and transport properties of selected materials, with a focus on low-atomic number (Z) materials that exhibit very high-temperature superconductivity and other exotic physical properties. Theoretical and computational methods are used to predict stable compositions and structures at high pressures, and advanced high pressure-temperature P-T methods are employed to synthesize and characterize these materials in-situ. The focus of this work is hydrogen-dominant materials, such as superhydrides, that our group has shown to exhibit very high Tc superconductivity in the vicinity of, and possibly above, room temperature, at megabar pressures. Theory and computation are used to interpret the results and guide subsequent synthesis and characterization. This proven joint theoretical-experimental ‘materials by design’ approach that led to our previous discoveries are applied to address new questions that include expanding the range of compositions and extreme conditions of pressure-temperature-magnetic field explored and understanding underlying transport mechanisms, including quantum effects expected for these low-Z systems. The full range of relevant experimental and theoretical techniques, including new modeling and simulation methods, are brought to bear on the study of these materials. In particular, new and emerging capabilities at national user facilities are applied to probe the structural, electronic, and transport properties of materials with new integrated approaches. The work has the potential to advance our understanding of matter at extreme conditions, and thereby improve our picture of the fundamental interactions that govern the behavior of materials, as well as lead to the creation of new useful materials for practical applications.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.